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arXiv:1111.5380 · Journal of the Optical Society of America B

Quantum discord induced by white noises

Jiasen Jin, Chang‐shui Yu, Pei Pei, He‐Shan Song

Published Aug 12, 2010• 22 citations
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Abstract

We discuss the creation of quantum discord between two two-level atoms trapped in an optical cavity in a noisy environment. It is shown that nonzero steady-state quantum discord between atoms can be obtained when the white-noise field is separately imposed on atoms or cavity mode, while the steady-state quantum discord reaches zero if both cavity mode and atoms are driven simultaneously by white-noise fields. In particular, we demonstrate that white-noise field in different cases can play a variously constructive role in the generation of quantum discord.

DOI
10.1364/josab.27.001799

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We discuss the creation of quantum discord between two two-level atoms trapped in an optical cavity in a noisy environment. It is shown that nonzero steady-state quantum discord between atoms can be obtained when the white-noise field is separately imposed on atoms or cavity mode, while the steady-state quantum discord reaches zero if both cavity mode and atoms are driven simultaneously by white-noise fields. In particular, we demonstrate that white-noise field in different cases can play a variously constructive role in the generation of quantum discord.
We study a physical system for creation of quantum correlations by quantum feedback control. The system is composed of two three-level atoms, each of which interacts with one of two coupled cavities. By appropriately choosing the feedback strength, we show that an arbitrary initial state can be deterministically driven to a steady-state that has a nonzero quantum discord or entanglement. It is also found that the effect of atomic spontaneous emission on quantum correlations is suppressed efficiently by increasing the frequency detuning.
An atom that couples to two distinct leaky optical cavities is driven by an external optical white noise field. We describe how entanglement between the light fields sustained by two optical cavities arises in such a situation. The entanglement is maximized for intermediate values of the cavity damping rates and the intensity of the white noise field, vanishing both for small and for large values of these parameters and thus exhibiting a stochastic-resonancelike behavior. This example illustrates the possibility of generating entanglement by exclusively incoherent means and sheds new light on the constructive role noise may play in certain tasks of interest for quantum information processing.
The dynamics of two identical atoms is studied, which is resonantly coupled to a single-mode cavity under two different quantum feedback controls, i.e., the symmetric feedback control and the nonsymmetric feedback control. Correspondingly, the quantum discord of the system is induced to reach steady values under these two kinds of feedback controls. Furthermore, in some cases, the steady value of quantum discord of the system under symmetric feedback control is much larger than the steady value under nonsymmetric feedback control. The situation is just the opposite when the initial state is |eg〉. It is also found that the feedback is not good for getting a high discord when the initial state is in the form of Werner-like state (d = 0).
We employ external optical white-noise fields as the actual driving fields of two atoms inside an optical cavity and investigate how controllable entanglement between two atoms arises in such a situation. Two different action configurations of noise are considered. If two atoms are simultaneously driven by two independent white-noise fields with the same intensity, the entanglement between them is suppressed and eventually completely destroyed by the noise. However, if only one atom is exposed in the white-noise fields, the steady state of the two atoms exhibits entanglement. A stochastic-resonance-like behaviour of steady state entanglement is also revealed. Finally, we examine the Bell violation between atoms and show that the steady state does not violate the Bell inequality even though it is inseparable. The stochastic-resonance-like behaviour cannot be observed in the Bell violation of two atoms during the evolution. The stronger the noise intensity, the more rapidly the Bell violation disappears.
Quantum discord, and related indicators, are raising a relentless interest as a novel paradigm of nonclassical correlations beyond entanglement. Here, we discover a discord-activated mechanism yielding steady-state entanglement production in a realistic continuous-variable setup. This comprises two coupled optomechanical cavities, where the optical modes (OMs) communicate through a fiber. We first use a simplified model to highlight the creation of steady-state discord between the OMs. We show next that such discord improves the level of stationary optomechanical entanglement attainable in the system, making it more robust against temperature and thermal noise.
We discuss the generation of entangled states of two two-level atoms inside an optical cavity. The cavity mode is supposed to be coupled to a white noise with adjustable intensity. We describe how the entanglement between the atoms arise in such a situation. The entanglement is maximized for intermediate values of the noise intensity, while it is a monotonic function of the atomic decay rate. This resembles the phenomenon of stochastic resonance and sheds more light on the idea to exploit the white noise in quantum-information processing.