We investigate the effect of disorder on the propagation of one-dimensional polariton condensates in semiconductor microcavities. We observe a strong suppression of the backscattering produced by the imperfections of the structure when increasing the condensate density. This suppression occurs in the supersonic regime and is simultaneous to the onset of parametric instabilities which enable the "hopping" of the condensate through the disorder. Our results evidence a new mechanism for the strong scattering reduction of polaritons at high speeds.

The dynamics of propagating polariton condensates in one-dimensional microcavities is investigated through time resolved experiments. We find a strong increase in the condensate intensity when it travels through the nonresonantly excited area. This amplification is shown to come from bosonic stimulated relaxation of reservoir excitons into the polariton condensate, allowing for the repopulation of the condensate through nonresonant pumping. Thus, we experimentally demonstrate a polariton amplifier with a large band width, opening the way towards the transport of polaritons with high densities over macroscopic distances.

In high finesse semiconductor microcavities containing quantum wells, photons emitted by the quantum well excitons can oscillate long enough inside the cavity to be reabsorbed reemitted again and so forth. The system enters the so-called strong coupling regime, with the formation of entangled exciton-photon eigenstates, named cavity polaritons, which governs all the physics of the system. After an introduction to cavity polaritons, we will review in this paper some of their original physical properties and discuss their potential in terms of new photonic devices. In a first part, we will show how polaritons can massively occupy a single quantum state, thus acquiring spatial and temporal coherence reflected in the emitted light. Such polariton laser could provide a low threshold source of coherent light. Then the properties of polariton diodes will be addressed and in particular we will describe a new optical bistability based on the control of the light matter coupling via the intra cavity electric field.

Long-lived polariton condensates can propagate well beyond the area of their initial excitation while still maintaining spatial coherence. This enables direct and controllable manipulation of the condensate wavefunction. Cavity exciton-polaritons1,2 (polaritons) are bosonic quasi-particles offering a unique solid-state system for investigating interacting condensates3,4,5,6,7,8,9,10. Up to now, disorder-induced localization and short lifetimes4,6,11 have prevented the establishment of long-range off-diagonal order12 needed for any quantum manipulation of the condensate wavefunction. In this work, using a wire microcavity with polariton lifetimes much longer than in previous samples, we show that polariton condensates can propagate over macroscopic distances outside the excitation area, while preserving their spontaneous spatial coherence. An extended condensate wavefunction builds up with a degree of spatial coherence larger than 50% over distances 50 times the polariton de Broglie wavelength. The expansion of the condensate is shown to be governed by the repulsive potential induced by photogenerated excitons within the excitation area. The control of this local potential offers a new and versatile method to manipulate extended polariton condensates. As an illustration, we demonstrate synchronization of extended condensates by controlled tunnel coupling13,14 and localization of condensates in a trap with optically controlled dimensions.

We observe spontaneously driven non-ground state polariton condensation in GaAs pillar microcavities under non-resonant optical excitation. We identify a regime where the interplay of exciton-exciton and pair polariton scattering can lead to mode switching from non-ground state to ground state polariton condensation. A simple kinematic model satisfactorily describes the observed mode switching as each of the above scattering mechanisms becomes prevalent at different carrier densities.

The polarisation dynamics of a GaAs/AlGaAs micropillar in the non-linear regime under non-resonant excitation is studied.The polarisation of photoluminescence from a microcavity in the strong coupling regime is directly linked to the spin state of the polaritons when they decay, i.e. polaritons with spin-up or spin-down. This splitting leads to an oscillation in the linear polarisation of the photoluminescence. The energy splitting required producing the oscillation period that we observe corresponds to an imbalance of a single polariton.

Semiconductor micropillars offer an interesting way of studying polaritons in zero-dimensional cavities. In such cavities, photons are confined vertically, by the Bragg mirrors, and laterally by the index of refraction contrast between the air and the semiconductor. Zero dimensional polariton modes are the result of this three-dimensional confinement. The first observation of polariton lasing in a GaAs micropillar showed single mode operation, with lasing from the lowest energy mode in the system. We demonstrate that by careful engineering of the system, competing relaxation mechanisms can be used to achieve lasing from higher energy modes.

