- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Bipartite Bell inequalities with three ternary-outcome measurements—from theory to experiments
摘要： We explore quantum nonlocality in one of the simplest bipartite scenarios. Several new facet-defining Bell inequalities for the {[3,3,3],[3,3,3]} scenario are obtained with their quantum violations analyzed in details. Surprisingly, all these inequalities involving only genuine ternary-outcome measurements can be violated maximally by some two-qubit entangled states, such as the maximally entangled two-qubit state. This gives further evidence that in analyzing the quantum violation of Bell inequalities, or in the application of the latter to device-independent quantum information processing tasks, the commonly held wisdom of equating the local Hilbert space dimension of the optimal state with the number of measurement outcomes is not necessarily justifiable. In addition, when restricted to the minimal qubit subspace, it can be shown that one of these Bell inequalities requires non-projective measurements to attain maximal quantum violation, thereby giving the first example of a facet-defining Bell inequality where a genuine positive-operator-valued measure is relevant. We experimentally demonstrate the quantum violation of this and two other Bell inequalities for this scenario using energy–time entangled photon pairs. Using the obtained measurement statistics, we demonstrate how characterization of the underlying resource in the spirit of device-independence, but supplemented with auxiliary assumptions, can be achieved. In particular, we discuss how one may get around the fact that, due to finite-size effects, raw measurement statistics typically violate the non-signaling condition.
关键词： quantum nonlocality,device-independent quantum information,POVM,Bell inequalities
更新于2025-09-23 15:23:52
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Operational Description of Single-Photon Detectors Including Timing-Jitter Effects
摘要： Discrete variable quantum optics stands as one of the most prominent platform for quantum technologies with an increasing number of encouraging out-of-the-laboratory implementations [1]. The quest for competitive quantum photonic systems, compatible with future engineered systems, has promoted huge developments concerning both source and detection devices [2]. To date, a critical point lies in experiments’ operation rates. Time multiplexing technics allow in principle to pump photonic sources at rates on the order of the GHz [3]. However, a strong limitation to ultra-fast operation lies in timing errors at the detection stage. Limited resolution directly affects the quality of any time-correlated single photon counting or quantum state engineering operations [3]. In particular, single photon detector’s timing-jitters lead counts associated with a given optical clock cycle to appear as temporally indistinguishable from those corresponding to neighbouring ones [2]. Fast and accurate time-tagging is mandatory in multiple operations, such as quantum teleportation [1], quantum state engineering [3] and quantum random number generation. In anticipation to further technological advances, as well as in the perspective of promoting novel conceptual developments on existing quantum communication protocols, it is thus of the utmost importance to correctly describe the effects of detectors’ timing performances. In our work, we explicitly address the problem of detection temporal uncertainties by means of an original theoretical model able to describe the temporal behaviour of standard single photon detectors, with no photon-number resolving abilities [2], affected by non negligible timing-jitter and in presence of dead-time [4]. We consider the case of standard ON/OFF detectors, say detectors with no photon-number resolving abilities [2], and we adopt the formalism of positive operator-valued measurements (POVM) [5]. This approach has already been employed to describe detector with photon-number resolving abilities and has been successfully used to experimentally investigate the characteristics of unknown single photon detectors [6]. Our model exploits a multi-mode formalism to describe temporal degrees of freedom to fully describe timing-resolution effects in ON/OFF detectors by a fully operational POVM description, taking into account the effect of dead-time and finite detection efficiency, without any a priori restriction on the number of photons impinging on the detector. We apply our results to the quantitative study of timing-jitter effects in some usual quantum optics experiments, such as direct photon detection, coincidence measurements, and heralded quantum state preparation. As an example, for a time correlation experiment, considering a source of simultaneous twin photons, our model allows expressing explicitly the delay probability density function. As another example, this fully quantum approach allows expressing the density matrix of a single-photon state obtained in a heralded single-photon generation experiment [3], by taking into account the imperfections of the heralding detector. In conclusion, we believe that our work fills a gap in the discussion on practical quantum technologies by providing a full operational POVM description of practical detection stages, with non negligible timing-jitter and in presence of dead-time. Although we mostly provide simple examples involving one or two photons impinging on the detectors, our formalism is capable of describing general experimental situations. We therefore think that these characteristics stand as a valuable help for a better comprehension of the timing-jitter effect in the perspective of developing ultra-fast quantum communication, including when detector’s timing-jitter is not negligible with respect to repetition period.
