D. B. Ion, P. Constantin, M. L. Ion
In this paper the coherence and crossing symmetry of the electromagnetic interaction of photons involved in the spontaneous parametric down conversion (SPDC) phenomena in nonlinear crystals, are investigated. On this basis a new interpretation of the recent results on the two photon entangled experiment is obtained. A new field of applications is suggested.
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We propose a paradigmatic demonstration of the potentialities of a deformable mirror for closed-loop control of a two-photon momentum-entangled state, subject to phase fluctuations. A custom-made membrane mirror is used to set a relative phase shift between the arms of an interferometric apparatus. The control algorithm estimates the phase of the quantum state, by measurements of the coincidence events at the output ports of the interferometer, and uses the measurements results to provide a feedback signal to the deformable mirror. Stabilization of the coincidence rate to within 1.5 standard d…
We study the resonance interaction between two entangled identical atoms coupled to a quantized scalar field vacuum, and accelerating between two mirrors. We show how radiative processes of the two-atom entangled state can be manipulated by the atomic configuration undergoing noninertial motion. Incorporating the Heisenberg picture with symmetric operator ordering, the vacuum fluctuation and the self-reaction contributions are distinguished. We evaluate the resonance energy shift and the relaxation rate of energy of the two atom system from the self-reaction contribution in the Heisenberg equa…
We propose a scheme for the remote preparation of entangled matter qubits in free space. For this purpose, a setup of two opposing parabolic mirrors is considered, each one with a single ion trapped at its focus. To get the required entanglement in this extreme multimode scenario, we take advantage of the spontaneous decay, which is usually considered as an apparent nuisance. Using semiclassical methods, we derive an efficient photon-path representation to deal with this problem. We also present a thorough examination of the experimental feasibility of the scheme. The vulnerabilities arising i…
Two criticisms which have prevented the realistic interpretation of entangled state from being widely accepted are addressed and shown to be unfounded. A local realistic theory, which reproduces all the quantum probabilistic predictions, is constructed for Hardy's experiment based on the realistic interpretation of the entangled two-particle Hardy state.
Mirrored Entanglement Witnesses for Multipartite and High-Dimensional Quantum Systems
本文提出镜像纠缠见证器用于多粒子和高维量子系统，以提高检测纠缠态的能力。
In 1935, Einstein, Podolsky and Rosen (EPR) considered two particles in an entangled state of motion to illustrate why they questioned the completeness of quantum theory. In the past decades, microscopic systems with entanglement in various degrees of freedom have successfully been generated, representing compelling evidence to support the completeness of quantum theory. Today, the generation of an EPR-entangled state of motion of two massive objects of up to the kilogram-scale seems feasible with state-of-the-art technology. Recently, the generation and verification of EPR-entangled mirror mo…
We present the proposition of an experiment in which the multiphoton quantum superposition consisting of N= 10^5 particles generated by a quantum-injected optical parametric amplifier (QI-OPA), seeded by a single-photon belonging to an EPR entangled pair, is made to interact with a Mirror-BEC shaped as a Bragg interference structure. The overall process will realize a Macroscopic Quantum Superposition (MQS) involving a microscopic single-photon state of polarization entangled with the coherent macroscopic transfer of momentum to the BEC structure, acting in space-like separated distant places.
Several no-go theorems showed the incompatibility between the locality assumption and quantum correlations obtained from maximally entangled spin states. We analyze these no-go theorems in the framework of Bohm's interpretation. The mechanism by which non-local correlations appear during the results of measurements performed on distant parts of entangled systems is explicitly put into evidence in terms of Bohmian trajectories. It is shown that a GHZ like contradiction of the type+1=-1 occurs for well-chosen initial positions of the Bohmian trajectories and that it is this essential non-classic…
A polarization correlation experiment with two maximally entangled photons created by spontaneous parametric down-conversion is studied in the Weyl-Wigner formalism, that reproduces the quantum predictions. An interpretation is proposed in terms of stochastic processes assuming that the quantum vacuum fields are real. This proves that local realism is compatible with the violation of Bell inequalities, thus rebutting the claim that local realism has been refuted by entangled photon experiments. Entanglement appears as a correlation between fluctuations of a signal field and vacuum fields.
