Vyacheslav Shatokhin

Coherent Inelastic Backscattering of Intense Laser Light by Cold Atoms

We present a nonperturbative treatment of coherent backscattering of intense laser light from cold atoms and predict a nonvanishing backscattering signal even at very large intensities, due to the constructive (self-)interference of inelastically scattered photons.

Universal entanglement decay of photonic-orbital-angular-momentum qubit states in atmospheric turbulence

The ability of photons carrying orbital angular momentum (OAM) to encode quantum states in a high dimensional Hilbert space makes them potentially very useful for quantum information purposes [1–8], among which free space quantum communication is one of the most promising future applications. Proof-of-principle experiments have shown a significant increase of the classical channel capacity using OAM multiplexing [9]. However, before the realization of (quantum) OAM multiplexing in free space, reliable transport of OAM photons through atmospheric turbulence has to be accomplished [10].

Spectrum of coherently backscattered light from two atoms

We present a detailed analytical and numerical analysis of the inelastic coherent backscattering spectrum of laser light incident on cold atoms. We identify frequency domains where the interference contribution can be positive as well as negative - or exhibits dispersive character. These distinctive features are explained by reciprocity arguments and dressed-state two-photon scattering amplitudes.

Elastic versus inelastic coherent backscattering of laser light by cold atoms: A master-equation treatment

We give a detailed derivation of the master-equation description of the coherent backscattering of laser light by cold atoms. In particular, our formalism accounts for the nonperturbative nonlinear response of the atoms when the injected intensity saturates the atomic transition. Explicit expressions are given for total and elastic backscattering intensities in the different polarization channels, for the simplest nontrivial multiple-scattering scenario of intense laser light multiply scattering from two randomly placed atoms.

Correlation functions in resonance fluorescence with spectral resolution: Signal-processing approach

In the framework of the signal processing approach to single-atom resonance fluorescence with spectral resolution, we diagrammatically derive an analytical formula for arbitrary-order spectral correlation functions of the scattered fields that pass through Fabry-Perot interferometers. Our general expression is then applied to study correlation signals in the limit of well separated spectral lines of the resonance fluorescence spectrum. In particular, we study the normalized second-order temporal intensity correlation functions in the case of the interferometers tuned to the components of the spectrum and obtain interferential corrections to the approximate results derived in the secular limit. In addition, we explore purely spectral correlations and show that they can fully be understood in terms of the two-photon cascades down the dressed state ladder.

Coherent inelastic backscattering of laser light from three isotropic atoms

We study the impact of double and triple scattering contributions on coherent backscattering of laser light from saturated isotropic atoms, in the helicity preserving polarization channel. Using the recently proposed diagrammatic pump-probe approach, we analytically derive single-atom spectral responses to a classical polychromatic driving field, combine them self-consistently to double and triple scattering processes, and numerically deduce the corresponding elastic and inelastic spectra, as well as the total backscattered intensities. We find that account of the triple scattering contribution leads to a faster decay of phase-coherence with increasing saturation of the atomic transition as compared to double scattering alone, and to a better agreement with the experiment on strontium atoms.

Rigorous derivation of the triple scattering signal from single-atom responses

We study coherent backscattering of intense laser light from three immobile two-level atoms using the master-equation approach. The master equation is solved analytically, and the triple scattering spectrum is expressed in quadratures. We show that this solution can be obtained via a self-consistent combination of single-atom spectral responses, and is equivalent to the solution following from the diagrammatic pump-probe approach. We deduce the general expressions for single-atom building blocks which can be used in simulations of multiple inelastic scattering of laser light in the bulk atomic medium.

Resonance fluorescence of a two-level atom excited by a superposition of coherent states, and the instability of the average atomic dipole moment

We find the evolution of average atomic variables in the resonance fluorescence of a two-level atom excited by a superposition of coherent states shifted in phase by π. A new effect is predicted, the quantum instability of the average atomic dipole moment, with a strong correlation between atom and field being the reason. We propose different ways of verifying the effect in experiments involving high-Q optical and microwave cavities.

Open System Model for Quantum Dynamical Maps with Classical Noise and Corresponding Master Equations

We show how random unitary dynamics arise from the coupling of an open quantum system to a static environment. Subsequently, we derive a master equation for the reduced system random unitary dynamics and study three specific cases: commuting system and interaction Hamiltonians, the short-time limit, and the Markov approximation.

Diagrammatic treatment of coherent backscattering of intense light by cold atoms with degenerate energy levels

We present a generalization of the diagrammatic pump-probe approach to coherent backscattering (CBS) of intense laser light for atoms with degenerate energy levels. We employ this approach for a characterization of the double scattering signal from optically pumped atoms with the transition Jg → Je = Jg + 1 in the helicity preserving polarization channel. We show that, in the saturation regime, the internal degeneracy becomes manifest for atoms with Jg ≥ 1, leading to a faster decrease of the CBS enhancement factor with increasing saturation parameter than in the non-degenerate case.