Jing-Ling Chen, Hong-Yi Su, Chunfeng Wu, Xiang-Jun Ye, Dong-Ling Deng, C. H. Oh
We investigate the connection between quantum no-cloning theorem and Bell's theorem. Designing some Bell's inequalities, we show that quantum no-cloning theorem can always be certified by Bell's theorem, and this fact in turn reflects that our physical world is essentially nonlocal.
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Recently Gupta and Panigrahi have shown how to deterministically identify an unknown Bell state. The present paper extends their result to deterministic cloning.
The necessary and sufficient amount of entanglement required for cloning of orthogonal Bell states by local operation and classical communication is derived, and using this result, we provide here some additional examples of reversible, as well as irreversible states.
We analyze various eavesdropping strategies on a quantum cryptographic channel. We present the optimal strategy for an eavesdropper restricted to a two-dimensional probe, interacting on-line with each transmitted signal. The link between safety of the transmission and the violation of Bell's inequality is discussed. We also use a quantum copying machine for eavesdropping and for broadcasting quantum information.
We analyze a possibility of using the two qubit output state from Buzek-Hillery quantum copying machine (not necessarily universal quantum cloning machine) as a teleportation channel. We show that there is a range of values of the machine parameter $ξ$ for which the two qubit output state is entangled and violates Bell-CHSH inequality and for a different range it remains entangled but does not violate Bell-CHSH inequality. Further we observe that for certain values of the machine parameter the two-qubit mixed state can be used as a teleportation channel. The use of the output state from the Bu…
One of the great challenges of quantum foundations and quantum information theory is the characterisation of the relationship between entanglement and the violation of Bell inequalities. It is well known that in specific scenarios these two can behave differently, from local hidden-variable models for entangled quantum states in restricted Bell scenarios, to maximal violations of Bell inequalities not concurring with maximal entanglement. In this paper we put forward a simple proof that there exist quantum states, whose entanglement content, as measured by the Schmidt number, cannot be device-…
We question the commonly accepted statement that random numbers certified by Bell's theorem carry some special sort of randomness, so to say, quantum randomness or intrinsic randomness. We show that such numbers can be easily generated by classical random generators.
Noise robustness of three outcome Bell certified quantum randomness
研究三方每方三输出的贝尔不等式对噪声的鲁棒性，发现多输出场景下许多不等式能认证高随机性，且对噪声具有鲁棒性。
Bell-certified retardance polarimetry from CHSH correlators
本文证明Bell-CHSH测量数据可同时用于非局域性见证和延迟量传感，通过CHSH关联推导Fisher信息下界，并阐明Bell违背与计量有用性为不同资源。
Robust self-testing and certified randomness based on chained Bell inequality
本文利用任意输入链式贝尔不等式，通过平方和方法推导最优量子违背，实现设备无关的自检验，并分析噪声下的鲁棒性及两比特随机性生成。
Genuine randomness can be certified from Bell tests without any detailed assumptions on the working of the devices with which the test is implemented. An important class of experiments for implementing such tests is optical setups based on polarisation measurements of entangled photons distributed from a spontaneous parametric down conversion source. Here we compute the maximal amount of randomness which can be certified in such setups under realistic conditions. We provide relevant yet unexpected numerical values for the physical parameters and achieve four times more randomness than previous…
Randomness is a fundamental feature in nature and a valuable resource for applications ranging from cryptography and gambling to numerical simulation of physical and biological systems. Random numbers, however, are difficult to characterize mathematically, and their generation must rely on an unpredictable physical process. Inaccuracies in the theoretical modelling of such processes or failures of the devices, possibly due to adversarial attacks, limit the reliability of random number generators in ways that are difficult to control and detect. Here, inspired by earlier work on nonlocality bas…
The intrinsic random nature of quantum physics offers novel tools for the generation of random numbers, a central challenge for a plethora of fields. Bell non-local correlations obtained by measurements on entangled states allow for the generation of bit strings whose randomness is guaranteed in a device-independent manner, i.e. without assumptions on the measurement and state-generation devices. Here, we generate this strong form of certified randomness on a new platform: the so-called instrumental scenario, which is central to the field of causal inference. First, we theoretically show that …
We investigate the security of continuous-variable (CV) quantum key distribution (QKD) using coherent states and reverse reconciliation against Gaussian individual attacks based on an optimal Gaussian $1 \to 2$ cloning machine. We provide an implementation of the optimal Gaussian individual attack. we also find a Bell-measurement attack which works without delayed choice of measurements and has better performance than the cloning attack.
