Query: Bose–Einstein condensation of exciton polaritons

Candidate papers:

abstract: Phase transitions to quantum condensed phases such as Bose Einstein condensation (BEC) superfluidity, and superconductivity have long fascinated scientists, as they bring pure quantum effects to a macroscopic scale. BEC has, for example, famously been demonstrated in dilute atom gas of rubidium atoms at temperatures below 200 nanokelvin. Much effort has been devoted to finding a solid state system in which BEC can take place. Promising candidate systems are semiconductor microcavities, in which photons are confined and strongly coupled to electronic excitations, leading to the creation of exciton polaritons. These bosonic quasi particles are 109 times lighter than rubidium atoms, thus theoretically permitting BEC to occur at standard cryogenic temperatures. Here we detail a comprehensive set of experiments giving compelling evidence for BEC of polaritons. Above a critical density, we observe massive occupation of the ground state developing from a polariton gas at thermal equilibrium at 19 K, an increase of temporal coherence, and the build up of long range spatial coherence and linear polarization, all of which indicate the spontaneous onset of a macroscopic quantum phase.
author_names: Jacek Kasprzak

Maxime Richard

Stefan Kundermann

Augustin Baas

P Jeambrun

John J Keeling

Francesca M Marchetti

Marzena H Szymanska

Regis Andre

J L Staehli

Vincenzo Savona

Peter B Littlewood

Benoit Deveaud

Le Si Dang
title: Bose Einstein condensation of exciton polaritons
venue: Nature
year: 2006

abstract: Bose Einstein condensation describes the macroscopic occupation of a single particle mode: the condensate. This state can in principle be realized for any particles obeying Bose Einstein statistics; this includes hybrid light matter excitations known as polaritons. Some of the unique optoelectronic properties of organic molecules make them especially well suited for the realization of polariton condensates. Exciton polaritons form in optical cavities when electronic excitations couple collectively to the optical mode supported by the cavity. Organic polaritons obey bosonic statistics at moderate densities, are stable at room temperature, and have been observed to form a condensed or lasing state. Understanding the optimal conditions for polariton condensation requires careful modeling of the complex photophysics of organic molecules. In this article, we introduce the basic physics of exciton polaritons and condensation and review experiments demonstrating polariton condensation in molecular materials. Expected final online publication date for the Annual Review of Physical Chemistry, Volume 71 is April 20, 2020. Please see http:/www.annualreviews.org/page/journal/pubdates for revised estimates.
author_names: Jonathan Keeling

Stephane Kena-Cohen
title: Bose Einstein Condensation of Exciton Polaritons in Organic Microcavities.
venue: Annual review of physical chemistry
year: 2020

abstract: We describe photonic crystal microcavities with very strong light matter interaction to realize room temperature, equilibrium, exciton polariton Bose Einstein condensation (BEC) This is achieved through a careful balance between strong light trapping in a photonic band gap (PBG) and large exciton density enabled by a multiple quantum well (QW) structure with moderate dielectric constant. This enables the formation of long lived, dense 10~\mu$m 1~cm scale cloud of exciton polaritons with vacuum Rabi splitting (VRS) that is roughly 7\ of the bare exciton recombination energy. We introduce a woodpile photonic crystal made of Cd$_{0.6}$Mg$_{0.4}$Te with a 3D PBG of 9.2\ (gap to central frequency ratio) that strongly focuses a planar guided optical field on CdTe QWs in the cavity. For 3~nm QWs with 5~nm barrier width the exciton photon coupling can be as large as \hbar\Ome=$55~meV (i.e. vacuum Rabi splitting $2\hbar\Ome=$110~meV) The exciton recombination energy of 1.65~eV corresponds to an optical wavelength of 750~nm. For $N=$106 QWs embedded in the cavity the collective exciton photon coupling per QW, \hbar\Ome/\sqrt{N}=5.4$~meV, is much larger than state of the art value of 3.3~meV, for CdTe Fabry P\'erot microcavity. The maximum BEC temperature is limited by the depth of the dispersion minimum for the lower polariton branch, over which the polariton has a small effective mass \sim 10^ 5}m_0$ where $m_0$ is the electron mass in vacuum. By detuning the bare exciton recombination energy above the planar guided optical mode, a larger dispersion depth is achieved, enabling room temperature BEC.
author_names: Jian-hua Jiang

