Kenji Kamide* and Tetsuo Ogawa Advanced Photons and Science Evolution 2010 (APSE2010) June 14-18, 2010, Osaka Japan Laser-like behaviors in a polariton condensate: the thermodynamic regime Kenji Kamide* and Tetsuo Ogawa Department of Physics, Osaka University, Toyonaka, Osaka, Japan * kamide@acty.phys.sci.osaka-u.ac.jp [1] K. Kamide and T. Ogawa, ArXiv:0912.0977. [2] K. Kamide and T. Ogawa, J. Phys.: Conf. Ser. 210, 012021 (2010). This work is supported by and Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST).

Observation of the BEC 1.67Pth 1.14Pth 0.55Pth P=Pth [3] J. Kasprzak et al, Nature 443, 409 (2006). condition: non-resonant pumping + 16 CdTe Q-Wells detection: angle resolved emission spectrum (Far-field) strong light-matter coupling Bose narrowing in the momentum and energy space 0.55Pth 1.14Pth Emission Spectrum Angular distribution 1.67Pth Q-Wells photon Pumping Laser Excitons Bragg Mirror P=Pth pump power energy Ground state occupancy linewidth momentum Polariton BEC is similar to Bose-Einstein Condensation of atomic gases in a thermal equilibrium!

Thermodynamic BEC Polariton Laser Conventional Laser What is the relationship among three type of the coherent light sources? : Thermodynamic BEC Polariton Laser Conventional Laser Crossover between Polariton Laser and Polariton BEC was investigated theoretically using the Bosonic description in: [6] A. Imamoglu et al., Phys. Rev. A 53, 4250 (1996). Crossover behavior among them was already reported in : [5] H. Deng et al., PNAS 100, 15318 (2003). The detuning effects are also seen.

Our recent results by a variational theory [1] K. Kamide and T. Ogawa, ArXiv:0912.0977. [2] K. Kamide and T. Ogawa, J. Phys.: Conf. Ser. 210, 012021 (2010).

Phase Diagram Conventional Laser (threshold-ful ) Polariton laser results for 2D systems (variational calculation) Phase Diagram Conventional Laser (threshold-ful ) Polariton laser (threshold-less) High density Low density Different ground states are expected to occur depending on the detuning and the pump power (total excitation density ntot).

Laser-like Behaviors: the detuning effect results for 2D systems (variational calculation) Laser-like Behaviors: the detuning effect Dependencies of the photon and carrier densities on the excitation density change from thresholdless-type to thresholdful-type as the detuning increases. threshold-less threshold-ful =RS =RS Photon density Carrier density In the strong coupling regime with small detuning, nph and ncar increase with pumping power (ntot) altogether. Thus, the threshold of lasing is unclear. In the weak coupling regime with large detuning, the threshold is clear.

Momentum Distribution of Carriers results for 2D systems (variational calculation) Momentum Distribution of Carriers The laser-like behaviors depend on whether or not the population inversion exists (fe(k)>0.5 or not) near the threshold density. threshold-less threshold-ful fe(k) RS= RS values near the threshold. There is “No population inversion”. There is “population inversion”.

Conclusions We determined the coherent ground states of microcavity polaritons by using interpolating variational theory, assuming the thermal equilibrium. It is shown that, even in an equilibrium situation, the photonic fraction and inversion density of carriers have characteristic dependencies on the pumping power. Lasing-like behaviors are found: the laser-like threshold in the input-output curve together with the saturation of the inversion density above the threshold are found, although their physical origin is quite different from the conventional laser in a kinetic regime. Laser-like behaviors depend on detuning parameters; for large detuning, the threshold is clearly defined where there exists population inversion; for small detuning, the threshold is unclear where there is no population inversion.

First report of the Stimulated Emission ・・・ [4] Le Si Dang et al First report of the Stimulated Emission ・・・ [4] Le Si Dang et al., Phys. Rev. Lett. 81, 3920 (1998). condition: non-resonant pumping + 16 CdTe Q-Wells detection: angle integrated intensity Lower Polariton Upper Polariton Absorption Spectrum Emission Spectrum Excitation density (Pumping Power) Cavity mode A B Polariton Laser Conventional Laser Polariton BEC density See also [5] H. Deng et al., PNAS 100, 15318 (2003).