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Laser Physics

Entanglement properties of a tunable non-Gaussian quantum state by virtue of multi-photon conditional measurement

Hong‐Chun Yuan, Xue-xiang Xu, Xiang‐Guo Meng

Published Oct 17, 2019• 8 citations
Publisher

Abstract

Abstract In this work, we present a theoretical scheme for generating a new kind of tunable non-Gaussian entangled state, by means of beam splitters and multi-photon conditional measurement with two-mode squeezed vacuum state (TMSVS) inputs. The output state is proven to be two-variable Hermite polynomial excited squeezed vacuum states, whose success probability of detection relates to the Jacobi polynomials. We then mainly study the entanglement properties of the output state for the symmetric case quantified by the von Neumann entropy and Einstein–Podolsky–Rosen correlation. It is shown that the entropy of entanglement is valid for verifying the improvement of entanglement within a certain range of squeezing parameter and transmissivity, and the resulting state case may possess a stronger correlation than the initial TMSVS by increasing the transmissivity or photon number of detection. In addition, the violation of the Clauser–Horne–Shimony–Holt (CHSH) inequality for the output state is also evaluated in terms of Wigner representation in phase space. It is found that the negative region of Wigner function distribution becomes more visible with the increase of the photon number of detection, and the degree of the violation of the CHSH inequality significantly increases as the photon number of detection for the symmetrical case increases. The resulting state with highly nonclassical characteristics will provide a useful application in the fields of quantum information processing.

