Creation of perfect long-distance quantum communication channel

Diffraction at a time grating in electron-positron pair creation from vacuum

The Sauter-Schwinger process of electron-positron pair creation from vacuum, driven by a sequence of time-dependent electric-field pulses, is studied in the framework of quantum-field theoretical approach. As demonstrated by our numerical results, the probability distributions of produced pairs exhibit intra- and inter-pulse interference structures. We show that such structures can be observed beyond the regime of applicability of the WKB theory, which was the focus of earlier investigations. Going beyond these developments, we perform the analysis of the time-evolution operator for an arbitra…

Creation and characterization of vector vortex modes for classical and quantum communication

Vector vortex beams are structured states of light that are non-separable in their polarisation and spatial mode, they are eigenmodes of free-space and many fibre systems, and have the capacity to be used as a modal basis for both classical and quantum communication. Here we outline recent progress in our understanding of these modes, from their creation to their characterization and detection. We then use these tools to study the propagation behaviour of such modes in free-space and optical fibre and show that modal cross-talk results in a decay of vector states into separable scalar modes, w…

The Basics of Perfect Communication through Quantum Networks

Perfect transfer of a quantum state through a one-dimensional chain is now well understood, allowing one not only to decide whether a fixed Hamiltonian achieves perfect transfer, but to design a suitable one. We are particularly interested in being able to design, or understand the limitations imposed upon, Hamiltonians subject to various naturally arising constraints such as a limited coupling topology with low connectivity (specified by a graph) and type of interaction. In this paper, we characterise the necessary and sufficient conditions for transfer through a network, and describe some na…

Creation of entanglement in a scalable spin quantum computer with long-range dipole-dipole interaction between qubits

Creation of entanglement is considered theoretically and numerically in an ensemble of spin chains with dipole-dipole interaction between the spins. The unwanted effect of the long-range dipole interaction is compensated by the optimal choice of the parameters of radio-frequency pulses implementing the protocol. The errors caused by (i) the influence of the environment,(ii) non-selective excitations, (iii) influence of different spin chains on each other, (iv) displacements of qubits from their perfect locations, and (v) fluctuations of the external magnetic field are estimated analytically an…

有界通信维度下的完美博弈

Perfect Games in Dimension-Bounded Communication

该研究针对有界通信维度的完美博弈，将二元输出博弈归约为冲突图，证明量子比特策略可经典比特实现，还给出13射线qutrit图的压缩博弈应用，关联了通信、图论等多个领域。

完美非局域性与零误差通信的正确纠缠

The right entanglement for perfect nonlocality and zero-error communication

本文通过构造带标志的魔方博弈，证明完美非局域性需要特定非最大纠缠态，并利用博弈到信道约化表明该纠缠在零误差通信中优于最大纠缠态。

Quantum no-key protocol for secure communication of classical message

We propose a class of quantum no-key protocols for private communication of classical message based on quantum computing of random Boolean permutations, and demonstrate that they are information-theoretic secure. These protocols are designed to resist middleman attack for two parties preshared authentication key, and achieve perfect mutual data origin authentication which ensures the permanent reusing of authentication key. Finally, we simplify the protocol to a 4-round one, and show that any protocol with 3 or less rounds cannot achieve perfect security without consuming preshared key.

使用完美涡旋光束通过环芯光纤传输光通信信号

Transmission of optical communication signals through ring core fiber using perfect vortex beams

本文实验研究了完美涡旋光束和 Laguerre-Gaussian 光束在环芯光纤中的生成与传输特性，发现完美涡旋光束能减小环半径变化并耦合更高光功率，从而降低通信链路功率要求，为高维量子通信奠定基础。

Quantum communication protocols by quantum walks with two coins

We introduce some new perfect state transfer and teleportation schemes by quantum walks with two coins. Encoding the transferred information in coin 1 state and alternatively using two coin operators, we can perfectly recover the information on coin 1 state at target position only by at most two times of flipping operation. Based on quantum walks with two coins either on the line or on the $N$-circle, we can perfectly transfer any qubit state. In addition, using quantum walks with two coins either on complete graphs or regular graphs, we can first implement perfect qudit state transfer by quan…