关键词： timing-jitter,quantum communication,POVM,quantum optics,single-photon detectors
更新于2025-09-16 10:30:52
-
Teleportation of two-qubit entangled state via non-maximally entangled GHZ state
摘要： Quantum teleportation is of significant meaning in quantum information. We study the probabilistic teleportation of unknown two-qubit entangled state utilizing non-maximally entangled GHZ state as quantum channel. We formulate it as unambiguous state discrimination problem and derive exact optimal POVM operator for maximizing the success probability of unambiguous state discrimination. Only one three-qubit POVM for the sender, one two-qubit unitary operation for the receiver and two cbits for outcome notification are required in this scheme. The unitary operation is given in the form of concise formula and average fidelity is calculated. We show that our scheme is applicable in the situation where the information of quantum channel is only available for the sender.
关键词： Probabilistic teleportation,Optimal POVM,Quantum information theory,Unambiguous state discrimination
更新于2025-09-12 10:27:22
-
Spin-orbit-coupled quantum memory of a double quantum dot
摘要： The concept of quantum memory plays an incisive role in the quantum information theory. As confirmed by the several recent rigorous mathematical studies, the quantum memory inmate in the bipartite system ρAB can reduce the uncertainty about part B, after measurements done on part A. In the present work, we extend this concept to systems with a spin-orbit coupling and introduce the notion of spin-orbit quantum memory. We self-consistently explore the Uhlmann fidelity, the pre- and the post-measurement entanglement entropy, and the post-measurement conditional quantum entropy of the system with spin-orbit coupling and show that measurement performed on the spin subsystem decreases the uncertainty of the orbital part. The uncovered effect enhances with the strength of the spin-orbit coupling. We study the concept of macroscopic realism introduced by Leggett and Garg [Phys. Rev. Lett. 54, 857 (1985)] and observe that POVM measurements done on the system under the particular protocol are noninvasive. For the extended system, we perform quantum Monte Carlo calculations and consider the reshuffling of the electron densities due to an external electric field.
关键词： quantum Monte Carlo,spin-orbit coupling,entanglement entropy,POVM measurements,conditional quantum entropy,quantum memory,Uhlmann fidelity
更新于2025-09-12 10:27:22
-
[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Robust Polarimetry with a Single Metagrating
摘要： One-shot optical polarimetry using ultra-thin nanostructured metagratings opens up new opportunities for diverse applications, facilitating the measurement of both classical and quantum polarization states. Despite the significant progress, there appeared fundamental limitations associated with a need to interleave multiple metagratings on a metasurface in order to split several distinct pairs of polarization components, which limited diffraction efficiency and negatively affected the beam quality. A recent study demonstrated polarimetry with a single metagrating, however it required an additional linear polarizer with the associated detrimental effects of attenuating the detected optical power, reducing the device compactness, and increasing the setup complexity. We formulate a new conceptual approach for polarization measurements with a single metagrating, which allows us to overcome the limitations that were inherent to the previous schemes. We find that those limitations occurred due to the attempts of replicating traditional polarimetry based on close-to-perfect polarizers, where each measurement characterizes a definite polarization component. Yet in general, metasurfaces can behave like sets of imperfect (partial) polarizers, and it is our key finding that full Stokes polarization reconstruction is possible in this regime. Specifically, we develop a rigorous polarimetry approach based on the positive operator-valued measure (POVM) formalism originating from quantum mechanics. This fundamentally lifts the restrictions on metasurface design and enables robust operation even under significant fabrication inaccuracies.
