Showing papers by "Stéphane Guérin published in 2011"

High-Fidelity Adiabatic Passage by Composite Sequences of Chirped Pulses

Abstract: We present a method for optimization of the technique of adiabatic passage between two quantum states by composite sequences of frequency-chirped pulses with specific relative phases: composite adiabatic passage (CAP). By choosing the composite phases appropriately the nonadiabatic losses can be canceled to any desired order with sufficiently long sequences, regardless of the nonadiabatic coupling. The values of the composite phases are universal for they do not depend on the pulse shapes and the chirp. The accuracy of the CAP technique and its robustness against parameter variations make CAP suitable for high-fidelity quantum information processing.

Optimal adiabatic passage by shaped pulses: Efficiency and robustness

Abstract: We explore the efficiency and robustness of population transfer in two-state systems by adiabatic passage (i) when the driving pulse is optimally designed in order to lead to parallel adiabatic passage or (ii) with a linear chirping. We show how one could practically implement the corresponding designs of the pulses in the spectral domain. We analyze the robustness of the two shapings taking into account fluctuations of the phase, amplitude, and the area of the pulse. We show the overall superiority of the parallel adiabatic passage especially when one faces the issue of a pulse area that is not well known. We show that the robustness of parallel adiabatic passage is not improved when it is complemented by a correcting field that cancels out the nonadiabatic losses.

Superposition of states by adiabatic passage in N-pod systems

Abstract: We study the stimulated Raman adiabatic passage technique in an $N$-pod system driven by $N$ pulsed fields when $N\ensuremath{-}2$ and $N\ensuremath{-}1$ pulses not connected to the initial state have the same shape. We show that, for properly timed pulses, robust population transfer from an initial ground state to an arbitrary coherent superposition of the ground states can be achieved in a single step. The case of $N\ensuremath{-}2$ pulses of the same shape involves a geometric phase of the same type as the one appearing in tripod systems.

Quantum dynamics by the constrained adiabatic trajectory method

Abstract: We develop the constrained adiabatic trajectory method (CATM), which allows one to solve the time-dependent Schr\"odinger equation constraining the dynamics to a single Floquet eigenstate, as if it were adiabatic. This constrained Floquet state (CFS) is determined from the Hamiltonian modified by an artificial time-dependent absorbing potential whose forms are derived according to the initial conditions. The main advantage of this technique for practical implementation is that the CFS is easy to determine even for large systems since its corresponding eigenvalue is well isolated from the others through its imaginary part. The properties and limitations of the CATM are explored through simple examples.

Superluminal pulse propagation in a non-linear Λ-type atomic medium

Abstract: Propagation of two optical pulses in a non-linear Λ-type atomic medium is considered. The analytical solution to the self-consistent Maxwell-Schrodinger equations in the adiabatic following condition is obtained. Superluminal effects during propagation of pulses in the medium are studied.

Deterministic generation of indistinguishable single-photon pulses in the single-atom-cavity qed system

Abstract: We present a mechanism to produce indistinguishable single-photon pulses on demand from a single atom-optical cavity system. We use sequences of two laser pulses of alternate circular polarizations at the two Raman transitions of a four-level atom. They allow the production of the same cavity-mode photons without repumping of the atom between photon generations. Photons that are emitted from the cavity with near-unity efficiency in well-defined temporal modes, feature the same polarization, frequency and identical shapes, controlled by the laser fields. The second order correlation function reveals the single-photon nature of the proposed source. A realistic setup for the experimental implementation is presented.

Bichromatic field propagation in a resonant medium: Floquet analysis

Abstract: We study the propagation of a bichromatic field in a resonant medium. The two modes of the incoming fields are pulsed and delayed with respect to each other. It is shown that in the course of the propagation, new Raman sidebands will be generated. The achievable frequency spacing between the sidebands is determined from experimental data. A numerical example is shown for realistic physical parameters.