We show that for pure and mixed states the problem of maximizing the correlation measure in the CHSH inequality reduces to maximizing the perimeter of a parallelogram enclosed by an ellipse characterized by the entanglement contained in the bipartite system. Since our geometrical description is also valid for a non-maximally entangled state we can determine the corresponding optimal measurements.
We analyze radiative processes of a quantum system composed by two identical two-level atoms interacting with a massless scalar field prepared in the vacuum state in the presence of perfect reflecting flat mirrors. We consider that the atoms are prepared in a stationary maximally entangled state. We investigate the spontaneous transitions rates from the entangled states to the collective ground state induced by vacuum fluctuations. In the empty-space case, the spontaneous decay rates can be enhanced or inhibited depending on the specific entangled state and changes with the distance between th…
The Statistical Interpretation of Entangled States
本文提出用统计系综解释处理纠缠EPR自旋对，将量子化轴作为隐变量，指出无论自旋是否解纠缠，该解释均能解决EPR佯谬并提供无需超距作用的量子隐形传态机制。
We report the experimental observations of Bell Inequality Violations (BIV) in entangled photons causally separated by a rotating mirror. A Foucault mirror gating geometry is used to causally isolate the entangled photon source and detectors. We report an observed BIV of CHSH-$S = 2.30 \pm 0.07 > 2.00$. This result rules out theories that explain correlations with traveling communication between source and detectors.
We propose a new all-fiber source of polarization-entangled photon pairs for quantum communications. Fiber birefringence is compensated using Faraday rotator mirror, resulting in enhanced stability against random polarization drifts compared to existing schemes.
We propose a simple scheme to generate deterministic entanglement between two movable end mirrors in a Fabry-Perot cavity using a single photon superposition state. We derive analytically the expressions of the generated entangled states and the degree of entanglement for each state. We show that strong entanglement can be obtained either in the single-photon strong coupling regime deterministically or in the single-photon weak coupling regime conditionally.
The radiation pressure of two detuned laser beams can create a stable trap for a suspended cavity mirror; here it is shown that such a configuration entangles the output light fields via interaction with the mirror. Intra-cavity, the opto-mechanical system can become entangled also. The degree of entanglement is quantified spectrally using the logarithmic negativity. Entanglement survives in the experimentally accessible regime of gram-scale masses subject to thermal noise at room temperature.
The entanglement of the two movable mirrors in a single mode cavity field is studied in an ideal situation without thermal noise. When gn/w <<1 where g is the coupling coefficient between the mirror and the field, w is the mirror' vibration frequency and n is photon number of the cavity field, we work out Wootters concurrence of the system initially with the field in Fock number state and the two mirrors in vacuum states, and find that the states of the mirrors are entangled into space spanned by |0>,|1> via radiation pressure, though the concurrence is very small.
We propose a double-cavity set-up capable of generating a stationary entangled state of two movable mirrors at cryogenic temperatures. The scheme is based on the optimal transfer of squeezing of input optical fields to mechanical vibrational modes of the mirrors, realized by the radiation pressure of the intracavity light. We show that the presence of macroscopic entanglement can be demonstrated by an appropriate read out of the output light of the two cavities.
A Lagrangian formulation is constructed for particle interpretations of quantum mechanics, a well-known example of such an interpretation being the Bohm model. The advantages of such a description are that the equations for particle motion, field evolution and conservation laws can all be deduced from a single Lagrangian density expression. The formalism presented is Lorentz invariant. This paper follows on from a previous one which was limited to the single-particle case. The present paper treats the more general case of many particles in an entangled state. It is found that describing more t…
The problem of the reflectance of a photon by a metallic mirror whose position is treated quantum mechanically is considered. The interaction between the metallic surface and the light is treated classically. It is shown that the reflectance depends on the spread of the wavefunction describing the reflecting surface along its normal. Considering this decrease on the mirror reflectance, it is shown by first principles that it is impossible to achieve a highly entangled state between a photon and a mirror when the photon can be reflected only once.
