Renzhi Yuan
This paper gives a brief introduction to Positive-Operator Valued Measure (POVM) of quantum communications. The Projection-Valued Measure (PVM) is first introduced and then the POVM. The relation between POVM and PVM is discussed and an example of POVM in practical measurement is given. This paper provides some insight of POVM measurement for quantum communications.
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We present a classical protocol for simulating correlations obtained by bipartite POVMs on an EPR pair. The protocol uses shared random variables (also known as local hidden variables) augmented by six bits of expected communication.
Secure and Efficient n-Qubit Entangled State Teleportation Using Partially Entangled GHZ Channels and Optimal POVM
针对特定n量子比特纠缠态，提出基于部分纠缠GHZ信道和最优POVM的量子隐形传态协议，实现无歧义态区分，降低经典通信成本，可集成传统协议并增强量子逐跳通信安全性。
The quantum Cramér-Rao bound (QCRB) provides an ultimate precision limit allowed by quantum mechanics in parameter estimation. Given any quantum state dependent on a single parameter, there is always a positive-operator valued measurement (POVM) saturating the QCRB. However, the QCRB-saturating POVM cannot always be implemented efficiently, especially in multipartite systems. In this paper, we show that the POVM based on local operations and classical communication (LOCC) is QCRB-saturating for arbitrary pure states or rank-two mixed states with varying probability distributions over fixed eig…
Positive operator valued measurements (POVMs) play an important role in efficient quantum communication and computation. While optical systems are one of the strongest candidates for long distance quantum communication and information processing, efficient methods to implement POVMs in these systems are scarce. Here we propose an all-optical scheme to implement an arbitrary POVM using linear optical components on m-dimensional Hilbert space of internal degrees of freedom. Linear optical nature of the proposed scheme makes it efficient and robust. We show how the scheme can be applied for state…
Information entropies provide powerful and flexible way to express restrictions imposed by the uncertainty principle. This approach seems to be very suitable in application to problems of quantum information theory. It is typical that questions of such a kind involve measurements having one or another specific structure. The latter often allows us to improve entropic bounds that follow from uncertainty relations of sufficiently general scope. Quantum designs have found use in many issues of quantum information theory, whence uncertainty relations for related measurements are of interest. In th…
Observations of quantum systems carried out by finite observers who subsequently communicate their results using classical data structures can be described as "local operations, classical communication" (LOCC) observations. The implementation of LOCC observations by the Hamiltonian dynamics prescribed by minimal quantum mechanics is investigated. It is shown that LOCC observations cannot be described using decoherence considerations alone, but rather require the \textit{a priori} stipulation of a positive operator-valued measure (POVM) about which communicating observers agree. It is also show…
We consider general prepare-and-measure scenarios in which Alice can transmit qubit states to Bob, who can perform general measurements in the form of positive operator-valued measures (POVMs). We show that the statistics obtained in any such quantum protocol can be simulated by the purely classical means of shared randomness and two bits of communication. Furthermore, we prove that two bits of communication is the minimal cost of a perfect classical simulation. In addition, we apply our methods to Bell scenarios, which extends the well-known Toner and Bacon protocol. In particular, two bits o…
Utility of noiseless linear amplification and attenuation in single-rail discrete-variable quantum communications
本文研究了无噪声线性放大和衰减在单轨离散变量量子通信中的应用，通过优化测量提升传送保真度和超密集编码的量子优势。
Complementarity relations for design-structured POVMs in terms of generalized entropies of order $α\in(0,2)$
针对量子设计对应的结构化 POVM，本文利用阶 $α\in(0,2)$ 的 Rényi 与 Tsallis 广义熵，将概率约束转化为双侧熵界，建立不确定性与确定性互补关系。
Minimal informationally complete positive operator-valued measures (MIC-POVMs) are special kinds of measurement in quantum theory in which the statistics of their $d^2$-outcomes are enough to reconstruct any $d$-dimensional quantum state. For this reason, MIC-POVMs are referred to as standard measurements for quantum information. Here, we report an experiment with entangled photon pairs that certifies, for what we believe is the first time, a MIC-POVM for qubits following a device-independent protocol (i.e., modeling the state preparation and the measurement devices as black boxes, and using o…
Unifying different notions of quantum incompatibility into a strict hierarchy of resource theories of communication
本文提出 q-compatibility 概念，将 POVM、信道和仪器的多种量子不相容性统一为严格的通信资源理论层级，并给出完备自由操作、可测单调量及操作性解释。
These notes provide a brief primer on the basic aspects of "observational entropy" (also known as "quantum coarse-grained entropy"), a general framework for applying the concept of coarse-graining to quantum systems. We review the basic formalism, survey applications to thermodynamics, make a connection to quantum correlations and entanglement entropy, compare to the corresponding classical theory, and discuss a generalization based on POVM measurements.
