Oscillations de Rabi | EPFL Graph Search

thumb|Système à deux états d'énergie Les oscillations de Rabi sont des oscillations dans l'occupation des états d'un système à deux niveaux excité à une fréquence proche de la résonance. Initialement observé entre deux états de spin dans la résonance magnétique nucléaire, ce phénomène se produit également lorsqu'un champ électrique extérieur agit sur les transitions d'un système quantique – atome ou molécule – d'un état électronique de ce système à un autre. Le nom de Rabi a été donné en l'honneur de Isidor Isaac Rabi (1898 - 1988). La formule des oscillations de Rabi sert à décrire mathématiquement la résonance du champ extérieur avec la transition. Dans le cas général et au premier ordre en l'amplitude v de l'excitation électromagnétique extérieure (pulsation ω), la formule de Rabi s'écrit : a_2(t) = \frac{e^\left ( \frac{-iE_2.t}{\hbar} \right )}{i\hbar}\int_0^t v(t')\cos (\omega t').e^\left ( \frac{i(E_2-E_1).t'}{\hbar} \right )\mathrm{d}t' où |a_2(t)|^2

Rabi oscillation in a quantum cavity: Markovian and non-Markovian dynamics

Pierre-Olivier Guimond, Alexandre Roulet

We investigate the Rabi oscillation of an atom placed inside a quantum cavity where each mirror is formed by a chain of atoms trapped near a one-dimensional waveguide. This proposal was studied previously with the use of Markov approximation, where the delay due to the finite travel time of light between the two cavity mirrors is neglected. We show that Rabi oscillation analogous to that obtained with high-finesse classical cavities is achieved only when this travel time is much larger than the time scale that characterizes the superradiant response of the mirrors. Therefore, the delay must be taken into account and the dynamics of the problem is inherently non-Markovian. Parameters of interest such as the Rabi frequency and the cavity loss rate due to photon leakage through the mirrors are obtained.

Amer Physical Soc2016

Femtosecond dynamics and non-linearities of exciton-photon coupling in semiconductor microstructures

Cristiano Ciuti, Benoît Marie Joseph Deveaud, Michele Saba

We have studied the femtosecond dynamics of excitonic resonances in quantum well microcavities under strong excitation. Very strong non-linearities are observed, which bear clear resemblance to the non-linearities of an atomic two-level system. The fact that the excitonic system undergoes Rabi flopping and AC Stark splitting is clearly evidenced in a number of cases. Excitation induced dephasing shows an effect much stronger than the light dressing and prevents the observation of the Rabi flopping only when exciting in the continuum. Most of the experimental findings are well reproduced by a dynamical solution of the Maxwell-Bloch equations for an ensemble of two-level systems. This allows in particular understanding of the occurrence of strong coherent gain in microcavitics. An exhaustive description of the experiments is given within the framework of semiconductor Maxwell-Bloch optical equations at the Hartree-Fock level. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

2001

Phase-Resolved Imaging of Exciton Polaritons

Gaël Nardin

In this PhD thesis, new imaging techniques have been developed in order to explore the physics of semiconductor microcavities. In these structures, composite bosons called exciton polaritons are the result of strong coupling between the cavity mode and quantum well excitons. A spectroscopic imaging technique has been developed to image the eigenstates of polaritons confined in the traps of a patterned GaAs microcavity. Polariton probability densities have been reconstructed in three dimensions – two spatial dimensions and energy – allowing to retrieve two-dimensional probability density mappings of the eigenstates. In order to image the wave functions (and not the probability densities only), a phase-resolved imaging setup has been built. Interfering the near field or far field of the polariton emission with a reference laser beam allowed to retrieve the full information (amplitude and phase) of the polariton wave functions. This tool allowed to evidence the effect of trap ellipticity on the confined polariton wave functions. Polariton vortices were also identified as a superposition of eigenmodes of the elliptical traps, and a selective excitation method has been used to optically control the sign and value of the vortex charge. Combining phase-resolved imaging with ultrafast optics allowed to probe the time evolution of coherent superpositions of confined polariton states. In particular, Rabi oscillations between vortex and anti-vortex states have been observed. Eventually, the time and phase resolved imaging tools have been used to explore the physics of quantum fluids. The scattering of polariton wave packets on a structural defect has been studied. Different flow regimes have been identified, and, in particular, quantum turbulence has been observed in the form of quantized vortices nucleating in the wake of the defect. The nucleation conditions have been established in terms of local fluid velocity and density on the obstacle perimeter. The results were successfully reproduced by numerical simulations based on generalized Gross-Pitaevskii equations.

EPFL2011

Phase-Resolved Imaging of Exciton Polaritons

Gaël Nardin

EPFL2011