arXiv subjects

Hyunchul Nha

Publications and source records attributed to Hyunchul Nha.

80 records · Page 5Linked to original sources

arXiv2004

Decoherence of a two-state atom driven by coherent light

Recent studies of the decoherence induced by the quantum nature of the laser field driving a two-state atom [J. Gea-Banacloche, Phys. Rev. A 65, 022308 (2002); S. J. van Enk and H. J. Kimble, Quantum Inf. and Comp. 2, 1 (2002)] have been questioned by Itano [W. M. Itano, Phys. Rev. A 68, 046301 (2003)] and the proposal made that all decoherence is due to spontaneous emission. We analyze the problem within the formalism of cascaded open quantum systems. Our conclusions agree with the Itano proposal. We show that the decoherence, nevertheless, may be divided into two parts--that due to forwards scattering and to scattering out of the laser mode. Previous authors attribute the former to the quantum nature of the laser field.

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arXiv2004

Entanglement within the Quantum Trajectory Description of Open Quantum Systems

The degree of entanglement in an open quantum system varies according to how information in the environment is read. A measure of this contextual entanglement is introduced based on quantum trajectory unravelings of the open system dynamics. It is used to characterize the entanglement in a driven quantum system of dimension $2\times\infty$ where the entanglement is induced by the environmental interaction. A detailed mechanism for the environment-induced entanglement is given.

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arXiv2004

Proposed Test of Quantum Nonlocality for Continuous Variables

We propose a test of nonlocality for continuous variables using a two-mode squeezed state as the source of nonlocal correlations and a measurement scheme based on conditional homodyne detection. Both the CHSH- and the CH-inequality are constructed from the conditional homodyne data and found to be violated for a squeezing parameter larger than $r\approx0.48$.

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arXiv2004

Vacuum fluctuations and the conditional homodyne detection of squeezed light

Conditional homodyne detection of quadrature squeezing is compared with standard nonconditional detection. Whereas the latter identifies nonclassicality in a quantitative way, as a reduction of the noise power below the shot noise level, conditional detection makes a qualitative distinction between vacuum state squeezing and squeezed classical noise. Implications of this comparison for the realistic interpretation of vacuum fluctuations (stochastic electrodynamics) are discussed.

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arXiv2001

Decoherence-induced wave packet splitting

We provide an intuitive interpretation of the optical Stern-Gerlach effect (OSGE) in the dressed-state point of view. We also analyze the effect of atomic damping in an experiment on the OSGE. We show that the atomic damping also causes the wave packet splitting, in a non-mechanical fashion, as opposed to the coherent process that is mechanical.

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arXiv2001

Atomic position localization via dual measurement

We study localization of atomic position when a three-level atom interacts with a quantized standing-wave field in the Ramsey interferometer setup. Both the field quadrature amplitude and the atomic internal state are measured to obtain the atomic position information. It is found that this dual measurement scheme produces an interference pattern superimposed on a diffraction-like pattern in the atomic position distribution, where the former pattern originates from the state-selective measurement and the latter from the field measurement. The present scheme results in a better resolution in the position localization than the field-alone measurement schemes. We also discuss the measurement-correlated mechanical action of the standing-wave field on the atom in the light of Popper's test.

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arXiv2001

Squeezing enhancement by damping in a driven atom-cavity system

In a driven atom-cavity coupled system in which the two-level atom is driven by a classical field, the cavity mode which should be in a coherent state in the absence of its reservoir, can be squeezed by coupling to its reservoir. The squeezing effect is enhanced as the damping rate of the cavity is increased to some extent.

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arXiv2001

Cavity-damping-induced transitions in a driven atom-cavity system

We investigate the fluorescence spectrum of a two-level atom in a cavity when the atom is driven by a classical field. We show that forbidden dipole transitions in the Jaynes-Cummings Ladder structure are induced in the presence of the cavity damping, which deteriorates the degree of otherwise perfect destructive interference among the transition channels. With the larger cavity decay, these transitions are more enhanced.

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