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Entanglement, Quantum teleportation

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18.08.2022
06:52 Arxiv.org Math Transceiver designs to attain the entanglement assisted communications capacity. (arXiv:2208.07979v1 [quant-ph])

Pre-shared entanglement can significantly boost communication rates in the high thermal noise and low-brightness transmitter regime. In this regime, for a lossy-bosonic channel with additive thermal noise, the ratio between the entanglement-assisted capacity and the Holevo capacity - the maximum reliable-communications rate permitted by quantum mechanics without any pre-shared entanglement - scales as $\log(1/{\bar N}_{\rm S})$, where the mean transmitted photon number per mode, ${\bar N}_{\rm S} \ll 1$. Thus, pre-shared entanglement, e.g., distributed by the quantum internet or a satellite-assisted quantum link, promises to significantly improve low-power radio-frequency communications. In this paper, we propose a pair of structured quantum transceiver designs that leverage continuous-variable pre-shared entanglement generated, e.g., from a down-conversion source, binary phase modulation, and non-Gaussian joint detection over a code word block, to achieve this scaling law of capacity

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06:52 Arxiv.org Physics Enhancement in the mean square range delay accuracy by means of multiple entangled photon states quantum illumination. (arXiv:2208.04691v1 [quant-ph] CROSS LISTED)

Zhuang and Shapiro have recently discussed how quantum illumination can be used to increase the mean value range delay. In this paper it is shown how multiple entangled photon quantum illumination helps to reduce the integration time when evaluating range delay. The analysis is conveyed in the setting of three entangled photon states discrete quantum illumination models, but it is argued the extension of the main result to the setting of continuous quantum illumination models.

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06:52 Arxiv.org CS Transceiver designs to attain the entanglement assisted communications capacity. (arXiv:2208.07979v1 [quant-ph])

Pre-shared entanglement can significantly boost communication rates in the high thermal noise and low-brightness transmitter regime. In this regime, for a lossy-bosonic channel with additive thermal noise, the ratio between the entanglement-assisted capacity and the Holevo capacity - the maximum reliable-communications rate permitted by quantum mechanics without any pre-shared entanglement - scales as $\log(1/{\bar N}_{\rm S})$, where the mean transmitted photon number per mode, ${\bar N}_{\rm S} \ll 1$. Thus, pre-shared entanglement, e.g., distributed by the quantum internet or a satellite-assisted quantum link, promises to significantly improve low-power radio-frequency communications. In this paper, we propose a pair of structured quantum transceiver designs that leverage continuous-variable pre-shared entanglement generated, e.g., from a down-conversion source, binary phase modulation, and non-Gaussian joint detection over a code word block, to achieve this scaling law of capacity

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16.08.2022
19:02 Google news Sci/Tech 4moms Recalls More than 2 Million MamaRoo and RockaRoo Infant Swings and Rockers Due to Entanglement and Strangulation Hazards; One Death Reported - Consumer Product Safety Commission

4moms Recalls More than 2 Million MamaRoo and RockaRoo Infant Swings and Rockers Due to Entanglement and Strangulation Hazards; One Death Reported  Consumer Product Safety CommissionMore than 2 million infant swings, rockers recalled after 10-month-old dies  CBS New York4moms recalls millions of baby swings and rockers  CNNRecall Roundup: Baby swings, frozen pizzas, Capri Sun pouches pulled from stores  KSAT 12View Full Coverage on Google News

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14:03 Phys.org The entanglement of two quantum memory systems 12.5 km apart from each other

Quantum computing technology could have notable advantages over classical computing technology, including a faster speed and the ability to tackle more complex problems. In recent years, some researchers have also been exploring the possible establishment of a "quantum internet," a network that would allow quantum devices to exchange information, just like classical computing devices exchange information today.

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15.08.2022
11:03 Technology.org A new connection between topology and quantum entanglement

Topology and entanglement are two powerful principles for characterizing the structure of complex quantum states. In a new

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12.08.2022
08:23 Arxiv.org Physics Entanglement-Enhanced Quantum Metrology in Colored Noise by Quantum Zeno Effect. (arXiv:2208.05847v1 [quant-ph])

In open quantum systems, the precision of metrology inevitably suffers from the noise. {In Markovian open quantum dynamics, the precision can not be improved by using entangled probes although the measurement time is effectively shortened.} However, it was predicted over one decade ago that in a non-Markovian one, the error can be significantly reduced by the quantum Zeno effect (QZE) [Chin, Huelga, and Plenio, Phys. Rev. Lett. \textbf{109}, 233601 (2012)]. In this work, we apply a recently-developed quantum simulation approach to experimentally verify that entangled probes can improve the precision of metrology by the QZE. Up to $n=7$ qubits, we demonstrate that the precision has been improved by a factor of $n^{1/4}$, which is consistent with the theoretical prediction. Our quantum simulation approach may provide an intriguing platform for experimental verification of various quantum metrology schemes.

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11.08.2022
23:33 Phys.org Researchers explore a new connection between topology and quantum entanglement

Topology and entanglement are two powerful principles for characterizing the structure of complex quantum states. In a new paper in the journal Physical Review X, researchers from the University of Pennsylvania establish a relationship between the two.

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04:12 Arxiv.org Physics Light-matter entanglement after above-threshold ionization processes in atoms. (arXiv:2208.05245v1 [quant-ph])

It was recently shown in [P. Stammer et al, arXiv:2206.04308 (2022)] that, in above-threshold ionization processes, the displacement generated in the quantum state of the electromagnetic field after the interaction with the atomic system, depends on the kinetic energy and emission direction of the generated photoelectrons. Since the electron can get ionized with different values of momentum, this allows us to write an entangled state between light and matter where different values of the photoelectron momentum are associated to different displacements in the quantum optical state. Here, we study the light-matter entanglement by means of the entropy of entanglement, and we analyze its dependence on the final kinetic energy of the emitted photoelectrons. We first study the range of laser parameters under which the displacement starts to be significant at the single-atom level. Additionally, we use the Wigner function of the light state of the driving field mode to motivate the

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09.08.2022
17:30 Aps.org Editors' Suggestions Radio-Frequency Manipulation of State Populations in an Entangled Fluorine-Muon-Fluorine System

Author(s): David Billington, Edward Riordan, Majdi Salman, Daniel Margineda, George J. W. Gill, Stephen P. Cottrell, Iain McKenzie, Tom Lancaster, Michael J. Graf, and Sean R. GiblinMuon spin relaxation is used to demonstrate the experimental manipulation of entangled states of the spin of implanted positive muons in a bulk crystal. [Phys. Rev. Lett. 129, 077201] Published Tue Aug 09, 2022

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08.08.2022
05:13 Arxiv.org Math Toeplitz separability, entanglement, and complete positivity using operator system duality. (arXiv:2208.03236v1 [math.OA])

A new proof is presented of a theorem of L.~Gurvits, which states that the cone of positive block-Toeplitz matrices with matrix entries has no entangled elements. We also show that in the cone of positive Toeplitz matrices with Toeplitz entries, entangled elements exist in all dimensions. The proof of the Gurvits separation theorem is achieved by making use of the structure of the operator system dual of the operator system $C(S^1)^{(n)}$ of $n\times n$ Toeplitz matrices over the complex field, and by determining precisely the structure of the generators of the extremal rays of the positive cones of the operator systems $C(S^1)^{(n)}\otimes_{\rm min} \mathcal B (\mathcal H)$ and $C(S^1)_{(n)}\otimes_{\rm min} \mathcal B (\mathcal H)$, where $\mathcal H$ is an arbitrary Hilbert space and $C(S^1)_{(n)}$ is the operator system dual of $C(S^1)^{(n)}$. Our approach also has the advantage of providing some new information concerning positive Toeplitz matrices whose entries are from the type

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03.08.2022
03:53 Arxiv.org Math Quantum teleportation in the commuting operator framework. (arXiv:2208.01181v1 [math.OA])

We introduce a notion of teleportation scheme between subalgebras of semi-finite von Neumann algebras in the commuting operator model of locality. Using techniques from subfactor theory, we present unbiased teleportation schemes for relative commutants $N'\cap M$ of a large class of finite-index inclusions $N\subseteq M$ of tracial von Neumann algebras, where the unbiased condition means that no information about the teleported observables are contained in the classical communication sent between the parties. For a large class of subalgebras $N$ of matrix algebras $M_n(\mathbb{C})$, including those relevant to hybrid classical/quantum codes, we show that any tight teleportation scheme for $N$ necessarily arises from an orthonormal unitary Pimsner-Popa basis of $M_n(\mathbb{C})$ over $N'$, generalising work of Werner. Combining our techniques with those of Brannan-Ganesan-Harris, we compute quantum chromatic numbers for a variety of quantum graphs arising from finite-dimensional

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03:52 Arxiv.org Physics Entangled X-ray Photon Pair Generation by Free Electron Lasers. (arXiv:2208.01335v1 [quant-ph])

Einstein, Podolsky and Rosen's prediction on incompleteness of quantum mechanics was overturned by experimental tests on Bell's inequality that confirmed the existence of quantum entanglement. In X-ray optics, entangled photon pairs can be generated by X-ray parametric down conversion (XPDC), which is limited by relatively low efficiency. Meanwhile, free electron laser (FEL) has successfully lased at X-ray frequencies recently. However, FEL is usually seen as a classical light source, and its quantum effects are considered minor corrections to the classical theory. Here we investigate entangled X-ray photon pair emissions in FEL. We establish a theory for coherently amplified entangled photon pair emission from microbunched electron pulses in the undulator. We also propose an experimental scheme for the observation of the entangled photon pairs via energy and spatial correlation measurements. Such an entangled X-ray photon pair source is of great importance in quantum optics and other

