1,720,981 research outputs found
Polariton condensates in optical traps and strong magnetic fields
No full textSemiconductor Microcavities in the strong coupling regime are an ideal test bed for studying light matter interactions at the micro-scale. The eigenstates of thesesystems, exciton-polaritons, are bosonic hybrid light matter quasi-particles that have been demonstrated to undergo Bose condensation. Owing to their photoniccomponent polaritons are lighter than atoms so their Bose-Einstein condensation (BEC) is attainable at higher temperatures than traditional BEC phase transitionsin atomic systems, while the reduced dimensionality of the system has the implication that the BEC phase transition spontaneously occurs only in the presence of a confining potential. In this thesis, the underlying mechanisms of polariton condensation in optically imprinted trapping potential landscapes is examined. Condensation in the ground state of an optical trap, de-localised from the excitation light is demonstrated and investigated and the confined condensate is shown to exhibit well defined quantum mechanical properties.A comparative study of the observed spectral features with a condensate formed with typical non-resonant excitation methods is conducted revealing a significant reduction of the excitation density threshold due to efficient trapping and relaxation of polaritons inside the trap. Decoupling of the optically induced excitonic reservoir results in increased temporal coherence in this system by suppression of the strong interactions with un-condensed particles. Modification of the geometrical properties of the trap results in single excited-state condensation. Contrary to defect and stress induced trapping schemes the condensation process is here driven by polaritons injected into the potential-trap from the trap barriers. This leads to more efficient pumping of the energetically higher modes extending into the trap boundary. We demonstrate how this feature can be exploited to manifest transitions between energetically neighbouring coherent quantum states in the steady state dynamic equilibrium regime and in the transient domain were the intensity tuning of coherent tunnelling modes is also examined. A by-product of the localisation of the condensate inside the photonic trap and the decoupling from the reservoir is the strong susceptibility of this system to small imbalances in the optical pumping of spin states.The population of the two spin states of the condensate can be controlled by small imbalances of the circular components of the excitation. The high density regime in this configuration is then investigated where a linearisation of the polariton dispersion is observed under pulsed excitation. However, a vigorous examination of the transient dynamics in this regime demonstrates the artificial nature of this effect due to transient relaxation and momentum narrowing in the transition from photon lasing to a confined polariton condensate. The confined condensate is an ideal subject for studying strong magnetic field effects on the spin properties of polariton condensates as it emits in a single energy mode for a wide range of excitation powers above threshold compared to the "untrapped" case and doesn’t suffer from de-coherence effects induced from the reservoir that causes line broadening and inhibits the spectral resolution of the spin components. We have performed initial reference strong magnetic field experiments with "unconfined" polariton condensates and present the predicted density dependent collapse of the Zeeman splitting and the modulation of the previously observed paramagnetic screening by the polarisation of the exciting beam. In the final chapter of the thesis we investigate the modulation of the condensation threshold for the non-optically confined case by the application of a magnetic field in the Faraday geometry. The experimental observations are explained by a model based on the suppression of diffusion in the reservoir and the shrinking of the Bohr radius by the application of the magnetic field.<br/
Dataset for Non-resonant optical control of a spinor polariton condensate
No full textDataset supports:
Askitopoulos, Alexis et al (2016) Non-resonant optical control of a spinor polariton condensate. Physical Review B.