Resource-Efficient Teleportation of High-Dimensional Quantum Coherence via Initial Phase Engineering
本研究提出一种资源高效的高维相干态传送协议，通过优化测量基和相位工程实现高效量子通信。
Entanglement cost of discriminating quantum states under locality constraints
本文研究局部约束下区分量子态的纠缠代价，引入谱PPT距离量化测量局域性并给出下界，同时建立上界，证明单个Bell态可辅助纯态最优区分任意其他态。
POVM generated quantum trajectories without stochastic differential equations
本文提出了一种无需随机微分方程的方法，通过量子力学直接推导出由POVM生成的量子轨迹的渐进行为，揭示了轨迹趋于系统本征态或由退化本征态张成的密度矩阵。
Heralded enhancement in quantum state discrimination
本文探讨了部分测量是否能提升两个未知非正交纯态的鉴别性能，通过局部操作与经典通信实现单轮反馈，展示在特定后选集下可降低误差概率。
Bipartite entanglement detection by local generalized measurements
本文研究了基于局部测量相关矩阵和联合概率分布的二分纠缠检测充分条件，发现$(N,M)$-POVMs的对称性使不同局部检测场景具有同等效力，并通过Monte-Carlo算法数值验证了典型量子态的检测有效性。
Recently foundational issues of applicability of the formalism of quantum mechanics (QM) to cognitive psychology, decision making, and psychophysics attracted a lot of interest. In particular, in \cite{DKBB} the possibility to use of the projection postulate and representation of "mental observables" by Hermitian operators was discussed in very detail. The main conclusion of the recent discussions on the foundations of "quantum(-like) cognitive psychology" is that one has to be careful in determination of conditions of applicability of the projection postulate as a mathematical tool for descri…
Generalized quantum measurements (POVMs or POMs) are important for optimally extracting information for quantum communication and computation. The standard realization via the Neumark extension requires extensive resources in the form of operations in an extended Hilbert space. For an arbitrary measurement, we show how to construct a binary search tree with a depth logarithmic in the number of possible outcomes. This could be implemented experimentally by coupling the measured quantum system to a probe qubit which is measured, and then iterating.