关键词： metagrating,polarization reconstruction,polarimetry,metasurface,POVM
更新于2025-09-11 14:15:04
-
Hierarchical and probabilistic quantum information splitting of an arbitrary two-qubit state via two cluster states
摘要： Based on non-maximally entangled four-particle cluster states, we propose a new hierarchical information splitting protocol to probabilistically realize the quantum state sharing of an arbitrary unknown two-qubit state. In this scheme, the sender transmits the two-qubit secret state to three agents who are divided into two grades with two Bell-state measurements, and broadcasts the measurement results via a classical channel. One agent is in the upper grade and two agents are in the lower grade. The agent in the upper grade only needs to cooperate with one of the other two agents to recover the secret state but both of the agents in the lower grade need help from all of the agents. Every agent who wants to recover the secret state needs to introduce two ancillary qubits and performs a positive operator-valued measurement (POVM) instead of the usual projective measurement. Moreover, due to the symmetry of the cluster state, we extend this protocol to multiparty agents.
关键词： hierarchical quantum information splitting,cluster state,positive operator-valued measurement (POVM)
更新于2025-09-09 09:28:46
-
Unified treatment of the total angular momentum of single photons via generalized quantum observables
摘要： In this paper, we provide a consistent framework to address the notorious difficult decomposition of the single-photon total angular momentum (TAM) into a spin (SAM) and an orbital (OAM) component. We discuss the canonical decomposition into SAM and OAM components, which are the generators of internal and spatial rotations in the space of physical states. We find that those operators are mutually compatible but unsharp quantum observables, therefore POVM (Positive Operator-Valued Measures) describe their joint measurements. We present another decomposition of the TAM, which we denote as a non-canonical one. The operators resulting from this decomposition are mutually incompatible but sharp quantum observables, thus PVM (Projector-Valued Measurements). This fact reflects their consistency with the transversality condition of single-photon wavefunctions, thus explains the underlying physics from a quantum information theoretic view. Furthermore, we discuss the implementations on joint measurements for both decompositions and provide an explicit calculation of all these quantities for circularly polarized Gaussian single-photon states. The difference between the canonical and non-canonical momenta leads to observable differences in higher-order statistical moments.
关键词： spin angular momentum,total angular momentum,quantum observables,orbital angular momentum,PVM,single photons,POVM
更新于2025-09-09 09:28:46
-
Decomposing qubit positive-operator-valued measurements into continuous destructive weak measurements
摘要： It has been shown that any generalized measurement can be decomposed into a sequence of weak measurements corresponding to a stochastic process. However, the weak measurements may require almost arbitrary unitaries, which are unlikely to be realized by any real measurement device. Furthermore, many measurement processes are destructive, like photon counting procedures that terminate once all photons are consumed. One cannot expect to have full control of the evolution of a state under such destructive measurements, and the possible unitaries allow only a limited set of weak measurements. In this paper, we consider a qubit model of destructive weak measurements, which is a toy version of an optical cavity, in which the state of an electromagnetic ?eld mode inside the cavity leaks out and is measured destructively while the vacuum state |0? leaks into the cavity. At long times, the state of the qubit inevitably evolves to be |0?, and the only available control is the choice of measurement on the external ancilla system. Surprisingly, this very limited model can still perform an arbitrary projective measurement on the qubit in any basis, where the probability of getting an outcome satis?es the usual Born rule. Combining this method with probabilistic postprocessing, the result can be extended to any generalized measurement with commuting positive-operator-valued measurement (POVM) elements. This implies, among other results, that any two-outcome POVM on a qubit can be decomposed into a sequence of destructive weak measurements by this restricted measurement device.
关键词： quantum measurement,destructive measurements,weak measurements,qubit,POVM
更新于2025-09-04 15:30:14