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Alexis Askitopoulos

Alexis Askitopoulos
Qubitech · Quantum Technologies

BSc MSc, PhD
CSO & Co-Founder Qubitech - [a private R'n'D initiative on Quantum Technologies in Southeast Med.]

About

54
Publications
9,332
Reads
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968
Citations
Introduction
Experimental Research Physicist, 12 years hands-on experience on light-matter interaction experiments at the nanoscale and quantum enhanced technologies. CRI: Quantum Computation with PICs, Quantum Spectroscopy hardware and software, Quantum Optics and Squeezed Many Body States (BECs).
Additional affiliations
February 2018 - December 2020
Skolkovo Institute of Science and Technology
Position
  • Senior Researcher
April 2015 - February 2018
University of Southampton
Position
  • PostDoc Position
October 2010 - March 2015
University of Southampton
Position
  • PhD Student
Education
October 2010 - June 2015
University of Southampton
Field of study
  • Solid state Physics, Polariton condensates
October 2008 - September 2010
University of Crete
Field of study
  • Micro-Opto electronics
September 2001 - June 2007
University of Crete
Field of study
  • Physics

Publications

Publications (54)
Article
Full-text available
Periodic incorporation of quantum wells inside a one--dimensional Bragg structure is shown to enhance coherent coupling of excitons to the electromagnetic Bloch waves. We demonstrate strong coupling of quantum well excitons to photonic crystal Bragg modes at the edge of the photonic bandgap, which gives rise to mixed Bragg polariton eigenstates. Th...
Article
Full-text available
We demonstrate experimentally the condensation of exciton polaritons through optical trapping. The nonresonant pump profile is shaped into a ring and projected to a high quality factor microcavity where it forms a two-dimensional repulsive optical potential originating from the interactions of polaritons with the excitonic reservoir. Increasing the...
Article
We propose a method of generating and detecting entanglement via spin squeezing in an exciton-polariton condensate. Spin squeezing is a sensitive detector of entanglement because any squeezing below shot noise implies entanglement. In our scheme, two polariton spin species are resonantly pumped, forming a particle number fluctuating effective spin....
Article
Full-text available
A 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 clas...
Article
We 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 statistic...
Article
Full-text available
One of the recently established paradigms in condensed matter physics is examining a system’s behaviour in artificial potentials, giving insight into phenomena of quantum fluids in hard-to-reach settings. A prominent example is the matter-wave scatterer lattice, where high energy matter waves undergo transmission and reflection through narrow width...
Preprint
Full-text available
We implement full polarization tomography on the 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 stati...
Preprint
Full-text available
A condensed matter platform for analogue 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 cl...
Article
Full-text available
We investigate the optical orientation, polarization pinning, and depolarization of optically confined semiconductor exciton-polariton condensates. We perform a complete mapping of the condensate polarization as a function of incident nonresonant excitation polarization and power. We utilize a ring-shaped excitation pattern to generate an exciton-i...
Preprint
Full-text available
One of the recently established paradigms in the study of condensed matter physics is examining a system's behaviour in artificially constructed potentials. This allows one to obtain insight on a range of physical phenomena which may require non-feasible or hardly achievable experimental conditions. Here, we devise and implement an all-optical appr...
Poster
Full-text available
Abbreviated abstract: We present experimental evidence of a persistent Larmor precession of the collective pseudo-spin of a polariton condensate due to a self-induced out of plane magnetic field and demonstrate optical control over the precession frequency. We demonstrate that this precession survives, with great stability, for more than 6 orders o...
Preprint
Full-text available
First order coherence measurements of a polariton condensate, reveal a regime where the condensate pseudo-spin precesses persistently within the driving optical pulse. Within a single 20 $\mu$s optical pulse the condensate pseudo-spin performs over $10^5$ precessions with striking frequency stability. The condensate maintains its phase coherence ev...
Cover Page
Full-text available
Experimentally measured phase map of polariton condensates with all-optical control of coupling
Article
Full-text available
We 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 rese...
Preprint
Full-text available
We investigate the optical orientation, polarization pinning, and depolarization of optically confined semiconductor exciton-polariton condensates. We perform a complete mapping of the condensate polarization as a function of incident nonresonant excitation polarization and power. We utilize a ring-shaped excitation pattern to generate an exciton-i...
Conference Paper
Full-text available