We present a scheme for cavity-assisted generation of hybrid entanglement between a moving mirror belonging to an optomechanical cavity and a single trapped ion located inside a second cavity. Due to radiation pressure, it is possible to entangle the moving mirror with one of the cavity fields. Also, by tuning the second cavity field with the internal degrees of freedom of the ion, an entangled state of the cavity field/ion can be independently generated. The fields leaking from each cavity are then combined in a beam-splitter, and following the detection of the outgoing photons by convenientl…
The multiphoton quantum superposition generated by a quantum-injected optical parametric amplifier (QI-OPA) seeded by a single-photon belonging to an EPR entangled pair is made to interact with a Mirror-BEC shaped as a Bragg interference structure. The effect can be greatly enhanced if the mirror is part of a cavity structure or is used within an optical interferometer. The overall process will realize an Entangled Macroscopic Quantum Superposition involving a ''microscopic'' singe-photon state of polarization and the coherent ''macroscopic'' displacement of the BEC structure acting in space-l…
We suggest a variant of the recently proposed experiment for the generation of a new kind of Schroedinger-cat states, using two coupled parametric down-converter nonlinear crystals [F. De Martini, Phys. Rev. Lett. 81, 2842 (1998)]. We study the parametric oscillator case and find that an entangled Schroedinger-cat type state of two cavities, whose mirrors are placed along the output beams of the nonlinear crystals, can be realized under suitable conditions.
We present a scheme to produce an entangled four-photon W-state by using linear optical elements. The symmetrical setup of linear optical elements consists of four beam splitters, four polarization beam splitters and four mirrors. A photon EPR-pair and two single photons are required as the input modes. The projection on the W-state can be made by a four-photon coincidence measurement. Further, we show that by means of a horizontally oriented polarizer in front of one detector the W-state of three photons can be generated.
We consider the cooperative spontaneous emission of a system of two identical atoms, interacting with the electromagnetic field in the vacuum state and in the presence of an oscillating mirror. We assume that the two atoms, one in the ground state and the other in the excited state, are prepared in a correlated (symmetric or antisymmetric) {\em Bell}-type state. We also suppose that the perfectly reflecting plate oscillates adiabatically, with the field modes satisfying the boundary conditions at the mirror surface at any given instant, so that the time-dependence of the interaction Hamiltonia…
The macro-objectivation problem derives from the fact that the Schrodinger equation is linear and thus requires that a macroscopic system interacting with an entangled state must be entangled as well. However, such a requirement entails that the Schrodinger equation must also be solvable in the macroscopic world in the same way as it is solvable in the microscopic world, which itself is an assumption. In this work, the alternative assumption that the Schrodinger equation is in general an intractable problem is considered.
Creating mirror-mirror quantum correlations in optomechanics
本文研究两个经光子跃迁耦合、由宽带压缩光分隔的 Fabry-Pérot 腔可移动镜之间的量子关联转移，利用 Gaussian 定向、对数负性和量子失谐进行刻画，表明强光力学耦合下转移最优且受热效应削弱。
By virtue of the integration method within P-ordered product of operators and the property of entangled state representation, we reveal new physical interpretation of the generalized two-mode squeezing operator (GTSO), and find it be decomposed as the product of free-space propagation operator, single-mode and two-mode squeezing operators, as well as thin lens transformation operator. This docomposition is useful to design of opticl devices for generating various squeezed states of light. Transformation of entangled state representation induced by GTSO is emphasized.
We describe a quantum model of simple choice game (constructed upon entangled state of two qubits), which involves the fundamental problem of transitive - intransitive preferences. We compare attainability of optimal intransitive strategies in both classical and quantum models with the use of geometrical interpretation.