We provide an interesting two-party parity oblivious communication game whose success probability is solely determined by the Bell expression. The parity-oblivious condition in an operational quantum theory implies the preparation non-contextuality in an ontological model of it. We find that the aforementioned Bell expression has two upper bounds in an ontological model; the usual local bound and a non-trivial preparation non-contextual bound arising from the non-trivial parity-oblivious condition, which is smaller that the local bound. We first demonstrate the communication game when both Ali…
In this work, we consider the task of faithfully simulating a quantum measurement, acting on a joint bipartite quantum state, in a distributed manner. In the distributed setup, the constituent sub-systems of the joint quantum state are measured by two agents, Alice and Bob. A third agent, Charlie receives the measurement outcomes sent by Alice and Bob. Charlie uses local and pairwise shared randomness to compute a bivariate function of the measurement outcomes. The objective of three agents is to faithfully simulate the given distributed quantum measurement acting on the given quantum state wh…
We study the distinguishability norms associated to families of locally restricted POVMs on multipartite systems. These norms (introduced by Matthews, Wehner and Winter) quantify how quantum measurements, subject to locality constraints, perform in the task of discriminating two multipartite quantum states. We mainly address the following question regarding the behaviour of these distinguishability norms in the high-dimensional regime: On a bipartite space, what are the relative strengths of standard classes of locally restricted measurements? We show that the class of PPT measurements typical…
The statistics of local measurements performed on certain entangled states can be reproduced using a local hidden variable (LHV) model. While all known models make use of an infinite amount of shared randomness---the physical relevance of which is questionable---we show that essentially all entangled states admitting a LHV model can be simulated with finite shared randomness. Our most economical model simulates noisy two-qubit Werner states using only 3.58 bits of shared randomness. We also discuss the case of POVMs, and the simulation of nonlocal states with finite shared randomness and finit…
Earth-Space quantum communication is the next challenge of telecommunications. As long as we want to know the outcome of a quantum communication by means of single photons, we have to face the interaction between a single photon and the atmosphere. In this brief article, we want to report some preliminary simulation results for realistic and generic atmospheric conditions.
In this contribution we will give a brief overview on the methods used to overcome decoherence in quantum communication protocols. We give an introduction to quantum error correction, entanglement purification and quantum cryptography. It is shown that entanglement purification can be used to create ``private entanglement'', which makes it a useful tool for cryptographic protocols.
Single-Photon-Memory Measurement-Device-Independent Quantum Secure Direct Communication -- Part I: Its Fundamentals and Evolution
本文综述量子安全直接通信的基本原理、安全性证明、性能改进与实际实现，并展望其未来发展方向。
The general formalism of quantum mechanics for the description of statistical experiments is briefly reviewed, introducing in particular position and momentum observables as POVM characterized by their covariance properties with respect to the isochronous Galilei group. Mappings describing state transformations both as a consequence of measurement and of dynamical evolution for a closed or open system are considered with respect to the general constraints they have to obey and their covariance properties with respect to symmetry groups. In particular different master equations are analyzed in …
Quantum Information Processing: A brief overview on Quantum Teleportation
本文教学性地介绍量子信息理论的数学基础，重点阐述量子隐形传态协议、纠缠资源的作用及性能度量，并综述其最新进展。
On Optimal Quantum Data Hiding and Maximal Separable Ball
本研究针对量子数据隐藏问题，在 bipartite 系统等场景下，推导了不同受限测量下的最优数据隐藏比，强化了经典可分球定理并改进了相关上界。
Randomness-free Test of Non-classicality: a Proof of Concept
本文提出并实验验证了一种无需种子随机性的半设备无关认证技术，通过纠缠光子对产生关联硬币，证明其量子优势并认证非投影测量，为量子通信提供了经济有效的认证方案。
We present a brief survey of results where quantum information processing is useful to solve distributed computation tasks. We describe problems that are impossible to solve using classical resources but that become feasible with the help of quantum mechanics. We also give examples where the use of quantum information significantly reduces the need for communication. The main focus of the survey is on communication complexity but we also address other distributed tasks.
Distinguishability of locally diagonal orthogonally invariant quantum states
研究在LOCC、可分离和PPT测量下局部对角正交不变态的可区分性，证明最优PPT和可分离测量可取为LDOI，从而将优化问题维度从n^4降至O(n^2)。
In this paper, we present an efficient implementation method of physical layer of Y-00 which can support a secure communication and a quantum key distribution (more generally key expansion) by IMDD(intensity modulation/direct detection) or FSK(frequency shift keying)optical fiber communication network. Although the general proof of the security is not yet given, a brief sketch of security analysis is shown, which involve an entanglement attack.
