arXiv subjects

T. C. H. Liew

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

At least 73 records · Page 4Linked to original sources

arXiv2013

Motion of spin polariton bullets in semiconductor microcavities

The dynamics of optical switching in semiconductor microcavities in the strong coupling regime is studied using time- and spatially-resolved spectroscopy. The switching is triggered by polarised short pulses which create spin bullets of high polariton density. The spin packets travel with speeds of the order of 106 m/s due to the ballistic propagation and drift of exciton-polaritons from high to low density areas. The speed is controlled by the angle of incidence of the excitation beams, which changes the polariton group velocity.

cond-mat.mes-hall↗

arXiv2013

Optical diode based on exciton-polaritons

We propose theoretically an optical diode based on exciton-polaritons in semiconductor microcavities. A flow of polaritons in the bistable regime is used to send signals through an asymmetric fixed potential that favours the tunneling of particles in one direction. Through dynamic modelling of the coherent polariton field, we demonstrate the characteristics of an ideal diode, namely that the forward signal is fully transmitted while the transmission in the reverse direction tends to zero, without any additional external control. Moreover, the system proves to be robust to the presence of disorder, intrinsic to microcavities, and can function at gigahertz repetition rates.

cond-mat.mes-hall↗

arXiv2013

Continuous THz emission from dipolaritons

We propose a scheme of continuous tunable THz emission based on dipolaritons --- mixtures of strongly interacting cavity photons and direct excitons, where the latter are coupled to indirect excitons via tunnelling. We investigate the property of multistability under continuous wave (CW) pumping, and the stability of the solutions. We establish the conditions of parametric instability, giving rise to oscillations in density between the direct exciton and indirect modes under CW pumping. In this way we achieve continuous and tunable emission in the THz range in a compact single-crystal device. We show that the emission frequency can be tuned in a certain range by varying an applied electric field and pumping conditions. Finally, we demonstrate the dynamic switching between different phases in our system, allowing rapid control of THz radiation.

cond-mat.mes-hall↗

arXiv2013

Optomechanics with Cavity Polaritons: Dissipative Coupling and Unconventional Bistability

We study a hybrid system formed from an optomechanical resonator and a cavity mode strongly coupled to an excitonic transition inside a quantum well. We show that due to the mixing of cavity photon and exciton states, the emergent quasiparticles - polaritons - possess coupling to the mechanical mode of both dispersive and dissipative nature. We calculate the occupancies of polariton modes and reveal bistable behavior, which deviates from conventional Kerr nonlinearity or dispersive coupling cases due to the dissipative coupling. The described system serves as a good candidate for future polaritonic devices and solid state quantum information processing.

cond-mat.mes-hall↗

arXiv2013

Theory of an excitonic THz laser with two-photon excitation

We consider theoretically THz lasing in a system consisting of a quantum well placed inside an optical microcavity and a THz cavity in the regime of two-photon excitation of 2p dark exciton states. The stability of the system with varying parameters of the microcavity under coherent pumping is studied. We show that the nonlinearity provided by two photon absorption can give rise to bistability and hysteresis in the THz output.

cond-mat.mes-hall↗

arXiv2013

Nonlinear Effects in Multi-Photon Polaritonics

We consider theoretically nonlinear effects in a semiconductor quantum well embedded inside a photonic microcavity. Two-photon absorption by a 2p exciton state is considered and investigated; the matrix element of two-photon absorption is calculated. We compute the emission spectrum of the sample and demonstrate that under coherent pumping the nonlinearity of the two photon absorption process gives rise to bistability.

cond-mat.mes-hall↗

arXiv2013

Magnetic Field Control of the Optical Spin Hall Effect

We investigate theoretically the effect of an external magnetic field on polarization patterns appearing in quantum microcavities due to the optical spin Hall effect (OSHE). We show that increase of the magnetic field perpendicular to the plane of the cavity resulting in the increase of the Zeeman splitting leads to the transition from azimuthal separation of polarizations to their radial separation. This effect can be straightforwardly detected experimentally.

cond-mat.mes-hall↗

arXiv2013

A complete architecture of integrated photonic circuits based on AND and NOT logic gates of exciton-polaritons in semiconductor microcavities

In this letter we introduce a complete photonic logic gate architecture, making use of the non-linear and spintronic properties of exciton-polaritons in semiconductor microcavities. This hybrid light-matter design is highly compact and offers the advantages expected of photonic circuits including: no distance-dependent loss or signal gradation; electrical isolation and immunity to electromagnetic interference; reduced error-checking overhead; and direct coupling to external light, useful for fibre optic communication.

cond-mat.mes-hall↗

arXiv2013

Stochastic Gross-Pitaevskii Equation for the Dynamical Thermalization of Bose-Einstein Condensates

We present a theory for the description of energy relaxation in a nonequilibrium condensate of bosonic particles. The approach is based on coupling to a thermal bath of other particles (e.g., phonons in a crystal, or noncondensed atoms in a cold atom system), which are treated with a Monte Carlo type approach. Together with a full account of particle-particle interactions, dynamic driving, and particle loss, this offers a complete description of recent experiments in which Bose-Einstein condensates are seen to relax their energy as they propagate in real space and time. As an example, we apply the theory to the solid-state system of microcavity exciton polaritons, in which nonequilibrium effects are particularly prominent.