Discussed in the study are gravitational noise and the nature of entanglement states. Their role in forming of entangled states. Nonlocal nature of entangled states can be brought about by Polarization Variables. Polarization Variables consists of sum a background of random classical gravitational fields and waves, random electromagnets fields and so on known or unknown, distributed average isotropically in the space. This background is capable of correlating phases the oscillations of microobjects. From this follow, that entanglement polarizations states is the functions of Polarization Varia…
In this paper we present a compact source of narrow-band energy-time entangled photon pairs in the telecom regime based on a Ti-indiffused Periodically Poled Lithium Niobate (PPLN) waveguide resonator, i.e. a waveguide with end-face dielectric multi-layer mirrors. This is a monolithic doubly resonant Optical Parametric Oscillator (OPO) far below threshold, which generates photon pairs by Spontaneous Parametric Down Conversion (SPDC) at around 1560nm with a 117MHz (0.91 pm)- bandwidth. A coherence time of 2.7 ns is estimated by a time correlation measurement and a high quality of the entangled …
We report an experimental quantum simulation of unitary dynamics of an XY spin chain with pre-engineered couplings. Using this simulation, we demonstrate the mirror inversion of quantum states, proposed by Albanese et al. [Phys. Rev. Lett. 93, 230502 (2004)]. The experiment is performed with a 5-qubit dipolar coupled spin system using nuclear magnetic resonance techniques. To perform quantum simulation we make use of the recently proposed unitary operator decomposition algorithm of Ajoy et al. [Phys. Rev. A 85, 030303 (2012)] along with numerical pulse optimization techniques. Further, using m…
A general entangled qubit pair is analyzed in the de Broglie-Bohm formalism corresponding to two spin-1/2 quantum rotors. Several spin-spin correlators of Bohm's hidden variables are analyzed numerically and a detailed comparison with results obtained by standard quantum mechanics is outlined. In addition to various expectation values the Bohm interpretation allows also a study of the corresponding probability distributions, which enables a novel understanding of entangled qubit dynamics. In particular, it is shown how the angular momenta of two qubits in this formalism can be viewed geometric…
We propose a simple method to generate quantum entanglement between two macroscopic mechanical resonators in a two-cavity optomechanical system. This entanglement is induced by the radiation pressure of a single photon hopping between the two cavities. Our results are analytical, so that the entangled states are explicitly shown. Up to local operations, these states are two-mode three-component states, and hence the degree of entanglement can be well quantified by the concurrence. By analyzing the system parameters, we find that, to achieve a maximum average entanglement, the system should wor…
It is shown that a number of experiments designed to use entangled photon pairs in order to demonstrate the viability of quantum "teleportation" can, in fact, also be understood using disentanglement. Whether entangled or not, using an ensemble approach, the experiments can be explained without any non-local communication between Alice's photon and Bob's photon. Moreover, it is emphasized that entanglement maintains a symmetry property between the two photons that is absent in disentanglment, the symmetry being parity due to phase conerence.
We demonstrate experimentally and theoretically that a coherent image of a pure phase object may be obtained by use of a spatially incoherent illumination beam. This is accomplished by employing a two-beam source of entangled photons generated by spontaneous parametric down-conversion. Though each of the beams is, in and of itself, spatially incoherent, the pair of beams exhibits higher-order inter-beam coherence. One of the beams probes the phase object while the other is scanned. The image is recorded by measuring the photon coincidence rate using a photon-counting detector in each beam. Usi…
If quantum gravity does not lead to a breakdown of predictability, then Almheiri, Marolf, Polchinski and Sully (AMPS) have argued that an observer falling into a black hole can perform an experiment which verifies a violation of entanglement monogamy - that late time Hawking radiation is maximally entangled with early time Hawking radiation and also with infalling radiation - something impossible in quantum field theory. However, as pointed out by Hayden and Harlow, this experiment is infeasible, as the time required to perform the experiment is almost certainly longer than the lifetime of the…
Generating entangled polaritonic condensates by pumping with entangled pairs of photons
该研究通过纠缠光子对泵浦生成纠缠极化子凝聚体，并分析了其稳态特性及纠缠寿命。
We introduce the entangled coherent state representation, which provides a powerful technique for efficiently and elegantly describing and analyzing quantum optics sources and detectors while respecting the photon number superselection rule that is satisfied by all known quantum optics experiments. We apply the entangled coherent state representation to elucidate and resolve the longstanding puzzles of the coherence of a laser output field, interference between two number states, and dichotomous interpretations of quantum teleportation of coherent states.
