Enhancing microcavity polaritons for technological applications

Microcavity exciton-polaritons, semiconductor quasiparticles that are a unique mixture of light and matter, are routinely used to study quantum many-body phenomena. Due to the light mass of the polariton, $\sim 10^{-4}$ times the bare electron mass, polaritons manifest noticeable quantum effects even at room temperature. As solid state systems, microcavity polaritons are generally robust and compatible with current semiconductor technology. Microcavity chips could be integrated into electronic or optical circuits. I present a demonstration of microcavity polaritons as an all-optical transistor, where the strong nonlinearity of the system leads to a change in the reflectivity for a signal light-ray from high to low. I also discuss the promise of using strongly coupled microcavities as low-threshold polariton lasers, which could replace traditional lasers in some cases. The last two decades have seen great strides in the material systems used in microcavities, even demonstrating strong coupling at room temperature. GaN, CdZnSe, organic semiconductors and more recently, MoS$_2$ have supported strong coupling at ambient conditions. This makes technological applications more promising. I present our current progress in this field. Also, the general quality of microcavities has advanced steadily over this time. I demonstrate that our long-lifetime polaritons persist for an order of magnitude longer than in similar samples. This opens up new regimes of study and technological application as these particles thermalize better and carry quantum coherence over macroscopic distances

The role of intolerance of uncertainty in the relationship between daily search for and presence of meaning in life

People who are highly intolerant of uncertainty have a propensity to fear the unknown, which influences perceptions and desires for control and predictability (Carleton, 2016). Processes related to searching for and maintaining meaning might deviate based on intolerance of uncertainty as meaning-making can be spurred by breakdowns in one’s sense of understanding or predictability (Park, 2010). The current study was designed to examine within-person relationships between daily search for and presence of meaning, while investigating how people’s intolerance of uncertainty (IU) influences the search-presence relationship. During a three-week daily diary study, results showed that daily search significantly predicted same-day presence and presence the following day. IU significantly moderated the effects of search on presence such that people who were highly intolerant of uncertainty experienced less presence when they engaged in searching than low IU participants. Results suggest researchers should consider the potential consequences of IU in limiting the development of a vital well-being resource, presence of meaning

Bose-Einstein Condensation of Long-Lifetime Polaritons in Thermal Equilibrium

Exciton-polaritons in semiconductor microcavities have been used to demonstrate quantum effects such as Bose-Einstein condensation, superfluity, and quantized vortices. However, in these experiments, the polaritons have not reached thermal equilibrium when they undergo the transition to a coherent state. This has prevented the verification of one of the canonical predictions for condensation, namely the phase diagram. In this work, we have created a polariton gas in a semiconductor microcavity in which the quasiparticles have a lifetime much longer than their thermalization time. This allows them to reach thermal equilibrium in a laser-generated confining trap. Their energy distributions are well fit by equilibrium Bose-Einstein distributions over a broad range of densities and temperatures from very low densities all the way up to the threshold for Bose-Einstein condensation. The good fits of the Bose-Einstein distribution over a broad range of density and temperature imply that the particles obey the predicted power law for the phase boundary of Bose-Einstein condensation

Observation of quantum depletion in a nonequilibrium exciton-polariton condensate

The property of superfluidity, first discovered in liquid 4He, is closely related to Bose-Einstein condensation (BEC) of interacting bosons. However, even at zero temperature, when one would expect the whole bosonic quantum liquid to become condensed, a fraction of it is excited into higher momentum states via interparticle interactions and quantum fluctuations -- the phenomenon of quantum depletion. Quantum depletion of weakly interacting atomic BECs in thermal equilibrium is well understood theoretically but is difficult to measure. This is even more challenging in driven-dissipative systems such as exciton-polariton condensates(photons coupled to electron-hole pairs in a semiconductor), since their nonequilibrium nature is predicted to suppress quantum depletion. Here, we observe quantum depletion of an optically trapped high-density exciton-polariton condensate by directly detecting the spectral branch of elementary excitations populated by this process. Analysis of the population of this branch in momentum space shows that quantum depletion of an exciton-polariton condensate can closely follow or strongly deviate from the equilibrium Bogoliubov theory, depending on the fraction of matter (exciton) in an exciton-polariton. Our results reveal the effects of exciton-polariton interactions beyond the mean-field description and call for a deeper understanding of the relationship between equilibrium and nonequilibrium BECs.Comment: 18 pages, 5 figures, with supplementary informatio