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02.08.2022
06:32 Arxiv.org Math Growth of entanglement of generic states under dual-unitary dynamics. (arXiv:2208.00030v1 [cond-mat.stat-mech])

Dual-unitary circuits are a class of locally-interacting quantum many-body systems displaying unitary dynamics also when the roles of space and time are exchanged. These systems have recently emerged as a remarkable framework where certain features of many-body quantum chaos can be studied exactly. In particular, they admit a class of "solvable" initial states for which, in the thermodynamic limit, one can access the full non-equilibrium dynamics. This reveals a surprising property: when a dual-unitary circuit is prepared in a solvable state the quantum entanglement between two complementary spatial regions grows at the maximal speed allowed by the local structure of the evolution. Here we investigate the fate of this property when the system is prepared in a generic pair-product state. We show that in this case the entanglement increment during a time step is sub-maximal for finite times, however, it approaches the maximal value in the infinite-time limit. This statement is proven

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01.08.2022
09:33 Arxiv.org Physics Generation of entanglement from mechanical rotation. (arXiv:2207.14371v1 [quant-ph])

Many phenomena and fundamental predictions, ranging from Hawking radiation to the early evolution of the Universe rely on the interplay between quantum mechanics and gravity or more generally, quantum mechanics in curved spacetimes. However, our understanding is hindered by the lack of experiments that actually allow us to probe quantum mechanics in curved spacetime in a repeatable and accessible way. Here we propose an experimental scheme for a photon that is prepared in a path superposition state across two rotating Sagnac interferometers that have different diameters and thus represent a superposition of two different spacetimes. We predict the generation of genuine entanglement even at low rotation frequencies and show how these effects could be observed even due to the Earth's rotation. These predictions provide an accessible platform in which to study the role of the underlying spacetime in the generation of entanglement.

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09:13 Arxiv.org CS Entangled Rendezvous: A Possible Application of Bell Non-Locality For Mobile Agents on Networks. (arXiv:2207.14404v1 [quant-ph])

Rendezvous is an old problem of assuring that two or more parties, initially separated, not knowing the position of each other, and not allowed to communicate, meet without pre-agreement on the meeting point. This problem has been extensively studied in classical computer science and has vivid importance to modern applications like coordinating a fleet of drones in an enemy's territory. Quantum non-locality, like Bell inequality violation, has shown that in many cases quantum entanglement allows for improved coordination of two separated parties compared to classical sources. The non-signaling correlations in many cases even strengthened such phenomena. In this work, we analyze, how Bell non-locality can be used by asymmetric location-aware agents trying to rendezvous on a finite network with a limited number of steps. We provide the optimal solution to this problem for both agents using quantum resources, and agents with only ``classical'' computing power. Our results show that for

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28.07.2022
18:31 Physics.Aps.org Distant Memories Entangled

Author(s): Michael SchirberOn the road to a quantum internet, researchers demonstrate entanglement of two memory elements located 12.5 km apart in an urban environment. [Physics 15, s101] Published Thu Jul 28, 2022

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17:30 Aps.org Editors' Suggestions Postselected Entanglement Between Two Atomic Ensembles Separated by 12.5 km

Author(s): Xi-Yu Luo, Yong Yu, Jian-Long Liu, Ming-Yang Zheng, Chao-Yang Wang, Bin Wang, Jun Li, Xiao Jiang, Xiu-Ping Xie, Qiang Zhang, Xiao-Hui Bao, and Jian-Wei PanOn the road to a quantum internet, researchers demonstrate entanglement of two memory elements located 12.5 kilometers apart in an urban environment. [Phys. Rev. Lett. 129, 050503] Published Thu Jul 28, 2022

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06:03 Arxiv.org Physics Entanglement between a trapped ion qubit and a 780-nm photon via quantum frequency conversion. (arXiv:2207.13680v1 [quant-ph])

Future quantum networks will require the ability to produce matter-photon entanglement at photon frequencies not naturally emitted from the matter qubit. This allows for a hybrid network architecture, where these photons can couple to other tools and quantum technologies useful for tasks such as multiplexing, routing, and storage, but which operate at wavelengths different from that of the matter qubit source, while also reducing network losses. Here, we demonstrate entanglement between a trapped ion and a 780 nm photon, a wavelength which can interact with neutral-Rb-based quantum networking devices. A single barium ion is used to produce 493 nm photons, entangled with the ion, which are then frequency converted to 780 nm while preserving the entanglement. We generate ion-photon entanglement with fidelities $\geq$ 0.93(2) and $\geq$ 0.84(2) for 493 nm and 780 nm photons respectively with the fidelity drop arising predominantly from a reduction in the signal-noise of our detectors at

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05:43 Arxiv.org Math Entangled Quantum States of Causal Fermion Systems and Unitary Group Integrals. (arXiv:2207.13157v1 [math-ph])

This paper is dedicated to a detailed analysis and computation of quantum states of causal fermion systems. The mathematical core is to compute integrals over the unitary group asymptotically for a large dimension of the group, for various integrands with a specific scaling behavior in this dimension. It is shown that, in a well-defined limiting case, the localized refined pre-state is positive and allows for the description of general entangled states.

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27.07.2022
22:10 ScienceDaily.com A key role for quantum entanglement

A method known as quantum key distribution has long held the promise of communication security unattainable in conventional cryptography. An international team of scientists has now demonstrated experimentally, for the first time, an approach to quantum key distribution that is based on high-quality quantum entanglement -- offering much broader security guarantees than previous schemes.

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21:00 Nature.Com Quantum entanglement provides a key to improved security

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19:31 Physics.Aps.org Hiding Secrets Using Quantum Entanglement

Author(s): Sophia ChenThree experiments demonstrate the key elements of a quantum cryptographic scheme that predictions indicate should be unhackable, bringing the promise of quantum encryption technologies a step closer to reality. [Physics 15, 116] Published Wed Jul 27, 2022

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18:03 Phys.org Quantum key distribution based on high-quality quantum entanglement

A method known as quantum key distribution has long held the promise of communication security unattainable in conventional cryptography. An international team of scientists has now demonstrated experimentally, for the first time, an approach to quantum key distribution that is based on high-quality quantum entanglement—offering much broader security guarantees than previous schemes.

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26.07.2022
11:13 Arxiv.org Physics PIGSFLI: A Path Integral Ground State Monte Carlo Algorithm for Entanglement of Lattice Bosons. (arXiv:2207.11301v1 [cond-mat.quant-gas])

A ground state path integral quantum Monte Carlo algorithm is introduced that allows for the simulation of lattice bosons at zero temperature. The method is successfully benchmarked against the one dimensional Bose-Hubbard model through comparison with the potential and kinetic energy computed via exact diagonalization. After successful validation, an estimator is introduced to measure the R\'enyi entanglement entropy between spatial subregions which is explored across the phase diagram of the one dimensional Bose-Hubbard model for systems consisting of up to 256 sites at unit-filling, far beyond the reach of exact diagonalization. The favorable scaling of the algorithm is demonstrated through a further measurement of the R\'enyi entanglement entropy at the two dimensional superfluid-insulator critical point for large system sizes, confirming the existence of the expected entanglement boundary law in the ground state. The R\'enyi entanglement estimator is extended to measure the

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10:43 Arxiv.org CS Maximizing Entanglement Routing Rate in Quantum Networks: Approximation Algorithms. (arXiv:2207.11821v1 [cs.NI])

There will be a fast-paced shift from conventional network systems to novel quantum networks that are supported by the quantum entanglement and teleportation, key technologies of the quantum era, to enable secured data transmissions in the next-generation of the Internet. Despite this prospect, migration to quantum networks cannot be done at once, especially on the aspect of quantum routing. In this paper, we study the maximizing entangled routing rate (MERR) problem. In particular, given a set of demands, we try to determine entangled routing paths for the maximum number of demands in the quantum network while meeting the network's fidelity. We first formulate the MERR problem using an integer linear programming (ILP) model to capture the traffic patent for all demands in the network. We then leverage the theory of relaxation of ILP to devise two efficient algorithms including HBRA and RRA with provable approximation ratios for the objective function. To deal with the challenge of the

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10:43 Arxiv.org CS A Multiple-Entanglement Routing Framework for Quantum Networks. (arXiv:2207.11817v1 [cs.NI])

Quantum networks are gaining momentum in finding applications in a wide range of domains. However, little research has investigated the potential of a quantum network framework to enable highly reliable communications. The goal of this work is to investigate and design the multiple-entanglement routing framework, namely k-entangled routing. In particular, the $k$-entangled routing will enable k paths connecting all demands (source-destination pairs) in the network. To design the $k$-entangled routing, we propose two algorithms that are called Sequential Multi-path Scheduling Algorithm and Min-Cut-based Multi-path Scheduling Algorithm. In addition, we evaluate the performance of the proposed algorithms and models through a realistic quantum network simulator, NetSquid, that models the stochastic processes underlying quantum communications. The results show that the proposed algorithms (SMPSA and MCSA) largely enhance the network's traffic flexibility. The proposed paradigms would lay