Zero-Quantum filtered Perfect NOESY: Enhanced sensitivity for NOE cross peaks perturbed by Zero Quantum artefacts

Evolution of homonuclear J-coupling during t1 period creates Zero Quantum artefacts which seriously degrade the performance of 2D NOESY. In our previous work [28], it is demonstrated that creation of such artefacts can be prevented by incorporation of a perfect echo based broadband homo-nuclear decoupling technique during t1 period that also allows chemical shift encoding. However, such experiments have limited F1 resolution as the perfect echo based decoupling remains efficient for interpulse delay 2τ (=t1) short compared to 1/J. A solution to this problem is provided in the present work wher…

Perfect Transfer of Arbitrary States in Quantum Spin Networks

We propose a class of qubit networks that admit perfect state transfer of any two-dimensional quantum state in a fixed period of time. We further show that such networks can distribute arbitrary entangled states between two distant parties, and can, by using such systems in parallel, transmit the higher dimensional systems states across the network. Unlike many other schemes for quantum computation and communication, these networks do not require qubit couplings to be switched on and off. When restricted to $N$-qubit spin networks of identical qubit couplings, we show that $2\log_3 N$ is the m…

Perfect Quantum Network Communication Protocol Based on Classical Network Coding

This paper considers a problem of quantum communication between parties that are connected through a network of quantum channels. The model in this paper assumes that there is no prior entanglement shared among any of the parties, but that classical communication is free. The task is to perfectly transfer an unknown quantum state from a source subsystem to a target subsystem, where both source and target are formed by ordered sets of some of the nodes. It is proved that a lower bound of the rate at which this quantum communication task is possible is given by the classical min-cut max-flow the…

Reducing the quantum communication cost of quantum secret sharing

We demonstrate a new construction for perfect quantum secret sharing (QSS) schemes based on imperfect "ramp" secret sharing combined with classical encryption, in which the individual parties' shares are split into quantum and classical components, allowing the former to be of lower dimension than the secret itself. We show that such schemes can be performed with smaller quantum components and lower overall quantum communication than required for existing methods. We further demonstrate that one may combine both imperfect quantum and imperfect classical secret sharing to produce an overall per…

Conditional quantum distinguishability and pure quantum communication

I design a simple way of distinguishing non-orthogonal quantum states with perfect reliability using only quantum control-not gates in one condition. In this way, we can implement pure quantum communication in directly sending classical information, Ekert quantum cryptography and quantum teleportation without the help of classical communications channel.

Remote Creation of Quantum Coherence via Indefinite Causal Order

Quantum coherence is a prime resource in quantum computing and quantum communication. Quantum coherence of an arbitrary qubit state can be created at a remote location using maximally entangled state, local operation and classical communication. However, if there is a noisy channel acting on one side of the shared resource, then, it is not possible to create perfect quantum coherence remotely. Here, we present a method for the creation of quantum coherence at a remote location via the use of entangled state and indefinite causal order. We show this specifically for the superposition of two com…

Remote Creation of Quantum Coherence

We study remote creation of coherence (RCC) for a quantum system, A, with the help of quantum operations on another system, B, and one-way classical communication.We show that all the nonincoherent quantum states are useful for RCC and all the incoherent-quantum states are not. The necessary and sufficient conditions of RCC for the quantum operations on system B are presented for pure states. The upper bound of average RCC is derived, giving a relation among the entanglement (concurrence), the RCC of the given quantum state, and the RCC of the corresponding maximally entangled state. Moreover,…

Robust creation of entanglement between remote memory qubits

In this Letter we propose a robust quantum repeater architecture building on the original DLCZ protocol [L.M. Duan \textit{et al.}, Nature \textbf{414}, 413 (2001)]. The architecture is based on two-photon Hong-Ou-Mandel-type interference which relaxes the long distance stability requirements by about 7 orders of magnitude, from sub wavelength for the single photon interference required by DLCZ to the coherence length of the photons. Our proposal provides an exciting possibility for robust and realistic long distance quantum communication.

