Photonic Crystal Architecture for RoomTemperature Equilibrium BoseEinstein Condensation of Exciton Polaritons
Abstract
We describe photonic crystal microcavities with very strong lightmatter interaction to realize roomtemperature, equilibrium, excitonpolariton BoseEinstein condensation (BEC). This goal is achieved through a careful balance between strong light trapping in a photonic band gap (PBG) and large exciton density enabled by a multiple quantumwell (QW) structure with a moderate dielectric constant. This approach enables the formation of a longlived, dense 10μ_{m1cm scale cloud of exciton polaritons with vacuum Rabi splitting that is roughly 7% of the bare excitonrecombination energy. We introduce a woodpile photonic crystal made of Cd0.6 Mg0.4Te with a 3D PBG of 9.2% (gaptocentralfrequency ratio) that strongly focuses a planar guided optical field on CdTe QWs in the cavity. For 3nm QWs with 5nm barrier width, the excitonphoton coupling can be as large as ℏΩ=55 meV (i.e., a vacuum Rabi splitting of 2ℏΩ=110 meV). The excitonrecombination energy of 1.65 eV corresponds to an optical wavelength of 750 nm. For N =106 QWs embedded in the cavity, the collective excitonphoton coupling per QW (ℏΩ/√N =5.4 meV) is much larger than the stateoftheart value of 3.3 meV, for the CdTe FabryPérot 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 of approximately 105m0, where m0 is the electron mass in vacuum. By detuning the bare excitonrecombination energy above the planar guided optical mode, a larger dispersion depth is achieved, enabling roomtemperature BEC. The BEC transition temperature ranges as high as 500 K when the polariton density per QW is increased to (11aB)2, where aB}≃3.5 nm is the exciton Bohr radius and the excitoncavity detuning is increased to 30 meV. A highquality PBG can suppress exciton radiative decay and enhance the polariton lifetime to beyond 150 ps at room temperature, sufficient for thermal equilibrium BEC.
 Publication:

Physical Review X
 Pub Date:
 July 2014
 DOI:
 10.1103/PhysRevX.4.031025
 arXiv:
 arXiv:1408.4806
 Bibcode:
 2014PhRvX...4c1025J
 Keywords:

 42.70.Qs;
 71.35.y;
 67.85.Hj;
 42.50.p;
 Photonic bandgap materials;
 Excitons and related phenomena;
 BoseEinstein condensates in optical potentials;
 Quantum optics;
 Condensed Matter  Quantum Gases;
 Condensed Matter  Mesoscale and Nanoscale Physics
 EPrint:
 Phys. Rev. X 4, 031025 (2014)