Polaritons are quantum bosonic admixtures of excitons and photons, that have been shown to undergo the BEC phase transition and have been proposed as a platform for simulations of classical Hamiltonians [1]. The polariton architecture is advantageous for such endeavors, featuring extreme optical control and scalability enables straightforward reali...
Conference Paper
Full-text available
We investigate optically confined spinor polariton condensate under non-resonant excitation by performing time-resolved full-Stokes polarimetry. Under balanced spin injection, we reveal depolarized, unstable regime attributed to the enhanced condensate-reservoir interactions and consequent pseudo-spin fluctuations.
Article
Full-text available
Researchers have optically connected organic semiconductors and inorganic thin films to produce a light-emitting diode powered by quasi-particles that are part light and part matter. Polaritons, which form when electron–hole pairs in a semiconductor interact with photons, can be energy efficient sources of coherent light. Rahul Jayaprakash from the...
Preprint
Full-text available
We 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 rese...
Poster
Full-text available
Two-component Bose Einstein Condensates (BECs) have previously been considered for quantum computation, although the large number of particles in these states that induce decoherence of the wavefunction via inter-particle interactions have hindered realization of using them in this context. Nevertheless, it has been proposed [1] that by utilizing t...
Article
Full-text available
We investigate the spin behaviour of the first excited state of a polariton condensate in an optical trap by means of polarisation resolved spectroscopy. The interplay between the repulsive polariton interactions and the gain saturation results in a non-trivial spontaneous switching between the two quasi-degenerate spatial modes of the polariton co...
Article
Full-text available
We explore the generation of anti-Stokes fluorescence from strongly coupled organic dye microcavities following resonant ground-state excitation. We observe polariton emission along the lower polariton branch, with our results indicating that this process involves a return to the exciton reservoir and the absorption of thermal energy from molecules...
Article
Full-text available
The vast majority of real-life optimization problems with a large number of degrees of freedom are intractable by classical computers, since their complexity grows exponentially fast with the number of variables. Many of these problems can be mapped into classical spin models, such as the Ising, the XY or the Heisenberg models, so that optimization...
Poster
Full-text available
Integratable spintronic devices are a key stepping stone towards implementation of spintronic circuits and eventually spin based quantum processors [1]. A key element of this architecture is a coherent spin beam splitter that can separate particles based on their spin orientation. Since the experimental demonstration of stimulated amplification and...
Article
Full-text available
We realise bistability in the spinor of polariton condensates under non-resonant optical excitation and in the absence of biasing external fields. Numerical modelling of the system using the Ginzburg-Landau equation with an internal Josephson coupling between the two spin components of the condensate qualitatively describes the experimental observa...
Article
Full-text available
We study the polarization dynamics of a spatially expanding polariton condensate under nonresonant linearly polarized optical excitation. The spatially and temporally resolved polariton emission reveals the formation of nontrivial spin textures in the form of a quadruplet polarization pattern both in the linear and circular Stokes parameters, and a...
Article
Full-text available
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...
Article
Full-text available
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...
Article
Full-text available
We study the polarisation dynamics of a spatially expanding polariton condensate under nonresonant linearly polarized optical excitation. The spatially and temporally resolved polariton emission reveals the formation of Skyrmions in the form of a quadruplet polarisation pattern both in the linear and circular Stokes parameters and an octuplet in th...
Article
Full-text available
Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also...
Raw Data
The folder ”Raw_Data_Spin_Whirls” contains the following subfolders: 1) Paper_Data_Figs In this folder there are the raw data of all the figures used in the paper. The figure are not scaled (see “Spin_Whirls_Scaling_Notes.docx” for details on the scaling). We have performed a bilinear interpolation on Figs.1, Figs.4, Figs.S6 to reduce the pixelatio...
Data
The supplementary video shows the full dynamics of the polariton spin whirls (Fig.1 of the paper Phys. Rev. B 92, 155308). We have experimentally observed rotating spin textures in polariton condensates and reported their full dynamics on a picosecond scale by means of a time resolved tomographic technique. Please see: - Video 1 https://www.dro...
Article
Full-text available
We report on the observation of spin whirls in a radially expanding polariton condensate formed under nonresonant optical excitation. Real space imaging of polarization- and time-resolved photoluminescence reveals a spiralling polarization pattern in the plane of the microcavity. Simulations of the spatiotemporal dynamics of a spinor condensate rev...