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10:43 Arxiv.org CS Orientation and Context Entangled Network for Retinal Vessel Segmentation. (arXiv:2207.11396v1 [cs.CV])

Most of the existing deep learning based methods for vessel segmentation neglect two important aspects of retinal vessels, one is the orientation information of vessels, and the other is the contextual information of the whole fundus region. In this paper, we propose a robust Orientation and Context Entangled Network (denoted as OCE-Net), which has the capability of extracting complex orientation and context information of the blood vessels. To achieve complex orientation aware, a Dynamic Complex Orientation Aware Convolution (DCOA Conv) is proposed to extract complex vessels with multiple orientations for improving the vessel continuity. To simultaneously capture the global context information and emphasize the important local information, a Global and Local Fusion Module (GLFM) is developed to simultaneously model the long-range dependency of vessels and focus sufficient attention on local thin vessels. A novel Orientation and Context Entangled Non-local (OCE-NL) module is proposed

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25.07.2022
19:30 Aps.org Editors' Suggestions Entanglement Estimation in Tensor Network States via Sampling

Author(s): Noa Feldman, Augustine Kshetrimayum, Jens Eisert, and Moshe GoldsteinA new method allows for the estimation of entanglement in quantum states represented by high dimensional tensor networks, extending the size of tractable systems beyond exact methods. [PRX Quantum 3, 030312] Published Mon Jul 25, 2022

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06:53 Arxiv.org Physics On-chip generation of hybrid polarization-frequency entangled biphoton states. (arXiv:2207.10943v1 [quant-ph])

We demonstrate a chip-integrated semiconductor source that combines polarization and frequency entanglement, allowing the generation of entangled biphoton states in a hybrid degree of freedom without postmanipulation. Our AlGaAs device is based on type-II spontaneous parametric down-conversion (SPDC) in a counterpropagating phase-matching scheme, in which the modal birefringence lifts the degeneracy between the two possible nonlinear interactions. This allows the direct generation of polarization-frequency entangled photons, at room temperature and telecom wavelength, and in two distinct spatial modes, offering enhanced flexibility for quantum information protocols. The state entanglement is quantified by a combined measurement of the joint spectrum and Hong-ou-Mandel interference of the biphotons, allowing to reconstruct a restricted density matrix in the hybrid polarization-frequency space.

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22.07.2022
16:13 Phys.org Physicists find signatures of highly entangled quantum matter

Via large-scale simulations on supercomputers, a research team from the Department of Physics, the University of Hong Kong (HKU), discovered clear evidence to characterize a highly entangled quantum matter phase—the quantum spin liquid (QSL), a phase of matter that remains disordered even at very low temperatures. This research has recently been published in npj Quantum Materials.

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07:13 Arxiv.org Math Entanglement properties of one-dimensional chiral topological insulators. (arXiv:2207.10558v1 [cond-mat.str-el])

We consider a general one-dimensional chiral topological insulator with winding number $\mathcal{I}$. We prove that when the system is divided spatially into two equal halves, the single particle entanglement spectrum has $2|\mathcal{I}|$ protected eigenvalues at $1/2$. Therefore the number fluctuations in one half are bounded from below by $\Delta N^2\geq |\mathcal{I}|/2$ and the entanglement entropy by $S\geq 2|\mathcal{I}|\ln 2$.

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20.07.2022
18:30 Aps.org Editors' Suggestions Generalized Gibbs ensemble description of real-space entanglement spectra of $(2+1)$-dimensional chiral topological systems with SU(2) symmetry

Author(s): Mark J. Arildsen and Andreas W. W. LudwigLi and Haldane observed that low-lying entanglement spectra of ground states of (2+1)D chiral topological phases display characteristic degeneracies of the (1+1)D conformal field theory (CFT) appearing at a physical boundary. This work explains the finite-size splittings of these degeneracies by irrelevant deformations of a (1+0)D boundary of the CFT, representing the ground state. These intriguingly arise from operators of fractional dimension in certain entanglement spectra. This approach has applications for diagnosing chirality in topological projected entangled pair states (PEPS). [Phys. Rev. B 106, 035138] Published Wed Jul 20, 2022

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05:53 Arxiv.org Physics Broadband polarization-entangled source for C+L-band flex-grid quantum networks. (arXiv:2207.08909v1 [quant-ph])

The rising demand for transmission capacity in optical networks has motivated steady interest in expansion beyond the standard C-band (1530-1565 nm) into the adjacent L-band (1565-1625 nm), for an approximate doubling of capacity in a single stroke. However, in the context of quantum networking, the ability to leverage the L-band will require advanced tools for characterization and management of entanglement resources which have so far been lagging. In this work, we demonstrate an ultrabroadband two-photon source integrating both C- and L-band wavelength-selective switches for complete control of spectral routing and allocation across 7.5 THz in a single setup. Polarization state tomography of all 150 pairs of 25 GHz-wide channels reveals an average fidelity of 0.98 and total distillable entanglement greater than 181 kebits/s. This source is explicitly designed for flex-grid optical networks and can facilitate optimal utilization of entanglement resources across the full C+L-band.

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19.07.2022
08:32 Arxiv.org Math R\'{e}nyi entanglement entropy after a quantum quench starting from insulating states in a free boson system. (arXiv:2207.08353v1 [quant-ph])

We investigate the time-dependent R\'{e}nyi entanglement entropy after a quantum quench starting from the Mott-insulating and charge-density-wave states in a one-dimensional free boson system. The second R\'{e}nyi entanglement entropy is found to be the negative of the logarithm of the permanent of a matrix consisting of time-dependent single-particle correlation functions. From this relation and a permanent inequality, we obtain rigorous conditions for satisfying the volume-law entanglement growth. We also succeed in calculating the time evolution of the entanglement entropy in unprecedentedly large systems by brute-force computations of the permanent. We discuss possible applications of our findings to the real-time dynamics of noninteracting bosonic systems.

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08:32 Arxiv.org Math MDS Entanglement-Assisted Quantum Codes of Arbitrary Lengths and Arbitrary Distances. (arXiv:2207.08093v1 [quant-ph])

Quantum error correction is fundamentally important for quantum information processing and computation. Quantum error correction codes have been studied and constructed since the pioneering work of Shor and Steane. Optimal (called MDS) $q$-qubit quantum codes attaining the quantum Singleton bound were constructed for very restricted lengths $n \leq q^2+1$. Entanglement-assisted quantum error correction (EAQEC) code was proposed to use the pre-shared maximally entangled state for the purpose of enhancing error correction capability. Recently there have been a lot of constructions of such MDS EAQEC codes attaining the quantum Singleton bound for very restricted lengths. In this paper we construct such MDS EAQEC $[[n, k, d, c]]_q$ codes for arbitrary $n$ satisfying $n \leq q^2+1$ and arbitrary distance $d\leq \frac{n+2}{2}$. It is proved that for any given length $n$ satisfying $O(q^2)=n \leq q^2+1$ and any given distance $ O(q^2)=d \leq \frac{n+2}{2}$, there exist at least $O(q^2)$ MDS

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08:32 Arxiv.org CS MDS Entanglement-Assisted Quantum Codes of Arbitrary Lengths and Arbitrary Distances. (arXiv:2207.08093v1 [quant-ph])

Quantum error correction is fundamentally important for quantum information processing and computation. Quantum error correction codes have been studied and constructed since the pioneering work of Shor and Steane. Optimal (called MDS) $q$-qubit quantum codes attaining the quantum Singleton bound were constructed for very restricted lengths $n \leq q^2+1$. Entanglement-assisted quantum error correction (EAQEC) code was proposed to use the pre-shared maximally entangled state for the purpose of enhancing error correction capability. Recently there have been a lot of constructions of such MDS EAQEC codes attaining the quantum Singleton bound for very restricted lengths. In this paper we construct such MDS EAQEC $[[n, k, d, c]]_q$ codes for arbitrary $n$ satisfying $n \leq q^2+1$ and arbitrary distance $d\leq \frac{n+2}{2}$. It is proved that for any given length $n$ satisfying $O(q^2)=n \leq q^2+1$ and any given distance $ O(q^2)=d \leq \frac{n+2}{2}$, there exist at least $O(q^2)$ MDS

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18.07.2022
19:26 QuantaMagazine.org Computer Science Proof Unveils Unexpected Form of Entanglement

Three computer scientists have solved the NLTS conjecture, proving that systems of entangled particles can remain difficult to analyze even away from extremes. The post Computer Science Proof Unveils Unexpected Form of Entanglement first appeared on Quanta Magazine

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15.07.2022
05:03 Arxiv.org Physics Fulfilling entanglement's benefit via converting correlation to coherence. (arXiv:2207.06609v1 [quant-ph])

Entanglement boosts performance limits in sensing and communication, and surprisingly even more in presence of entanglement-breaking noise. However, to fulfill such advantages requires a practical receiver design, a challenging task as information is encoded in the feeble quantum correlation after entanglement's death. We propose a conversion module to capture and transform such correlation to coherent quadrature displacement, and therefore enables the optimal receiver design for a wide range of entanglement-enhanced protocols, including target detection (quantum illumination), phase estimation, classical communication, target ranging and arbitrary thermal-loss channel pattern classification. The conversion module maps the quantum detection problem to the semi-classical detection of noisy coherent states via heterodyne and passive linear optics. Our module is completely off-the-shelf and provides a paradigm for processing noisy quantum correlations.