Semiconductor microcavities in the strong coupling regime have been the subject of intensive research efforts these last years. In this system, the eigenstates are exciton-photon entangled states (named cavity polaritons). Polaritons present strong non-linearities due to their excitonic part and obey to bosonic statistics, thus being able to massively occupy a single quantum state (quantum degeneracy). The paper discusses the potentiality of cavity polaritons for the realization of a low threshold source of coherent light, and for the generation of quantum correlated photons.

Ultrathin underdoped films of YBa2Cu3O7 d (YBCO) exhibit a prominent and abrupt downturn in ab-plane superfluid density nS(T) at a temperature consistent with a 2D vortex-pair unbinding transition. In this paper, we show that this characteristic feature of 2D superconductors diminishes with increasing film thickness consistent with theory, provided one uses the full film thickness rather than a copper-oxide bilayer thickness to calculate TC. In thick films, there is no evidence for 3D-XY fluctuations preceding the 2D downturn, as would be expected in a quasi-2D superconductor. 2007 Elsevier B.V. All rights reserved. PACS: 74.25.Fy; 74.40.+k; 74.76.Bz; 74.72.Bk

Ultrathin underdoped films of YBa2Cu3O7−δ (YBCO) exhibit a prominent and abrupt downturn in ab-plane superfluid density nS(T) at a temperature consistent with a 2D vortex-pair unbinding transition. In this paper, we show that this characteristic feature of 2D superconductors diminishes with increasing film thickness consistent with theory, provided one uses the full film thickness rather than a copper-oxide bilayer thickness to calculate TC. In thick films, there is no evidence for 3D-XY fluctuations preceding the 2D downturn, as would be expected in a quasi-2D superconductor.

We describe the physics of cavity polaritons in semiconductor micropillars. Cavity polaritons are exciton–photon entangled states arising from the strong coupling between excitons and the optical modes of a cavity. In micropillars, the photon three-dimensional confinement results in a discrete spectrum of 0D polariton states. Characterization of the linear properties of these micropillars will be presented. Then we will show how this system can be used to generate parametric photons and to obtain polariton lasing.

Periodic adiabatic rapid passage from counterpropagating light pulses is used in a parameter domain outside of the conventionally expected successful range to produce large optical forces on atoms by coherent control of the momentum exchange between the light and atoms. Both the magnitude and velocity range are much larger than those of the usual radiative force. We observed the force on metastable He atoms by the deflection of the atomic beam with periodic pulse sequences. We have also been able to map out the force magnitude in the two-dimensional parameter space of peak Rabi frequency and sweep range, and we find qualitative agreement with our model.

Light that is both frequency and amplitude modulated can produce huge optical forces by adiabatic exchange of momentum between atoms and the light field. Such forces can both manipulate and cool atomic beams and vapors. We have measured such forces in metastable 23S He to be up to 10 × stronger than the ordinary radiative force.

The effect of thermal phase fluctuations (TPF's) on the ab-plane penetration depth, lambda(T), of thin YBa2Cu3O(7-delta) (YBCO) films is found to be much smaller than expected from the paradigm of cuprates as weakly-coupled 2D superconducting layers. A 2D vortex-pair-unbinding transition is observed, but the effective thickness for fluctuations is the film thickness, not a CuO bilayer thickness. In a strongly underdoped YBCO film, Tc= 34 K, TPF's suppress Tc by only about 3 K. They cannot be a significant factor in the suppression of Tc and emergence of the pseudogap with underdoping.

A simple method for penetrating the barrier layer of an anodic aluminum oxide (AAO) film and for detaching the AAO film from residual Al foil was developed by reversing the bias voltage in situ after the anodization process is completed. With this technique, we have been able to obtain large pieces of free-standing AAO membranes with regular pore sizes of sub-10 nm. By combining Ar ion milling and wetting enhancement processes, Au nanowires were grown in the sub-10 nm pores of the AAO films, Further scaling down of the pore size and extension to the deposition of nanowires and nanotubes of materials other than Au should be possible by further optimizing this procedure.