Einstein-Podolsky-Rosen Research Articles

A Physical Origin for Quantum Entanglement and Probabilistic Behaviors

Quantum Mechanics’ entanglement and probabilistic behaviors are viewed in the light of Quantum Field Theory’s (QFT’s) advances made during the last century. In particular, Bohm’s version (B-EPR) of the Einstein, Podolsky, Rosen (EPR) experiment is now viewed with the aid of QFT’s modern description of electrons. In QFT, free electrons possess a bare core surrounded by a “dressing”. The dressing consists of one or more virtual particles/fields pulled from the vacuum during the bound electron’s parturition. In QFT, a bound electron’s freedom is aided by eliminating its energy losses from bremsstrahlung. The paper develops a “Shimony” numerical model using QFT’s free electron structure with the aid of a “random vector paradigm” (RVP). The RVP simply expresses QFT’s free electron as a bare core surrounded by an EM dressing. Using this RVP, we imbue newly freed electrons with a vector-like EM spin property of 1/2. From this, the Shimony Monte Carlo computer analysis provides a detailed comparison of the B-EPR experiment as described by Bell. The entanglement property can serve to provide a way to transport shared encoded information. Overall, the electron dressing can convey random elements that may provide QM with its entanglement and probabilistic behaviors.

Einstein-Podolsky-Rosen steering in spontaneous parametric down-conversion cascaded with a sum-frequency generation

Einstein-Podolsky-Rosen (EPR) steering has potential applications in quantum information processing. Here the genuine tripartite EPR steering is investigated in cascaded nonlinear process of spontaneous parametric down-conversion cascaded with a sum-frequency generation in an optical cavity for a wide range of the nonlinear parameters. The threshold properties of the cascaded nonlinear precess are also analyzed both below and without threshold regime, respectively. The genuine tripartite EPR steering is demonstrated based on the criteria for genuine multipartite EPR steering. Our scheme of the generation of genuine tripartite EPR steering can be used as a suggestion for the potential experiments and the applications in quantum communication and computation.

Quantum field theory motivated model for the Einstein, Podolsky, Rosen (EPR) experiment

Bell deduced the nature and form of “nonlocal hidden variables” that could yield the unusual pattern of responses in the paradoxical Bohm (B-EPR) version of the Einstein, Podolsky, Rosen (EPR) experiment. We consider that quantum field theory (QFT) allows for the existence of Bell’s hidden variables in the “dressing” of free electrons that may explain the EPR experimental results. Specifically, the dressing of free electrons can convey random vector information. Motivated by this, we use a random vector paradigm (RVP) to explore how well a Monte Carlo computer program compares with the experimental B-EPR statistics. In this algorithm, the random vector provides a unique fingerprint that allows these charged leptons to bear unique responses when their spin is read by Stern–Gerlach detectors. The program’s numerical results compare well with Bell’s experimental summary. This work offers the opportunity to consider that virtual particles play a role in understanding the origins of quantum mechanics (QM)’s unique entanglement and probabilistic behaviors.

Quantum-feedback-controlled macroscopic quantum nonlocality in cavity optomechanics

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 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 only be prepared in steady weakly entangled states which however do not display EPR steering and Bell nonlocality, due to the so-called 3 dB limit. But when the feedback is present, it is found that the mechanical entanglement is considerably enhanced such that strong mechanical steering and Bell nonlocality can be obtained in the steady-state regime. We analytically reveal that this is because the feedback drives the mechanical oscillators into a steady approximate two-mode squeezed vacuum state, with arbitrary squeezing in principle. It is shown that the feedback can also obviously improve the purity of the nonclassical mechanical states. The dependences of the mechanical quantum nonlocality on the feedback strength and thermal fluctuations are studied, and it is found that Bell nonlocality is much more vulnerable to thermal noise than EPR steerable nonlocality.

