Dmitriy V. Kupriyanov

Experimental investigation of the transition between Autler-Townes splitting and electromagnetically-induced transparency models

Summary form only given. If in general the transparency of an initially absorbing medium for a probe field is increased by the presence of a control field on an adjacent transition, two very different processes can be invoked to explain it. One of them is a quantum Fano interference between two paths in the three-level system, which occurs even at low control intensity and gives rise to electromagnetically-induced transparency (EIT), the other one is the appearance of two dressed states in the excited level at higher control intensity, corresponding to the Autler-Townes splitting (ATS). This distinction is particularly critical for instance for the implementation of slow light or optical quantum memories. In a recent paper, P. M. Anisimov, J. P. Dowling and B. C. Sanders proposed a quantitative test to objectively discerning ATS from EIT. We experimentally investigated this test with cold atoms and demonstrated that it is very sensitive to the specific properties of the medium. In this study, we use an ensemble of cold Cesium atoms trapped in a MOT, interacting with light via a Λ-type scheme on the D2 line. Absorption profiles are obtained for various values of the control Rabi frequency Ω between 0.1Γ and 4Γ, where Γ is the natural linewidth.

Multimode entanglement of light and atomic ensembles via off-resonant coherent forward scattering

Quantum theoretical treatment of coherent forward scattering of light in a polarized atomic ensemble with an arbitrary angular momentum is developed. We consider coherent forward scattering of a weak radiation field interacting with a realistic multi-level atomic transition. Based on the concept of an effective Hamiltonian and on the Heisenberg formalism, we discuss the coupled dynamics of the quantum fluctuations of the polarization Stokes components of propagating light and of the collective spin fluctuations of the scattering atoms. We show that in the process of coherent forward scattering this dynamics can be described in terms of a polariton-type spin wave created in the atomic sample. Our work presents a general example of entangling process in the system of collective quantum states of light and atomic angular momenta, previously considered only for the case of spin 1/2 atoms. We use the developed general formalism to test the applicability of spin 1/2 approximation for modelling the quantum non-demolishing measurement of atoms with a higher angular momentum.

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.

Diffuse light scattering dynamics under conditions of electromagnetically induced transparency

We show that under conditions typical of electromagnetically induced transparency (EIT) in an ultracold atomic sample in a magneto-optical trap, a significant portion of the incident probe pulse is transferred into Rayleigh and Raman scattering channels. The light scattered into the Rayleigh channel emerges from the sample with an EIT time delay. We show that a proper description of the probe light propagation in the sample should include, in the diffusion dynamics, a spin polariton generated by the two-photon EIT process. The results have important implications for studies of weak light localization and for manipulation of single and few photon states in ultracold atomic gases.

Spectral theory of quantum memory and entanglement via raman scattering of light by an atomic ensemble

We discuss theoretically quantum interface between light and a spin polarized ensemble of atoms with the spin >= 1 based on an off-resonant Raman scattering. We present the spectral theory of the light-atoms interaction and show how particular spectral modes of quantum light couple to spatial modes of the extended atomic ensemble. We show how this interaction can be used for quantum memory storage and retrieval and for deterministic entanglement protocols. The proposed protocols are attractive due to their simplicity since they involve just a single pass of light through atoms without the need for elaborate pulse shaping or quantum feedback. As a practically relevant example we consider the interaction of a light pulse with hyperfine components of D1 line of 87Rb. The quality of the proposed protocols is verified via analytical and numerical analysis.

Optical control of diffuse light storage in an ultracold atomic gas

We show that coherent multiple light scattering, or diffuse light propagation, in a disordered atomic media prepared at ultralow temperatures can be effectively delayed in the presence of a strong control field initiating a stimulated Raman process. On a relatively short time scale, when the atomic system can preserve its configuration and effects of atomic motion can be ignored, the scattered signal pulse, diffusely propagating via multiple coherent scattering through the media, can be stored in the spin subsystem through its stimulated Raman-type conversion into spin coherence. We demonstrate how this mechanism, potentially interesting for developing quantum memories, would work for the example of a coherent light pulse propagating through an alkali-metal atomic vapor under typical conditions attainable in experiments with ultracold atoms.

Weak localization of light in ultracold atomic gases

We summarize recent experimental and theoretical advances in the physics of coherent multiple light scattering in ultracold atomic gases. Current outstanding problems are reviewed, along with prospects for significant new insights into mesoscopic physics in ultracold atomic samples. The possibility of experimental demonstration of strong localization of light in atomic gases is discussed.

On a theory of light scattering from a Bose-Einstein condensate

We consider a quantum theory of elastic light scattering from a macroscopic atomic sample existing in the Bose-Einstein condensate (BEC) phase. Following the second quantized formalism we introduce a set of coupled and closed diagram equations for the polariton propagator contributing to the T -matrix and scattering amplitude. Our approach allows us to follow important density corrections to the quasi-energy structure caused by static interaction and radiation losses associated with incoherent scattering in the case of near resonance excitation.

Raman process under condition of radiation trapping in a disordered atomic medium

We consider the Raman process developing in a disordered medium of alkali-metal atoms when the scattered modes are trapped on a closed transition. Our theoretical analysis, based on numerical simulations of the Bethe-Salpeter equation for the light correlation function, which includes all Zeeman states and light polarization, lets us track the stimulated amplification as well as the losses associated with the inverse anti-Stokes scattering channel. We discuss possible conditions when this process could approach the instability point and enter the regime of random lasing.