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A Simple Scheme of Generating EPR Entangled States

Bojun Yang

Published Jan 1, 2004• 0 citations
OpenAlex

Abstract

It is theoretically proved that the two output light beams can be used as a pair of EPR(Einstin-Podolsky-Rosen) entangled beams when the incident light upon a beam splitter is a single mode quadrature-squeezed coherent state or a squeezed quantum soliton. It is the simplest scheme for preparing entangled states to our knowledge. The formulas explicitly show the correlation between the two nonclassical optical fields: squeezed states and entangled states. The affection of squeezing degree on entanglement is also investigated.

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It is theoretically proved that the two output light beams can be used as a pair of EPR(Einstin-Podolsky-Rosen) entangled beams when the incident light upon a beam splitter is a single mode quadrature-squeezed coherent state or a squeezed quantum soliton. It is the simplest scheme for preparing entangled states to our knowledge. The formulas explicitly show the correlation between the two nonclassical optical fields: squeezed states and entangled states. The affection of squeezing degree on entanglement is also investigated.
In this paper we present a scheme in which the amplitude-quadrature difference and phase-quadrature difference of two bright nonclassical beams serve as a pair of observed complementary variables that can be measured directly and can form a new squeezed state. Mixing such two quadrature-difference squeezed-state beams on a beam splitter produces characteristic of the Einstein-Podolsky-Rosen quantum entanglement. The experimental schemes producing such nonclassical beams and its possible applications in quantum information are discussed.
Einstein-Podolsky-Rosen (EPR) entanglement is a criterion that is more demanding than just certifying entanglement. We theoretically and experimentally analyze the low-resource generation of bipartite continuous-variable entanglement, as realized by mixing a squeezed mode with a vacuum mode at a balanced beam splitter, i.e., the generation of so-called vacuum-class entanglement. We find that in order to observe EPR entanglement the total optical loss must be smaller than 33.333.333.3 %. However, arbitrarily strong EPR entanglement is generally possible with this scheme. We realize continuous-wave squeezed light at 155015501550 nm with up to 9.99.99.9 dB of nonclassical noise reduction, which is the highest value at a telecom wavelength so far. Using two phase-controlled balanced homodyne detectors we observe an EPR covariance product of $0.502\ifmmode\pm\else\textpm\fi{}0.006<1$, where 111 is the critical value. We discuss the feasibility of strong Gaussian entanglement and its application for quantum key distribution in a short-distance fiber network.
We show that general Einstein-Podolsky-Rosen-type (EPR-type) entanglement of continuous variables with arbitrary eigenvalues for bosons can be yielded. For bosons of nonzero resting mass EPR-type entangled state can be achieved by the use of atomic beam splitters in particles of a position eigenstate and $n\ensuremath{-}1$ momentum eigenstates. For light field in which resting mass of the photon is zero, approximate EPR-type entanglement can be experimentally generated when we apply optical beam splitters to one position-squeezed coherence state and $n\ensuremath{-}1$ momentum-squeezed coherence states, this approximate version tends to perfect EPR entanglement in the limit of infinite squeezing.
Abstract We propose a method to generate an entangled squeezed state using an optical parametric amplifier (OPA) and a beam splitter (BS). This device can manipulate the output quantum light field by modulating two parameters: the intensity of the OPA and the transmittance of the optical BS. For the output quantum state associated with a symmetric BS, there is no quadrature squeezing. Moreover, neither photon correlation nor entanglement are observed. However, in terms of sum squeezing, the quantum state corresponding to the symmetric BS is the strongest. Therefore, an asymmetric BS and a highly squeezing OPA are the best choices for generating the quantum entangled squeezed states.
We report on the generation of a continuous variable Einstein-Podolsky-Rosen (EPR) entanglement using an optical fiber interferometer. The Kerr nonlinearity in the fiber is exploited for the generation of two independent squeezed beams. These interfere at a beam splitter and EPR entanglement is obtained between the output beams. The correlation of the amplitude (phase) quadratures is measured to be 4.0+/-0.2 (4.0+/-0.4) dB below the quantum noise limit. The sum criterion for these squeezing variances 0.80+/-0.03<2 verifies the nonseparability of the state. The product of the inferred uncertainties for one beam (0.64+/-0.08) is well below the EPR limit of unity.
Photon subtraction is useful to produce nonclassical states of light addressed to applications in photonic quantum technologies. After a very accelerated development, this technique makes possible obtaining either single photons or optical cats on demand. However, it lacks theoretical formulation enabling precise predictions for the produced fields. Based on the representation generated by the two-mode SU(2) coherent states, we introduce a model of entangled light beams leading to the subtraction of photons in one of the modes, conditioned to the detection of any photon in the other mode. We show that photon subtraction does not produce nonclassical fields from classical fields. It is also derived a compact expression for the output field from which the calculation of conditional probabilities is straightforward for any input state. Examples include the analysis of squeezed-vacuum and odd-squeezed states. We also show that injecting optical cats into a beam splitter gives rise to entangled states in the Bell representation.