Perfect Quantum State Transfer in Glauber-Fock Cavity Array

We study transfer of single photon in an one-dimensional finite Glauber-Fock cavity array whose coupling strengths satisfy a square root law. The evolved state in the array can be mapped to an upper truncated coherent state if the cavities are resonant. Appropriate choices of resonance frequencies provide perfect transfer of a photon between any two cavities in the array. Perfect transfer of the photon allows perfect quantum state transfer between the cavities. Our findings may help in realizing quantum communication and information processing in photonic lattices.

量子超密编码的经典类比与单个量子系统的通信优势

Classical analogue of quantum superdense coding and communication advantage of a single quantum system

提出无共享关联的两方通信博弈，证明单量子比特通信可超越1比特经典通信及多边形玩具系统，并揭示其优势依赖收发两端的量子干涉且对非理想编解码鲁棒。

通过纠缠浓缩从不完美的加权图态中提取完美GHZ态

Extracting perfect GHZ states from imperfect weighted graph states via entanglement concentration

针对多光子高保真GHZ态制备受相干与非相干误差限制的问题，提出仅需对不完美加权图态做局域门和测量的纠缠浓缩协议，可高效生成完美GHZ态且对非相干噪声鲁棒。

表面码的流水线相关最小权完美匹配

Pipelined correlated minimum weight perfect matching of the surface code

本文提出表面码相关最小权完美匹配的流水线解码算法，通过可并行的重加权与高置信度匹配阶段简化流程，在多种容错表面码上保持逻辑错误率不变并利于实时处理。

Perfect and flexible quantum state transfer in the hybrid system atom coupled-cavity

We investigate a system composed of $N$ coupled cavities and two-level atoms interacting one at a time. Adjusting appropriately the atom-field detuning, and make the hopping rate of photons between neighboring cavities, $A$, greater than the atom-field coupling $g$ (i.e. $A>>g$), we can eliminate the interaction of the atom with the nonresonant normal modes reducing the dynamics to the interaction of the atom with only a single-mode. As an application of this interaction, we analyze the transmission of an arbitrary atomic quantum state between distant coupled cavities. In the ideal case, we ob…

Perfect state transfer in quantum spin networks

We propose a class of qubit networks that admit perfect transfer of any quantum state in a fixed period of time. Unlike many other schemes for quantum computation and communication, these networks do not require qubit couplings to be switched on and off. When restricted to N-qubit spin networks of identical qubit couplings, we show that 2 log_3 N is the maximal perfect communication distance for hypercube geometries. Moreover, if one allows fixed but different couplings between the qubits then perfect state transfer can be achieved over arbitrarily long distances in a linear chain.

General Scheme for Perfect Quantum Network Coding with Free Classical Communication

This paper considers the problem of efficiently transmitting quantum states through a network. It has been known for some time that without additional assumptions it is impossible to achieve this task perfectly in general -- indeed, it is impossible even for the simple butterfly network. As additional resource we allow free classical communication between any pair of network nodes. It is shown that perfect quantum network coding is achievable in this model whenever classical network coding is possible over the same network when replacing all quantum capacities by classical capacities. More pre…

Quantum Experiments and Graphs: Multiparty States as coherent superpositions of Perfect Matchings

We show a surprising link between experimental setups to realize high-dimensional multipartite quantum states and Graph Theory. In these setups, the paths of photons are identified such that the photon-source information is never created. We find that each of these setups corresponds to an undirected graph, and every undirected graph corresponds to an experimental setup. Every term in the emerging quantum superposition corresponds to a perfect matching in the graph. Calculating the final quantum state is in the complexity class #P-complete, thus cannot be done efficiently. To strengthen the li…

量子扩频 CDMA 通信系统：数学基础

Quantum Spread-Spectrum CDMA Communication Systems: Mathematical Foundations

本文提出产生算符的码片时间分解方法，建立 QCDMA 系统量子信号演化与接收端窄带滤波的数学基础，并揭示相干态与 Fock 态下的干扰、纠缠及 Hong-Ou-Mandel 效应。

