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Physical Review A

Effect of vacuum-induced coherences on coherent population trapping of moving atoms

Guojian Yang, Min Xie, Ze Zhang, Kaige Wang

Published Jun 16, 2008• 7 citations
Publisher

Abstract

We study an extended velocity-selective coherent population trapping (VSCPT) model where vacuum-induced coherence (VIC) is considered. This effect takes place when two nonorthogonal electric dipole moments of a $\ensuremath{\Lambda}$-type three-level atom couple with a common continuous vacuum. First, we introduce the main results of a conventional VSCPT model in the nondegenerate and unsymmetrically driven situation. Then, we work out the dynamic equation of the system in the presence of VIC expressed in both internal and external degrees of freedom. We report on the generation of atomic external coherences due to VIC, which counteract the feeding action of spontaneous emission to the trapping state and indicate its limited function negative to the formation of the trapping state if the atomic center-of-mass motion is considered.

DOI
10.1103/physreva.77.063825

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We study an extended velocity-selective coherent population trapping (VSCPT) model where vacuum-induced coherence (VIC) is considered. This effect takes place when two nonorthogonal electric dipole moments of a \ensuremathΛ\ensuremath{\Lambda}\ensuremathΛ-type three-level atom couple with a common continuous vacuum. First, we introduce the main results of a conventional VSCPT model in the nondegenerate and unsymmetrically driven situation. Then, we work out the dynamic equation of the system in the presence of VIC expressed in both internal and external degrees of freedom. We report on the generation of atomic external coherences due to VIC, which counteract the feeding action of spontaneous emission to the trapping state and indicate its limited function negative to the formation of the trapping state if the atomic center-of-mass motion is considered.
Abstract The entanglement dynamics of a pair of three-level V-type atoms decaying spontaneously in a common vacuum reservoir is investigated. Under the condition that the decaying transitions in the atoms have parallel dipole moments, the effect of coherences induced by spontaneous emission is considered in the atomic dynamics. We show that vacuum-induced coherence (VIC) and collective effects in atomic decay play a significant role in the creation of entanglement. By using negativity as a measure of entanglement, we study the time evolution of entanglement for initial separable and generalized Dicke states as well as maximally entangled qutrit states. We show that the effects of VIC enhance the production of entanglement from initial separable states of the atoms. We also show that the entanglement can be protected in steady-state for atoms evolving from initial entangled states. The amount of entanglement that can be preserved is more in the presence of VIC than in its absence.
ABSTRACT In this work we present an investigation of velocity-selective coherent population trapping (VSCPT) in asym- metric three-level schemes. The light force in such schemes is of an intrinsically transient character and shouldnot be described in a quasiclassical approach. Instead, results of the full quantum-mechanical calculations are presented with emphasis on their meaning to the efficiency of subrecoil laser cooling. 1 INTRODUCTION Laser cooling of neutral atoms has received significant advances by the introduction of velocity-selectivecoherent population trapping ((VSCPT) some years ago.1 Since it leads to atomic temperatures well below therecoil limit, studies of ultracold atoms and atomic interactions may be improved by magnitudes.The effect of VSCPT relies on optical pumping of atoms into a state WNC) which is a trap state for a certaincenter-of-mass velocity vO. This trap state is created by a destructive superposition of atomic states within amultilevel quantum system. Once being in such a state LWNC) the laser light does not interact anymore with theatom which leads to a decoupling with the rest of the system at vo. Atoms located outside this small velocityregion get a chance to be trapped by the momentum diffusion due to spontaneous emission of photons. Aftera sufficient long interaction time nearly all atoms are trapped inside a narrow momentum distribution whichcan be interpreted as cooling. The theoretical and experimental investigation of VSCPT is usually consideredby use of a three-level A-system as shown in Fig.1. Such a system can be found for example in a symmetrical
We study the mean-field dynamics of atoms in a velocity-selective coherent population trapping (VSCPT) configuration, under the influence of resonant dipole-dipole interactions. By elimination of the transverse electromagnetic field we derive a Heisenberg master equation for an arbitrary atomic operator. A closed equation of motion for the one-particle density matrix can be given by employing a time-dependent Hartree-Fock (TDHF) factorization of the two-particle density matrix, thereby neglecting two-particle correlations, i.e., collisional effects. In the case of bosons, the mean-field evolution mainly shows a quantum-statistical enhancement of the spontaneous emission rates, sensitive to the final-state occupation. The description is specialized to treat atoms with a J=1\ensuremath{\rightarrow}${\mathit{J}}^{\ensuremath{'}}$=1 transition in a one-dimensional ${\mathrm{\ensuremath{\sigma}}}^{+}$-${\mathrm{\ensuremath{\sigma}}}^{\mathrm{\ensuremath{-}}}$ VSCPT configuration. The TDHF equations are integrated numerically. It is shown that for a density at which the gas is optically dense, the number of atoms, trapped in the dark state, is increased and its momentum width is decreased. \textcopyright{} 1996 The American Physical Society.
We have demonstrated velocity-selective coherent population trapping (VSCPT) in a two-level system created by circularly polarized light driving the $2{}^{3}{S}_{1}\ensuremath{\rightarrow}3{}^{3}{P}_{2}$ transition in metastable helium. It is quite different from the usual VSCPT because there need be no consideration of selection rules, polarization, or internal atomic states. This most primitive case elicits the simple nature of VSCPT as a special kind of quantum interference, and demonstrates the presence of VSCPT in a system that has only two internal levels. It is readily observed for this transition because the ratio of the recoil frequency to the natural linewidth is 0.22, two orders of magnitude larger than for most laser cooling experiments. Our trapped state is fed by Doppler cooling, which is unusually effective here because of the large recoil, and is totally absent in previously described VSCPT experiments.
Abstract We theoretically investigate how population can be trapped in the closely spaced excited levels in presence of vacuum-induced coherence (VIC). We employ delayed pulses to transfer population from a meta-stable state to the excited states. Subsequently, spontaneous emission from these excited states builds coherence between them. This coherence can be probed by using chirping, which leads to the decoupling of the excited states from the ground state thereby ensuring population transfer via delayed pulses. Our results indicate that the existence of VIC leads to the generation of a mixed state in the excited state manifold, where trapping of the population occurs even in the presence of large decay. This trapping may be realized in molecular systems and can be interpreted as a sensitive probe of VIC. We present suitable numerical analysis to support our results.