arXiv subjects

T. C. H. Liew

Publications and source records attributed to T. C. H. Liew.

82 records · Page 5Linked to original sources

arXiv2011

Spin-to-Orbital Angular Momentum Conversion in Semiconductor Microcavities

We experimentally demonstrate a technique for the generation of optical beams carrying orbital angular momentum using a planar semiconductor microcavity. Despite being isotropic systems, the transverse electric - transverse magnetic (TE-TM) polarization splitting featured by semiconductor microcavities allows for the conversion of the circular polarization of an incoming laser beam into the orbital angular momentum of the transmitted light field. The process implies the formation of topological entities, a pair of optical half-vortices, in the intracavity field.

cond-mat.other↗

arXiv2011

Probing the Dynamics of Spontaneous Quantum Vortices in Polariton Superfluids

The experimental investigation of spontaneously created vortices is of utmost importance for the understanding of quantum phase transitions towards a superfluid phase, especially for two dimensional systems that are expected to be governed by the Berezinski-Kosterlitz-Thouless physics. By means of time resolved near-field interferometry we track the path of such vortices, created at random locations in an exciton-polariton condensate under pulsed non-resonant excitation, to their final pinning positions imposed by the stationary disorder. We formulate a theoretical model that successfully reproduces the experimental observations.

cond-mat.quant-gas↗

arXiv2011

Energy Relaxation in a 1-D Polariton Condensate

We study the kinetics of polariton condensation accounting for the condensation process as well as the energy relaxation of condensed polaritons due to their scattering with phonons and excitons. By assuming a Boltzmann kinetic description of the scattering process, we show that intra-condensate relaxation can be accounted for by an additional time-dependent term in the Gross-Pitaevskii equation. As an example, we apply the formalism to the experimental results recently obtained in polariton microwires [E. Wertz, et al., Nature Phys. 6, 860 (2010)]. In the presence of a local non-resonant optical pump, a dynamic balance between spatially dependent relaxation and particle loss develops and excites a series of modes, roughly equally spaced in energy. Upon comparison, excellent agreement is found with the experimental data.

cond-mat.mes-hall↗

arXiv2010

Spin rings in bi-stable planar semiconductor microcavities

A unique feature of exciton-polaritons, inherited from their mixed light-matter origin, is the strongly spin-dependent polariton-polariton interaction, which has been predicted to result in the formation of spin rings in real space [Shelykh et al., Phys. Rev. Lett. 100, 116401 (2008)]. Here we experimentally demonstrate the spin bi-stability of exciton-polaritons in an InGaAs-based semiconductor microcavity under resonant optical pumping. We observe the formation of spin rings whose size can be finely controlled in a spatial scale down to the micrometer range, much smaller than the spot size. We additionally evaluate the sign and magnitude of the antiparallel polariton spin interaction constant.

cond-mat.mes-hall↗

arXiv2009

Device independent state estimation based on Bell's inequalities

The only information available about an alleged source of entangled quantum states is the amount $S$ by which the Clauser-Horne-Shimony-Holt (CHSH) inequality is violated: nothing is known about the nature of the system or the measurements that are performed. We discuss how the quality of the source can be assessed in this black-box scenario, as compared to an ideal source that would produce maximally entangled states (more precisely, any state for which $S=2\sqrt{2}$). To this end, we introduce several inequivalent notions of fidelity, each one related to the use one can make of the source after having assessed it; and we derive quantitative bounds for each of them in terms of the violation $S$. We also derive a lower bound on the entanglement of the source as a function of $S$ only.

quant-ph↗

arXiv2009

Anisotropic Optical Spin Hall Effect in Semiconductor Microcavities

Propagating, directionally dependent, polarized spin-currents are created in an anisotropic planar semiconductor microcavity, via Rayleigh scattering of optically injected polaritons in the optical spin Hall regime. The influence of anisotropy results in the suppression or enhancement of the pseudospin precession of polaritons scattered into different directions. This is exploited to create intense spin currents by excitation on top of localized defects. A theoretical model considering the influence of the total effective magnetic field on the polariton pseudospin quantitatively reproduces the experimental observations.

cond-mat.mes-hall↗

arXiv2009

Signature of the microcavity exciton-polariton relaxation mechanism in the polarization of emitted light

We have performed real and momentum space spin-dependent spectroscopy of spontaneously formed exciton polariton condensates for a non-resonant pumping scheme. Under linearly polarized pump, our results can be understood in terms of spin-dependent Boltzmann equations in a two-state model. This suggests that relaxation into the ground state occurs after multiple phonon scattering events and only one polariton-polariton scattering. For the circular pumping case, in which only excitons of one spin are injected, a bottleneck effect is observed, implying inefficient relaxation.

cond-mat.mes-hall↗

arXiv2008

Stochastic polarization formation in exciton-polariton Bose-Einstein condensates

We demonstrate theoretically the spontaneous formation of a stochastic polarization in exciton-polariton Bose-Einstein condensates in planar microcavities under pulsed excitation. Below the threshold pumping intensity (dependent on the polariton life-time) the average polarization degree is close to zero, whilst above threshold the condensate acquires a polarization described by a (pseudospin) vector with random orientation, in general. We establish the link between second order coherence of the polariton condensate and the distribution function of its polarization. We examine also the mechanisms of polarization dephasing and relaxation.

cond-mat.mes-hall↗

arXiv2008

Optical circuits based on Polariton Neurons in Semiconductor Microcavities

By exploiting the polarization multistability of polaritons, we show that polarized signals can be conducted in the plane of a semiconductor microcavity along controlled channels or "neurons". Furthermore due to the interaction of polaritons with opposite spins it is possible to realize binary logic gates operating on the polarization degree of freedom. Multiple gates can be integrated together to form an optical circuit contained in a single semiconductor microcavity.

cond-mat.mes-hall↗

arXiv2008

Suppression of Zeeman splitting and polarization steps in localized exciton-polariton condensates

We show that the condensation of exciton-polaritons in semiconductor microcavities in an applied magnetic field manifests itself in the quenching of the Zeeman splitting of an elliptically polarized condensate. The circular polarization degree of a localized condensate with a finite number of particles increases as a function of the magnetic field with a step-like behavior. The width of each polarization step is fixed by the polariton-polariton interaction constants and the number of steps is fixed by the number of polaritons in the condensate. The magnetic susceptibility of the condensate depends qualitatively on the parity of the number of polaritons.

cond-mat.mes-hall↗