We investigate the spin dynamics of polariton condensates spatially separated from and effectively confined by the pumping exciton reservoir. We obtain a strong correlation between the ellipticity of the non-resonant optical pump and the degree of circular polarisation (DCP) of the condensate at the onset of condensation. With increasing excitation density we observe a reversal of the DCP. The spin dynamics of the trapped condensate are described within the framework of the spinor complex Ginzburg-Landau equations in the Josephson regime, where the dynamics of the system are reduced to a current-driven Josephson junction. We show that the observed spin reversal is due to the interplay between an internal Josephson coupling effect and the detuning of the two projections of the spinor condensate via transition from a synchronised to a desynchronised regime. These results suggest that spinor polariton condensates can be controlled by tuning the non-resonant excitation density offering applications in electrically pumped polariton spin switches.</span
Optically controlled polariton condensate molecules
Full text linkA condensed-matter platform for analog simulation of complex two-dimensional molecular bonding configurations, based on optically trapped exciton-polariton condensates is proposed. The stable occupation of polariton condensates in the excited states of their optically configurable potential traps permits emulation of excited atomic orbitals. A classical mean-field model describing the dissipative coupling mechanism between p-orbital condensates is derived, identifying lowest-threshold condensation solutions as a function of trap parameters corresponding to bound and antibound π and σ bonding configurations, similar to those in quantum chemistry
Data for Quantum fluids of light in all-optical scatterer lattices
No full textExperimental data and numerical simulation results used to create the figures in the paper Alyatkin, S., Sigurdsson, H., Askitopoulos, A., Töpfer, J.D., & Lagoudakis, P.G. (2021) Quantum fluids of light in all-optical scatterer lattices. Nature Communications.</span
Data for Engineering photon statistics in a spinor polariton condensate
No full textExperimental data and numerical simulation results used to create the figures in the paper Baryshev, S., Zasedatelev, A., Sigurdsson, H., Gnusov, I., Töpfer, J.D., Askitopoulos, A., & Lagoudakis, P.G. (2022) Engineering photon statistics in a spinor polariton condensate. Physical Review Letters.</span
Data for: Optical orientation, polarization pinning, and depolarization dynamics in optically confined polariton condensates
No full textExperimental data and numerical simulation results used to create the figures in the paper Gnusov, I., Sigurdsson, H., Baryshev, S., Ermatov, T., Askitopoulos, A. & Lagoudakis, P.G. (2020). Optical orientation, polarization pinning, and depolarization dynamics in optically confined polariton condensates. Physical Review B.</span
Persistent self-induced Larmor precession evidenced through periodic revivals of coherence
No full textInterferometric measurements of an optically trapped exciton-polariton condensate reveal a regime where the condensate pseudo-spin precesses persistently within the driving optical pulse. For a single 20 μs optical pulse, the condensate pseudo-spin undergoes over 105 full precessions with striking frequency stability. The emergence of the precession is traced to polariton nonlinear interactions that give rise to a self-induced out-of-plane magnetic field, which in turn drives the system spin dynamics. The Larmor precession frequency and trajectory are directly influenced by the condensate density, enabling the control of this effect with optical means. Our results accentuate the system's potential for the realization of magnetometry devices and can lead to the emergence of spin-squeezed polariton condensates.</p
Data for Optical Control of Couplings in Polariton Condensate Lattices
No full textExperimental data and numerical simulation results used to create the figures in the paper Alyatkin, S., Töpfer, J.D., Askitopoulos, A., Sigurdsson, H. & Lagoudakis, P.G. (2020). Optical Control of Couplings in Polariton Condensate Lattices. Physical Review Letters.</span
Optical control of couplings in polariton condensate lattices
No full textWe demonstrate deterministic control of the nearest and next-nearest neighbor coupling in the unit cell of a square lattice of microcavity exciton-polariton condensates. We tune the coupling in a continuous and reversible manner by optically imprinting potential barriers of variable height, in the form of spatially localized incoherent exciton reservoirs that modify the particle flow between condensates. By controlling the couplings in a 2×2 polariton cluster, we realize ferromagnetic, antiferromagnetic, and paired ferromagnetic phases and demonstrate the potential scalability of the system.</p
Engineering Photon Statistics in a Spinor Polariton Condensate
No full textWe implement full polarization tomography on photon correlations in a spinor exciton-polariton condensate. Our measurements reveal condensate pseudospin mean-field dynamics spanning from stochastic switching between linear polarization components, limit cycles, and stable fixed points, and their intrinsic relation to the condensate photon statistics. We optically harness the cavity birefringence, polariton interactions, and the optical orientation of an incoherent exciton reservoir to engineer photon statistics with precise control. Our results demonstrate a smooth transition from a highly coherent to a super-thermal state of the condensate polarization components
- …
