The Einstein–Podolsky–Rosen Effect: Paradox or Gate?

The Einstein–Podolsky–Rosen (EPR) paradox represents one of the most controversial aspects of quantum mechanics (QM). In this paper, we suggest that it can be solved by taking into account the fact that physical quantum phenomena can be extended backward in time (i.e. we take into account two arrows of time instead of one). We derive such a strong statement as a consequence of symmetries and conservation laws implying field equations which are invariant under time reversal. Our approach, violating Einstein's locality postulate, confirms QM predictions and explains the failure of Bell's inequalities.     

A compact Einstein–Podolsky–Rosen entangled light source

We present a stable entangled light source that integrates the pump laser, entanglement generator, detectors, and electronic control systems. By optimizing the design of the mechanical elements and the optical path, the size of the source is minimized, and the quantum correlations over 6 d B can be directly provided by the entangled source. The compact and stable entangled light source is suitable for practical applications in quantum information science and technology. The presented protocol provides a useful reference for manufacturing products of bright entangled light sources.     

Improving Einstein–Podolsky–Rosen steering inequalities with state information

We discuss the relationship between entropic Einstein–Podolsky–Rosen (EPR)-steering inequalities and their underlying uncertainty relations along with the hypothesis that improved uncertainty relations lead to tighter EPR-steering inequalities. In particular, we discuss how using information about the state of a quantum system affects one?s ability to witness EPR-steering. As an example, we consider the recent improvement to the entropic uncertainty relation between pairs of discrete observables (Berta et al., 2010 [10]). By considering the assumptions that enter into the development of a steering inequality, we derive correct steering inequalities from these improved uncertainty relations and find that they are identical to ones already developed (Schneeloch et al., 2013 [9]). In addition, we consider how one can use state information to improve our ability to witness EPR-steering, and develop a new continuous variable symmetric EPR-steering inequality as a result.     

Towards a Deeper Understanding of the Einstein–Podolsky–Rosen Problem

Most of the nearly innumerable attempts to provide for a sound understanding of the gedanken experiment of Einstein, Podolsky, and Rosen (EPR) contain additional ideas, notions or features imposed on pioneer or traditional quantum mechanics (TQM). In the present paper the problem is analyzed without employing any new or philosophically contested concept. We do even without referring to the probability calculus, and we especially avoid any admixture of realistic ideas. Neither entanglement nor special features of states are used. Instead, formulating strictly within the framework of TQM and using an ensemble approach, the crucial point is boiled down to the decision between separability and non-separability. The corresponding second-order correlation functions _s and _n–s, resp., which predict the experimental outcome, may differ by a factor of 2 if certain operator pairs are maximally non-commuting. Even in the case of commuting pairs, an experimentally relevant difference between the -functions might exist. Taking into account the experimental evidence, it is unavoidable to accept that the sub-ensembles involved in EPR-type experiments are in fact non-separable. This result has been obtained without resort to Bell's inequality.     

Generation of tripartite Einstein–Podolsky–Rosen steering by cascaded nonlinear process

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.     

Demonstration of Einstein–Podolsky–Rosen Steering with Multiple Observers via Sequential Measurements

Quantum correlation is a fundamental property that distinguishes quantum systems from classical ones,and is also a fragile resource under projective measurements.Recently,it has been shown that a subsystem in entangled pairs can share nonlocalities with multiple observers in sequence.Here we present a new steering scenario where both subsystems are accessible by multiple observers.Simulation results show that the two qubits in a singlet state can be simultaneously steered separately by two seque...     

Einstein—Podolsky—Rosen Correlations and the Preferred Frame

The correlation function of spin measurements of two spin- particles in two moving inertial frames is derived within the framework of the Lorentz covariant quantum mechanics with the preferred frame. The localization of the particles during the detection and proper transformation properties under the action of the Lorentz group of the spin operator are taken into account. Some special cases and approximations of the calculated correlation function are discussed.     

Einstein–Podolsky–Rosen entanglement in time-dependent broadband pumping frequency non-degenerate optical parametric amplifier

This paper investigates quantum fluctuations characteristic of time-dependent broadband pumping frequency non-degenerate optical parametric amplifier for below and above threshold regions. It finds that a high squeezing and entanglement can be achieved.     