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05:03 Arxiv.org CS Optimal entanglement distribution policies in homogeneous repeater chains with cutoffs. (arXiv:2207.06533v1 [quant-ph])

Quantum repeater chains can be used to distribute bipartite entanglement among two end nodes. We study the limits of entanglement distribution using a chain of quantum repeaters that have quantum memories. A maximum storage time, known as cutoff, is enforced on these memories to ensure high-quality end-to-end entanglement. To generate end-to-end entanglement, the nodes can perform the following operations: wait, attempt the generation of an elementary entangled link with its neighbor(s), or perform an entanglement swapping measurement. Nodes follow a policy that determines what operation they must perform in each time step. Global-knowledge policies take into account all the information about the entanglement already produced. Here, we find global-knowledge policies that minimize the expected time to produce end-to-end entanglement. We model the evolution of this system as a Markov decision process, and find optimal policies using value and policy iteration. We compare optimal

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14.07.2022
17:30 Aps.org Editors' Suggestions Reduced density matrix and entanglement of interacting quantum field theories with Hamiltonian truncation

Author(s): Patrick Emonts and Ivan KukuljanThe authors develop a method to compute entanglement measures of quantum field theories directly in the continuum based on Hamiltonian truncation. [Phys. Rev. Research 4, 033039] Published Thu Jul 14, 2022

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07:43 Arxiv.org Physics Bright entangled photon source without stringent crystal temperature and laser frequency stabilization. (arXiv:2207.06117v1 [quant-ph])

Entangled photon sources (EPS), the major building block for a variety of quantum communication protocols, are commonly developed by utilizing the spontaneous parametric down-conversion (SPDC) in $\chi^{2}$ nonlinear bulk optical materials. While high nonlinearity and long interaction length have established the superiority of the periodically poled crystals for EPSs, the phase-matching condition of such crystals is very sensitive to the fluctuation of the crystal temperature and the laser wavelength. As a result, deploying such sources outside the laboratory, for example, satellite-based applications, demands a stringent mass and power budget, thus enhancing the mission complexity and cost. We report a bright, stable entangled photon source with a relaxed requirement of crystal temperature and laser wavelength stabilization. Using a periodically poled KTP crystal inside a polarization Sagnac interferometer producing degenerate, type-0 phase-matched entangled photon pairs at 810 nm in

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07:43 Arxiv.org Physics Unsupervised Recognition of Informative Features via Tensor Network Machine Learning and Quantum Entanglement Variations. (arXiv:2207.06031v1 [quant-ph])

Given an image of a white shoe drawn on a blackboard, how are the white pixels deemed (say by human minds) to be informative for recognizing the shoe without any labeling information on the pixels? Here we investigate such a "white shoe" recognition problem from the perspective of tensor network (TN) machine learning and quantum entanglement. Utilizing a generative TN that captures the probability distribution of the features as quantum amplitudes, we propose an unsupervised recognition scheme of informative features with the variations of entanglement entropy (EE) caused by designed measurements. In this way, a given sample, where the values of its features are statistically meaningless, is mapped to the variations of EE that are statistically meaningful. We show that the EE variations identify the features that are critical to recognize this specific sample, and the EE itself reveals the information distribution from the TN model. The signs of the variations further reveal the

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07:43 Arxiv.org CS Unsupervised Recognition of Informative Features via Tensor Network Machine Learning and Quantum Entanglement Variations. (arXiv:2207.06031v1 [quant-ph])

Given an image of a white shoe drawn on a blackboard, how are the white pixels deemed (say by human minds) to be informative for recognizing the shoe without any labeling information on the pixels? Here we investigate such a "white shoe" recognition problem from the perspective of tensor network (TN) machine learning and quantum entanglement. Utilizing a generative TN that captures the probability distribution of the features as quantum amplitudes, we propose an unsupervised recognition scheme of informative features with the variations of entanglement entropy (EE) caused by designed measurements. In this way, a given sample, where the values of its features are statistically meaningless, is mapped to the variations of EE that are statistically meaningful. We show that the EE variations identify the features that are critical to recognize this specific sample, and the EE itself reveals the information distribution from the TN model. The signs of the variations further reveal the

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13.07.2022
10:23 Arxiv.org Math How Much Entanglement Does a Quantum Code Need?. (arXiv:2207.05647v1 [quant-ph])

In the setting of entanglement-assisted quantum error-correcting codes (EAQECCs), the sender and the receiver have access to pre-shared entanglement. Such codes promise better information rates or improved error handling properties. Entanglement incurs costs and must be judiciously calibrated in designing quantum codes with good performance, relative to their deployment parameters. Revisiting known constructions, we devise tools from classical coding theory to better understand how the amount of entanglement can be varied. We present three new propagation rules and discuss how each of them affects the error handling. Tables listing the parameters of the best performing qubit and qutrit EAQECCs that we can explicitly construct are supplied for reference and comparison.

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10:23 Arxiv.org CS How Much Entanglement Does a Quantum Code Need?. (arXiv:2207.05647v1 [quant-ph])

In the setting of entanglement-assisted quantum error-correcting codes (EAQECCs), the sender and the receiver have access to pre-shared entanglement. Such codes promise better information rates or improved error handling properties. Entanglement incurs costs and must be judiciously calibrated in designing quantum codes with good performance, relative to their deployment parameters. Revisiting known constructions, we devise tools from classical coding theory to better understand how the amount of entanglement can be varied. We present three new propagation rules and discuss how each of them affects the error handling. Tables listing the parameters of the best performing qubit and qutrit EAQECCs that we can explicitly construct are supplied for reference and comparison.

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12.07.2022
16:43 ExtremeTech.com Researchers Set New Quantum Entanglement Distance Record

An experiment in Germany that set a new entanglement distance record -- with atoms rather than photons -- could help shed some light on this quirk of the universe.  The post Researchers Set New Quantum Entanglement Distance Record appeared first on ExtremeTech.

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06:03 Arxiv.org Math Remarks on Entanglement for Fuzzy Geometry and Gravity. (arXiv:2207.04776v1 [hep-th])

We consider defining a fuzzy space by a specific state in a fermionic field theory in terms of which all the observables for the space can be evaluated. This allows for a definition of entanglement for a fuzzy space by direct integration of the fields over a certain region. Even though the resulting formula for the entanglement entropy (EE) is similar to what has been used in the quantum Hall effect, our derivation provides a novel perspective. We also review and strengthen the arguments for the EE to be described by a generalized Chern-Simons form.

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06:03 Arxiv.org Math Information Rates with Non Ideal Photon Detectors in Time-Entanglement Based QKD. (arXiv:2207.04146v1 [cs.IT])

We develop new methods of quantifying the impact of photon detector imperfections on achievable secret key rates in Time-Entanglement based Quantum Key Distribution (QKD). We address photon detection timing jitter, detector downtime, and photon dark counts and show how each may decrease the maximum achievable secret key rate in different ways. We begin with a standard Discrete Memoryless Channel (DMC) model to get a good bound on the mutual information lost due to the timing jitter, then introduce a novel Markov Chain (MC) based model to characterize the effect of detector downtime and show how it introduces memory to the key generation process. Finally, we propose a new method of including dark counts in the analysis that shows how dark counts can be especially detrimental when using the common Pulse Position Modulation (PPM) for key generation. Our results show that these three imperfections can significantly reduce the achievable secret key rate when using PPM for QKD. Additionally,

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06:03 Arxiv.org CS Information Rates with Non Ideal Photon Detectors in Time-Entanglement Based QKD. (arXiv:2207.04146v1 [cs.IT])

We develop new methods of quantifying the impact of photon detector imperfections on achievable secret key rates in Time-Entanglement based Quantum Key Distribution (QKD). We address photon detection timing jitter, detector downtime, and photon dark counts and show how each may decrease the maximum achievable secret key rate in different ways. We begin with a standard Discrete Memoryless Channel (DMC) model to get a good bound on the mutual information lost due to the timing jitter, then introduce a novel Markov Chain (MC) based model to characterize the effect of detector downtime and show how it introduces memory to the key generation process. Finally, we propose a new method of including dark counts in the analysis that shows how dark counts can be especially detrimental when using the common Pulse Position Modulation (PPM) for key generation. Our results show that these three imperfections can significantly reduce the achievable secret key rate when using PPM for QKD. Additionally,

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11.07.2022
08:43 Arxiv.org Math Quantum Entanglement in String Theory. (arXiv:2207.03624v1 [hep-th])

We define entanglement entropy in string perturbation theory using the orbifold method -- a stringy analog of the replica method in field theory. To this end, we use the Newton series to analytically continue in $N$ the partition functions for string orbifolds on $\mathbb{C}/\mathbb{Z}_N$ conical spaces, known for all odd integer $N$. In the concrete example of ten-dimensional Type-IIB strings, the one-loop partition function can be computed explicitly and the one-loop entropy can be expressed as a manifestly modular invariant series in terms of the Weierstrass $\wp$ function. The convergence of the series is not evident but, from physical arguments based on holography, it is expected to yield a finite answer together with the tree level contribution. This method has a natural generalization to other string compactifications and to higher genus Riemann surfaces; it can provide a modular invariant definition of generalized entropy in a given string vacuum to all orders, of potential

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08:42 Arxiv.org Physics Fermionic Entanglement and Correlation. (arXiv:2207.03848v1 [quant-ph])

