Radim Filip, L. Mista
Transfer of nonlocal two-mode squeezed vacuum state through symmetrical and asymmetrical lossy channel is analysed and we demonstrate that the nonlocality is more robust against losses, than it has been previously suggested. It can be important for security of continuous-variable quantum cryptography employing entangled states.
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We investigate the time evolution of nonlocality for a two-mode squeezed state in the thermal environment. The initial two-mode pure squeezed state is nonlocal with a stronger nonlocality for a larger degree of squeezing. It is found that the larger the degree of initial squeezing is, the more rapidly the squeezed state loses its nonlocality. We explain this by the rapid destruction of quantum coherence for the strongly squeezed state.
We investigate the entanglement and nonlocality properties of one- and two-mode combination squeezed vacuum state (OTCSS, with two-parameter lamda and gamma) by analyzing the logarithmic negativity and the Bell's inequality. It is found that this state exhibits larger entanglement than that of the usual two-mode squeezed vacuum state (TSVS), and that in a certain regime of lamda, the violation of Bell's inequality becomes more obvious, which indicates that the nonlocality of OTCSS can be stronger than that of TSVS. As an application of OTCSS, the quantum teleportaion is examined, which shows t…
Bell Nonlocality Test on Two-Mode Squeezed Output Generated in Double-Cavity Optomechanical
研究通过共振工程在双腔声光机械系统中生成双模压缩输出，探讨压缩与非局域性之间的关系，发现非局域性可在低压缩状态下出现，且高精细度参数区域可扩大非局域性支持区域。
Applying the recently developed formalism of quantum-state transformation at absorbing dielectric four-port devices [L.~Knöll, S.~Scheel, E.~Schmidt, D.-G.~Welsch, and A.V.~Chizhov, Phys. Rev. A {\bf 59}, 4716 (1999)], we calculate the quantum state of the outgoing modes of a two-mode squeezed vacuum transmitted through optical fibers of given extinction coefficients. Using the Peres--Horodecki separability criterion for continuous variable systems [R.~Simon, Phys. Rev. Lett. {\bf 84}, 2726 (2000)], we compute the maximal length of transmission of a two-mode squeezed vacuum through an absorbin…
We investigate the properties of quantum entanglement of two-mode squeezed states interacting with linear baths with general gain and loss parameters. By explicitly solving for ρfrom the master equation, we determine analytical expressions of eigenvalues and eigenvectors of ρ^{T_A} (the partial transposition of density matrix ρ). In Fock space, ρ^{T_A} is shown to maintain a block diagonal structure as the system evolves. In addition, we discover that the decoherence induced by the baths would break the degeneracy of ρ^{T_A}, and leads to a novel set of eigenvectors for the construction of ent…
In this Letter we experimentally demonstrate the generation of squeezed, bright twin beams which arise due to competing gain and absorption, in a medium that is overall transparent. To accomplish this, we make use of a non-degenerate four-wave mixing process in warm potassium vapor, such that one of the twin beams experiences strong on-resonant absorption. At room temperature and above, due to Doppler broadening and smaller frequency detunings compared to other schemes, the ground state hyperfine splittings used in the present double-$Λ$ setup are completely overlapped. We show that despite th…
We analyse how nonclassical features of squeezed radiation (in particular the sub-Poissonian noise) are degraded when it is transmitted through an amplifying or absorbing medium with randomly located scattering centra. Both the cases of direct photodetection and of homodyne detection are considered. Explicit results are obtained for the dependence of the Fano factor (the ratio of the noise power and the mean current) on the degree of squeezing of the incident state, on the length and the mean free path of the medium, the temperature, and on the absorption or amplification rate.
We propose a test of nonlocality for continuous variables using a two-mode squeezed state as the source of nonlocal correlations and a measurement scheme based on conditional homodyne detection. Both the CHSH- and the CH-inequality are constructed from the conditional homodyne data and found to be violated for a squeezing parameter larger than $r\approx0.48$.
We examine the quantum states produced through parametric amplification with internal quantum noise. The internal diffusion arises by coupling both modes of light to a reservoir for the duration of the interaction time. The Wigner function for the diffused two-mode squeezed state is calculated. The nonlocality, separability, and purity of these quantum states of light are discussed. In addition, we conclude by studying the nonlocality of two other continuous variable states: the Werner state and the phase-diffused state for two light modes.
We derive a Bell inequality based on a generalized quasiprobability function which is parameterized by one non-positive real value. Two types of known Bell inequalities formulated in terms of the Wigner and Q functions are included as limiting cases. We investigate violations of our Bell inequalities for single photon entangled states and two-mode squeezed vacuum states when varying the detector efficiency. We show that the Bell inequality for the Q function allows the lowest detection efficiency for violations of local realism.
