Kenichiro Kusudo

Exciton?polariton condensates with flat bands in a two-dimensional kagome lattice

Microcavity exciton–polariton condensates, as coherent matter waves, have provided a great opportunity to investigate hydrodynamic vortex properties, superfluidity and low-energy quantum state dynamics. Recently, exciton condensates were trapped in various artificial periodic potential geometries: one-dimensional (1D), 2D square, triangular and hexagonal lattices. The 2D kagome lattice, which has been of interest for many decades, exhibits spin frustration, giving rise to magnetic phase order in real materials. In particular, flat bands in the 2D kagome lattice are physically interesting in that localized states in the real space are formed. Here, we realize exciton–polariton condensates in a 2D kagome lattice potential and examine their photoluminescence properties. Above quantum degeneracy threshold values, we observe meta-stable condensation in high-energy bands; the third band exhibits a signature of weaker dispersive band structures, a flat band. We perform a single-particle band structure calculation to compare measured band structures.

Quantum simulation of Fermi-Hubbard models in semiconductor quantum-dot arrays

We propose a device for studying the Fermi-Hubbard model with long-range Coulomb interactions using an array of quantum dots defined in a semiconductor two-dimensional electron gas system. Bands with energies above the lowest energy band are used to form the Hubbard model, which allows for an experimentally simpler realization of the device. We find that depending on average electron density, the system is well described by a one- or two-band Hubbard model. Our device design enables the control of the ratio of the Coulomb interaction to the kinetic energy of the electrons independently to the filling of the quantum dots, such that a large portion of the Hubbard phase diagram may be probed. Estimates of the Hubbard parameters suggest that a metal-Mott insulator quantum phase transition and a d-wave superconducting phase should be observable using current fabrication technologies.

Exciton-polariton condensates near the Dirac point in a triangular lattice

Dirac particles, massless relativistic entities, obey linear energy dispersions and hold important implications in particle physics. The recent discovery of Dirac fermions in condensed matter systems including graphene and topological insulators has generated a great deal of interest in exploring the relativistic properties associated with Dirac physics in solid-state materials. In addition, there are stimulating research activities to engineer Dirac particles, elucidating their exotic physical properties in a controllable setting. One of the successful platforms is the ultracold atom-optical lattice system, whose dynamics can be manipulated and probed in a clean environment. A microcavity exciton-polariton-lattice system offers the advantage of forming high-orbital condensation in non-equilibrium conditions, which enables one to explore novel quantum orbital order in two dimensions. In this paper, we experimentally construct the band structures near Dirac points, the vertices of the first hexagonal Brillouin zone with exciton-polariton condensates trapped in a triangular lattice.

Stochastic Formation of Polariton Condensates in Two Degenerate Orbital States

Technische Physik and Wilhelm-Conrad-Rontgen-Research Center for Complex Material Systems,Universitat Wurzburg, D-97074 Wurzburg, Am Hubland, Germany(Dated: December 30, 2012)We explore the exciton-polariton condensation in the two degenerate orbital states. In the honey-comb lattice potential, at the third band we have two degenerate vortex-antivortex lattice states atthe inequivalent K and K

Highly excited exciton-polariton condensates

This research was supported by the Japan Society for the Promotion of Science (JSPS) through its FIRST Program and KAKENHI Grant Numbers 24740277 and 25800181, a Space and Naval Warfare Systems (SPAWAR) Grant Number N66001-09-1-2024, the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), the National Institution of Information and Communication Technology (NICT), the joint study program at Institute for Molecular Science. T. H. acknowledges the support of Toray Science Foundation, KDDI Foundation, the Asahi Glass Foundation, ther Murata Science Foundation, and REFEC. T.B. acknowledges the support of the Shanghai Research Challenge Fund, New York University Global Seed Grants for Collaborative Research, National Natural Science Foundation of China (Grant No. 61571301), the Thousand Talents Program for Distinguished Young Scholars (Grant No. D1210036A), and the NSFC Research Fund for International Young Scientists (Grant No. 11650110425).

Exciton-Polariton Condensates in Zero-, One-, and Two-Dimensional Lattices

Microcavity exciton-polaritons are quantum quasi-particles arising from the strong light-matter coupling. They have exhibited rich quantum dynamics rooted from bosonic nature and inherent non-equilibrium condition. Dynamical condensation in microcavity exciton-polaritons has been observed at much elevated temperatures in comparison to ultracold atom condensates. Recently, we have investigated the behavior of exciton-polariton condensates in artificial trap and lattice geometries in zero-dimension, one-dimension (1D) and two-dimension (2D). Coherent π-state with p-wave order in a 1D condensate array and d-orbital state in a 2D square lattice are observed. We anticipate that the preparation of high-orbital condensates can be further extended to probe dynamical quantum phase transition in a controlled manner as quantum emulation applications.

High-Orbital Exciton-Polariton Condensation: Towards Quantum-Simulator Applications

We review high-orbital exciton-polariton condensation experiments in various two-dimensional lattices. The dynamical nature of exciton-polaritons spontaneously forms condensates at non-zero momentum, resulting from the competition between the finite lifetime and the cooling time. We describe the basics of exciton-polariton condensation, methods used to create lattices, and identification of their orbital order via photoluminescence in real and momentum spaces. We discuss the current status of high-orbital exciton-polariton condensates and the implications towards the bosonic quantum simulators.

Spatial and temporal dynamics of the crossover from exciton–polariton condensation to photon lasing

At a sufficiently high density, the bosonic exciton–polariton system breaks down and the constituent electron, hole, and photon nature is revealed. Although conventional photon lasing is expected in this regime, the nature of the crossover from polariton condensation to photon lasing is not yet well understood. Through detailed mapping, we deconvolute the spatial, temporal, momentum, and energy dependences of the photoluminescence from this system at the crossover point. Photon lasing is distinctly observed far above this crossover.

Degenerate high-orbital microcavity exciton-polariton condensates in a lattice

We explore two degenerate high-orbital exciton-polariton condensates in a honeycomb lattice. We measure the order parameter of the condensates, identifying the vortex-antivortex lattice order. We also study the intensity correlation relation between two condensates.