Sajeev John
title: Photonic Crystal Architecture for Room Temperature Equilibrium Bose Einstein Condensation of Exciton Polaritons
year: 2014

abstract: It is shown theoretically that Bose condensation of spin degenerated exciton polaritons results in spontaneous buildup of the linear polarization in emission spectra of semiconductor microcavities and therefore that linear polarization is a good order parameter for the polariton Bose condensation under unpolarized pumping. If spin degeneracy is lifted, an elliptically polarized light is emitted by the polariton condensate. The main axis of the ellipse rotates in time due to self induced Larmor precession of the polariton condensate pseudospin. The polarization decay time is governed by the dephasing induced by the polariton polariton interaction and is strongly dependent on the statistics of the condensed state. If the elliptical polarization preexists in the system as a result of pumping, the lifetime of the linear part of the polarization is also extremely sensitive to the degree of circular polarization induced in the system by pumping. This decay time can be used to measure the coherence degree of the condensate as a function of the polarization of the emitted light, as opposed to more conventional but harder particle counting experiments of the Hanbury Brown Twiss type.
author_names: F Laussy

Ivan Andreevich Shelykh

Guillaume Malpuech

Alexey Vitalievich Kavokin
title: Effects of Bose Einstein condensation of exciton polaritons in microcavities on the polarization of emitted light
year: 2006

abstract: A Bose Einstein condensate (BEC) is a state of matter in which extensive collective coherence leads to intriguing macroscopic quantum phenomena. In crystalline semiconductor microcavities, bosonic quasiparticles, known as exciton polaritons, can be created through strong coupling between bound electron hole pairs and the photon field. Recently, a non equilibrium BEC (ref. and superfluidity have been demonstrated in such structures. With organic crystals grown inside dielectric microcavities, signatures of polariton lasing have been observed. However, owing to the deleterious effects of disorder and material imperfection on the condensed phase, only crystalline materials of the highest quality have been used until now. Here we demonstrate non equilibrium BEC of exciton polaritons in a polymer filled microcavity at room temperature. We observe thermalization of polaritons and, above a critical excitation density, clear evidence of condensation at zero in plane momentum, namely nonlinear behaviour, blueshifted emission and long range coherence. The key signatures distinguishing the behaviour from conventional photon lasing are presented. As no crystal growth is involved, our approach radically reduces the complexity of experiments to investigate BEC physics and paves the way for a new generation of opto electronic devices, taking advantage of the processability and flexibility of polymers.
author_names: Johannes D Plumhof

Thilo Stoferle

Lijian Mai

Ullrich Scherf

Rainer F Mahrt
title: Room temperature Bose Einstein condensation of cavity exciton polaritons in a polymer.
venue: Nature materials
year: 2014

abstract: Condensation of exciton polaritons in planar microcavities with GaAs/AlAs quantum wells in the active area has been studied. It has been found that an increase in the lifetime of polaritons up to ~10 15 ps when the Q factor of a microcavity exceeds 7000 makes it possible to detect Bose Einstein condensation of polaritons with a dominant >90% photon component. Condensation occurs under thermodynamically nonequilibrium conditions in lateral traps with diameters ~10 mm formed due to long range fluctuations of the polariton potential. The violet shift of the polariton emission line at the condensation threshold significantly exceeds the energy of the repulsive interaction between polaritons in the condensate. It has been shown that the shift is mainly due to a decrease in the oscillator strength of bright excitons in lateral traps, caused by the localization of photoexcited long living dark excitons.
author_names: Vladimir D Kulakovskii