Two dimensional quantum repeaters

The endeavour to develop quantum networks gave rise to a rapidly developing field with far reaching applications such as secure communication and the realisation of distributed computing tasks. This ultimately calls for the creation of flexible multi-user structures that allow for quantum communication between arbitrary pairs of parties in the network and facilitate also multi-user applications. To address this challenge, we propose a 2D quantum repeater architecture to establish long-distance entanglement shared between multiple communication partners in the presence of channel noise and impe…

具有高密钥生成效率的量子密钥分发现场测试

Field Test of Quantum Key Distribution with High Key Creation Efficiency

本文开发微型1550纳米单光子源，在50个时间仓中生成近最优波形的窄带单光子，并在现场测试中实现97%密钥生成效率的差分相移QKD。

Creation and manipulation of entanglement in spin chains far from equilibrium

We investigate creation, manipulation, and steering of entanglement in spin chains from the viewpoint of quantum communication between distant parties. We demonstrate how global parametric driving of the spin-spin coupling and/or local time-dependent Zeeman fields produce a large amount of entanglement between the first and the last spin of the chain. This occurs whenever the driving frequency meets a resonance condition, identified as "entanglement resonance". Our approach marks a promising step towards an efficient quantum state transfer or teleportation in solid state system. Following the …

Perfect Optical Nonreciprocity in a Double-Cavity Optomechanical System

Nonreciprocal devices are indispensable for building quantum networks and ubiquitous in modern communication technology. Here, we use optomechanical interaction and linearly-coupled interaction to realize optical nonreciprocal transmission in a double-cavity optomechanical system. The scheme relies on the interference between the two interactions. We derive the essential conditions to realize perfect optical nonreciprocity in the system, and analyse the properties of optical nonreciprocal transmission and the output fields from mechanical mode. These results can be used to control optical tran…

Asymptotically perfect discrimination in the LOCC paradigm

We revisit the problem of discriminating orthogonal quantum states within the local quantum operation and classical communication (LOCC) paradigm. Our particular focus is on the asymptotic situation where the parties have infinite resources and the protocol may become arbitrarily long. Our main result is a necessary condition for perfect asymptotic LOCC discrimination. As an application, we prove that for complete product bases, unlimited resources are of no advantage. On the other hand, we identify an example, for which it still remains undecided whether unlimited resources are superior.

基于半经典预测的薛定谔猫态的制备与操控

Creation and manipulation of Schrödinger cat states based on semiclassical predictions

本文提出利用量子测量诱导逻辑门和半经典方法生成薛定谔猫态，证明输出态可表示为受最小扰动的类猫态，且与精确解的保真度超过0.99。

噪声经典和完美量子信道对中零误差容量的超加性

Superadditivity of Zero-Error Capacity in Noisy Classical and Perfect Quantum Channel Pairs

该研究展示了在噪声经典和完美量子信道并行使用时，零误差容量的超加性现象，并揭示了量子优势源于Kochen-Specker上下文性。

Entanglement generation and perfect state transfer in ferromagnetic qubit chains

We propose to use ferromagnetic systems for entanglement generation and distribution together with perfect state transfer between distant parties in a qubit chain. The scheme relies on an effective 2-qubit dynamics, realized by leaving two empty sites in a uniformly filled chain. This allows long-range interacting qubit chains to serve as quantum channels for both tasks with optimal performances. Remarkably, the entanglement between sender and receiver sites is independent of both the transmission distance and of system size. This property opens new perspectives for short and mid-range quantum…

Efficient and perfect state transfer in quantum chains

We present a communication protocol for chains of permanently coupled qubits which achieves perfect quantum state transfer and which is efficient with respect to the number chains employed in the scheme. The system consists of $M$ uncoupled identical quantum chains. Local control (gates, measurements) is only allowed at the sending/receiving end of the chains. Under a quite general hypothesis on the interaction Hamiltonian of the qubits a theorem is proved which shows that the receiver is able to asymptotically recover the messages by repetitive monitoring of his qubits.

