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arXiv:1110.3456

Dissipative dynamics of few-photons superposition states: A dynamical invariant

Hong-Yan Wen, Jing Cheng, Yang, Y., L. F. Wei

Published Oct 16, 2011• 0 citations
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Abstract

By numerically calculating the time-evolved Wigner functions, we investigate the dynamics of a few-photon superposed (e.g., up to two ones) state in a dissipating cavity. It is shown that, the negativity of the Wigner function of the photonic state unquestionably vanishes with the cavity's dissipation. As a consequence, the nonclassical effects related to the negativity of the Wigner function should be weakened gradually. However, it is found that the value of the second-order correlation function $g^{(2)}(0)$ (which serves usually as the standard criterion of a typical nonclassical effect, i.e., $g^{(2)}(0)<1$ implies that the photon is anti-bunching) is a dynamical invariant during the dissipative process of the cavity. This feature is also proven analytically and suggests that $g^{(2)}(0)$ might not be a good physical parameter to describe the photonic decays. Alternatively, we find that the anti-normal-order correlation function $g^{(2A)}(0)$ changes with the cavity's dissipation and thus is more suitable to describe the dissipative-dependent cavity. Finally, we propose an experimental approach to test the above arguments with a practically-existing cavity QED system.

DOI
10.48550/arxiv.1110.3456

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By numerically calculating the time-evolved Wigner functions, we investigate the dynamics of a few-photon superposed (e.g., up to two ones) state in a dissipating cavity. It is shown that, the negativity of the Wigner function of the photonic state unquestionably vanishes with the cavity's dissipation. As a consequence, the nonclassical effects related to the negativity of the Wigner function should be weakened gradually. However, it is found that the value of the second-order correlation function g(2)(0)g^{(2)}(0)g(2)(0) (which serves usually as the standard criterion of a typical nonclassical effect, i.e., g(2)(0)<1g^{(2)}(0)<1g(2)(0)<1 implies that the photon is anti-bunching) is a dynamical invariant during the dissipative process of the cavity. This feature is also proven analytically and suggests that g(2)(0)g^{(2)}(0)g(2)(0) might not be a good physical parameter to describe the photonic decays. Alternatively, we find that the anti-normal-order correlation function g(2A)(0)g^{(2A)}(0)g(2A)(0) changes with the cavity's dissipation and thus is more suitable to describe the dissipative-dependent cavity. Finally, we propose an experimental approach to test the above arguments with a practically-existing cavity QED system.
Detections and manipulations of quantum optical state at single-photon level have received much attention in the current experiments. Here, by numerically calculating the time-evolved Wigner functions, we investigate the dynamics of the typical non-classical state, i.e., few-photon superposition states in a dissipating optical microcavity. It is shown that the negativity of their Wigner function vanishes with dissipation. But this does not imply that all the non-classical features of the dissipative quantum state disappear. In fact, it is shown that the value of the second-order correlation function g(2)(0) (which serves usually as the standard criterion of a typical non-classical effect, i.e., the anti-bunching of photons, if g(2)(0)g(2A)(0) varies with the cavity dissipation and thus could be used to describe the physical effects of the dissipative cavity. Finally, we discuss the experimental feasibility of our proposal with a practically-existing cavity QED system.
Non-Gaussian quantum states, described by negative valued Wigner functions, are important both for fundamental tests of quantum physics and for emerging quantum information technologies. However, they are vulnerable to dissipation. It is known, that the Wigner functions negativity could exist only if the overall quantum efficiency η\etaη of the setup is higher than 1/2. Here we prove that this condition is not only necessary but also a sufficient one: the negativity always persists while this condition is fulfilled. At the same time, in the case of bright (multi-photon) non-Gaussian quantum states, the negativity dependence on η\etaη is highly non-linear. With the loss of several photons, it drops by orders of magnitude, hampering its experimental detection.
Master equations of density operators can be concisely solved by virtue of thermo entangled state representation and the technique of integration within an ordered product of operators.The solution of master equations of density operators is given.We get the Wigner function evolution formula in phase space and photon number distribution formula of the state,which is a superposition of vacuum state and single-photon state initially in laser process.By numerical calculation we plot its Wigner function and photon number distribution evolution curves,when cavity gain constant and cavity loss constant are both equal to certain values.The effect of decoherence on nonclassical property of the state is discussed by comparing negative area size and the depth of negativity of Wigner function.Numerical results show that the negativity area size and the depth of negativity of its Wigner function decrease and then vanish with dissipation.In addition,we calculate the variation of negative volume of Wigner function with dissipation time.We find that it decreases with dissipation time increasing.These results show that the nonclassical properties of the state are weakened and then disappear with dissipation time increasing.
In this paper we discuss the nonclassical properties of quantum superpositions of coherent states of light. Using general expressions for the Wigner functions of superposition states we analyze the consequences of quantum interference between coherent states. We describe in detail nonclassical properties of a superposition of two coherent states. In particular, we study the oscillatory behavior of the photon number distribution of the even and odd coherent states. We show under which conditions a superposition of two coherent states can exhibit second- and fourth-order squeezing or sub-Poissonian photon statistics. We examine the sensitivity of nonclassical effects such as oscillations in the photon number distribution or second-order squeezing to dissipation. We demonstrate that quantities such as the photon number distribution and interferences in phase space are highly sensitive to even a quite small dissipative coupling, because they depend on all moments of the field observables, and higher moments decay more rapidly than lower moments. Quantities such as quadrature squeezing, on the other hand, are more robust against dissipation because they involve only lower moments. Finally, we find a remarkable effect whereby fourth-order squeezing is generated by damping.
The Wigner functions of the Fock states and their superposition states have negative value clearly. We focus on discussing the time evolution of the Fock states and their superposition states by the Wigner function under the coherent drive (pumping laser) and dissipation channels (cavity radiation). The results show that the negative region of their Wigner function gradually diminishes as the time kt or the gain coefficient g increasing. In addition, the disappearing time is related to the value of g - k. The loss of non-classical features becomes slower when g increases with the k > g; there is the "frozen zone" when k = g; then the loss of non-classical features becomes faster when g increases with k < g.