Quantum entanglement and teleportation in superposition of multiple-photon-added two-mode squeezed vacuum state

In this paper, a new state called superposition of multiple-photon-added two-mode squeezed vacuum state (SMPA-TMSVS) is introduced by adding the multiple photons to both modes of a two-mode squeezed vacuum state (TMSVS). We explicitly investigate the degree of quantum entanglement, the Einstein–Podolsky–Rosen (EPR) correlation and the quantum steering in the SMPA-TMSVS. The results show in the SMPA-TMSVS that the degree of entanglement and the EPR correlation can be enhanced by nonlocal adding photons to a TMSVS. The quantum steering appears in the SMPA-TMSVS in case the superposition of single-photon addition [Formula: see text], in which mode [Formula: see text] can steer mode [Formula: see text]. By using the SMPA-TMSVS as an entangled resource, the quantum teleportation process is studied in detail based on the Vaidman–Braunstein–Kimble (VBK) protocol.

Role of EPR correlation in Gaussian quantum teleportation

Quantum teleportation (QT) plays a central role in state-of-the-art information science and technology that necessitates proper characterization of the resources. While entanglement is known to be necessary, condition of sufficiency for QT still remains an open question. Here, we partially answer this question in light of Einstein-Podolsky-Rosen (EPR) correlation. In the case of input coherent state, we provide an analytic proof that with a general two-mode Gaussian entangled resources EPR correlation is sufficient for QT. For a relatively restricted set of Gaussian states, however bigger than that of the symmetric states, we further show that EPR correlation is both necessary and sufficient. On the other hand, in the case of Gaussian pure input, our numerical results hint that EPR correlation mostly appears to be a necessary condition only. However, the necessary and/or sufficient condition for QT of a Gaussian mixed input state, apart from the entanglement, still remains an open question.

Enhanced entanglement and asymmetric EPR steering between magnons

The generation and manipulation of strong entanglement and Einstein-Podolsky-Rosen (EPR) steering in macroscopic systems are outstanding challenges in modern physics. Especially, the observation of asymmetric EPR steering is important for both its fundamental role in interpreting the nature of quantum mechanics and its application as resource for the tasks where the levels of trust at different parties are highly asymmetric. Here, we study the entanglement and EPR steering between two macroscopic magnons in a hybrid ferrimagnet—light system. In the absence of light, the two types of magnons on the two sublattices can be entangled, but no quantum steering occurs when they are damped with the same rates. In the presence of the cavity field, the entanglement can be significantly enhanced, and strong two-way asymmetric quantum steering appears between two magnons with equal dissipation. This is very different from the conventional protocols to produce asymmetric steering by imposing additional unbalanced losses or noises on the two parties at the cost of reducing steerability. The essential physics is well understood by the unbalanced population of acoustic and optical magnons under the cooling effect of cavity photons. Our finding may provide a novel platform to manipulate the quantum steering and the detection of bi-party steering provides a knob to probe the magnetic damping on each sublattice of a magnet.

A quantum similarity discussion about Einstein–Podolsky–Rosen (EPR) paradox in Gaussian enfolded spaces

The Einstein–Podolsky–Rosen discussion about the completeness of quantum mechanics is examined using Gaussian enfolded Euclidian spaces. The research is performed within a quantum similarity framework, forming Gaussian quantum polyhedra. The analysis is achieved through simplified descriptions of quantum systems using appropriate Minkowski normalized Gaussian density functions.

Quasi-fine-grained uncertainty relations

Nonlocality, which is the key feature of quantum theory, has been linked with the uncertainty principle by fine-grained uncertainty relations, by considering combinations of outcomes for different measurements. However, this approach assumes that information about the system to be fine-grained is local, and does not present an explicitly computable bound. Here, we generalize above approach to general quasi-fine-grained uncertainty relations (QFGURs) which applies in the presence of quantum memory and provides conspicuously computable bounds to quantitatively link the uncertainty to entanglement and Einstein–Podolsky–Rosen (EPR) steering, respectively. Moreover, our QFGURs provide a framework to unify three important forms of uncertainty relations, i.e., universal uncertainty relations, the uncertainty principle in the presence of quantum memory, and fine-grained uncertainty relation. This result gives a direct significance to uncertainty principle, and allows us to determine whether a quantum measurement exhibits typical quantum correlations, meanwhile, it reveals a fundamental connection between basic elements of quantum theory, specifically, uncertainty measures, combined outcomes for different measurements, quantum memory, entanglement and EPR steering.

