Michele Dall'Arno, Alessandro Bisio, Giacomo Mauro D'Ariano, Martina Mikova, Miroslav Jezek, Miloslav Dusek
We provide the optimal strategy for unambiguous quantum reading of optical memories, namely when perfect retrieving of information is achieved probabilistically, for the case where noise and loss are negligible. We describe the experimental quantum optical implementations, and provide experimental results for the single photon case.
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We address the problem of quantum reading of optical memories, namely the retrieving of classical information stored in the optical properties of a media with minimum energy. We present optimal strategies for ambiguous and unambiguous quantum reading of unitary optical memories, namely when one's task is to minimize the probability of errors in the retrieved information and when perfect retrieving of information is achieved probabilistically, respectively. A comparison of the optimal strategy with coherent probes and homodyne detection shows that the former saves orders of magnitude of energy …
Unambiguous State Discrimination of Coherent States with Linear Optics: Application to Quantum Cryptography
讨论了利用线性光学和光电探测器对N个对称相干态进行无模糊态鉴别的几种方法。一种类型的测量被证明是最佳的小光子数的限制为任何N。对于N=4的特殊情况，该测量可以由接收端（Bob）在使用微弱激光脉冲的BB84量子密钥分发协议的实现中有效地使用。特别地，如果Bob仅检测到单个光子，则该过程等同于他在BB 84的单光子实现中必须执行的标准测量，如果他检测到两个光子，则Bob将在50%的情况下明确地知道发送给他的比特，而不必交换基础信息，并且如果检测到三个光子，则Bob将明确地知道发送了哪个量子态。
Unambiguous quantum state filtering
在本文中，我们考虑广义测量，其中一个特定的量子信号是明确地从一组非交换量子信号中提取，其他信号被过滤掉。最大检测概率及其POVM的简单表达式推导。我们将这种明确的量子态滤波应用于退相干信道的检测。讨论了探测器在给定量子态下的精度极限和可能的器件实现。
We consider the unambiguous discrimination between two unknown qudit states in $n$-dimensional ($n\geqslant2$) Hilbert space. By equivalence of unknown pure states to known mixed states and with the Jordan-basis method, we demonstrate that the optimal success probability of the discrimination between two unknown states is independent of the dimension $n$. We also give a scheme for a physical implementation of the programmable state discriminator that unambiguously discriminate between two unknown states with optimal probability of success.
An approach to quantum random number generation based on unambiguous quantum state discrimination (USD) is developed. We consider a prepare-and-measure protocol, where two non-orthogonal quantum states can be prepared, and a measurement device aims at unambiguously discriminating between them. Because the states are non-orthogonal, this necessarily leads to a minimal rate of inconclusive events whose occurrence must be genuinely random and which provide the randomness source that we exploit. Our protocol is semi-device-independent in the sense that the output entropy can be lower bounded based…
Unambiguous non-orthogonal state discrimination has fundamental importance in quantum information and quantum cryptography. The discrimination is carried out by POVM generalized measurements. For this process, we find a tradeoff between the needed energy resources and the evolution time, and express it in terms of action-like cost inequality. We find the realization that minimizes this action-like cost and show that in this case the cost is determined by the maximal population transfer from the system to the ancilla needed for the POVM implementation.
We present an experimental implementation of optimum measurements for quantum state discrimination. Optimum maximum-confidence discrimination and optimum unambiguous discrimination of two mixed single-photon polarization states were performed. For the latter the states of rank two in a four-dimensional Hilbert space are prepared using both path and polarization encoding. Linear optics and single photons from a true single-photon source based on a semiconductor quantum dot are utilized.
