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Journal of Optics B Quantum and Semiclassical Optics

Measurement-induced enhancement of entanglement of a two-mode squeezed-vacuum state

Masashi Ban

Published Jan 14, 2005• 6 citations
Publisher

Abstract

A two-mode squeezed-vacuum state is one of the most important resources in quantum information processing of continuous variables. Measurement-induced enhancement of entanglement of a two-mode squeezed-vacuum state is considered, where the degenerate Raman interaction between a Λ-type atom and the field in a high- Q cavity is applied. It is shown that, under certain conditions, the entanglement can be enhanced with finite probability.

DOI
10.1088/1464-4266/7/2/l02

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A two-mode squeezed-vacuum state is one of the most important resources in quantum information processing of continuous variables. Measurement-induced enhancement of entanglement of a two-mode squeezed-vacuum state is considered, where the degenerate Raman interaction between a Λ-type atom and the field in a high- Q cavity is applied. It is shown that, under certain conditions, the entanglement can be enhanced with finite probability.
We study the measurement-induced non-Gaussian operation on the single- and two-mode \\textit{Gaussian} squeezed vacuum states with beam splitters and on-off type photon detectors, with which \\textit{mixed non-Gaussian} states are generally obtained in the conditional process. It is known that the entanglement can be enhanced via this non-Gaussian operation on the two-mode squeezed vacuum state. We show that, in the range of practical squeezing parameters, the conditional outputs are still close to Gaussian states, but their second order variances of quantum fluctuations and correlations are effectively suppressed and enhanced, respectively. To investigate an operational meaning of these states, especially entangled states, we also evaluate the quantum dense coding scheme from the viewpoint of the mutual information, and we show that non-Gaussian entangled state can be advantageous compared with the original two-mode squeezed state.
We study the measurement-induced non-Gaussian operation on the single- and two-mode Gaussian squeezed vacuum states with beam splitters and on-off type photon detectors, with which mixed non-Gaussian states are generally obtained in the conditional process. It is known that the entanglement can be enhanced via this non-Gaussian operation on the two-mode squeezed vacuum state. We show that, in the range of practical squeezing parameters, the conditional outputs are still close to Gaussian states, but their second order variances of quantum fluctuations and correlations are effectively suppressed and enhanced, respectively. To investigate an operational meaning of these states, especially entangled states, we also evaluate the quantum dense coding scheme from the viewpoint of the mutual information, and we show that non-Gaussian entangled state can be advantageous compared with the original two-mode squeezed state.
In quantum communication and quantum computing, the Bell state acts as an important role.For two qubit of discrete variable, Bell state is composted by two orthogonal to each other's physical state of a physical system.For the physical system consisting of continuous variables, a scheme is presented for generating the quasi-Bell-states of entangled squeezed states by using the Raman interaction of an Λ-type three-level atom with squeezed vacuum states (SVS) cavity fields.In this scheme, an atom initially prepared in its ground state is injected in proper order into several cavities initially prepared each in the SVS.After the atom interacting with these cavities, the entanglement of atom-cavity-field is generated.Afterwards, by measuring the atom we obtain the quasi-Bell-states of the entangled squeezed states.Also, the entanglement properties of bipartite entangled quasi-Bell-states as well as multipartite entangled SVSs are discussed.
Under the condition of two-mode squeezed vacuum state field interacting with an atom via the intensity-dependent coupling,the degree of entanglement between the two mode fields is investigated by using quantum relative entropy.It is found that the evolution of degree of two-mode fields entanglement is periodic.When the initial field is strong,the degree of entanglement reach maximum at scaled time gt=kπ(k=0,1,2,…),and the different between the maximum and minimum of the entanglement measures is about 1.3 generally.When the initial field is very weak,the influence of atom initial state on the entanglement evolution is sensitive.And the maximum entanglement appears under the situation of atom in a superposition state of upper level and lower level with equal probability.The entanglement of the two mode fields can be adjusted by controlling the time of the atom passing the cavity and the initial state of the atom.
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.