Entanglement plays a central role in numerous fields of quantum science. However, as one departs from the typical "Alice versus Bob" setting into the world of indistinguishable fermions, it is not immediately clear how the concept of entanglement is defined among these identical particles. Our endeavor to recover the notion of subsystems, or mathematically speaking, the tensor product structure of the Hilbert space, lead to two natural pictures of defining fermionic entanglement: the particle picture and the mode picture. In the particle picture, entanglement characterizes the deviation of a fermionic quantum state from the non-interacting ones, e.g., single Slater determinants. In the mode picture, we recover the notion of subsystems, by referring to the partitioning of the orbital/mode that the fermions occupy, which allows us to naturally adopt the formalism of entanglement between distinguishable constituents. Both pictures reveal essential and interconnected aspects of fermionic

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08:42 Arxiv.org Physics Amorphous Entangled Active Matter. (arXiv:2207.03665v1 [cond-mat.soft])

The design of amorphous entangled systems, specifically from soft and active materials, has the potential to open exciting new classes of active, shape-shifting, and task-capable 'smart' materials. However, the global emergent mechanics that arises from the local interactions of individual particles are not well understood. In this study, we examine the emergent properties of amorphous entangled systems in three different examples: an in-silico "smarticle" collection, its robophysical chain, and living entangled aggregate of worm blobs (L. variegatus). In simulations, we examine how material properties change for a collective composed of dynamic three-link robots. We compare three methods of controlling entanglement in a collective: externally oscillations, shape-changes, and internal oscillations. We find that large-amplitude changes of the particle's shape using the shape-change procedure produced the highest average number of entanglements, with respect to the aspect ratio (l/w),

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08.07.2022
09:13 Arxiv.org Physics Quantifying Electron Entanglement Faithfully. (arXiv:2207.03377v1 [quant-ph])

Entanglement is one of the most fascinating concepts of modern physics. In striking contrast to its abstract, mathematical foundation, its practical side is, however, remarkably underdeveloped. Even for systems of just two orbitals or sites no faithful entanglement measure is known yet. By exploiting the spin symmetries of realistic many-electron systems, we succeed in deriving a closed formula for the relative entropy of entanglement between electron orbitals. Its broad applicability in the quantum sciences is demonstrated: (i) in light of the second quantum revolution, it quantifies the true physical entanglement by incorporating the crucial fermionic superselection rule (ii) an analytic description of the long-distance entanglement in free electron chains is found, refining Kohn's locality principle (iii) the bond-order wave phase in the extended Hubbard model can be confirmed, and (iv) the quantum complexity of common molecular bonding structures could be marginalized through

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07.07.2022
18:50 ScienceDaily.com Quantum physics: Record entanglement of quantum memories

Researchers have entangled two quantum memories over a 33-kilometer-long fiber optic connection -- a record and an important step toward the quantum internet.

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17:30 Aps.org Editors' Suggestions Tracking the evolution from isolated dimers to many-body entanglement in ${\mathrm{NaLu}}_{x}{\mathrm{Yb}}_{1\text{−}x}{\mathrm{Se}}_{2}$

Author(s): Luke Pritchard Cairns, Ryan Day, Shannon Haley, Nikola Maksimovic, Josue Rodriguez, Hossein Taghinejad, John Singleton, and James AnalytisDetecting signatures of many-body entanglement in frustrated magnetic systems remains a grand challenge in condensed matter. In this work, the authors show that this problem can be made more tractable by looking at the evolution of dilute magnetic systems to fully packed frustrated magnets. They study the system NaLu 1 − x Yb x Se 2 as a model

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17:13 Phys.org Researchers achieve record entanglement of quantum memories

A network in which data transmission is perfectly secure against hacking? If physicists have their way, this will become reality one day with the help of the quantum mechanical phenomenon known as entanglement. For entangled particles, the rule is: If you measure the state of one of the particles, then you automatically know the state of the other. It makes no difference how far away the entangled particles are from each other. This is an ideal state of affairs for transmitting information over long distances in a way that renders eavesdropping impossible.

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04:33 Arxiv.org Math Positive maps and entanglement in real Hilbert spaces. (arXiv:2207.02510v1 [quant-ph])

The theory of positive maps plays a central role in operator algebras and functional analysis, and has countless applications in quantum information science. The theory was originally developed for operators acting on complex Hilbert spaces, and little is known about its variant on real Hilbert spaces. In this article we study positive maps acting on a full matrix algebra over the reals, pointing out a number of fundamental differences with the complex case and discussing their implications in quantum information. We provide a necessary and sufficient condition for a real map to admit a positive complexification, and connect the existence of positive maps with non-positive complexification with the existence of mixed states that are entangled in real Hilbert space quantum mechanics, but separable in the complex version, providing explicit examples both for the maps and for the states. Finally, we discuss entanglement breaking and PPT maps, and we show that a straightforward real

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06.07.2022
19:01 Nature.Com Quantum memories entangled over tens of kilometres of optical fibre

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04.07.2022
05:33 Arxiv.org Math Bipartite entanglement and the arrow of time. (arXiv:2207.00024v1 [quant-ph])

We provide a new perspective on the close relationship between entanglement and time. Our main focus is on bipartite entanglement, where this connection is foreshadowed both in the positive partial transpose criterion due to Peres [A. Peres, Phys. Rev. Lett., 77, 1413 (1996)] and in the classification of quantum within more general non-signalling bipartite correlations [M. Frembs and A. D\"oring, arXiv:2204.11471]. Extracting the relevant common features, we identify a necessary and sufficient condition for bipartite entanglement in terms of a compatibility condition with respect to time orientations in local observable algebras, which express the dynamics in the respective subsystems. We discuss the relevance of the latter in the broader context of von Neumann algebras and the thermodynamical notion of time naturally arising within the latter.

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29.06.2022
04:03 Arxiv.org Math Entanglement between uncoupled modes with time-dependent complex frequency. (arXiv:2206.14149v1 [quant-ph])

In this work we present the general unified description for the unitary time-evolution generated by time-dependent non-Hermitian Hamiltonians embedding the bosonic representations of $\mathfrak{su}(1,1)$ and $\mathfrak{su}(2)$ Lie algebras. We take into account a time-dependent Hermitian Dyson maps written in terms of the elements of those algebras with the relation between non-Hermitian and its Hermitian counterpart being independent of the algebra realization. As a direct consequence, we verify that a time-evolved state of uncoupled modes modulated by a time-dependent complex frequency may exhibits a non-zero entanglement even when the cross-operators, typical of the interaction between modes, are absent. This is due the non-local nature of the non-trivial dynamical Hilbert space metric encoded in the time-dependent parameters of the general Hermitian Dyson map, which depend on the imaginary part of the complex frequency.

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04:03 Arxiv.org Math New MDS Entanglement-Assisted Quantum Codes from $h$-Dimension Hermitian Hull MDS Codes. (arXiv:2206.13995v1 [cs.IT])

The intersection ${\bf C}\bigcap {\bf C}^{\perp_H}$ of a linear code ${\bf C} \subset {\bf F}_{q^2}$ and its Hermitian dual ${\bf C}^{\perp_H}$ is called the Hermitian hull of this code. A linear code ${\bf C} \subset {\bf F}_{q^2}$ satisfying ${\bf C} \subset {\bf C}^{\perp_H}$ is called Hermitian self-orthogonal. Many Hermitian self-orthogonal codes were given for the construction of MDS quantum error correction codes (QECCs). In this paper we prove that for a nonnegative integer $h$ satisfying $0 \leq h \leq k$, a linear Hermitian self-orthogonal $[n, k]_{q^2}$ code is equivalent to a linear $h$-dimension Hermitian hull code. Therefore a lot of new MDS entanglement-assisted quantum error correction (EAQEC) codes can be constructed from previous known Hermitian self-orthogonal codes. Actually our method shows that previous constructed quantum MDS codes from Hermitian self-orthogonal codes can be transformed to MDS entanglement-assisted quantum codes with nonzero consumption parameter

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04:02 Arxiv.org CS New MDS Entanglement-Assisted Quantum Codes from $h$-Dimension Hermitian Hull MDS Codes. (arXiv:2206.13995v1 [cs.IT])

The intersection ${\bf C}\bigcap {\bf C}^{\perp_H}$ of a linear code ${\bf C} \subset {\bf F}_{q^2}$ and its Hermitian dual ${\bf C}^{\perp_H}$ is called the Hermitian hull of this code. A linear code ${\bf C} \subset {\bf F}_{q^2}$ satisfying ${\bf C} \subset {\bf C}^{\perp_H}$ is called Hermitian self-orthogonal. Many Hermitian self-orthogonal codes were given for the construction of MDS quantum error correction codes (QECCs). In this paper we prove that for a nonnegative integer $h$ satisfying $0 \leq h \leq k$, a linear Hermitian self-orthogonal $[n, k]_{q^2}$ code is equivalent to a linear $h$-dimension Hermitian hull code. Therefore a lot of new MDS entanglement-assisted quantum error correction (EAQEC) codes can be constructed from previous known Hermitian self-orthogonal codes. Actually our method shows that previous constructed quantum MDS codes from Hermitian self-orthogonal codes can be transformed to MDS entanglement-assisted quantum codes with nonzero consumption parameter

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28.06.2022
17:30 Aps.org Editors' Suggestions Entanglement transitions from stochastic resetting of non-Hermitian quasiparticles

