M. D. Havey

Direct measurements of excited-state lifetimes in Mg, Ca, and Sr†

The lifetimes of the lowest 3S1 states in Mg, Ca, and Sr have been measured. In addition, the lifetimes of a number of excited 1S0 and 1D2 states in Ca have been determined, as well as the lifetime of the 4s4p1P1 state of Ca. The measurements were made by observing the exponential decay of the intensity of the fluorescence emitted from excited states selectively populated by one- and two-step dye-laser excitation. The values obtained for the 3S1 lifetimes were τ(Mg) = (9.7 ± 0.5) ns, τ(Ca) = (11.7 ± 0.6) ns, and τ(Sr) = (12.9 ± 0.7) ns.

Observation of single-photon superradiance and the cooperative Lamb shift in an extended sample of cold atoms

We report direct, time-resolved observations of single-photon superradiance in a highly extended, elliptical sample of cold ^{87}Rb atoms. The observed rapid decay rate is accompanied by its counterpart, the cooperative Lamb shift. The rate of the strongly directional decay, and the associated shift, scale linearly with the number of atoms, demonstrating the collective nature of the observed quantities.

Dispersion of the dielectric permittivity of dense and cold atomic gases

On the basis of general theoretical results developed previously in [JETP 112, 246 (2011)], we analyze the atomic polarization created by weak monochromatic light in an optically thick, dense, and cold atomic ensemble. We show that the amplitude of the polarization averaged over a uniform random atomic distribution decreases exponentially beyond the boundary regions. The phase of this polarization increases linearly with increasing penetration into the medium. On these grounds, we determine numerically the wavelength of the light in the dense atomic medium, its extinction coefficient, and the complex refractive index and dielectric constant of the medium. The dispersion of the permittivity is investigated for different atomic densities. It is shown that, for dense clouds, the real part of the permittivity is negative in some spectral domains.

Microscopic theory of scattering of weak electromagnetic radiation by a dense ensemble of ultracold atoms

Based on the developed quantum microscopic theory, the interaction of weak electromagnetic radiation with dense ultracold atomic clouds is described in detail. The differential and total cooperative scattering cross sections are calculated for monochromatic radiation as particular examples of application of the general theory. The angular, spectral, and polarization properties of scattered light are determined. The dependence of these quantities on the sample size and concentration of atoms is studied and the influence of collective effects is analyzed.

Coherent backscattering of light from ultracold and optically dense atomic ensembles

We review experimental and theoretical studies of coherent backscattering of near resonant radiation from an ultracold atomic gas in the weak localization regime. Recent accomplishments in high resolution spectroscopy of atomic ensembles based on the coherent backscattering process are discussed. We also propose several new experimental schemes for time-dependent spectroscopy as applied to multiple scattering in the regime of weak localization.

Light scattering from a dense and ultracold atomic gas

The quantum optical response of high density ultracold atomic systems is critical to a wide range of fundamentally and technically important physical processes. These include quantum image storage, optically based quantum repeaters and ultracold molecule formation. We present here a microscopic analysis of the light scattering on such a system, and we compare it with a corresponding description based on macroscopic Maxwell theory. Results are discussed in the context of the spectral resonance structure, time-dependent response, and the light localization problem.

Antilocalization in coherent backscattering of light in a multi-resonance atomic system

Abstract Theoretical prediction of antilocalization of light in ultracold atomic gas samples, in the weak localization regime, is reported. Calculations and Monte-Carlo simulations show that, for selected spectral ranges in the vicinity of atomic 85 Rb hyperfine transitions, quantum coherence in optical transitions through nondegenerate hyperfine levels in multiple light scattering generates destructive interference in otherwise reciprocal scattering paths. This effect leads to enhancement factors less than unity in a coherent backscattering geometry, and suggests the possibility of enhanced diffusion of light in ultracold atomic vapors.

Spatial distribution of optically induced atomic excitation in a dense and cold atomic ensemble

On the basis of our general theoretical results developed previously in JETP 112, 246 (2011), we calculate the spatial distribution of atoms excited in a dense and cold atomic cloud by weak monochromatic light. We also study the atomic distribution over different Zeeman sublevels of the excited state in different parts of the cloud. The dependence of this distribution of atomic excitation on the density of the atomic ensemble and the frequency of external emission is investigated. We show that in the boundary regions of the cloud the orientation and alignment of atomic angular momentum takes place. Analysis of the spatial distribution of atomic excitation shows no noticeable signs of light localization effects even in those parameter regimes where the Ioffe-Regel criterium of strong localization is satisfied. However, comparative calculations performed in the framework of the scalar approximation to the dipole-dipole interaction reveals explicit manifestation of strong localization under some conditions.

Measurement of the lowest S-state lifetime of Al, Ga, In, and Tl†

The lifetimes of the lowest 2S1/2 state in Al, Ga, In, and Tl have been measured by observing the exponential decay of the fluorescence arising from the 2S1/2–2P3/2 transition in each atom, following selective excitation of the 2S1/2 state by an N2 laser-pumped dye laser. The values obtained for the 2S1/2 state lifetimes were τ(A1) = (6.8 ± 0.3) ns, τ(Ga) = (7.0 ± 0.4) ns, τ(In) = (7.4 ± 0.3) ns, τ(Tl) = (7.8 ± 0.3) ns.

Light trapping in high-density ultracold atomic gases for quantum memory applications

High-density and ultracold atomic gases have emerged as promising media for storage of individual photons for quantum memory applications. In this paper we provide an overview of our theoretical and experimental efforts in this direction, with particular attention paid to manipulation of light storage (a) through complex recurrent optical scattering processes in very high density gases (b) by an external control field in a characteristic electromagnetically induced transparency configuration.