Randomness in Bell test data can be device-independently certified by Bell's theorem without placing assumptions about the experimental devices. The device-independent randomness has very demanding requirement about the experimental devices and relatively lower output randomness. With the same Bell test data we can extract substantially more randomness without using Bell's theorem. To achieve this goal, we introduce a remote state preparation dimension witness and a semi-device-independent randomness certification model which is based on it. This is one important step towards practical use of …
We show theoretically that the multi-photon states obtained by cloning single-photon qubits via stimulated emission can be distinguished with the naked human eye with high efficiency and fidelity. Focusing on the "micro-macro" situation realized in a recent experiment [F. De Martini, F. Sciarrino, and C. Vitelli, Phys. Rev. Lett. 100, 253601 (2008)], where one photon from an original entangled pair is detected directly, whereas the other one is greatly amplified, we show that performing a Bell experiment with human-eye detectors for the amplified photon appears realistic, even when losses are …
Certifying measurement incompatibility in prepare-and-measure and Bell scenarios
本文研究准备-测量场景中量子比特测量不相容性的认证条件，证明其与共享最大纠缠态的贝尔场景认证等价，并提出基于经典模拟维度的不相容性强弱层级，给出量子比特可达到的最强认证示例。
We propose a feasible scheme of conditional quantum partial teleportation of a qubit as optimal asymmetric cloning at a distance. In this scheme, Alice preserves one imperfect clone whereas other clone is teleported to Bob. Fidelities of the clones can be simply controlled by an asymmetry in Bell-state measurement. The optimality means that tightest inequality for the fidelities in the asymmetric cloning is saturated. Further we design a conditional teleportation as symmetric optimal N-> N+1 cloning from N Alice's replicas on single distant clone. We shortly discussed two feasible experimental…
Random numbers are an important resource for applications such as numerical simulation and secure communication. However, it is difficult to certify whether a physical random number generator is truly unpredictable. Here, we exploit the phenomenon of quantum nonlocality in a loophole-free photonic Bell test experiment for the generation of randomness that cannot be predicted within any physical theory that allows one to make independent measurement choices and prohibits superluminal signaling. To certify and quantify the randomness, we describe a new protocol that performs well in an experimen…
Experimentally Certified Transmission of a Quantum Message through an Untrusted and Lossy Quantum Channel via Bell's Theorem
本文提出一种设备无关协议，通过贝尔定理认证量子消息在不可信且损耗的量子通道中的传输，并评估传输质量。
We propose a probabilistic quantum cloning scheme using Greenberger-Horne-Zeilinger states, Bell basis measurements, single-qubit unitary operations and generalized measurements, all of which are within the reach of current technology. Compared to another possible scheme via Tele-CNOT gate [D. Gottesman and I. L. Chuang, Nature 402, 390 (1999)], the present scheme may be used in experiment to clone the states of one particle to those of two different particles with higher probability and less GHZ resources.
We derive monogamy relations (tradeoffs) between strengths of violations of Bell's inequalities from the non-signaling condition. Our result applies to general Bell inequalities with an arbitrary large number of partners, outcomes and measurement settings. The method is simple, efficient and does not require linear programming. The results are used to derive optimal fidelity for asymmetric cloning in nonsignaling theories.
We investigate the problem of cloning a set of states that is invariant under the action of an irreducible group representation. We then characterize the cloners that are "extremal" in the convex set of group covariant cloning machines, among which one can restrict the search for optimal cloners. For a set of states that is invariant under the discrete Weyl-Heisenberg group, we show that all extremal cloners can be unitarily realized using the so-called "double-Bell states", whence providing a general proof of the popular ansatz used in the literature for finding optimal cloners in a variety o…
We analyze a reversibility of optimal Gaussian $1\to 2$ quantum cloning of a coherent state using only local operations on the clones and classical communication between them and propose a feasible experimental test of this feature. Performing Bell-type homodyne measurement on one clone and anti-clone, an arbitrary unknown input state (not only a coherent state) can be restored in the other clone by applying appropriate local unitary displacement operation. We generalize this concept to a partial LOCC reversal of the cloning and we show that this procedure converts the symmetric cloner to an a…
We present a novel Bell-state analyzer for time-bin qubits allowing the detection of three out of four Bell-states with linear optics, only two detectors and no auxiliary photons. The theoretical success rate of this scheme is 50%. A teleportation experiment was performed to demonstrate its functionality. We also present a teleportation experiment with a fidelity larger than the cloning limit.