Genuine quadripartite quantum steering generated by an optical parametric oscillation cascaded with a sum-frequency process

Quantum steering is the essential resource for quantum information processing. In this letter, a scheme is proposed to generate genuine quadripartite Einstein-Podolsky-Rosen (EPR) steering by an optical parametric oscillation cascaded with a sum-frequency process. Idler beam is generated by a difference frequency generation process between pump and injected signal in an optical superlattice. Then, a sum-frequency beam is produced by the cascaded sum-frequency process between pump and idler beams in the same optical superlattice by the quasi-phase-matching technique. The genuine quadripartite EPR steering among pump, signal, idler, and sum-frequency beams is confirmed in this scheme by applying a criteria for genuine multipartite EPR steering. The variation properties of the EPR steering with pump and nonlinear coupling coefficients are also discussed.

Einstein synchronisation by quantum teleportation

We present a protocol of Einstein’s synchronization of two spatially separated clocks on the basis of quantum teleportation in which the Einstein-Podolsky-Rosen (EPR) state plays a central role. Our scheme does not contain the frame defining problem nor the phase contamination problem for the EPR state which appeared in the quantum clock synchronization (Jozsa et al 2000 Phys. Rev. Lett. 85, 2010).

Securing Blockchain Transactions Using Quantum Teleportation and Quantum Digital Signature

Blockchain is the new disruptive technology which is gaining momentum in several domains of real-world applications such as Bitcoin—the most well-known example, and primarily in the financial sector. Distributed ledger system which is the main feature of blockchain technology protected across harmful updates using cryptographic techniques, e.g. hashing and digital signatures, is spread over the network so that no one is the owner of the ledger. This poses a significant challenge in the areas of performance, security, and privacy using this emerging technology. We propose an algorithm to provide a secure mechanism for performing transactions on the Blockchain network by adopting quantum digital signatures (QDS) and quantum teleportation phenomenon of quantum computing. The proposed algorithm uses key pairs to generate private keys and corresponding public keys; the quantum digital signatures are used to sign the message which are then distributed over the blockchain network using the teleportation phenomenon. The security of the keys is dependent on the fundamental principles of quantum mechanics that doesn’t allow forging. The Einstein–Podolsky–Rosen (EPR) pair of particles is used to communicate the quantum information via a quantum channel for teleportation, which is generated by operating Bell measurements with corresponding EPR pairs. The original state of the particle (sender) is destroyed once the information is transported to the other particle (receiver) and the QDS scheme also validates the qubits received. The twofold validation process thereby provides high-level security in the transactions.

Monogamy relations within quadripartite Einstein-Podolsky-Rosen steering based on cascaded four-wave mixing processes

Multipartite Einstein-Podolsky-Rosen (EPR) steering has been recognized as an essential resource for secure quantum communication tasks composed of several spatially separated parties who cannot be fully trusted. Nevertheless, this resource cannot be distributed arbitrarily over many parties; for instance, two independent players cannot simultaneously steer the third party by two-setting measurements. This feature is referred to as monogamy of steering, which ensures the security of quantum cryptographic protocols and is thus a very desired property to investigate for multipartite steering. Here, we propose symmetric and asymmetric structures of cascaded four-wave mixing of rubidium atoms to generate versatile quadripartite EPR steering and investigate four distinct types of monogamy relations of Gaussian steering. We find that the distribution constraint described by one of the monogamy relations can be lifted only for the quadripartite steering created by the symmetric setup. This result paves the way for a better understanding of the distribution rules of multipartite EPR steering and its potential applications for secure quantum communication.