Thesis
Full-text available
Semiconductor Microcavities in the strong coupling regime are an ideal test bed for studying light matter interactions at the micro-scale. The eigenstates of these systems, exciton-polaritons, are bosonic hybrid light matter quasi-particles that have been demonstrated to undergo Bose condensation. Owing to their photonic component polaritons are li...
Article
Full-text available
DOI:https://doi.org/10.1103/PhysRevLett.115.089402
Article
Full-text available
We report on pure-quantum-state polariton condensates in optical annular traps. The study of the underlying mechanism reveals that the polariton wavefunction always coalesces in a single pure-quantum-state that, counter-intuitively, is always the uppermost confined state with the highest overlap to the exciton reservoir. The tunability of such stat...
Data
Transition from 01 to 00 polariton-condensate state in the time domain. Supplemementary material to article Phys. Rev. B 92, 035305. Video acquired with a transient real space tomography technique. The 0 ps time-frame marks the onset of the transition.
Conference Paper
Full-text available
Strong coupling in semiconductor microcavities gives rise to hybrid light-matter particles, polaritons. It has been widely demonstrated that polaritons can undergo a phase transition and condense in the ground state of the system. Moreover it has been shown that the polariton energy landscape can be optically molded due to the repulsive exciton-pol...
Article
Full-text available
The investigation of intrinsic interactions in polariton condensates is currently limited by the photonic disorder of semiconductor microcavity structures. Here, we use a strain compensated planar GaAs/AlAs0.98P0.02 microcavity with embedded InGaAs quantum wells having a reduced cross-hatch disorder to overcome this issue. Using real and reciprocal...
Cover Page
Full-text available
Experimental (left) and simulated (right) real-space optical intensity and interference patterns of a linear polariton wave in a GaAs microcavity propagating across a point-like defect. [Phys. Rev. Lett. 113, 103901 (2014)]
Article
Full-text available
Polariton lattice condensates provide a platform for on chip quantum emulations. Interactions in extended polariton lattices are currently limited by the intrinsic photonic disorder of microcavities. Here, we fabricate a strain compensated planar GaAs/AlAs microcavity with embedded InGaAs quantum wells and report on polariton condensation under non...
Conference Paper
Full-text available
We investigate the propagation and scattering of polaritons in a planar GaAs microcavity in the linear regime under resonant excitation. The propagation of the coherent polariton wave across an extended defect creates phase and intensity patterns with identical qualitative features previously attributed to dark and half-dark solitons of polaritons....
Conference Paper
Full-text available
We demonstrate a linear to circular polarization conversion mechanism of a confined polariton condensate created by an optical potential trap. This system features a high degree of circular polarization under linear polarization pumping and is favorable for the development of spin logic operations. The physical mechanism behind this process is expl...
Article
Full-text available
We investigate the propagation and scattering of polaritons in a planar GaAs microcavity in the linear regime under resonant excitation. The propagation of the coherent polariton wave across an extended defect creates phase and intensity patterns with identical qualitative features previously attributed to dark and half-dark solitons of polaritons....
Article
Full-text available
The magnetic field effect on phase transitions in electrically neutral bosonic systems is much less studied than those in fermionic systems, such as superconducting or ferromagnetic phase transitions. Nevertheless, composite bosons are strongly sensitive to magnetic fields: both their internal structure and motion as whole particles may be affected...
Conference Paper
Full-text available
We report on a fully optically confined polariton condensate, spatially separated from the pump induced excitonic reservoir. The optically trapped condensate has improved coherence features and an order of magnitude lower excitation density threshold with respect to previous excitation schemes.
Article
Full-text available
We demonstrate experimentally the condensation of exciton-polaritons through optical trapping. The non-resonant pump profile is shaped into a ring and projected to a high quality factor microcavity where it forms a 2D repulsive optical potential originating from the interactions of polaritons with the excitonic reservoir. Increasing the population...
Article
Full-text available
Replacing independent single quantum wells inside a strongly-coupled semiconductor microcavity with double quantum wells produces a special type of polariton. Using asymmetric double quantum wells in devices processed into mesas allows the alignment of the electron levels to be voltage-tuned. At the resonant electronic tunnelling condition, we demo...

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Projects

Projects (2)
Project
Study Polariton Condensates in the optical trap configuration