cond-mat.mes-hall↗

arXiv2013

Spontaneous self-ordered states of vortex-antivortex pairs in a Polariton Condensate

Polariton condensates have proved to be model systems to investigate topological defects, as they allow for direct and non-destructive imaging of the condensate complex order parameter. The fundamental topological excitations of such systems are quantized vortices. In specific configurations, further ordering can bring the formation of vortex lattices. In this work we demonstrate the spontaneous formation of ordered vortical states, consisting in geometrically self-arranged vortex-antivortex pairs. A mean-field generalized Gross-Pitaevskii model reproduces and supports the physics of the observed phenomenology.

cond-mat.quant-gas↗

arXiv2012

Dynamics of a polariton condensate transistor switch

We present a time-resolved study of the logical operation of a polariton condensate transistor switch. Creating a polariton condensate (source) in a GaAs ridge-shaped microcavity with a non-resonant pulsed laser beam, the polariton propagation towards a collector, at the ridge edge, is controlled by a second weak pulse (gate), located between the source and the collector. The experimental results are interpreted in the light of simulations based on the generalized Gross-Pitaevskii equation, including incoherent pumping, decay and energy relaxation within the condensate.

cond-mat.mes-hall↗

arXiv2012

Propagation and amplification dynamics of 1D polariton condensates

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 non-resonantly 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 non-resonant 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.

cond-mat.quant-gas↗

arXiv2012

Polariton Condensate Transistor Switch

A polariton condensate transistor switch is realized through optical excitation of a microcavity ridge with two beams. The ballistically ejected polaritons from a condensate formed at the source are gated using the 20 times weaker second beam to switch on and off the flux of polaritons. In the absence of the gate beam the small built-in detuning creates potential landscape in which ejected polaritons are channelled toward the end of the ridge where they condense. The low loss photon-like propagation combined with strong nonlinearities associated with their excitonic component makes polariton based transistors particularly attractive for the implementation of all-optical integrated circuits.

cond-mat.mtrl-sci↗

arXiv2012

Bosonic Cascade Laser

We propose a concept of a quantum cascade laser based on transitions of bosonic quasiparticles (excitons and exciton-polaritons) in a parabolic potential trap in a semiconductor microcavity. This laser would emit terahertz radiation due to bosonic stimulation of excitonic transitions. Dynamics of a bosonic cascade is strongly different from the dynamics of a conventional fermionic cascade laser. We show that populations of excitonic ladders are parity-dependent and quantized if the laser operates without an external terahertz cavity.

cond-mat.mes-hall↗

arXiv2012

Quantum Entanglement in Nanocavity Arrays

We show theoretically how quantum interference between linearly coupled modes with weak local nonlinearity allows the generation of continuous variable entanglement. By solving the quantum master equation for the density matrix, we show how the entanglement survives realistic levels of pure dephasing. The generation mechanism forms a new paradigm for entanglement generation in arrays of coupled quantum modes.

cond-mat.mes-hall↗

arXiv2012

Spin Texture in a Cold Exciton Gas

We report on the observation of a spin texture in a cold exciton gas in a GaAs/AlGaAs coupled quantum well structure. The spin texture is observed around the exciton rings. The observed phenomena include: a ring of linear polarization, a vortex of linear polarization with polarization perpendicular to the radial direction, an anisotropy in the exciton flux, a skew of the exciton fluxes in orthogonal circular polarizations and a corresponding four-leaf pattern of circular polarization, a periodic spin texture, and extended exciton coherence in the region of the polarization vortex. The data indicate a transport regime where the spin polarization is locked to the direction of particle propagation and scattering is suppressed.

cond-mat.mes-hall↗

arXiv2011

Spontaneous Pattern Formation in a Polariton Condensate

Polariton condensation can be regarded as a self-organization phenomenon, where phase ordering is established among particles in the system. In such condensed systems, further ordering can possibly occur in the particle density distribution, under particular experimental conditions. In this work we report on spontaneous pattern formation in a polariton condensate under non-resonant optical pumping. The slightly elliptical ring-shaped excitation laser we employ is such to force condensation to occur in a single-energy state with periodic boundary conditions, giving rise to a multi-lobe standing wave patterned state.

cond-mat.quant-gas↗

arXiv2011

Optically erasing disorder in semiconductor microcavities with dynamic nuclear polarization

The mean squared value of the photonic disorder is found to be reduced by a factor of 100 in a typical GaAs based microcavity, when exposed to a circularly polarized continuous wave optical pump without any special spatial patterning. Resonant excitation of the cavity mode excites a spatially non-uniform distribution of spin-polarized electrons, which depends on the photonic disorder profile. Electrons transfer spin to nuclei via the hyperfine contact interaction, inducing a long-living Overhauser magnetic field able to modify the potential of exciton-polaritons.

cond-mat.mes-hall↗