A Novel Deterministic Secure Quantum Communication Scheme with Einstein–Podolsky–Rosen Pairs and Single Photons

A novel deterministic secure quantum communication(DSQC)scheme is presented based on EinsteinPodolsky-Rosen(EPR)pairs and single photons in this study.In this scheme,the secret message can be encoded directly on the first particles of the prepared Bell states by simple unitary operations and decoded by performing the Bell-basis measurement after the additional classic information is exchanged.In addition,the strategy with two-step transmission of quantum data blocks and the technique of decoy-particle checking both are exploited to guarantee the security of the communication.Compared with some previous DSQC schemes,this scheme not only has a higher resource capacity,intrinsic efciency and total efciency,but also is more realizable in practical applications.Security analysis shows that the proposed scheme is unconditionally secure against various attacks over an ideal quantum channel and still conditionally robust over a noisy and lossy quantum channel.     

New Three—Mode Einstein—Podolsky—Rosen Entangled State Prepresentation and Its Application in Squeezing Theory

By extending the Einstein-Podolsky-Rosen bipartite entanglement to the tripartite case,we construct the common eigenvector of the tripartite centre-of -mass coordinate and two mass-weighted relative momenta,which is a new entangled state of continuum variables.The classical dilation transform of varibles in such a state induces new entangled state of continum variables,The classical dilation transform of variables in such a state induces a new three-mode squeezing operator related to a three-mode bosonic operator realization of SU(1,1) Lie algebra.a new three-mode squeezing operator related to a three-mode bosonic operator realization of SU(1,1) Lie algebra.     

Energetics of the Einstein–Rosen Spacetime

A study covering some aspects of the Einstein–Rosen metric is presented. The electric and magnetic parts of the Weyl tensor are calculated. It is shown that there are no purely magnetic E-R spacetimes, and also that a purely electric E-R spacetime is necessarily static. The geodesics equations are found and circular ones are analyzed in detail. The super-Poynting and the “Lagrangian” Poynting vectors are calculated and their expressions are found for two specific examples. It is shown that for a pulse-type solution, both expressions describe an inward radially directed flow of energy, far behind the wave front. The physical significance of such an effect is discussed.     

Fast Generation of Einstein–Podolsky–Rosen States for Two Cavity Modes with a Collection of Driven Atoms

We propose an efficient scheme for realizing two-mode squeezing for two cavity modes with an atomic ensemble trapped in the cavity and driven by two classical fields. Through a suitable choice of the driving classical fields, the evolution dynamics of the two cavity modes is decoupled with the atomic system and described by a two-mode squeezing operator. We show that a highly squeezed state can be obtained at the output even with a bad cavity. The required experimental techniques are within the scope of what can be obtained in the BEG-cavity setup.     

A realizable multi-bit dense coding scheme with an Einstein—Podolsky—Rosen channel

We propose a multi-bit dense coding scheme by using only an Einstein-Podolsky-Rosen(EPR) channel and assistant qubits.It is shown that no matter how many classical bits there are,the quantum channel is always a Bell state.The present dense coding process can also prepare non-local multi-particle Greenberger-Horne-Zeilinger(GHZ) states at one of the participants.The quantum circuits for this dense coding process are constructed,the deterministic implementation method in an optical system based on the cross-Kerr nonlinearities is shown.     

Einstein–Rosen solutions from Kaluza–Klein theory

From a time-dependent boost-rotational symmetric vacuum solution of the Einstein Equations in five dimensions, through the Kaluza–Klein reduction the corresponding Einstein–Maxwell-dilaton solutions are obtained. The four dimensional counterpart turns out to be generalized Einstein–Rosen spacetimes representing unpolarized gravitational waves traveling in an inhomogeneous cosmology. Restricting the parameters we are able to obtain different 4D time-dependent solutions equipped with scalar and electromagnetic fields.     