Quantum state redistribution with local coherence

Quantum entanglement and coherence are two fundamental resources for quantum information processing. Recent results clearly demonstrate their relevance in quantum technological tasks, including quantum communication and quantum algorithms. In this Letter we study the role of quantum coherence for quantum state redistribution, a fundamental task where two parties aim to relocate a quantum particle by using a limited amount of quantum communication and shared entanglement. We provide general bounds for the resource rates required for this process, and show that these bounds are tight under addit…

Femtosecond Time-Bin Entangled Qubits for Quantum Communication

We create pairs of non-degenerate time-bin entangled photons at telecom wavelengths with ultra-short pump pulses. Entanglement is shown by performing Bell kind tests of the Franson type with visibilities of up to 91%. As time-bin entanglement can easily be protected from decoherence as encountered in optical fibers, this experiment opens the road for complex quantum communication protocols over long distances. We also investigate the creation of more than one photon pair in a laser pulse and present a simple tool to quantify the probability of such events to happen.

Quantum Teleportation and Beam Splitting

Following the previous paper in which quantum teleportation is rig orously discussed with coherent entangled states given by beam splittings, we further discuss two types of models, perfect teleportation model and non-perfect teleportation model, in general scheme. Then the difference among several models, i.e., the perfect models and the non-perfect models, is studied. Our teleportation models are constructed by means of coherent states in some Fock space with counting measures, so that our model can be treated in the frame of usual optical communication.

Noise effects and perfect controlled remote state preparation

We investigate all possible noise environments for controlled remote state preparation. We find that the optimal efficiency is not only dependent on the isolate decay rate but also dependent on the coupling term of environments. Such a coupling provides a clue to control the noisy quantum system for realistic quantum communication. We show that, furthermore, the noise channel can be used as an important resource for quantum information tasks. Especially, an approach is proposed to realize a perfect controlled remote state preparation under the noisy effects environments by choosing the noisy e…

Perfect transfer of coherent state-based qubits via coupled cavities

Motivated by the need for communication of coherent state-based qubits in quantum computers, we introduce a method for perfect transferring of an arbitrary superposition of coherent states between two distant nodes of a linear array of three semiconductor QDs. The QDs trapped in a system of coupled cavities. In this method, the field mode of the cavities, as the resource of transferring of quantum states, are only virtually excited which minimizes the effect of decoherence due to photon loss.

Classical and quantum communication without a shared reference frame

We show that communication without a shared reference frame is possible using entangled states. Both classical and quantum information can be communicated with perfect fidelity without a shared reference frame at a rate that asymptotically approaches one classical bit or one encoded qubit per transmitted qubit. We present an optical scheme to communicate classical bits without a shared reference frame using entangled photon pairs and linear optical Bell state measurements.

Quantum communication in the spin chain with multiplespin exchange interaction

The transmission of quantum states in the anisotropic Heisenberg XXZ chain model with three-spin exchange interaction is studied. The average fidelity is used to evaluate the state transfer. It is found out that quantum communication can be enhanced by the anisotropic coupling and multiple spin interaction. Such spin model can reduce the time required for the perfect state transmission where the fidelity is unity. The maximally entangled Bell states can be generated and separated from the whole quantum systems.

Conclusive and arbitrarily perfect quantum state transfer using parallel spin chain channels

We suggest a protocol for perfect quantum communication through spin chain channels. By combining a dual-rail encoding with measurements only at the receiving end, we can get conclusively perfect state transfer, whose probability of success can be made arbitrarily close to unity. As an example of such an amplitude delaying channel, we show how two parallel Heisenberg spin chains can be used as quantum wires. Perfect state transfer with a probability of failure lower than P in a Heisenberg chain of N spin-1/2 particles can be achieved in a timescale of the order of N^1.7|ln(P)|. We demonstrate …

量子通信复杂度中与共享纠缠有关和无关的最大分离

Maximum Separation of Quantum Communication Complexity With and Without Shared Entanglement