Author(s): Xhek Turkeshi, Marcello Dalmonte, Rosario Fazio, and Marco SchiròEntanglement is a key tool to classify quantum phases of matter in and out of equilibrium. Here, the authors introduce a phenomenological quasiparticle picture for entanglement dynamics in monitored systems evolving under the effect of quantum jumps. Within this picture, entanglement is carried by non-Hermitian quasiparticles, associated to the no-click limit of the measurement protocol, that propagate ballistically and are randomly reset with a rate given by their inverse lifetime. The authors show how this picture qualitatively reproduces the entanglement transition in the monitored Ising chain. [Phys. Rev. B 105, L241114] Published Tue Jun 28, 2022

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06:43 Arxiv.org Physics Tripartite high-dimensional magnon-photon entanglement in PT -symmetry broken phases of a non-Hermitian hybrid system. (arXiv:2206.12769v1 [quant-ph])

Hybrid systems that combine spin ensembles and superconducting circuits provide a promising platform for implementing quantum information processing. We propose a non-Hermitian magnoncircuit-QED hybrid model consisting of two cavities and an yttrium iron garnet (YIG) sphere placed in one of the cavities. Abundant exceptional points (EPs), parity-time (PT )-symmetry phases and PT -symmetry broken phases are investigated in the parameter space. Tripartite highdimensional entangled states can be generated steadily among modes of the magnon and photons in PT -symmetry broken phases, corresponding to which the stable quantum coherence exists. Results show that the tripartite high-dimensional entangled state is robust against the dissipation of hybrid system, independent of a certain initial state, and insensitive to the fluctuation of magnonphoton coupling. Further, we propose to simulate the hybrid model with an equivalent LCR circuit. This work may provide prospects for realizing

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24.06.2022
10:03 Arxiv.org Math Monogamy of entanglement between cones. (arXiv:2206.11805v1 [quant-ph])

A separable quantum state shared between parties $A$ and $B$ can be symmetrically extended to a quantum state shared between party $A$ and parties $B_1,\ldots ,B_k$ for every $k\in\mathbf{N}$. Quantum states that are not separable, i.e., entangled, do not have this property. This phenomenon is known as "monogamy of entanglement". We show that monogamy is not only a feature of quantum theory, but that it characterizes the minimal tensor product of general pairs of convex cones $\mathsf{C}_A$ and $\mathsf{C}_B$: The elements of the minimal tensor product $\mathsf{C}_A\otimes_{\min} \mathsf{C}_B$ are precisely the tensors that can be symmetrically extended to elements in the maximal tensor product $\mathsf{C}_A\otimes_{\max} \mathsf{C}^{\otimes_{\max} k}_B$ for every $k\in\mathbf{N}$. Equivalently, the minimal tensor product of two cones is the intersection of the nested sets of $k$-extendible tensors. It is a natural question when the minimal tensor product $\mathsf{C}_A\otimes_{\min}

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10:03 Arxiv.org Physics Perturbation theory under the truncated Wigner approximation reveals how system-environment entanglement formation drives quantum decoherence. (arXiv:2206.11306v1 [quant-ph])

Quantum decoherence is the disappearance of simple phase relations within a discrete quantum system as a result of interactions with an environment. For many applications, the question is not necessarily how to avoid (inevitable) system-environment interactions, but rather how to design environments that optimally preserve a system's phase relations in spite of such interactions. The formation of system-environment entanglement is a major driving mechanism for decoherence, and a detailed understanding of this process could inform strategies for conserving coherence optimally. This requires scalable, flexible, and systematically improvable quantum dynamical methods that retain detailed information about the entanglement properties of the environment, yet very few current methods offer this combination of features. Here, we address this need by introducing a theoretical framework wherein we combine the truncated Wigner approximation with standard time-dependent perturbation theory

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23.06.2022
05:43 Arxiv.org Math Entanglement in phase-space distribution for an anisotropic harmonic oscillator in noncommutative space. (arXiv:2206.10599v1 [quant-ph])

The bi-partite Gaussian state, corresponding to an anisotropic harmonic oscillator in a noncommutative-space, is investigated with the help of the Simon's separability condition (generalized Peres-Horodecki criterion). It turns out that, in order to exhibit the entanglement between the noncommutative co-ordinates, the parameters (mass and frequency) have to satisfy an unique constraint equation. Exact solutions for the system are obtained after diagonalizing the model, keeping the intrinsic symplectic structure intact. It is shown that, the identification of the entangled degrees of freedom is possible by studying the Wigner quasiprobability distribution in phase-space. We have shown that the co-ordinates are entangled only with the conjugate momentum corresponding to other co-ordinates.

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22.06.2022
08:23 Arxiv.org Math Entanglement-Assisted and Subsystem Quantum Codes: New Propagation Rules and Constructions. (arXiv:2206.09782v1 [cs.IT])

This paper proposes new propagation rules on quantum codes in the entanglement-assisted and in quantum subsystem scenarios. The rules lead to new families of such quantum codes whose parameters are demonstrably optimal. To obtain the results, we devise tools to puncture and shorten codes in ways that ensure their Hermitian hulls have certain desirable properties. More specifically, we give a general framework to construct $k$-dimensional generalized Reed-Solomon codes whose Hermitian hulls are $(k-1)$-dimensional maximum distance separable codes.

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08:23 Arxiv.org Physics Realizing an entanglement-based multi-user quantum network with integrated photonics. (arXiv:2206.09785v1 [quant-ph])

Quantum network facilitates the secure transmission of information between different users. Establishing communication links among multiple users in a scalable and efficient way is important for realizing a large-scale quantum network. Here we develop an energy-time entanglement-based dense wavelength division multiplexed network based on an integrated silicon nitride micro-ring resonator, which offers a wide frequency span (covering at least the entire C-band) and narrow bandwidth modes (~ 650MHz). Six pairs of photons are selected to form a fully and simultaneously connected four-user quantum network. The observed quantum interference visibilities are well above the classical limits among all users. Each pair of users perform the BBM92 protocol for quantum key distribution. Our results pave the way for realizing large-scale quantum networks with integrated photonic architecture.

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20.06.2022
06:43 Arxiv.org Physics Fully on-chip photonic turnkey quantum source for entangled qubit/qudit state generation. (arXiv:2206.08715v1 [physics.optics])

Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust and scalable chip formats with applications in long-distance quantum-secured communication, quantum-accelerated information processing and non-classical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers making them impractical, not reproducible prototype devices, hindering scalability and the transfer out of the lab into real-world applications. Here we demonstrate a fully integrated quantum light source, which overcomes these challenges through the combined integration of a laser cavity, a highly efficient tunable noise suppression filter ($> 55$ dB) exploiting the Vernier effect and a nonlinear microring for entangled photon pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically-pumped InP gain section and a Si$_3$N$_4$ low-loss

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17.06.2022
07:52 Arxiv.org CS Learning Interpretable Representations of Entanglement in Quantum Optics Experiments using Deep Generative Models. (arXiv:2109.02490v2 [cs.LG] UPDATED)

Quantum physics experiments produce interesting phenomena such as interference or entanglement, which are core properties of numerous future quantum technologies. The complex relationship between the setup structure of a quantum experiment and its entanglement properties is essential to fundamental research in quantum optics but is difficult to intuitively understand. We present a deep generative model of quantum optics experiments where a variational autoencoder is trained on a dataset of quantum optics experimental setups. In a series of computational experiments, we investigate the learned representation of our Quantum Optics Variational Auto Encoder (QOVAE) and its internal understanding of the quantum optics world. We demonstrate that the QOVAE learns an interpretable representation of quantum optics experiments and the relationship between experiment structure and entanglement. We show the QOVAE is able to generate novel experiments for highly entangled quantum states with

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07:52 Arxiv.org CS Searching Entangled Program Spaces. (arXiv:2206.07828v1 [cs.PL])

Many problem domains, including program synthesis and rewrite-based optimization, require searching astronomically large spaces of programs. Existing approaches often rely on building specialized data structures -- version-space algebras, finite tree automata, or e-graphs -- to compactly represent these programs. To find a compact representation, existing data structures exploit independence of subterms; they blow up when the choices of subterms are entangled. We introduce equality-constrained tree automata (ECTAs), a generalization of the three aforementioned data structures that can efficiently represent large spaces of programs with entangled subterms. We present efficient algorithms for extracting programs from ECTAs, implemented in a performant Haskell library, \texttt{ecta}. Using \texttt{ecta} we construct \textsc{Hectare}, a type-driven program synthesizer for Haskell. \textsc{Hectare} significantly outperforms a state-of-the-art synthesizer Hoogle+ -- providing an average

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15.06.2022
06:03 Arxiv.org Math Entanglement of inhomogeneous free fermions on hyperplane lattices. (arXiv:2206.06509v1 [cond-mat.stat-mech])

We introduce an inhomogeneous model of free fermions on a $(D-1)$-dimensional lattice with $D(D-1)/2$ continuous parameters that control the hopping strength between adjacent sites. We solve this model exactly, and find that the eigenfunctions are given by multidimensional generalizations of Krawtchouk polynomials. We construct a Heun operator that commutes with the chopped correlation matrix, and compute the entanglement entropy numerically for $D=2,3,4$, for a wide range of parameters. For $D=2$, we observe oscillations in the sub-leading contribution to the entanglement entropy, for which we conjecture an exact expression. For $D>2$, we find logarithmic violations of the area law for the entanglement entropy with nontrivial dependence on the parameters.