Quantum discord is Bohr’s notion of non-mechanical disturbance introduced to counter the Einstein–Podolsky–Rosen argument

By rigorously formalizing the Einstein–Podolsky–Rosen (EPR) argument, and Bohr’s reply, one can appreciate that both arguments were technically correct. Their opposed conclusions about the completeness of quantum mechanics hinged upon an explicit difference in their criteria for when a measurement on Alice’s system can be regarded as not disturbing Bob’s system. The EPR criteria allow their conclusion–incompleteness–to be reached by establishing the physical reality of just a single observable q$q$ (not of both q$q$ and its conjugate observable p$p$), but I show that Bohr’s definition of disturbance prevents the EPR chain of reasoning from establishing even this. Moreover, I show that Bohr’s definition is intimately related to the asymmetric concept of quantum discord from quantum information theory: if and only if the joint state has no Alice-discord, she can measure any observable without disturbing (in Bohr’s sense) Bob’s system. Discord can be present even when systems are unentangled, and this has implications for our understanding of the historical development of notions of quantum nonlocality.     

Einstein——Podolsky——Rosen entanglement in time-dependent periodic pumping non-degenerate optical parametric amplifier

The solution of the time-dependent periodic pumping non-degenerate optical parametric amplifier (NOPA) is derived when the pump depletion is considered both above and below thresholds. Based on this solution, the quantum fluctuation calculated shows that a high entanglement and a good squeezing degree of the parametric light beams are achieved near and above thresholds. We adopt two kinds of pump fields: (i) a continuously modulated pump with a sinusoidal envelope; (ii) a sequence of laser pulses with Gaussian envelopes. We analyse the time evolution of continuous variable entanglement by analytical and numerical calculations, and show that the periodic driven pumping also improves the degree of entanglement. The squeezing and Einstein-Podolsky-Rosen (EPR) entanglement by using the two pumping driven functions are investigated from below to above the threshold regions, the tendencies are nearly the same, and the Gaussian driven function is superior to that of the sine driven function, when the maximum squeezing and the minimum variance of quantum fluctuation are considered. In the meantime, the generalization of frequency degenerate OPA to frequency non-degenerated OPA problem is investigated.     

Bell’s inequality, Einstein, Podolsky, Rosen arguments and von Neumann’s projection postulate

This paper is devoted to analysis of the role of projection postulate in Einstein, Podolsky, and Rosen-EPR [1] argument against completeness of QM. It will be shown that the EPR considerations do not match with von Neumann’s quantum measurement theory (QMT). The root of EPR’s conclusion on incompleteness of QM is the misuse of von Neumann’s projection postulate. EPR applied this postulate to observables with degenerate spectra (which is totally forbidden by von Neumann’s axiomatics of QM). Consequences for Bell’s inequality and quantum information theory are analyzed. This paper might stimulate discussion on the role of projection postulate in quantum information theory, especially quantum cryptography and teleportation.     

Einstein–Podolski–Rosen paradox,non-commuting operator,complete wavefunction and entanglement

Einstein, Podolski and Rosen (EPR) have shown that any wavefunction (subject to the Schrödinger equation) can describe the physical reality completely, and any two observables associated with two non-commuting operators can have simultaneous reality. In contrast, quantum theory claims that the wavefunction can capture the physical reality completely, and the physical quantities associated with two non-commuting operators cannot have simultaneous reality. The above contradiction is known as the EPR paradox. Here, we unambiguously expose that there is a hidden assumption made by EPR, which gives rise to this famous paradox. Putting the assumption right this time leads us not to the paradox, but only reinforces the correctness of the quantum theory. However, it is shown here that the entanglement phenomenon between two physically separated particles (they were entangled prior to separation) can only be proven to exist with a ‘proper’ measurement.     

The extended conformal Einstein field equations with matter: The Einstein–Maxwell field

A discussion is given of the conformal Einstein field equations coupled with matter whose energy–momentum tensor is trace-free. These resulting equations are expressed in terms of a generic Weyl connection. The article shows how in the presence of matter it is possible to construct a conformal gauge which allows to know a priori the location of the conformal boundary. In vacuum this gauge reduces to the so-called conformal Gaussian gauge. These ideas are applied to obtain (i) a new proof of the stability of Einstein–Maxwell de Sitter-like spacetimes; (ii) a proof of the semi-global stability of purely radiative Einstein–Maxwell spacetimes.