Master Equation for Retrodiction of Quantum Communication Signals
Stephen M. Barnett, David T. Pegg, John Jeffers, Ottavia Jedrkiewicz
我们推导出了主方程，该方程支配着开放系统中测量状态随时间向后的演化。这使我们能够从后续测量的结果中确定一组给定准备事件的概率，这与量子通信特别相关。
We derive the master equation that governs the evolution of the measured state backwards in time in an open system. This allows us to determine probabilities for a given set of preparation events from the results of subsequent measurements, which has particular relevance to quantum communication.
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Quantum retrodiction in open systems
量子回溯涉及找到给定测量事件的各种准备事件的概率。这个理论已经被研究了一段时间，但主要是作为一个有趣的概念，与量子力学中的时间不对称性有关。然而，最近对量子通信和密码学的兴趣为追溯提供了潜在的实际应用。为此目的，开放系统中的量子追溯应该比与环境隔离的封闭系统更相关。本文研究了开放系统中的回溯问题，提出了一个测量态向后时间演化的一般主方程，它可用于计算制备几率。我们解决的主方程，作为例子，驱动的二能级原子耦合到电磁场。
Quantum retrodiction is a time-symmetric approach to quantum mechanics with applications in a number of important problems. One of the major challenges to its more widespread applicability is the restriction of its symmetric formalism to unbiased sources. The main result of this paper is to develop a general theory yielding a symmetric formalism for arbitrary sources. We then highlight on a specific example, by presenting the optimal solution to the retrodiction problem that is dual to unambiguous state discrimination, how the generalized approach works. We also show how this formalism leads t…
Radical-ion-pair reactions, central in photosynthesis and the avian magnetic compass mechanism, have recently shown to be a paradigm system for applying quantum information science in a biochemical setting. The fundamental quantum master equation describing radical-ion-pair reactions is still under debate. We here use quantum retrodiction to produce a rigorous refinement of the theory put forward in Phys. Rev. E {\bf 83}, 056118 (2011). We also provide a rigorous analysis of the measure of singlet-triplet coherence required for deriving the radical-pair master equation. A Monte-Carlo simulatio…
In quantum theory, the retrodiction problem is not as clear as its classical counterpart because of the uncertainty principle of quantum mechanics. In classical physics, the measurement outcomes of the present state can be used directly for predicting the future events and inferring the past events which is known as retrodiction. However, as a probabilistic theory, quantum-mechanical retrodiction is a nontrivial problem that has been investigated for a long time, of which the Mean King Problem is one of the most extensively studied issues. Here, we present the first experimental test of a vari…
We define a time continuous version of the concept of "local operations and classical communication" (LOCC), ubiquitous in quantum information theory. It allows us to construct GKLS master equations for particle systems that have (1) an arbitrary pair potential, and (2) local decoherence terms, but that do not entangle the constituents. The local decoherence terms take a particularly simple form if a principle of least decoherence is applied.
Intercontinental quantum liaisons between entangled electrons in ion traps of thermoluminescent crystals
本文报道的实验是在美国路易斯安那州巴吞鲁日和法国Givarlais用空间分离的纠缠热释光剂量测量（NST）晶体在纠缠样品之间的8,182公里处进行的。样品由掺杂的氟化锂锂组成，其在一个位置处通过由Varian CABAC单元产生的韧致辐射同时成对地一起照射。其中一个成对的水晶被邮寄到巴吞鲁日，而它纠缠在一起的对应物则留在了吉瓦莱。巴吞鲁日（主）的晶体然后受到热刺激，在Givarlais的光电倍增管下引起对应物（从）的可测量的光发射响应。高度相关的被动光发射中观察到的非加热的从散热器，而主散热器的温度斜升，然后允许冷却到环境温度。在转向温度处观察到从机散热器光发射的最大相关性，该转向温度是允许主机散热器温度降低的点。因此，Girvalais的实验者能够高精度地确定主加热炉关闭的时间点（转向点），而在实验的加热-冷却阶段期间实验者之间没有任何通信。这些观测结果对量子通信技术具有重要意义。
This study presents the first two authenticated semi-quantum direct communication (ASQDC) protocols without using any classical channel. By pre-sharing the master secret key between two communicants, a sender with advanced quantum devices can transmit a secret message to a receiver who can only perform classical operations without any information leakage. The receiver is then capable of verifying the message up to the single qubit level, i.e., a one-qubit modification of the transmitted quantum sequence can be detected with a probability close to 1. Moreover, the proposed protocols are resista…
Master thesis: High-rate multipartite quantum secret sharing with continuous variables
本文综述了一种前沿城域级连续变量量子密码协议，该协议通过中继的广义贝尔检测生成多方关联并提炼共享密钥，可利用现成光学组件实现高速率安全多方量子秘密共享，推动量子密码领域发展。
Two level quantum system (Qubit) and non-classical states of light such as single photon and superposition of coherent state are under special attention in quantum technologies such as quantum computing, quantum communication and quantum computers. So, behavior of two-level system driven by such inputs is important. In this paper, the behavior of two-level quantum system driven by vacuum state, single photon and superposition of coherent state was investigated by assuming Pauli matrices as system operators in quantum filtering equations. The purity of conditioned and unconditioned state are al…
Synchronization of quantum communication over an optical classical communication channel
针对高损耗量子信道同步难题，本文提出利用共用主时钟的同向经典光通信链路进行时钟数据恢复，以在无需额外硬件的情况下实现QKD同步。
Quantum contextuality turns out to be a necessary resource for universal quantum computation and also has applications in quantum communication. Thus it becomes important to generate contextual sets of arbitrary structure and complexity to enable a variety of implementations. In recent years, such generation has been done for contextual sets known as Kochen-Specker sets. Up to now, two approaches have been used for massive generation of non-isomorphic Kochen-Specker sets: exhaustive generation up to a given size and downward generation from master sets and their associated coordinatizations. M…
The classical capacity for the quantum Markov channel of continuous variables
利用连续变量的量子通信是一种相当成熟的实验技术，相关的理论已经用各种方法得到了广泛的研究。本文从另一个角度研究连续变量量子信道，即，通过探索主方程。最后给出了信道的容量。在本文的最后，我们推导出高斯信道的最佳容量与其保真度的准则。
Path integral Lindblad master equation through transfer tensor method & the generalized quantum master equation
本文结合 Nakajima-Zwanzig 主方程与路径积分，提出可免费纳入经验 Lindblad 耗散时间尺度的数值精确非微扰方法，并用于 FMO 4 位点模型。
On the Discretization Error of the Discrete Generalized Quantum Master Equation
本文分析TTM的离散化结构，解释初始时刻虚假修正项的来源，建立其离散记忆核与连续NZ-QME核的一致关系，并经spin-boson模型验证收敛性。
Recognition of multifrequency microwave (MW) electric fields is challenging because of the complex interference of multifrequency fields in practical applications. Rydberg atom-based measurements for multifrequency MW electric fields is promising in MW radar and MW communications. However, Rydberg atoms are sensitive not only to the MW signal but also to noise from atomic collisions and the environment, meaning that solution of the governing Lindblad master equation of light-atom interactions is complicated by the inclusion of noise and high-order terms. Here, we solve these problems by combin…
Hybrid Six-Level Rydberg Atomic Quantum Receiver for Multi-Band Wireless Communications
本文提出一种六级混合瑞利原子量子接收机，通过串联和并联射频耦合路径实现单个蒸气细胞平台内的多频段射频接收，提升了吞吐量。
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