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Chinese Physics B

The Wigner function and phase properties of superposition of two coherent states with the vacuum state

Wang Yue-Yuan, Jicheng Wang, Shutian Liu

Published Jul 1, 2010• 3 citations
Publisher

Abstract

This paper discusses some statistical properties of the superposition of two coherent states with a vacuum state, such as sub-Poissonian photon statistics and negativity of the Wigner function. Phase probability distribution and phase variance are calculated. Special cases of the constructed superposition states are presented. The results show that depending on the vacuum state coefficient γ and the coherent state coefficient α, it can generate a variety of nonclassical states.

DOI
10.1088/1674-1056/19/7/074206

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This paper discusses some statistical properties of the superposition of two coherent states with a vacuum state, such as sub-Poissonian photon statistics and negativity of the Wigner function. Phase probability distribution and phase variance are calculated. Special cases of the constructed superposition states are presented. The results show that depending on the vacuum state coefficient γ and the coherent state coefficient α, it can generate a variety of nonclassical states.
We consider the quantum superposition of two coherent states shifted in phase by 3π/2, |α⟩ and |− i α⟩, as well as special states that are characterized solely with respect to amplitude α. According to analysis of nonclassical properties such as oscillatory and sub-Poissonian distribution of photon numbers, photon antibunching, quadrature squeezing, and negativity of Wigner function, it is concluded that the considered superposition state is a nonclassical state. Also, the special state is found to exhibit even stronger nonclassical features when relative phase ϕ of the superposition is equal to the average photon number |α| 2 .
With a squeezing operation on the qubit state,we obtain a coherent superposition state of a squeezed vacuum state and a squeezed single photon state with certain weight rate.The coherent superposition state depends on the squeezing parameter and weight factor,I and its nonclassicality and non-Gaussian properties are researched.It is investigated by the sub-Poissonian statistics distribution of Mandel′s Q parameter and the negativity of the Wigner function.The non-Gaussianity of coherent superposition qubit state can be improved by adjusting the squeezing parameter and the weight factor.
Abstract Superposition of two coherent states, the Schrodinger’s cat state, can exhibit different nonclassical properties having foundational applications in quantum information processing. We consider the ‘superposition of Schrodinger’s cat state with the vacuum state (SCVS)’ of the optical field. We discuss different witness of nonclassicality properties such as lower- and higher-order squeezing (viz., squeezing, Hong & Mandel’s fourth-order squeezing, amplitude-squared squeezing) and sub-Poissonian photon statistics. Further, we discuss the negativity of the Wigner function of SCVS indicating the nonclassicality of the state under investigation. We find that the vacuum state contribution in SCVS exhibits different nonclassicalities under some conditions stronger where the nonclassicalities exhibited by the state without vacuum state contribution are weaker.
The quantum statistical properties of the superposition state, which involve two arbitrary coherent states |β〉 and |mβeiδ〉, are investigated from two aspects, such as the phase distribution and Winger function. The results show that the non-classical properties of the superposition state depend on β2, amplitude coefficient m, the phase difference between the coherent states δ, and the phase difference between the superposition coefficients . When selected suitable parameters the superposition state exhibits quantum effect. The phase distribution and Wigner function of an equally populated mixture of two coherent states are derived, too. By comparison the results show that the presence of the coherence terms makes the superposition state with full quantum-mechanical behavior.
The superposition of excited coherent states was constructed by superpositioning two excited coherent states of the same intensity and mutual phase conjugation,and their Wigner functions,second-order coherence degree and Mandel Q factors were calculated,upon which their non-classical properties were analyzed.The numerical results show that,the Wigner functions of the superposition of excited coherent states may become negative,and their second-order coherence degree and Mandel Q factors are both less than 1.Hence,the research shows that the quasi-probability distribution of the superposition of excited coherent states may become negative,and their light field has anti-bunching effects,with the distribution of photon number being of sub-Poisson distribution.Therefore,these superposition states are quantum states with non-classical properties.