We suggest a novel source of polarization-entangled photon pairs based on a cross-shaped plasmonic nanoantenna driven by a single quantum dot. The integration of the nanoantenna with a metal mirror overcomes the fundamental tradeoff between the spontaneous emission (SE) enhancement and the extraction efficiency typical of microcavity and nanowire-based architectures. With a very-high extraction efficiency of entangled photons (~90%) at 1.55 um and large SE enhancement (~90) over a broad 330 nm spectral range, the proposed design will pave the way toward reliable integrated sources of nonclassi…
Enhanced entanglement and controlling quantum steering in a Laguerre-Gaussian cavity optomechanical system with two rotating mirrors
该研究在含光学参量放大器的拉盖尔-高斯旋转腔光机系统中，通过调节参量增益、相位和旋转镜频率，增强了镜-镜及镜-腔纠缠并实现三部分纠缠，同时发现量子导引方向性由旋转镜频率决定，呈现单向或双向不对称性，有助于非局域关联理解与纠缠验证。
Bilateral photon emission from a vibrating mirror and multiphoton entanglement generation
本研究通过腔中双面镜的辐射压相互作用，实现双侧光子对发射与$2n$光子纠缠产生，并展示机械振子的非经典性，为量子技术提供新途径。
We propose a scheme for generating remote continuous steady-state entanglement of output light leaked from optomechanical system, in which two mechanical oscillators are coupled through long-range Coulomb interaction. we show that the entanglement of output light is affected by the detuning and the strength of the Coulomb interaction. We also demonstrate that two movable mirrors and two light beams can be entangled in the steady state. We suggest an experimental readout scheme to fully verify the characteristic of entangled state.
Quantum information transfer is an important part of quantum information processing. Several proposals for quantum information transfer along linear arrays of nearest-neighbor coupled qubits or spins were made recently. Perfect transfer was shown to exist in two models with specifically designed strongly inhomogeneous couplings. We show that perfect transfer occurs in an entire class of chains, including systems whose nearest-neighbor couplings vary only weakly along the chain. The key to these observations is the Jordan-Wigner mapping of spins to noninteracting lattice fermions which display …
Genuine multipartite entanglement is of great importance in quantum information, especially from the experimental point of view. Nevertheless, it is difficult to construct genuine multipartite entangled states systematically, because the genuine multipartite entanglement is unruly. We propose another product based on the Kronecker product in this paper. The Kronecker product is a common product in quantum information with good physical interpretation. We mainly investigate whether the proposed product of two genuine multipartite entangled states is still a genuine entangled one. We understand …
We propose a scheme via three-level cascade atoms to entangle two optomechanical oscillators as well as two-mode fields. We show that two movable mirrors and two-mode fields can be entangled even for bad cavity limit. We also study entanglement of the output two-mode fields in frequency domain. The results show that the frequency of the mirror oscillation and the injected atomic coherence affect the output entanglement of the two-mode fields.
