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arXiv:0807.2033 · Journal of Physics B Atomic Molecular and Optical Physics

Mean parity of a single quantum excitation of some optical fields in thermal environments

Shangbin Li

Published Feb 16, 2009• 1 citation
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Abstract

The mean parity (the Wigner function at the origin) of excited binomial states, excited coherent states and excited thermal states in thermal channel is investigated in details. It is found that the single-photon excited binomial state and the single-photon excited coherent state exhibit certain similarity in the aspect of their mean parity in the thermal channel. We show the negative mean parity can be regarded as an indicator of nonclassicality of single-photon excitation of optical fields with a little coherence, especially for the single-photon excited thermal states.

DOI
10.1088/0953-4075/42/5/055505

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The mean parity (the Wigner function at the origin) of excited binomial states, excited coherent states and excited thermal states in thermal channel is investigated in details. It is found that the single-photon excited binomial state and the single-photon excited coherent state exhibit certain similarity in the aspect of their mean parity in the thermal channel. We show the negative mean parity can be regarded as an indicator of nonclassicality of single-photon excitation of optical fields with a little coherence, especially for the single-photon excited thermal states.
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We investigate the nonclassicality of photon-added coherent states in the photon-loss channel by exploring the entanglement potential and negative Wigner distribution. The total negative probability defined by the volume of the negative part of the Wigner function reduces with the decay time. The total negative probability and the entanglement potential of pure photon-added coherent states exhibit the similar dependence on the beam intensity. The reduce of the total negative probability is consistent with the behavior of entanglement potential for the dissipative single-photon-added coherent state at short decay times.
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In this paper, photon-excited squeezed coherent states (PESCS) are studied theoretically by adding a photon to the squeezed coherent states repeatedly. By taking advantage of the normally ordered form of the density operator for PESCS, the analytical expressions of the normalization constant, Mandel Q -parameter, photon-number distribution, quadrature squeezing and Wigner function are derived and discussed in detail, and from these the sub-Poissonian photon statistics, photon-number oscillations, negative value of quadrature squeezing, and partial negativity and non-Gaussian distribution of a Wigner function are demonstrated, respectively. These criteria well exhibit the highly nonclassical properties and non-Gaussianity of PESCS. In addition, by deriving the normally ordered form of the density operator and Wigner function for PESCS in a thermal channel, the decoherence process of PESCS is analyzed both analytically and numerically.
We show the experimental observation of quantum states of light exhibiting nonclassical features obtained by single photon excitation of a thermal state. Such single-photon-added thermal states are the result of the single action of the creation operator on a mixed state that can be fully described classically. They show different degree of nonclassicality depending on the mean photon number of the original thermal state. The generated state is characterized by means of ultra-fast homodyne detection which allows us to reconstruct its density matrix and Wigner function by quantum tomography. We demonstrate the nonclassical behavior of single-photon added thermal states by an analysis of the negativity of the Wigner function.