One-way Einstein–Podolsky–Rosen steering via quantum interference from incoherent pumping

In this paper, we investigate the effects of incoherent pumping on quantum correlations in a Λ -type atomic system driven by coherent and incoherent fields simultaneously. With the adiabatic elimination treatment, we show that the stable “one-way” Einstein–Podolsky–Rosen (EPR) steering is generated without the requirement of good cavity limitation. More interestingly, the asymmetrical EPR steering is simply controlled by the polarized angle of the incoherent field. The internal mechanisms can be understood based on dressed-state representation, in which the population differences are strongly modified by the quantum interference from incoherent pumping. The phase-sensitive quantum correlations in the present scheme may find potential applications in quantum information processing.

Frequency-dependent squeezing generation with EPR entanglement

The sensitivity of gravitational wave interferometric detectors is ultimately limited by the quantum noise, which arises from the quantum nature of light and it is driven by vacuum fluctuations of the optical field entering from the dark port of the interferometer. One way to improve the sensitivity of gravitational wave interferometers is to inject squeezed vacuum into the dark port. This has been already demonstrated for the main gravitational wave detectors (GEO, Advanced LIGO and Advanced VIRGO). We are studying tricks to produce a “frequency- dependent squeezing”: a standard method is to filter the squeezed optical field with one or more optical cavities (300 m long cavities). An alternative method using a pair of squeezed EPR (Einstein-Podolsky-Rosen) entangled beams to produce frequency-dependent squeezing by a non-degenerate OPO (Optical Parametric Oscillator) will be discussed in this paper. This method promises to achieve a frequency-dependent optimization of the injected squeezed light fields without the need for an external filter cavity.

Experimental observation of Einstein-Podolsky-Rosen steering via entanglement detection

The Einstein-Podolsky-Rosen (EPR) steering is an intermediate quantum nonlocality between entanglement and Bell nonlocality, which plays an important role in quantum information processing tasks. In the past few years, the investigations concerning EPR steering have been demonstrated in a series of experiments. However, these studies rely on the relevant steering inequalities and the choices of measurement settings. Here, we experimentally verify the EPR steering via entanglement detection without using any steering inequality and measurement setting. By constructing two new states from a two-qubit target state, we observe the EPR steering by detecting the entanglement of these new states. The results show that the entanglement of the newly constructed states can be regarded as a new kind of steering witness for target states. Compared to the results of Xiao et al. [Phys. Rev. Lett. 118, 140404 (2017)], we find that the ability of detecting EPR steering in our scenario is stronger than two-setting projective measurements, which can observe more steerable states. Hence, our demonstrations can deepen the understanding of the connection between the EPR steering and entanglement.

Continuous‐Variable Entanglement and Wigner‐Function Negativity via Adding or Subtracting Photons

AbstractThe performance of adding or subtracting photons on two‐mode squeezed thermal states via examining the Einstein–Podolsky–Rosen (EPR) correlation, the Hillery–Zubairy (HZ) correlation, the fidelity of teleportation, and the negativity of Wigner function is theoretically investigated. The normalization factors and the teleportation fidelity are related to Jacobi polynomials, and the (evolved) Wigner functions are simply associated with two‐variable Hermite polynomials. Compared with the original squeezed thermal states, the EPR correlation and the teleportation fidelity can be enhanced by photon subtraction and basically weakened by photon addition symmetric operations, but they cannot be enhanced for both photon addition and subtraction asymmetric cases. Also, HZ correlation can provide a better option relative to the EPR correlation in detecting the entanglement, and the fidelity for teleporting a squeezed state with a large squeezing can also be enhanced via photon addition symmetric operations, in contrast to teleporting a coherent state. Additionally, the nonclassicality is discussed in terms of the negativity of the (evolved) Wigner functions, which shows that photon addition and subtraction and the squeezing cannot restrain the deteriorate of nonclassicality, and the evolved Wigner functions become Gaussian (corresponding to vacuum) with long decay times as a result of amplitude decay.

