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Josephson dynamics, spontaneous symmetry breaking and quantum criticality are fascinating physical phenomena that can be realized today in coupled dissipative optical cavities with nonlinear interactions. Among the different experimental test-beds, photonic crystal coupled nanocavities operating in the laser regime are outstanding systems since nonlinearity, gain/dissipation and intercavity coupling can be judiciously tailored [1].
Complex photon statistics is inherent to the nature of nanolasers due to the presence of strong spontaneous emission noise. Yet, although most common scenarios emerge from quasi-dynamical equilibrium where the gain nearly compensates for losses, little is known about far-from-equilibrium statistics resulting, for instance, from a rapid variation of a parameter or "quench".
Our nanolasers are fabricated in suspended 2D InP-based Photonic Crystal membranes, and studied as a function of pump power and coupling strength. The modification of coupling strength is obtained by an original engineering procedure that allows us to tune the coupling strength between the nanocavities without affecting the nanolaser performance [1].
Under short (100 ps) pulse pumping, the strongly coupled laser nanocavity system exhibits two modes: a strong lasing mode, which has an anti-symmetric energy distribution, and a weak nonlasing one, possessing a symmetric energy distribution. We implement a simple experimental technique –single pulse energy detection scheme– that allows us to measure the statistical distributions of the photon number of both modes simultaneously. In particular, we analyze the photon number distributions of the weak one and link, using a mean field model, both the emergence of fat tails in the distributions and the superthermal nature of the emission through second order correlation (g2) measurements. We conclude that transient dynamics after quench, when projected onto the nonlasing mode, generically exhibit long-tailed superthermal light.
Such an optical quench mechanism is akin to the fast cooling of a suspension of Brownian particles under gravity, with the inverse temperature of the reservoir playing the role of the intracavity intensity. We show that passing through the lasing threshold corresponds to an abrupt decrease of the contribution of spontaneous emission —that plays the role of an effective temperature— during which the statistics of the nanolaser trajectories in phase space are dominated by nonlinear transport.
Probability density functions enabled the experimental quantification of the distance from thermal equilibrium –and hence the degree of residual order– via the thermodynamic entropy. This allowed us to further detect mixing of thermal states and coherent broken parity phases, which are beyond the simple Brownian particle description [3].
REFERENCES
1. Hamel, P., et al., “Spontaneous mirror-symmetry breaking in coupled PhC nanolasers,” Nat. Phot., Vol. 9, 2015.
2. Marconi, M., et al., “Asymmetric mode scattering in strongly coupled photonic crystal nanolasers,” Optics Letters, Vol. 41, 5628, 2016.
3. Marconi, M., et al, “Quenched phases in strongly coupled dissipative optical cavities. ” arXiv preprint arXiv:1706.02993.
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