It is shown that the restrictions of what can be inferred from classically-recorded observational outcomes that are imposed by the no-cloning theorem, the Kochen-Specker theorem and Bell's theorem also follow from restrictions on inferences from observations formulated within classical automata theory. Similarities between the assumptions underlying classical automata theory and those underlying universally-unitary quantum theory are discussed.
We prove generic versions of the no-cloning and no-broadcasting theorems, applicable to essentially {\em any} non-classical finite-dimensional probabilistic model that satisfies a no-signaling criterion. This includes quantum theory as well as models supporting ``super-quantum'' correlations that violate the Bell inequalities to a larger extent than quantum theory. The proof of our no-broadcasting theorem is significantly more natural and more self-contained than others we have seen: we show that a set of states is broadcastable if, and only if, it is contained in a simplex whose vertices are …
We present a Bell-state analyzer for time-bin qubits allowing the detection of three out of four Bell-states with linear optics, two detectors and no auxiliary photons. The theoretical success rate of this scheme is 50%. A teleportation experiment was performed to demonstrate its functionality. We also present a teleportation experiment with a Fidelity larger than the cloning limit of F=5/6.
In this article we present an ongoing effort to formalise quantum algorithms and results in quantum information theory using the proof assistant Isabelle/HOL. Formal methods being critical for the safety and security of algorithms and protocols, we foresee their widespread use for quantum computing in the future. We have developed a large library for quantum computing in Isabelle based on a matrix representation for quantum circuits, successfully formalising the no-cloning theorem, quantum teleportation, Deutsch's algorithm, the Deutsch-Jozsa algorithm and the quantum Prisoner's Dilemma. We di…
From dice to modern complex circuits, there have been many attempts to build increasingly better devices to generate random numbers. Today, randomness is fundamental to security and cryptographic systems, as well as safeguarding privacy. A key challenge with random number generators is that it is hard to ensure that their outputs are unpredictable. For a random number generator based on a physical process, such as a noisy classical system or an elementary quantum measurement, a detailed model describing the underlying physics is required to assert unpredictability. Such a model must make a num…
The study of quantum cryptography and quantum entanglement has traditionally been based on two-level quantum systems (qubits) and more recently on three-level systems (qutrits). We investigate several classes of state-dependent quantum cloners for four-level systems (quartits). These results apply to symmetric as well as asymmetric cloners, so that the balance between the fidelity of the two clones can also be analyzed. We extend Cerf's formalism for cloning states in order to derive cloning machines that remain invariant under certain unitary transformations. Our results show that a different…
Quantum steering in a global state allows an observer to remotely steer a subsystem into different ensembles by performing different local measurements on the other part. We show that, in general, this property cannot be perfectly cloned by any joint operation between a steered subsystem and a third system. Perfect cloning is viable if and only if the initial state is of zero discord. We also investigate the process of cloning the steered qubit of a Bell state using a universal cloning machine. Einstein-Podolsky-Rosen (EPR) steering, which is a type of quantum correlation existing in the state…
After a brief introduction to the quantum no-cloning theorem and its link with the linearity and causality of quantum mechanics, the concept of quantum cloning machines is sketched, following, whenever possible, the chronology of the main results. The important classes of quantum cloning machines are reviewed, in particular state-independent and state-dependent cloning machines. The 1-to-2 cloning problem is then studied from a formal point of view, using the isomorphism between completely positive maps and operators, which leads to the so-called double-Bell ansatz. This also yields an efficie…