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14.06.2022
08:43 Arxiv.org Math Entanglement entropies of an interval in the free Schr\"odinger field theory on the half line. (arXiv:2206.06187v1 [hep-th])

We study the entanglement entropies of an interval adjacent to the boundary of the half line for the free fermionic spinless Schr\"odinger field theory at finite density and zero temperature, with either Neumann or Dirichlet boundary conditions. They are finite functions of the dimensionless parameter given by the product of the Fermi momentum and the length of the interval. The entanglement entropy displays an oscillatory behaviour, differently from the case of the interval on the whole line. This behaviour is related to the Friedel oscillations of the mean particle density on the half line at the entangling point. We find analytic expressions for the expansions of the entanglement entropies in the regimes of small and large values of the dimensionless parameter. They display a remarkable agreement with the curves obtained numerically. The analysis is extended to a family of free fermionic Lifshitz models labelled by their integer Lifshitz exponent, whose parity determines the

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08:43 Arxiv.org Physics Stationary Entanglement and Quantum State Transfer in Opto-magnomechanics. (arXiv:2206.05688v1 [quant-ph])

We show how to prepare a steady-state entangled state between magnons and optical photons in an opto-magnomechanical configuration, where a mechanical vibration mode couples to a magnon mode in a ferrimagnet by the dispersive magnetostrictive interaction, and to an optical cavity by the radiation pressure. We find that, by appropriately driving the magnon mode and the cavity to simultaneously activate the magnomechanical Stokes and the optomechanical anti-Stokes scattering, a stationary optomagnonic entangled state can be created. We further show that, by activating the magnomechanical state-swap interaction and by subsequently sending a weak red-detuned optical pulse to drive the cavity, the magnonic state can be read out in the cavity output field of the pulse via the mechanical transduction. The demonstrated entanglement and state readout protocols in such a novel opto-magnomechanical configuration allow us to optically control, prepare, and read out quantum states of collective

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09.06.2022
08:02 Arxiv.org Physics Slack-taut transition and emergent stiffness in bioinspired entangled filament networks. (arXiv:2206.04043v1 [physics.bio-ph])

Inspired by massive intermediate filament (IF) reorganization in superstretched epithelia, we examine computationally the principles controlling the mechanics of a set of entangled filaments whose ends slide on the cell boundary. We identify an entanglement metric and percolation threshold beyond which random loose networks self-organize into structurally optimal star-shaped configurations. A simple model connecting cellular and filament strains links emergent mechanics to cell geometry, network topology, and filament mechanics. We identify a safety net mechanism in IF networks and provide a framework to harness entanglement in soft materials.

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06.06.2022
09:12 Arxiv.org CS Entangled Residual Mappings. (arXiv:2206.01261v1 [cs.LG])

Residual mappings have been shown to perform representation learning in the first layers and iterative feature refinement in higher layers. This interplay, combined with their stabilizing effect on the gradient norms, enables them to train very deep networks. In this paper, we take a step further and introduce entangled residual mappings to generalize the structure of the residual connections and evaluate their role in iterative learning representations. An entangled residual mapping replaces the identity skip connections with specialized entangled mappings such as orthogonal, sparse, and structural correlation matrices that share key attributes (eigenvalues, structure, and Jacobian norm) with identity mappings. We show that while entangled mappings can preserve the iterative refinement of features across various deep models, they influence the representation learning process in convolutional networks differently than attention-based models and recurrent neural networks. In general, we

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02.06.2022
16:23 Phys.org Probing conjugation and parity symmetry with entangled double-strange baryons

The Beijing Spectrometer (BESIII) Collaboration has reported a new method for probing differences between matter and antimatter with extreme sensitivity. Results were published in Nature on June 2.

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05:22 Arxiv.org Physics Restoring and tailoring very high dimensional spatial entanglement of a biphoton state transmitted through a scattering medium. (arXiv:2206.00299v1 [quant-ph])

We report experimental results where a momentum entangled biphoton state with a giant dimensionality of 8000 is retrieved and manipulated when only one photon of the pair is transmitted through a thin scattering medium. For this purpose, the transmission matrix of the complex medium is first measured with a phase-shifting interferometry measurement method using a spatial light modulator (SLM) illuminated with a laser source. From this matrix, different phase masks are calculated and addressed on the SLM to spatially control the focusing of the laser through the complex medium. These same masks are used to manipulate the phase of the biphoton wave function transmitted by the thin diffuser in order to restore and control in the same way the momentum correlations between the far-field images of twin beams issued from strongly spatial-multi-mode spontaneous parametric down conversion.

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01.06.2022
18:50 Nature.Com Probing CP symmetry and weak phases with entangled double-strange baryons

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07:52 Arxiv.org CS Multi-Entanglement Routing Design over Quantum Networks. (arXiv:2205.15501v1 [cs.NI])

Quantum networks are considered as a promising future platform for quantum information exchange and quantum applications, which have capabilities far beyond the traditional communication networks. Remote quantum entanglement is an essential component of a quantum network. How to efficiently design a multi-routing entanglement protocol is a fundamental yet challenging problem. In this paper, we study a quantum entanglement routing problem to simultaneously maximize the number of quantum-user pairs and their expected throughput. Our approach is to formulate the problem as two sequential integer programming steps. We propose efficient entanglement routing algorithms for the two integer programming steps and analyze their time complexity and performance bounds. Results of evaluation highlight that our approach outperforms existing solutions in both served quantum-user pairs numbers and the network expected throughput.

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31.05.2022
10:23 Arxiv.org Physics Geometric measure of entanglement from Wehrl Moments using Artificial Neural Networks. (arXiv:2205.15095v1 [quant-ph])

In recent years, artificial neural networks (ANNs) have become an increasingly popular tool for studying problems in quantum theory, and in particular entanglement theory. In this work, we analyse to what extent ANNs can provide us with an accurate estimate of the geometric measure of entanglement of symmetric multiqubit states on the basis of a few Wehrl moments (moments of the Husimi function of the state). We compare the results we obtain by training ANNs with the informed use of convergence acceleration methods. We find that even some of the most powerful convergence acceleration algorithms do not compete with ANNs when given the same input data, provided that enough data is available to train these ANNs. More generally, this work opens up perspectives for the estimation of entanglement measures and other SU(2) invariant quantities, such as Wehrl entropy, on the basis of a few Wehrl moments that should be more easily accessible in experiments than full state tomography.

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30.05.2022
05:53 Arxiv.org Physics A protocol to create a multi-particle entangled state for quantum-enhanced sensing. (arXiv:2205.13591v1 [quant-ph])

We propose a protocol for generating multi-particle entangled states using coherent manipulation of atoms trapped in an optical cavity. We show how entanglement can be adiabatically produced with two control beams and by exploiting cavity-mediated interactions between the atoms. Our methods will allow for optimal generation of entanglement for the measurement protocol we propose. We discuss an experimental implementation and compare the performance of the states produced with those of classical states and ideal maximally-entangled Dicke states. We find that our states always feature metrological gain and even outperform ideal Dicke states in the measurement of magnetic field gradients. Due to the easy scalability, our entanglement protocol is a promising tool for quantum state engineering.

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27.05.2022
06:43 Arxiv.org Physics Ancilla mediated higher entanglement as T-duality, a categorial conjecture. (arXiv:2205.13388v1 [physics.gen-ph])

Using a higher categorial interpretation of entanglement involving gauge theories and $\sigma$-models instead of qubits, one recovers T-duality as a form of ancilla aided entanglement generation. This opens the way towards new dualities in gauge theories and $\sigma$-models produced by means of analogies with quantum circuits of various types.

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26.05.2022
09:32 Arxiv.org Physics Voltage-tunable integrated quantum entanglement device via nonlinear Fano resonances. (arXiv:2205.12741v1 [physics.optics])

Integration of devices generating nonclassical states~(such as entanglement) into photonic circuits is one of the major goals in achieving integrated quantum circuits~(IQCs). This is demonstrated successfully in the past decades. Controlling the nonclassicality generation in these micron-scale devices is also crucial for the robust operation of the IQCs. Here, we propose a micron-scale quantum entanglement device whose nonlinearity (so the generated nonclassicality) can be tuned by several orders of magnitude via an applied voltage. The level-spacing of quantum emitters~(QEs), which can be tuned by voltage, are embedded into the hotspot of a metal nanostructure~(MNS). QE-MNS coupling introduces a Fano resonance in the "nonlinear response". Nonlinearity, already enhanced extremely due to localization, can be controlled by the QEs' level-spacing. Nonlinearity can either be suppressed (also when the probe is on the device) or be further enhanced by several orders. Fano resonance takes

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09:32 Arxiv.org CS Optimal Entanglement Distribution using Satellite Based Quantum Networks. (arXiv:2205.12354v1 [quant-ph])

Recent technological advancements in satellite based quantum communication has made it a promising technology for realizing global scale quantum networks. Due to better loss distance scaling compared to ground based fiber communication, satellite quantum communication can distribute high quality quantum entanglements among ground stations that are geographically separated at very long distances. This work focuses on optimal distribution of bipartite entanglements to a set of pair of ground stations using a constellation of orbiting satellites. In particular, we characterize the optimal satellite-to-ground station transmission scheduling policy with respect to the aggregate entanglement distribution rate subject to various resource constraints at the satellites and ground stations. We cast the optimal transmission scheduling problem as an integer linear programming problem and solve it efficiently for some specific scenarios. Our framework can also be used as a benchmark tool to measure