Collisional decoherence during writing and reading quantum states
碰撞，即使它们不限制存储在基态超精细相干存储器中的量子信息的寿命，当它们发生在写入和读取过程中时，可能严重限制量子存储器的保真度。这对在热蒸气电池中实现量子过程及其作为量子存储器的性能施加了限制。我们在实验中研究了这些碰撞的影响。
General measurements with limited resources and their application to quantum unambiguous state discrimination
本研究提出仅需单个辅助量子比特的n结果POVM实现框架，可组合两结果部分测量，应用于量子无歧义态区分时展现出策略灵活性，为后续优化提供方向。
Unambiguous state discrimination in quantum cryptography with weak coherent states
在量子密钥分发（QKD）的实际实现中使用线性无关的信号状态使得窃听者能够执行明确的状态鉴别。考虑到接收器可以在一定程度上监测信号的光子数统计，即使与今天的标准检测方案，我们定量地探讨了这一事实所施加的安全QKD的限制。我们比较我们的攻击的分束攻击，并表明，对分束攻击的安全性并不一定意味着对这里考虑的攻击的安全。
Optimal unambiguous discrimination between subsets of non-orthogonal quantum states
众所周知，在非正交但线性独立的量子态之间的明确区分是可能的，具有一定的成功概率。在这里，我们考虑这个问题的一个变体。我们将只区分其中的两个子集，而不是区分所有不同的状态。特别是，对于三个非正交状态的情况下，我们表明，最佳的策略，以区分一组包含一个状态的集合包含其他两个具有更高的成功率比，如果我们希望区分所有三个状态。有些令人惊讶的是，为了明确的区分，子集不需要线性独立。一个完全解析的解决方案，我们还展示了如何构建广义干涉仪（多端口），提供了一个光学实现的最佳策略。
Nuclear Magnetic Resonance Implementation of a Quantum Clock Synchronization Algorithm
提出的量子时钟同步算法。L. Chuang（Phys.Rev.Lett，85，2006（2000））已经在三量子位核磁共振量子系统中实现。用空间平均法制备了有效纯态。两个分离的时钟之间的时间差可以通过NMR光谱直接读出来确定。
Optimal unambiguous state discrimination of two density matrices: A second class of exact solutions
本文研究了两个混合量子态的非对称态分辨。我们研究的排名和频谱的最佳USD测量的元素。这自然会导致部分第四归约定理。这个定理表明，或者失效概率等于其根据保真度给出的总体下界，或者可以从原始希尔伯特空间中分裂出一个二维子空间。然后，我们使用这个部分约化定理，推导出任何两个同等可能的几何均匀（GU）状态$ρ_0$和$ρ_1=Uρ_0 U^\dagger$，$U^2={\openone}$，在四维希尔伯特空间的最佳解决方案。这代表了USD问题的第二类解析解，这些解析解不能被简化为一些纯状态的情况。我们应用我们的结果来回答两个问题，是相关的Bennett和Bennard 1984年的量子密钥分发协议的实施，使用弱相干态。
Unambiguous discrimination of general quantum operations
本文首次实验演示了多达6个位移算子的最优明确区分及非酉量子操作的明确区分，为量子信息处理和量子传感提供了强大工具。
Following the B. Hiley belief that unresolved problems of conventional quantum mechanics could be the result of a wrong mathematical structure, an alternative basic structure is suggested. Critical part of the structure is modification of the sense of commonly used terms state, observable, measurement giving them a clear unambiguous definition. This concrete definition, along with using of variable complex plane, is quite natural in geometric algebra terms. It helps to establish a feasible language for the area of quantum computing. The suggested approach is used then in the fiber optics quant…
Implementing Non-Projective Measurements via Linear Optics: an Approach Based on Optimal Quantum State Discrimination
我们讨论的问题，实现广义测量（POVM）与线性光学，无论是基于静态线性阵列或包括条件动态。在我们的方法中，一个给定的POVM应被确定为一个选择的成本函数的优化问题的解决方案。我们制定了一个一般原则：实施是唯一可能的，如果存在的线性光学电路的量子力学最佳（最小值）仍然是可达到的失相后，相应的量子态。一般原则使我们能够，例如，推导出一组必要条件的线性光学实现的POVM，实现量子力学最佳明确的歧视两个纯粹的非正交状态。这推广了我们以前关于投影测量和正交态的精确判别的结果。
Programmable discriminator of coherent states - experimental realization
本文介绍了最近提出的相干态无模糊识别的光学实现方法。我们的系统作为一个可编程的两个，在一般非正交弱相干态之间。操作原理在于三个光束的干涉-两个程序状态和一个未知的相干状态，其可以等于两个程序状态中的任何一个。实验是基于纤维光学。其结果证实了理论预测和实验设置可以直接扩展到更高数量的程序状态。
We consider novel implementation of quantum teleportation protocol of unknown qubit by superposition of displacement operators with equal modulo but opposite in sign amplitudes. Entangled hybrid state with coherent components of small amplitude is used as quantum channel. Coherent components of the quantum channel displace the teleported qubit at the same absolute but opposite in sign values, so that any information about amount by which the qubit is displaced is lost despite the fact that one of these events has definitely occurred. Alice unambiguously distinguishes her measurement outcomes a…
A Simple Quantum Computer