A V Larionov

S I Novikov

Sven Hofling

Christian Schneider

Alfred Forchel
title: Bose einstein condensation of exciton polaritons in high Q planar microcavities with GaAs quantum wells
year: 2010

author_names: Yoshihisa Yamamoto

Hui Deng

Hartmut Haug
title: Bose einstein condensation of exciton polaritons
year: 2009

abstract: Physics Department and Center for Theoretical Physics,The University of Michigan, Ann Arbor, M1 48109 1040, USA(Dated: August 7, 2009)We examine the Bose Einstein condensation of exciton polaritons in a semiconductor microcavityvia an electrical current. We propose that by embedding a quantum dot p i n junction inside thecavity, the tunneling current through the device can reveal features of condensation due to a one to one correspondence of the photons to the condensate polaritons. Such a device can also be usedto observe the phase interference of the order parameters from two condensates.
author_names: Yueh-Nan Chen

Neill Lambert

Franco Nori
title: Detecting Bose Einstein condensation of exciton polaritons via electron transport
year: 2009

author_names: Helena Franke
title: PLD grown ZnO based Microcavities for Bose Einstein Condensation of Exciton Polaritons
year: 2012

abstract: Coherent control has been at the heart of the study of physical chemistry. Great advancement has been achieved in the past few decades in coherent control of classical systems by using spatially and temporally shaped electromagnetic waves. In this dissertation, we extend the concept of coherent control to a purely quantum mechanical collective system, namely, microcavity exciton polariton Bose Einstein condensates. Microcavity exciton polaritons, hereafter simply polaritons, are bosonic quasiparticles formed in a resonant semiconductor microcavity by coupling the excitonic polarizabilities in quantum wells to the transverse mode of the confined optical field in the cavity. The light matter dual nature allows direct control of polaritons through either their excitonic or photonic components. By utilizing the fact that polariton exciton and polariton polariton interactions are repulsive, all optical control of polaritons was realized. By shaping the intensity fronts of the optical beam incident on a microcavity, the potential landscape felt by polaritons can be easily tailored. This is the key ingredient of this dissertation work. The light matter dual nature endows polaritons a very small effective mass that is one hundred million times less than that of a hydrogen atom, leading to the observation of quantum phenomena such as condensation, superfluidity and quantized vortices at temperatures ranging from tens of Kelvin up to room temperatures. However, debates persist over whether the observed phenomena can be related to BoseEinstein condensation because polaritons are not in thermal equilibrium. By applying all optical trapping to a high quality microcavity structure, polaritons at both spatial and thermal equilibrium were achieved across a broad range of densities and bath temperatures, as evidenced by the observed equilibrium Bose Einstein distributions. A phase diagram for Bose Einstein condensation of polaritons was produced for the first time, which agrees with the predictions of basic quantum gas theory. The thermalization behavior depends crucially on the interactions among polaritons. By changing the underlying excitonic/photonic fractions in polaritons, the interaction strength of polaritons can be varied, leading to control between nonequilibrium and equilibrium behavior of the polariton gas. The interactions also play 5 a crucial role in polaritonic device operations. However, an accurate measurement of the polariton polariton interaction strength has been not possible because of the difficulty in separating polaritons and excitons that are created by the same optical excitation. After propagating to the center of a sufficiently large optically induced annular trap, polaritons were separated from the incoherent populations of free carriers and hot excitons. The polariton interaction strength was then extracted from energies measured as a function of the polariton density. The measured interaction strength was about two orders of magnitude larger than previous theoretical estimates, putting polaritons squarely into the strongly interacting regime. Optical control can also be utilized to directly manipulate polariton condensates. By tailoring the size and pumping intensity of the optical trap, polariton condensates can be switched among different high order modes and the homogeneous condensate mode. The redistribution of spatial densities is accompanied by a superlinear increase in the emission intensity as a function of excitation power, implying that polariton condensates in this geometry could be exploited as a multistate switch. The parameters for reproducible switching between the high order states in the optical trap have been measured experimentally, giving us a phase diagram for the mode switching. It will serve well to calibrate the implementation of an exciton polaritonic multistate switch. Thesis Supervisor: Keith A. Nelson Title: Haslam and Dewey Professor of Chemistry
author_names: Yongbao Sun
title: Exciton polaritons in thermal equilibrium from Bose Einstein condensation to exciton polaritonics
year: 2017