Generation of tripartite Einstein–Podolsky–Rosen steering by cascaded nonlinear process**Project supported by the National Natural Science Foundation of China (Grant Nos. 61975184, 91636108, and 61775043), the Natural Science Foundation of Zhejiang Province, China (Grant No. LY18A040007), the Science Foundation of Zhejiang Sci-Tech University (Grant Nos. 19062151-Y and 18062145-Y), and the Open Foundation of the Key Laboratory of Optical Field Manipulation of

A scheme is proposed to generate genuine tripartite Einstein–Podolsky–Rosen (EPR) steering in cascaded nonlinear process of the fourth-harmonic generation. The second-harmonic is generated by the first double-frequency process in an optical superlattice. Then, the fourth-harmonic is produced by the second cascaded double-frequency process through quasi-phase-matching technique in the same optical superlattice. The genuine tripartite EPR steering among the pump, the second-harmonic, and the fourth-harmonic beams can be obtained by this cascaded nonlinear process according to a criterion for genuine multipartite quantum steering. The quantum steering properties are discussed by adjusting the parameters related to the cascaded nonlinear system. The present research provides a reference scheme and data for obtaining good multipartite EPR steering in experiment and can advance the applications of quantum steering in the quantum information processing.

Nonlocality claims are inconsistent with Hilbert-space quantum mechanics

It is shown that when properly analyzed using principles consistent with the use of a Hilbert space to describe microscopic properties, quantum mechanics is a local theory: one system cannot influence another system with which it does not interact. Claims to the contrary based on quantum violations of Bell inequalities are shown to be incorrect. A specific example traces a violation of the CHSH Bell inequality in the case of a spin-3/2 particle to the noncommutation of certain quantum operators in a situation where (non)locality is not an issue. A consistent histories analysis of what quantum measurements measure, in terms of quantum properties, is used to identify the basic problem with derivations of Bell inequalities: the use of classical concepts (hidden variables) rather than a probabilistic structure appropriate to the quantum domain. A difficulty with the original Einstein-Podolsky-Rosen (EPR) argument for the incompleteness of quantum mechanics is the use of a counterfactual argument which is not valid if one assumes that Hilbert-space quantum mechanics is complete; locality is not an issue. The quantum correlations that violate Bell inequalities can be understood using local quantum common causes. Wavefunction collapse and Schr\"odinger steering are calculational procedures, not physical processes. A general Principle of Einstein Locality rules out nonlocal influences between noninteracting quantum systems. Some suggestions are made for changes in terminology that could clarify discussions of quantum foundations and be less confusing to students.

Generation and control of frequency-dependent squeezing via Einstein–Podolsky–Rosen entanglement

Quantum noise-limited displacement sensors such as gravitational wave detectors can be improved by using non-classical light1. This has been achieved in limited bands and in a single quadrature (that is, only one of a pair of conjugate variables) by injecting single-mode squeezed vacuum states2,3. Quantum noise in gravitational wave detectors, however, results from input noise in both quadratures, with the dominant quadrature being a function of Fourier frequency. Broadband reduction of this noise via squeezed light injection then requires a method of rotating this quadrature. This can be accomplished with a low-loss, all-pass optical filter with bandwidth in the low audio frequencies4,5, a substantial technical challenge. We present a proof-of-principle demonstration of a recent proposal6 to use two-mode squeezed vacuum states with Einstein–Podolsky–Rosen (EPR) entanglement, which allows the gravitational detector to simultaneously serve as the optical filter, eliminating the need for a separate apparatus. Einstein–Podolsky–Rosen entangled beams are sent to a 0.5-m-long optical resonator. To reduce quantum noise in a frequency-dependent manner in the gravitational detector, two-mode frequency-dependent squeezed vacuum states are generated.