研究提出一类输入规模为n的问题，其在有纠缠辅助的量子通信模型中无需通信即可解决，但在无先共享纠缠的双向量子通信模型中需要Ω(n)的量子比特通信。该结果展示了量子通信复杂度在有无共享纠缠时的最大分离，并首次给出了无共享纠缠情况下的下界。

Generating a perfect quantum optical vortex

In this article we introduce a novel quantum state, the perfect quantum optical vortex state which exhibits a highly localised distribution along a ring in the quadrature space. We examine its nonclassical properties using the Wigner function and the negativity volume. Such a quantum state can be a useful resource for quantum information processing and communication.

A Statistical Model of Information Evaporation of Perfectly Reflecting Black Holes

We provide a statistical communication model for the phenomenon of quantum information evaporation from black holes. A black hole behaves as a reflecting quantum channel in a very special regime, which allows for a receiver to perfectly recover the absorbed quantum information. The quantum channel of a perfectly reflecting (PR) black hole is the probabilistically weighted sum of infinitely many qubit cloning channels. In this work, we reveal the statistical communication background of the information evaporation process of PR black holes. We show that the density of the cloned quantum particle…

Robustness of spin-coupling distributions for perfect quantum state transfer

The transmission of quantum information between different parts of a quantum computer is of fundamental importance. Spin chains have been proposed as quantum channels for transferring information. Different configurations for the spin couplings were proposed in order to optimize the transfer. As imperfections in the creation of these specific spin-coupling distributions can never be completely avoided, it is important to find out which systems are optimally suited for information transfer by assessing their robustness against imperfections or disturbances. We analyze different spin coupling di…

通过聚焦离子束注入和高温退火在金刚石中高产率创建锗空位中心

High yield creation of germanium vacancy centers in diamond by focused ion beam implantation and high temperature annealing

本文通过聚焦离子束注入和高温退火，在金刚石中高效局域创建锗空位中心，实现深度5.5-30 nm内单中心创建，形成产率最高达33%。

Advantage of Quantum Theory Over Non-classical Models of Communication

Quantum correlations provide dramatic advantage over the corresponding classical resources in several communication tasks. However a broad class of probabilistic theories exists that attributes greater success than quantum theory in many of these tasks by allowing supra-quantum correlations in `space-like' and/or `time-like' paradigms. In this letter we propose a communication task involving three spatially separated parties where one party (verifier) aims to verify whether the bit strings possessed by the other two parties (terminals) are equal or not. We call this task {\it authentication wi…

Relativistic quantum communication with bosonic and fermionic interferometers

We derive the relativistic transformation laws for the annihilation operators of the scalar field, the massive spin-1 vector field, the electromagnetic field and the spinor field. The technique developed here involves straightforward mathematical techniques based on fundamental quantum field theory, and is applicable to the study of entanglement in arbitrary coordinate transformations. In particular, it predicts particle creation for non-inertial motion. Furthermore, we present a unified description of relativistic transformations and multi-particle interferometry with bosons and fermions, whi…

宇宙膨胀如何影响遥远量子系统之间的通信

How cosmological expansion affects communication between distant quantum systems

本文构建膨胀宇宙背景下谐振子探测器与量子场相互作用的通信协议，证明宇宙膨胀通常提升经典容量，并可借此探测宇宙流体参数及场与曲率的耦合。

离散时间马尔可夫动力学下的零误差通信

Zero-error communication under discrete-time Markovian dynamics

本文针对服从离散时间马尔可夫动力学的开放量子系统，明确了不同动力学特性下零误差信息存储的可行性边界，推导了信息扰乱时间上界、可保护最大信息量显式公式及完美编码的空间要求。

量子CSP策略的经典模拟

Classical Simulation of Quantum CSP Strategies

本文证明任何完美量子CSP策略可被带额外经典信道的经典策略模拟，信道大小仅取决于共享量子系统大小和CSP模板结构，并建立了经典与量子色数差距的有界性。