We present schemes for the generation and evaluation of continuous variable entanglement of bright optical beams and give a brief overview of the variety of optical techniques and quantum communication applications on this basis. A new entanglement-based quantum interferometry scheme with bright beams is suggested. The performance of the presented schemes is independent of the relative interference phase which is advantageous for quantum communication applications.
In 2000, an attractive new quantum cryptography was discovered by H.P.Yuen based on quantum communication theory. It is applicable to direct encryption, for example quantum stream cipher based on Yuen protocol(Y-00), with high speeds and for long distance by sophisticated optical devices which can work under the average photon number per signal light pulse:$<n> = 1000 \sim 10000$. In addition, it may provide information-theoretic security against known/chosen plaintext attack, which has no classical analogue. That is, one can provide secure communication, even the system has $H(K) << H(X)$. In…
In 2000, an attractive new quantum cryptography was discovered by H.P.Yuen, which can realize secure communication with high speeds and at long distance by conventional optical devices. Recently, a criticism of the Yuen protocol, so called Y-00, was made by Nishioka, and Imai group(Mitsubishi and University of Tokyo), and they claimed Y-00 is essentially a classical stream cipher. This paper shows that the claim is incorrect. In particular, it is shown that the relation $l_i=r_i\oplus \tilde{k}_i$, which is their basis for attack, has no essential role for any security analysis. In addition, w…
In majority of protocols of secure quantum communication (such as, BB84, B92, etc.), the unconditional security of the protocols are obtained by using conjugate coding (two or more mutually unbiased bases). Initially all the conjugate-coding-based protocols of secure quantum communication were restricted to quantum key distribution (QKD), but later on they were extended to other cryptographic tasks (such as, secure direct quantum communication and quantum key agreement). In contrast to the conjugate-coding-based protocols, a few completely orthogonal-state-based protocols of unconditionally se…
We briefly review the ideas that have shaped modern optics and have led to various applications of light ranging from spectroscopy to astrophysics, and street lights to quantum communication. The review is primarily focused on the modern applications of classical light and nonclassical light. Specific attention has been given to the applications of squeezed, antibunched, and entangled states of radiation field. Applications of Fock states (especially single photon states) in the field of quantum communication are also discussed.
We propose a communication protocol exploiting correlations between two events with a definite time-ordering: a) the outcome of a {\em weak measurement} on a spin, and b) the outcome of a subsequent ordinary measurement on the spin. In our protocol, Alice, first generates a "code" by performing weak measurements on a sample of N spins. The sample is sent to Bob, who later performs a post-selection by measuring the spin along either of two certain directions. The results of the post-selection define the "key', which he then broadcasts publicly. Using both her previously generated code and this …
Symmetric $N \to M$ telecloning and remote quantum state inference
本文提出仅用贝尔态测量（BSM）即可概率实现对称N→M远程量子克隆，其成功概率与接收者数量M无关，还能实现远程量子态推断，且N≥2时无需成对纠缠即可超越经典通信保真度界限。
A Review of Quantum communication using high-dimensional Hilbert spaces
本综述将量子密钥分发协议分为二维量子比特与高维量子多体两类，梳理其流程、理论与实验性能（以误码率容限、密钥率衡量），并给出统一数据视图分析不同协议的适用优劣。
In this brief review, we discuss the role that quantum correlations, as quantified by quantum discord, play in two interesting settings. The first one is discerning which unitaries have been applied on a quantum system, by taking advantage of knowledge regarding its initial configuration. Here discord captures the "quantum" component of this knowledge, useful only when we have access to a quantum memory. In particular, discord can be used to detect whether an untrusted party has certain quantum capabilities. The second setting is quantum cryptography. Here discord represents an important resou…