We present a local interpretation of what is usually considered to be a nonlocal de Broglie-Bohm trajectory prescription for an entangled singlet state of massive particles. After reviewing various meanings of the term ``nonlocal'', we show that by using appropriately retarded wavefunctions (i.e., the locality loophole) this local model can violate Bell's inequality, without making any appeal to detector inefficiencies. We analyze a possible experimental configuration appropriate to massive two-particle singlet wavefunctions and find that as long as the particles are not ultra-relativistic, a …
$1/N^2$ Precision Interferometry with Collectively Enhanced Atomic Mirror
本文提出一种无需纠缠态制备的量子干涉测量方法，利用集体增强原子镜实现$1/N^2$精度，超越海森堡极限，具有抗位移和耦合杂乱的优势。
We present an efficient method to control the spatial modes of entangled photons produced through SPDC process. Bi-photon beam propagation is controlled by a deformable mirror, that shapes a 404nm CW diode laser pump interacting with a nonlinear BBO type-I crystal. Thanks to adaptive optical system, the propagation of 808nm SPDC light produced is optimized over a distance of 2m. The whole system optimization is carried out by a feedback between deformable mirror action and entangled photon coincidence counts. We also demonstrated the improvement of the two-photon coupling into single mode fibe…
Deterministic generation of photonic entangled states using decoherence-free subspaces
该研究提出利用半波导中三个发射器的集体态资源，通过无消相干子空间内的量子门操作与亮态耦合的光子发射，确定性生成光子纠缠态，为量子信息技术提供基础支撑。
There exists a commonly accepted viewpoint that a movable mirror in an interferometer should cause interference breakdown due to a quantum jump to one of the two components of a photon mode. That effect goes back to Dirac. We argue that the conventional reasoning is inadequate: First, it would be more circumspect to interpret interference breakdown as being due to the entanglement of the photon with the mirror, not referring to quantum jumps. Second--and crucial--even in such an interpretation, the reasoning does not take into account the uncertainty of the mirror momentum. The effect of the e…
For a bipartite state with equal local dimension d, we prove that one can obtain work gain under Landauer's erasure process on one party in identically and independently distributed (iid) limit when the corresponding fully entangled fraction is larger than 1/d. By processing a given state to the maximally mixed state, we give an approximation for the largest extractable work with an error in the energy scale, which becomes negligible in the large system limit. As a step to link quantum thermodynamics and quantum nonlocality, we also provide a simple picture to approximate the optimal work extr…
We consider the radiative properties of a system of two identical correlated atoms interacting with the electromagnetic field in its vacuum state in the presence of a generic dielectric environment. We suppose that the two emitters are prepared in a symmetric or antisymmetric superposition of one ground state and one excited state and we evaluate the transition rate to the collective ground state, showing distinctive cooperative radiative features. Using a macroscopic quantum electrodynamics approach to describe the electromagnetic field, we first obtain an analytical expression for the decay …
We consider a composite particle formed by two fermions or two bosons. We discover that composite behavior is deeply related to the quantum entanglement between the constituent particles. By analyzing the properties of creation and annihilation operators, we show that bosonic character emerges if the constituent particles become strongly entangled. Such a connection is demonstrated explicitly in a class of two-particle wave functions.
A coherence interpretation of nonlocal realism in the delayed-choice quantum eraser
本文用相干性解释延迟选择量子擦除器中类空间分离光子的非局域条纹，指出其源于符合探测引起的选择性测量和积基叠加，并强调固定和相位关系是传统粒子性量子力学无法解释的先决条件。
We study the detection of weak coherent forces by means of an optomechanical device formed by a highly reflecting isolated mirror shined by an intense and highly monochromatic laser field. Radiation pressure excites a vibrational mode of the mirror, inducing sidebands of the incident field, which are then measured by heterodyne detection. We determine the sensitivity of such a scheme and show that the use of an entangled input state of the two sideband modes improves the detection, even in the presence of damping and noise acting on the mechanical mode.
We introduce a local concept of speed-up applicable to intermediate stages of a quantum algorithm. We use it to analyse the complementary roles played by quantum parallel computation and quantum measurement in yielding the speed-up. A severe conflict between there being a speed-up and the many worlds interpretation is highlighted.
Correlations in Entangled States
本文基于量子力学统计系综解释处理纠缠EPR自旋对，通过向单态引入无穷小相位退相干揭示其关联，证明单态不存在经典关联。
We derive from first principles the momentum exchange between a photon and a quantum mirror upon reflection, by considering the boundary conditions imposed by the mirror surface on the photon wave equation. We show that the system generally ends up in an entangled state, unless the mirror position uncertainty is much smaller than the photon wavelength, when the mirror behaves classically. Our treatment leads us directly to the conclusion that the photon momentum has the known value hk/2π. This implies that when the mirror is immersed in a dielectric medium the photon radiation pressure is prop…
We develop closed expressions for a time-resolved photon counting signal induced by an entangled photon pair in an interferometric spectroscopy setup. Superoperator expressions in Liouville-space are derived that can account for relaxation and dephasing induced by coupling to a bath. Interferometric setups mix matter and light variables non-trivially, which complicates their interpretation. We provide an intuitive modular framework for this setup that simplifies its description. Based on separation between the detection stage and the light-matter interaction processes. We show that the pair en…
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