# David Snoke

Our experimental group uses a wide array of optical methods to study fundamental questions of quantum mechanics in semiconductor systems. Our optical methods include ultrafast spectroscopy on femtosecond and picosecond time scales, single photon counting and correlation, real-space and momentum space (Fourier) imaging with CCD cameras, and nonlinear optics such as two-photon absorption and the optical Stark effect. We can also apply variable stress to samples to create potential gradients to move particles inside solids, vary temperature down to cryogenic temperatures, and measure transport with electronics.

One of the main efforts in our lab at present is the study of polariton condensates in microcavities. The polaritons are essentially photons dressed with an effective mass and strong interactions due to the special design of the solid-state microcavity structures we use. These interacting photons can undergo Bose-Einstein condensation, which is a state of matter with spontaneous coherence. We can see superfluid flow of the polariton condensate over millimeter distances; we can also trap the condensate in various potentials; and we can see interference due to the coherence of the condensate.

This work connects to several fundamental questions. One topic is how coherence can occur spontaneously ("enphasing") in systems like lasers and condensates and how coherence is lost ("dephasing") in standard quantum systems. This, in turn, relates to the deep question of why there is irreversibility in nature, that is, the arrow of time. Another topic is how phase transitions can occur in nonequilibrium systems. We have developed sophisticated numerical methods to compare the solution of a quantum Boltzmann equation (which gives the temporal evolution of a system in nonequilibrium) to our data on the momentum and energy distributions of gases of various particles.

A new effort in our group is looking at using a polariton condensate to modulate the two-photon absorption in our samples. This may be used for special nonlinear effects in quantum computing schemes. We have also looked at spin flip and other dynamic processes of electrons and holes in quantum dots, dipolar excitons in quantum wells, and various methods of modulating light in semiconductor lasers and microcavities for applied optical communications goals.

- "Bose-Einstein condensation of microcavity polaritons in a trap," R Balili, V Hartwell,
__D Snoke__, L Pfeiffer, K West, Science 316, 1007 (2007) - "Bose-Einstein condensation of excitons and biexcitons: and coherent nonlinear optics with excitons," SA Moskalenko,
__D Snoke__, Cambridge University Press (2000) - "Spontaneous Bose coherence of excitons and polaritons,"
__D Snoke__, Science 298, 1368 (2002) - "Bose-Einstein Condensation,"
__D Snoke__, Cambridge University Press (1996) - "Polariton lasing vs. photon lasing in a semiconductor microcavity," H Deng, G Weihs,
__D Snoke,__J Bloch, Y Yamamoto,__Proceedings of the National Academy of Sciences 100 15323 (2003)__

- "Direct measurement of polariton–polariton interaction strength," Yongbao Sun, Yoseob Yoon, Mark Steger, Gangqiang Liu, Loren N. Pfeiffer, Ken West,
__David W. Snoke__, & Keith A. Nelson, Nature Physics, Advanced Online - "Excitonic circuits: New tools for manipulating photons,"
__DW Snoke__, Perspectives 11, 00 (2017) - "Chiral modes at exceptional points in exciton-polariton quantum fluids," T. Gao, G. Li, E. Estrecho, T. C. H. Liew, D. Comber-Todd, A. Nalitov, M. Steger, K. West, L. Pfeiffer,
__D. Snoke__, A. V. Kavokin, A. G. Truscott, E. A. Ostrovskaya, arXiv:1705.09752 - "Edge Trapping of Exciton-Polariton Condensates in Etched Pillars," D. M. Myers, J. K. Wuenschell, B. Ozden, J. Beaumariage,
__D. W. Snoke__, L. Pfeiffer, and K. West, Appl. Phys. Lett. 110, 211104 (2017) - "Spontaneous condensation of exciton polaritons in the single-shot regime," E. Estrecho, T. Gao, N. Bobrovska, M. D. Fraser, M. Steger, L. Pfeiffer, K. West, T. C. H. Liew, M. Matuszewski,
__D. W. Snoke__, A. G. Truscott & E. A. Ostrovskaya, arXiv:1705.00469v1