Network-centric quantum communications (NQC) - a new, scalable instantiation of quantum cryptography providing key management with forward security for lightweight encryption, authentication and digital signatures in optical networks - is briefly described. Results from a multi-node experimental test-bed utilizing integrated photonics quantum communications components, known as QKarDs, include: quantum identification; verifiable quantum secret sharing; multi-party authenticated key establishment, including group keying; and single-fiber quantum-secured communications that can be applied as a s…
A Brief Introduction to Quantum Network Control
本文简要介绍了量子网络控制领域，阐述了量子比特与纠缠如何支撑纠缠交换等操作，提出了多跳量子网络中的纠缠分发模型，并指出了量子网络容量区域表征与吞吐量最优策略设计等开放研究问题。
The amount of information transferred during standard quantum teleportation or remote state preparation is equal to the preparation information of the transmitted state, rather than the classical communication required by respective protocol. This is shown by noting that the information required to specify the operation that verifies the transmitted state is identical to the preparation information, at the given level of precision m (in bits). Depending on the resolution of the projective Hilbert space, the preparation information can be made arbitrarily precise and hence indefinitely larger t…
A quantum ensemble $\{(p_x, ρ_x)\}$ is a set of quantum states each occurring randomly with a given probability. Quantum ensembles are necessary to describe situations with incomplete a priori information, such as the output of a stochastic quantum channel (generalized measurement), and play a central role in quantum communication. In this paper, we propose measures of distance and fidelity between two quantum ensembles. We consider two approaches: the first one is based on the ability to mimic one ensemble given the other one as a resource and is closely related to the Monge-Kantorovich optim…
We build and test a single-photon detector based on a Si avalanche photodiode Excelitas 30902SH thermoelectrically cooled to -100 deg. C. Our detector has dark count rate below 1 Hz, 500 um diameter photosensitive area, photon detection efficiency around 50%, afterpulsing less than 0.35%, and timing jitter under 1 ns. These characteristics make it suitable for long-distance free-space quantum communication links, which we briefly discuss. We also report an improved method that we call long-time afterpulsing analysis, used to determine and visualise long trap lifetimes at different temperatures…
Continuous variable one-way and controlled-two-way secure direct quantum communication schemes have been designed using Gaussian states. Specifically, a scheme for continuous variable quantum secure direct communication and another scheme for continuous variable controlled quantum dialogue are proposed using single-mode squeezed coherent states. The security of the proposed schemes against a set of attacks (e.g., Gaussian quantum cloning machine and intercept resend attacks) has been proved. Further, it is established that the proposed schemes do not require two-mode squeezed states which are …
Does there exist a quantum fingerprinting protocol without coherent measurements?
本文研究裁判仅能进行非相干测量时的量子指纹协议，证明单向LOCC需$\Omega(\sqrt{n})$量子比特通信，并对受限双向LOCC给出下界。
Quantum Information Processing, Sensing and Communications: Their Myths, Realities and Futures
本文综述量子信息处理、传感与通信的最新进展，分析知识缺口并制定路线图，涵盖量子误差缓解、量子机器学习、量子雷达及集成传感通信假设，提出最终安全量子通信的未来研究思路。
Inverse Laplace and Mellin integral transforms modified for use in quantum communications
本文探讨了反拉普拉斯和梅林积分变换在量子通信中的修改应用，结合量子场论和量子色动力学，提出改进方法以提升安全协议性能。
Towards Quantum-Native Communication Systems: State-of-the-Art, Trends, and Challenges
本综述提出量子原生通信理念，全面考察量子域MIMO、量子安全直接通信等关键技术，评估量子通信与计算在未来系统中的整合可行性，并指出了延长纠缠相干时间等研究空白与未来方向。
Terahertz (THz) communication is a topic of much research in the context of high-capacity next-generation wireless networks. Quantum communication is also a topic of intensive research, most recently in the context of space-based deployments. In this work we explore the use of THz frequencies as a means to achieve quantum communication within a constellation of micro-satellites in Low-Earth-Orbit (LEO). Quantum communication between the micro-satellite constellation and high-altitude terrestrial stations is also investigated. Our work demonstrates that THz quantum entanglement distribution and…
We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose.…
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