DOI
10.1088/1555-6611/ab4a07

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Abstract In this work, we present a theoretical scheme for generating a new kind of tunable non-Gaussian entangled state, by means of beam splitters and multi-photon conditional measurement with two-mode squeezed vacuum state (TMSVS) inputs. The output state is proven to be two-variable Hermite polynomial excited squeezed vacuum states, whose success probability of detection relates to the Jacobi polynomials. We then mainly study the entanglement properties of the output state for the symmetric case quantified by the von Neumann entropy and Einstein–Podolsky–Rosen correlation. It is shown that the entropy of entanglement is valid for verifying the improvement of entanglement within a certain range of squeezing parameter and transmissivity, and the resulting state case may possess a stronger correlation than the initial TMSVS by increasing the transmissivity or photon number of detection. In addition, the violation of the Clauser–Horne–Shimony–Holt (CHSH) inequality for the output state is also evaluated in terms of Wigner representation in phase space. It is found that the negative region of Wigner function distribution becomes more visible with the increase of the photon number of detection, and the degree of the violation of the CHSH inequality significantly increases as the photon number of detection for the symmetrical case increases. The resulting state with highly nonclassical characteristics will provide a useful application in the fields of quantum information processing.
Abstract A theoretical scheme of generating a new kind of two-mode non-Gaussian entangled state is presented by means of beam splitters (BSs) and conditional measurement. Here, after detecting photon numbers at the output port of each BS with two kinds of two-mode squeezed vacuum-state inputs, the output state is proved to be two-variable Hermite polynomial excited squeezed vacuum states. Its success probability of detection, namely, normalization factor, is derived in compact expression related to the Jacobi polynomials. Based on the general expression of expectation value, the statistical properties are discussed by exploring the cross-correlation function and anti-bunching effect. The entanglement properties are also investigated by using the Shchukin–Vogel criteria and Einstein–Podolsky–Rosen correlation. The results show that the entanglement of the output state can be enhanced with the increasing photon detection number under the condition of simultaneously detecting the same photon number at the two output ports, which may have good potential for applications in the field of quantum information processing.
Abstract We theoretically put forward a scheme to generate a new kind of the non-Gaussian state—two-mode squeezed Laguerre-polynomial-excited vacuum state (TMS-LPEVs) by using two beam splitters and conditional measurements with two kinds of TMS states inputs. It is interesting that the squeezed Bell state can be considered as a special case of TMS-LPEVs. Then we further examine its properties according to the entanglement entropy, the Einstein–Podolsky–Rosen correlation and the squeezing degree. It is found that for small auxiliary squeezing parameter r and high transmissivity, the entanglement entropy can be enhanced by single-photon measurement. When optimized over transmissivity, multiphoton measurements are beneficial to the improvement of the squeezing property and the teleportation fidelity in the region of larger λ accompanied by small auxiliary squeezing. More significantly, one can use a smaller squeezing parameter r to realize the improvements of the entanglement and the teleportation fidelity. These results may provide guidance for the implementation of experiments in quantum information and quantum computation.
Abstract A class of non-Gaussian entangled states is introduced by applying the nonlocal single-photon addition to two-mode squeezed vacuum state and the properties of entanglement are numerically investigated according to linear entropy and Einstein–Podolsky–Rosen (EPR) steering. After the nonlocal single-photon addition operation, Wigner function of the generated state appears some negative region and loses its Gaussian property in phase space. In essence, non-Gaussian entangled states are generated after applying nonlocal single-photon addition. Additionally, by studying the linear entropy and EPR steering, we find that single-photon addition can enhance their entanglement degree and non-Gaussian steering can be witnessed in a large range of squeezing parameter for the second-order quadratures, which may provide a well application in the fields of quantum information processing.
In this work, the basic idea of the quantum scissors (QS) device is slightly modified to generate finite-dimensional quantum states by means of conditional measurements on beam splitters (BSs). It turns out that a QS device with two single-photon inputs and two single-photon detections is just a projection operator composed of the vacuum state, one-photon state, and two-photon state, depending upon the transmission coefficients of BSs. As the most general example, we consider the squeezed coherent state as the input state and derive the analytical expression of the output state. Its nonclassical characteristics are analyzed in detail by means of the average photon number, intensity gain, and Wigner function. In addition, we extend this technique to the two-mode squeezed vacuum state (TMSVS). The resulting state is just the generalized Bell state, containing only the twin vacuum, twin one-photon, and twin two-photon components, whose entanglement properties are quantified by the von Neumann entropy and Einstein–Podolsky–Rosen correlation. The results show that the entanglement of the truncated TMSVS is stronger than that of TMSVS within a certain range of squeezing parameter and transmissivity.
Abstract This paper investigates the quantum features of non-Gaussian states generated by applying a two-mode squeezing operator S ˆ a b ( s ) to two generalized single-mode squeezed vacuum states (SVSs), each formed by the superposition of an SVS and a single–photon–subtracted SVS. The results show that, in the new states, the two-mode squeezing effect, the Einstein–Podolsky–Rosen (EPR) correlation, the Hillery–Zubairy entanglement, and the linear entropy are all enhanced as the two-mode squeezing parameter s increases. Moreover, both the degrees of squeezing and entanglement are improved and exceed those of the two-mode squeezed vacuum state (TMSVS) for stronger single-mode squeezing parameters. The optimal conditions for achieving such enhancements are identified for different regimes, depending on whether the generalized SVSs are purely Gaussian, maximally non-Gaussian, or intermediate states. In an application, the quantum Cramér–Rao bound (QCRB) is evaluated when the non-Gaussian states are employed as inputs to a Mach–Zehnder interferometer (MZI). The results further demonstrate that the enhanced phase sensitivity in the MZI originates from both the squeezing strengths and the intrinsic photon-subtraction operation. These findings highlight the potential of the new non-Gaussian states as promising resources for quantum metrology and quantum sensing.
Abstract We theoretically prepare a kind of two-mode entangled non-Gaussian state generated by combining quantum catalysis and parametric-down amplifier operated on the two-mode squeezing vacuum state. We then investigate the entanglement properties by examining Von Neumann entropy, EPR correlation, squeezing effect and the fidelity of teleportation. It is shown that only Von Neumann entropy can be enhanced by both single- and two-mode catalysis in a small squeezing region, while the other properties can be enhanced only by two-mode catalysis including symmetrical and asymmetrical cases. A comparison among these properties shows that the squeezing and the EPR correlation definitely lead to the improvement of both the entanglement and the fidelity, and the region of enhanced fidelity can be seen as a sub-region of the enhanced entanglement which indicates that the entanglement is not always beneficial for the fidelity. In addition, the effect of photon-loss after catalysis on the fidelity is considered and the symmetrical two-photon catalysis may present better behavior than the symmetrical single-photon case against the decoherence in a certain region.