Braiding of Majorana fermions gives accurate topological quantum operations that are intrinsically robust to noise and imperfection, providing a natural method to realize fault-tolerant quantum information processing. Unfortunately, it is known that braiding of Majorana fermions is not sufficient for implementation of universal quantum computation. Here we show that topological manipulation of Majorana fermions provides the full set of operations required to generate random numbers by way of quantum mechanics and to certify its genuine randomness through violation of a multipartite Bell inequa…
Generation of quantum-certified random numbers using on-chip path-entangled single photons from an LED
本文利用商用红色LED和光子集成芯片生成并操控单光子路径纠缠态，通过CHSH贝尔测试验证纠缠，并基于贝尔不等式违背实现半设备无关的量子随机数发生器，展示了33%的最小熵。
Direct Adaptive Certification of High-Dimensional Entanglement with Bell Tests
本文将CSPSA扩展至高维贝尔测试，基于CGLMP不等式通过数值研究实现高维纠缠直接自适应认证，在d=2-8范围内验证了其有效性，且测量成本与维度无关。
Strategic Non-Shareability of Quantum Correlations
研究量子关联在对抗性场景中的不可共享性，通过定义共谋阴影和策略性不可共享性，证明反共谋容量等于全变差距离，并给出CHSH场景下的精确边界及有限数据认证协议。
Certified exact identification of the I3322 quantum value
本文通过精确的变分约简和计算机辅助区间证明，确定了贝尔泛函I3322的量子值，并证明了有限维与无限维策略的差异。
Unpredictability, or randomness, of the outcomes of measurements made on an entangled state can be certified provided that the statistics violate a Bell inequality. In the standard Bell scenario where each party performs a single measurement on its share of the system, only a finite amount of randomness, of at most $4 log_2 d$ bits, can be certified from a pair of entangled particles of dimension $d$. Our work shows that this fundamental limitation can be overcome using sequences of (nonprojective) measurements on the same system. More precisely, we prove that one can certify any amount of ran…
Resonant dissipation-enabled adiabatic quantum state transfer processes between the polarization degrees of freedom of a single photon wave packet and quantum emitters are discussed. These investigations generalize previous work [N. Trautmann and G. Alber, Phys. Rev. A 93, 053807 (2015)] by taking into account the properties of the spontaneously emitted photon wave packet and of non adiabatic corrections. It is demonstrated that the photonic degrees of freedoms of these adiabatic one-photon quantum state transfer processes can be used for the passive, heralded and deterministic preparation of …
Experimental quantum key distribution certified by Bell's theorem
本研究实验实现了由贝尔定理认证的设备无关量子密钥分发协议，结合有限统计量分析、纠错和隐私放大，利用囚禁离子纠缠确保密钥安全性，证明真实设备下可证明安全的密码学可行。
Random generation and confidential distribution of cryptographic keys are fundamental building blocks of secure communication. Using quantum states in which the transmitted quantum bit is entangled with a stationary memory quantum bit allows the secure generation and distribution of keys to be based on fundamental properties of quantum mechanics. At the same time, the reach of secure communication networks can be enhanced, in particular, since this architecture would be compatible with quantum repeaters which are an integral part for scaling quantum networks. Here, we realize a true single-pho…
Certified Random Number Generation using Quantum Computers
针对单台量子计算机难以实施设备无关随机数认证的问题，本文利用违反 Leggett-Garg 不等式的时间关联协议，在现有设备上以单量子比特低深度电路实现安全的半设备无关随机数生成。
Quantum coherence (QCh) is considered to be a key ingredient in quantum resource theories and also plays a pivotal role in the design and implementation of various information processing tasks. Consequently, it becomes important for us to create more number coherent quantum states between two labs from a given coherent state shared initially. We call this process as \textbf{Broadcasting of Quantum Coherence (QCh)}. In this work we extensively study the problem of broadcasting of QCh. In order to have a holistic view of broadcasting, we start with a most general representation two qubit mixed s…
Linear optical logical Bell state measurements with optimal loss-tolerance threshold
本文通过对抗性框架推导了线性光学量子信息处理中损耗容忍阈值的紧致上限，证明线性光学逻辑Bell态测量能达到no-cloning定理的基本损耗阈值，并为非自适应测量给出了更严格的界限。
Major obstacles against efficient long distance quantum communication are photon losses during transmission and the probabilistic nature of Bell measurement causing exponential scaling in time and resource with distance. To overcome these difficulties, while conventional quantum repeaters require matter-based operations with long-lived quantum memories, recent proposals have employed encoded multiple photons in entanglement, providing an alternative way for scalability. In pursuing scalable quantum communications, naturally arising questions are thus whether any ultimate limit exists in all-op…