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25.05.2022
18:30 Aps.org Editors' Suggestions Variational methods for contracting projected entangled-pair states

Author(s): Laurens Vanderstraeten, Lander Burgelman, Boris Ponsioen, Maarten Van Damme, Bram Vanhecke, Philippe Corboz, Jutho Haegeman, and Frank VerstraeteProjected entangled-pair states (PEPS) provide excellent variational wave functions for ground states of strongly correlated quantum systems in two dimensions. Determining the expectation value of such a PEPS wave function requires the contraction of a two-dimensional tensor network. Here, the authors show that this contraction can itself be formulated as a variational problem, allowing one to compare the accuracies of two commonly used contraction schemes. The authors find good agreement between the different schemes, demonstrating the robustness of PEPS simulations. [Phys. Rev. B 105, 195140] Published Wed May 25, 2022

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05:06 Arxiv.org Math Conditional probability framework for entanglement and its decoupling from tensor product structure. (arXiv:2205.11510v1 [quant-ph])

Our aim is to make a step towards clarification of foundations for the notion of entanglement (both physical and mathematical) by representing it in the conditional probability framework. In Schr\"odinger's words, this is entanglement of knowledge which can be extracted via conditional measurements. In particular, quantum probabilities are interpreted as conditional ones (as, e.g., by Ballentine). We restrict considerations to perfect conditional correlations (PCC) induced by measurements ("EPR entanglement"). Such entanglement is coupled to the pairs of observables with the projection type state update as the back action of measurement. In this way, we determine a special class of entangled states. One of our aims is to decouple the notion of entanglement from the compound systems. The rigid association of entanglement with the state of a few body systems stimulated its linking with quantum nonlocality ("spooky action at a distance"). However, already by Schr\"odinger entanglement was

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05:06 Arxiv.org CS Quantum Internet: from Medium Access Control to Entanglement Access Control. (arXiv:2205.11923v1 [quant-ph])

Multipartite entanglement plays a crucial role for the design of the Quantum Internet, due to its potentiality of significantly increasing the network performance. In this paper, we design an entanglement access control protocol for multipartite state, which exhibits several attractive features. Specifically, the designed protocol is able to jointly extract in a distributed way an EPR pair from the original multipartite entangled state shared by the set of network nodes, and to univocally determines the identities of the transmitter node and the receiver node in charge of using the extracted EPR pair. Furthermore, the protocol avoids to delegate the signaling arising with entanglement access control to the classical network, with the exception of the unavoidable classical communications needed for EPR extraction and qubit teleportation. Finally, the protocol supports the anonymity of the entanglement accessing nodes.

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23.05.2022
10:43 Arxiv.org Physics Ultrabright Polarization-Entangled Photon Pair Source for Frequency-Multiplexed Quantum Communication in Free-Space. (arXiv:2205.10214v1 [quant-ph])

The distribution of entanglement via satellite links will drastically extend the reach of quantum networks. Highly efficient entangled photon sources are an essential requirement towards overcoming high channel loss and achieving practical transmission rates in long-distance satellite downlinks. Here we report on an ultrabright entangled photon source that is optimized for long-distance free-space transmission. It operates in a wavelength range that is efficiently detected with space-ready single photon avalanche diodes (Si-SPADs), and readily provides pair emission rates that exceed the detector bandwidth (i.e., the temporal resolution). To overcome this limitation, we demultiplex the photon flux into wavelength channels that can be handled by current single photon detector technology. This is achieved efficiently by using the spectral correlations due to hyper-entanglement in polarization and frequency as an auxiliary resource. Combined with recent demonstrations of space-proof

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19.05.2022
06:52 Arxiv.org CS Learning Quantum Entanglement Distillation with Noisy Classical Communications. (arXiv:2205.08561v1 [quant-ph])

Quantum networking relies on the management and exploitation of entanglement. Practical sources of entangled qubits are imperfect, producing mixed quantum state with reduced fidelity with respect to ideal Bell pairs. Therefore, an important primitive for quantum networking is entanglement distillation, whose goal is to enhance the fidelity of entangled qubits through local operations and classical communication (LOCC). Existing distillation protocols assume the availability of ideal, noiseless, communication channels. In this paper, we study the case in which communication takes place over noisy binary symmetric channels. We propose to implement local processing through parameterized quantum circuits (PQCs) that are optimized to maximize the average fidelity, while accounting for communication errors. The introduced approach, Noise Aware-LOCCNet (NA-LOCCNet), is shown to have significant advantages over existing protocols designed for noiseless communications.

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17.05.2022
05:12 Arxiv.org Math Entanglement and Quantum Correlation Measures from a Minimum Distance Principle. (arXiv:2205.07143v1 [quant-ph])

Entanglement, and quantum correlation, are precious resources for quantum technologies implementation based on quantum information science, such as, for instance, quantum communication, quantum computing, and quantum interferometry. Nevertheless, to our best knowledge, a directly computable measure for the entanglement of multipartite mixed-states is still lacking. In this work, {\it i)} we derive from a minimum distance principle, an explicit measure able to quantify the degree of quantum correlation for pure or mixed multipartite states; {\it ii)} through a regularization process of the density matrix, we derive an entanglement measure from such quantum correlation measure; {\it iii)} we prove that our entanglement measure is \textit{faithful} in the sense that it vanishes only on the set of separable states. Then, a comparison of the proposed measures, of quantum correlation and entanglement, allows one to distinguish between quantum correlation detached from entanglement and the

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16.05.2022
07:43 Arxiv.org Math Average capacity of quantum entanglement. (arXiv:2205.06343v1 [math-ph])

As an alternative to entanglement entropies, the capacity of entanglement becomes a promising candidate to probe and estimate the degree of entanglement of quantum bipartite systems. In this work, we study the typical behavior of entanglement capacity over major models of random states. In particular, the exact and asymptotic formulas of average capacity have been derived under the Hilbert-Schmidt and Bures-Hall ensembles. The obtained formulas generalize some partial results of average capacity computed recently in the literature. As a key ingredient in deriving the results, we make use of recent advances in random matrix theory pertaining to the underlying orthogonal polynomials and special functions. Numerical study has been performed to illustrate the usefulness of average capacity as an entanglement indicator.

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07:43 Arxiv.org CS Average capacity of quantum entanglement. (arXiv:2205.06343v1 [math-ph])

As an alternative to entanglement entropies, the capacity of entanglement becomes a promising candidate to probe and estimate the degree of entanglement of quantum bipartite systems. In this work, we study the typical behavior of entanglement capacity over major models of random states. In particular, the exact and asymptotic formulas of average capacity have been derived under the Hilbert-Schmidt and Bures-Hall ensembles. The obtained formulas generalize some partial results of average capacity computed recently in the literature. As a key ingredient in deriving the results, we make use of recent advances in random matrix theory pertaining to the underlying orthogonal polynomials and special functions. Numerical study has been performed to illustrate the usefulness of average capacity as an entanglement indicator.

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10.05.2022
09:43 Arxiv.org Math Dual Geometry of Entanglement Entropy via Deep Learning. (arXiv:2205.04445v1 [hep-th])

For a given entanglement entropy of QFT, we investigate how to reconstruct its dual geometry by applying the Ryu-Takayanagi formula and the deep learning method. In the holographic setup, the radial direction of the dual geometry is identified with the energy scale of the dual QFT. Therefore, the holographic dual geometry can describe how the QFT changes along the RG flow. Intriguingly, we show that the reconstructed geometry only from the entanglement entropy data can give us more information about other physical properties like thermodynamic quantities in the IR region.

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09.05.2022
05:23 Arxiv.org Physics Entanglement generation in a quantum network at distance-independent rate. (arXiv:2005.07247v2 [quant-ph] CROSS LISTED)

We develop a protocol for entanglement generation in the quantum internet that allows a repeater node to use $n$-qubit Greenberger-Horne-Zeilinger (GHZ) projective measurements that can fuse $n$ successfully-entangled {\em links}, i.e., two-qubit entangled Bell pairs shared across $n$ network edges, incident at that node. Implementing $n$-fusion, for $n \ge 3$, is in principle not much harder than $2$-fusions (Bell-basis measurements) in solid-state qubit memories. If we allow even $3$-fusions at the nodes, we find---by developing a connection to a modified version of the site-bond percolation problem---that despite lossy (hence probabilistic) link-level entanglement generation, and probabilistic success of the fusion measurements at nodes, one can generate entanglement between end parties Alice and Bob at a rate that stays constant as the distance between them increases. We prove that this powerful network property is not possible to attain with any quantum networking protocol built

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07.05.2022
21:40 ScienceDaily.com It takes three to tangle: Long-range quantum entanglement needs three-way interaction

A theoretical study shows that long-range entanglement can indeed survive at temperatures above absolute zero, if the correct conditions are met.

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06.05.2022
20:42 Phys.org It takes three to tangle: Long-range quantum entanglement needs three-way interaction

A theoretical study shows that long-range entanglement can indeed survive at temperatures above absolute zero, if the correct conditions are met.

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18:22 Phys.org A review of 'classical entanglement' blurring the quantum-classical divide

Entanglement or non-separability constitutes a cornerstone of quantum mechanics from which many of its unique characteristics arise. For example, non-separability in entangled particle pairs leads to apparent instantaneous transfer of information and counterintuitive states of matter. Such phenomena find applications in diverse areas, such as quantum computing or quantum cryptography.

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