We generalize Bell's inequalities to biparty systems with continuous quantum variables. This is achieved by introducing the Bell operator in perfect analogy to the usual spin-1/2 systems. It is then demonstrated that two-mode squeezed vacuum states display quantum nonlocality by using the generalized Bell operator. In particular, the original Einstein-Podolsky-Rosen entangled states, which are the limiting case of the two-mode squeezed vacuum states, can maximally violate Bell's inequality due to Clauser, Horne, Shimony and Holt. The experimental aspect of our scheme and nonlocality of arbitra…
We investigate coherent perfect absorption (CPA) in quantum optics, in particular when pairs of squeezed coherent states of light are superposed on an absorbing beam splitter. First, by employing quantum optical input-output relations, we derive the absorption coefficients for quantum coherence and for intensity, and reveal how these will differ for squeezed states. Secondly, we present the remarkable properties of a CPA-gate: two identical but otherwise arbitrary incoming squeezed coherent states can be completely stripped off their coherence, producing a pure entangled squeezed vacuum state …
In this paper, we propose a continuous measurement and feedback scheme to achieve strong Einstein-Podolsky-Rosen (EPR) steering and Bell nonlocality of two macroscopic mechanical oscillators in cavity optomechanics. Our system consists of two optomechanical cavities in which two cavity fields are coupled to each other via a nondegenerate parametric downconversion. The two cavity output fields are subject to continuous Bell-like homodyne detection and the detection currents are fed back to drive the cavity fields. It is found that when the feedback is absent, the two mechanical oscillators can …
Nonlocality in Continuous-Variable Quantum Networks
本文研究了连续变量量子网络中的非局域性，通过赝自旋测量方法分析了不同网络结构的非局域性表现，并展示了非高斯资源对非局域性的增强作用。
We consider a multiphoton Bell-type inequality to study nonlocality in four-mode continuous variable systems, which goes beyond two-photon states and can be applied to mixed as well as states with fluctuating photon number. We apply the inequality to a wide variety of states such as pure and mixed Gaussian states (including squeezed thermal states) and non-Gaussian states. We consider beam splitters as a model for leakage and show that the inequality is able to detect nonclassicality of noisy Gaussian states as well. Finally, we investigate nonlocality in pair-coherent states and entangled coh…
We analyze nonclassical correlations between outcomes of measurements conducted on two spatial radiation modes. These correlations cannot be simulated with statistical mixtures of coherent states or, more generally, with non-negative phase-space functions of quantum states and measurements. We argue that nonclassical correlations are naturally related to Bell nonlocality, the former being a more general class of quantum correlations. Indeed, it is known that local realistic as well as noncontextual models correspond to non-negative solutions to a system of linear equations for the joint probab…
Entangled coherent states are shown to emerge, with high fidelity, when mixing coherent and squeezed vacuum states of light on a beam-splitter. These maximally entangled states, where photons bunch at the exit of a beamsplitter, are measured experimentally by Fock-state projections. Entanglement is examined theoretically using a Bell-type nonlocality test and compared with ideal entangled coherent states. We experimentally show nearly perfect similarity with entangled coherent states for an optimal ratio of coherent and squeezed vacuum light. In our scheme, entangled coherent states are genera…
Dark-Mode Control of Contrasting Entanglement and Bell Nonlocality between Mechanical Oscillators
本研究提出耦合双机械振子的光机械系统方案，发现纠缠与贝尔非定域性存在权衡，引入相位依赖声子隧穿可选择性增强特定暗模式下的贝尔非定域性，为量子通信提供实验可行平台。
Quantum Metrology of Absorption and Gain Parameters using Two-Mode Bright Squeezed Light
本文提出利用双模明亮压缩光并结合平衡光电探测与时间反演计量方案，提升弱吸收损耗系数和光学增益参数的估计灵敏度，显著超越相干态并接近Cramér-Rao界。
Trajectory-based Measure of Nonlocality in the Double Caldeira-Leggett Formalism
本文在Bohmian力学框架下，通过Bohmian速度对粒子位置的敏感性度量量子非定域性，研究了压缩态双粒子系统在闭合与开放（Caldeira-Leggett主方程）环境下的关联动力学，揭示了环境结构对纠缠退相干时间尺度的关键影响。
Quantum steering is a kind of quantum correlations stronger than entanglement but weaker than Bell-nonlocality. In an optomechanical system pumped by squeezed light and driven in the red sideband, we study-under thermal effects-stationary Gaussian steering and its asymmetry of two mechanical modes. In the resolved sideband regime using experimentally feasible parameters, we show that Gaussian steering can be created by quantum fluctuations transfer from the squeezed light to the two mechanical modes. Moreover, one-way steering can be observed by controlling the squeezing degree or the environm…
A First Bound on the Moffat Energy and Thorium-229 Clock as a Probe of the Nonlocal Time-Energy Structure and a Proposed Experiment for the use of Nuclear Entanglement and Squeezed States to Test Nonlocal Quantum Field Theory
利用钍 - 229 核时钟测试时间 - 能量不确定性原理修正，推导非局部时间 - 能量不确定性原理，通过直接时钟 - 能量通道得出\(E_M\)不同尺度下限，表明核时钟为非局部性提供了从理论到实验室界限的实验途径。
Generation of bright quantum high-order harmonic driven by combined coherent and bright squeezed vacuum light
研究强相干光与弱明亮压缩真空激光和原子气体相互作用产生的量子高次谐波的宏观传播效应，发现吸收或发射BSV光子产生的谐波强度及相位受影响，为阿秒量子光谱学奠定基础。
Unidirectional Gaussian One-Way Steering
本文研究耦合双模压缩真空库的非简并三能级激光系统，证明两模式因强度差恒为正而仅存在 $\mathcal{A}\rightarrow\mathcal{B}$ 的高斯单向操控。
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