The powerful no-cloning principle of quantum mechanics can be leveraged to achieve interesting primitives, referred to as unclonable primitives, that are impossible to achieve classically. In the past few years, we have witnessed a surge of new unclonable primitives. While prior works have mainly focused on establishing feasibility results, another equally important direction, that of understanding the relationship between different unclonable primitives is still in its nascent stages. Moving forward, we need a more systematic study of unclonable primitives. To this end, we introduce a new fra…
Quantum nonlocality offers a secure way to produce random numbers: their unpredictability is intrinsic and can be certified just by observing the statistic of the measurement outcomes, without assumptions on how they are produced. To do this, entangled pairs are generated and measured to violate a Bell inequality with the outcome statistics. However, after a projective quantum measurement, entanglement is entirely destroyed and cannot be used again. This fact poses an upper bound to the number of random numbers that can be produced from each quantum state when projective measurements are emplo…
All incompatible measurements on qubits lead to multiparticle Bell nonlocality
本文证明量子比特上任意不相容测量集合在多粒子场景下均会导致Bell不等式违背，揭示了多粒子与两粒子非定域性的根本差异，并指出测量不相容性可作为资源被超激活且能以设备无关方式认证。
Genuine Bell locality and nonlocality in the networks
本文研究网络中的真正Bell局域性与非局域性，提出涉及更多关联子的线性和非线性Bell型不等式，利用Pauli算符设计Bell测试并证明其最大违背，最后演示纠缠交换替代联合测量。
Experimental construction of a symmetric three-qubit entangled state and its utility in testing the violation of a Bell inequality on an NMR quantum simulator
本研究在NMR量子模拟器上实验构建对称三量子比特纠缠态，并利用该态与最大不相容测量展示对Sliwa分类中第26号紧致贝尔不等式的最大违背。
The problem of quantum state reduction in the process of measurement has attracted attention of almost everyone who created, developed or explained quantum physics to the students. Absence of a solution is the basis for the statement that the physical laws alone are not enough to describe the reduction of state of the measured particle. In the presented study, it is taken into account that the measurement of all properties of quantum particles can not be carried out in one physical process (the no-cloning theorem). For such a measurement several series of incompatible observations are needed, …
In this paper we propose a quantum random number generator (QRNG) which utilizes an entangled photon pair in a Bell singlet state, and is certified explicitly by value indefiniteness. While "true randomness" is a mathematical impossibility, the certification by value indefiniteness ensures the quantum random bits are incomputable in the strongest sense. This is the first QRNG setup in which a physical principle (Kochen-Specker value indefiniteness) guarantees that no single quantum bit produced can be classically computed (reproduced and validated), the mathematical form of bitwise physical un…
We present a protocol for deterministic and highly efficient quantum cryptography with entangled photon pairs in a 4x4-dimentional Hilbert space. Two communicating parties, Alice and Bob first share a both polarization- and path-entangled photon pair, and then each performs a complete Bell-state measurement on their own photon in one of two complementary Bell-state bases. It is demonstrated that each measurement in which both Alice and Bob register a photon can build certain perfect correlation and generate 1.5 key bits on average. The security of our protocol is guaranteed by the non-cloning …
Automated generation of photonic circuits for Bell tests with homodyne measurements
本文提出自动化框架，利用深度强化学习和量子光学模拟设计光子电路，实现显著违反CHSH不等式的贝尔测试实验。
Quantum Mechanical description of Bell's experiment assumes Locality
本文证明贝尔实验的量子力学标准描述预设统计独立性而非非定域性，从而质疑非定域效应存在，并影响量子随机数生成与量子密钥分发安全性。
Complementarity have been an intriguing feature of physical systems for a long time. In this work we establish a new kind of complimentary relations in the frame work of quantum information processing tasks. In broadcasting of entanglement we create many pairs of less entangled states from a given entangled state both by local and non local cloning operations. These entangled states can be used in various information processing tasks like teleportation and superdense coding. Since these states are less entangled states it is quite intuitive that these states are not going to be as powerful res…
Certified Quantumness via Single-Shot Temporal Measurements
本文通过时间分离的单次测量提出非概率性证明，展示量子性认证方法，无需依赖不等式，可实验验证。
Certified randomness in tight space
提出一种在紧凑设备上生成认证随机性的方法，通过集成光子学实验结合固态发射器与玻璃芯片，利用上下文性框架抵御信息泄漏并实现可抵御量子对手的随机性扩展。
Improved Nonlocality Certification via Bouncing between Bell Operators and Inequalities
提出一种通过贝尔不等式与哈密顿量双向映射的优化方案，改进非定域性认证，并在70多个超导量子比特上成功演示，为抗噪声认证技术开辟新途径。
Broadcasting of non-locality
本文利用通用Buzek-Hillary局域量子克隆机研究非定域性的广播，证明在Bell-CHSH、CJWR导引及Svetlichny不等式框架下，两量子比特和三量子比特系统的非定域性及导引性均无法通过局域克隆广播。
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