我们提出了一个量子计算机的实现来解决Deutsch的问题，这需要在经典计算机上的指数时间，但只有线性时间与量子并行。通过使用双轨量子比特表示作为一种简单的纠错形式，我们的机器可以容忍一定量的退相干，并且仍然以很高的概率给出正确的结果。我们采用的设计也展示了量子并行性的签名，它明确地描绘了所需的量子行为，从仅仅是经典的。使用量子光学元件对我们的建议进行实验演示，需要开发单光子学的几个关键技术。
Both the electron transport-based qubits, implemented through double quantum dots, and the sources of indistinguishable single-photons like self-assembled quantum dots are strong candidates for the implementation of quantum technologies, such as quantum computers and quantum repeaters. Here, we demonstrate a reliable way of coupling these two types of qubits, uncovering the possibility of controlling and reading out the population of the double quantum dot via optical excitation. It is also showed that, in spite of the decoherence mechanisms affecting the qubits, the entanglement between them …
Quantum information processing using linear optics is challenging due to the limited set of deterministic operations achievable without using complicated resource-intensive methods. While techniques such as the use of ancillary photons can enhance the information processing capabilities of linear optical systems they are technologically demanding. Therefore, determining the constraints posed by linear optics and optimizing linear optical operations for specific tasks under those constraints, without the use of ancillas, can facilitate their potential implementation. Here, we consider the task …
We consider novel implementation of quantum teleportation protocol of unknown qubit with entangled hybrid state. Coherent components of the entangled hybrid state displace the teleported qubit at the same absolute but opposite in sign values, so that any information about amount by which the qubit is displaced is lost despite the fact that one of these events has definitely occurred. Alice unambiguously distinguishes her measurement outcomes and Bob obtains at his disposal states of a single photon in superposition of two modes with controllable amplitude distortions. We consider the implement…
The impossibility of deterministic and error-free discrimination among nonorthogonal quantum states lies at the core of quantum theory and constitutes a primitive for secure quantum communication. Demanding determinism leads to errors, while demanding certainty leads to some inconclusiveness. One of the most fundamental strategies developed for this task is the optimal unambiguous measurement. It encompasses conclusive results, which allow for error-free state retrodictions with the maximum success probability, and inconclusive results, which are discarded for not allowing perfect identificati…
Oblivious transfer is an important primitive in modern cryptography. Applications include secure multiparty computation, oblivious sampling, e-voting, and signatures. Information-theoretically secure perfect 1-out-of 2 oblivious transfer is impossible to achieve. Imperfect variants, where both participants' ability to cheat is still limited, are possible using quantum means while remaining classically impossible. Precisely what security parameters are attainable remains unknown. We introduce a theoretical framework for studying semirandom quantum oblivious transfer, which is shown to be equiva…
An alternative explicit circuit diagram for the quantum search algorithm by implementing a non-unitary gate
本文基于Grover搜索算法最终态的Gram-Schmidt归一化特性，提出利用非幺正矩阵平方根、模拟Gram-Schmidt过程的幺正矩阵等多种显式幺正实现方案，讨论复杂度变化，提供特定平台可用的替代电路，还可用于集合元素分组。
Optical phase encoding in pulsed approach to reservoir computing
本文提出在飞秒激光脉冲的光学相位上编码数据，并采用零差探测读取振幅与相位组合，以光子方式实现储备池计算，且在 NARMA 任务和激光动力学预测中完成数值与实验验证。
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