Rabi cycle | EPFL Graph Search

In physics, the Rabi cycle (or Rabi flop) is the cyclic behaviour of a two-level quantum system in the presence of an oscillatory driving field. A great variety of physical processes belonging to the areas of quantum computing, condensed matter, atomic and molecular physics, and nuclear and particle physics can be conveniently studied in terms of two-level quantum mechanical systems, and exhibit Rabi flopping when coupled to an optical driving field. The effect is important in quantum optics, magnetic resonance and quantum computing, and is named after Isidor Isaac Rabi. A two-level system is one that has two possible energy levels. These two levels are a ground state with lower energy and an excited state with higher energy. If the energy levels are not degenerate (i.e. not having equal energies), the system can absorb a quantum of energy and transition from the ground state to the "excited" state. When an atom (or some other two-level system) is illuminated by a coherent beam of ph

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