The ability to control and manipulate light with light is crucial for optical information and communication technology. However, all-optical information processing is hindered by the absence of interactions between photons in linear materials. Nonlinear materials mediate effective photon-photon interactions, but require large light intensity. Optical resonators store and confine light for many optical cycles, which increases the interaction time and reduces the nonlinearity threshold. However, monolithic optical resonators have limited variability of the intra-cavity medium. Instead, a wide variety of materials can be easily integrated in tunable open-access microcavities, making them an ideal platform for exploring novel materials for nonlinear optics. In this thesis, we present experiments using coherently driven tunable open-access microcavities hosting either oil or a perovskite semiconductor. In Chapter 2 we demonstrate steady-state room-temperature superfluidity of photons in an oil-filled cavity, and reveal how the fluid dynamics are influenced by the nonlocality of the effective interactions mediated by the oil. Chapters 3 and 4 describe experiments using a halide perovskite semiconductor in an open-access microcavity in a closed-cycle cryostat. We demonstrate continuous-wave nonlinearity in the halide perovskite material through optical bistability, and reveal signatures of a phase transition in the temperature dependence of the nonlinearity strength. Next we investigate the emergence of irreversibility in the bistable switching of our perovskite cavity. Finally, we present in Chapter 5 experimental observations of fast nonlinearity-enabled oscillations in the light intensity, that occur despite the slowness of thermal nonlinearity of the oil.
The ability to control and manipulate light with light is crucial for optical information and communication technology. However, all-optical information processing is hindered by the absence of interactions between photons in linear materials. Nonlinear materials mediate effective photon-photon interactions, but require large light intensity. Optical resonators store and confine light for many optical cycles, which increases the interaction time and reduces the nonlinearity threshold. However, monolithic optical resonators have limited variability of the intra-cavity medium. Instead, a wide variety of materials can be easily integrated in tunable open-access microcavities, making them an ideal platform for exploring novel materials for nonlinear optics. In this thesis, we present experiments using coherently driven tunable open-access microcavities hosting either oil or a perovskite semiconductor. In Chapter 2 we demonstrate steady-state room-temperature superfluidity of photons in an oil-filled cavity, and reveal how the fluid dynamics are influenced by the nonlocality of the effective interactions mediated by the oil. Chapters 3 and 4 describe experiments using a halide perovskite semiconductor in an open-access microcavity in a closed-cycle cryostat. We demonstrate continuous-wave nonlinearity in the halide perovskite material through optical bistability, and reveal signatures of a phase transition in the temperature dependence of the nonlinearity strength. Next we investigate the emergence of irreversibility in the bistable switching of our perovskite cavity. Finally, we present in Chapter 5 experimental observations of fast nonlinearity-enabled oscillations in the light intensity, that occur despite the slowness of thermal nonlinearity of the oil.
Understanding the effect of noise on light’s behavior is crucial, as light plays a central role in the study of many systems. This thesis explores the interplay between light, matter, and noise, demonstrating how this interaction can lead to fascinating phenomena and practical applications in sensing, signal transmission, and computing. Chapter 1 provides an overview of the history of noise in physical systems and fundamental discoveries that shaped our understanding of noisy systems. The focus then shifts to optical systems, particularly nanophotonic sensors and devices, and introduces a basic model describing nonlinear optical resonators, pivotal in modern photonics. Chapter 2 delves into the stochastic dynamics of light in a coherently-driven Kerr-nonlinear optical cavity, drawing analogies between light dynamics in the cavity and Brownian particles in a scalar potential. While this analogy holds in linear, on-resonance conditions, it breaks down in nonlinear or off-resonance scenarios due to non-conservative forces. An effective equilibrium description is proposed, providing accurate results in limited regimes but failing in deep bistability. This breakdown is marked by significant changes in the intra-cavity field fluctuation spectrum. Our findings lay the groundwork for an effective thermodynamic description of coherently driven cavities, bridging stochastic thermodynamics and resonant optics. Chapter 3 introduces an innovative optical sensing approach using a single-mode Kerr-nonlinear resonator, achieving exceptional precision at a square-root singularity. This sensor leverages the dynamic hysteresis of the resonator, with intensity splitting at hysteresis endpoints scaling with the square root of perturbation strength. This novel method enhances sensing precision even in noisy environments and overcomes the traditional trade-off between precision and averaging time. Chapter 4 presents the first experimental demonstration of non-Markovian stochastic resonance (SR), showing how memory effects from a non-instantaneous nonlinear response can broaden the SR bandwidth significantly. We imprint a signal on a laser by modulating the cavity length of a thermo-optical cavity. SR is evidenced by a peak in the signal-to-noise ratio as a function of noise variance. Our insights suggest broader implications for noise-assisted processes in various natural and engineered systems with a non-instantaneous response. Chapter 5 and 6 explore complex dynamics emerging from memory effects in nonlinear resonators. Memory effects lead to stable limit cycles and self-sustained oscillations, both in nonlinear optical and mechanical systems. We demonstrate that memory effects can greatly enhance the ability of a nonlinear mechanical resonator to harvest energy from ambient vibrations. Chapter 7 challenges the belief that enhancing clock precision requires more energy, demonstrating that precision can be altered at constant energy by varying laser-cavity detuning in a laser-driven thermo-optical dimer. Stochastic simulations show that detuning changes the limit cycle's confining potential and the phase diffusion strength, explaining the changes in precision. Finally, Chapter 8 demonstrates enhanced performance of an all-optical flip-flop by leveraging noise, reducing switching energy by approximately 90% while maintaining 95% reliability. This approach uses noise as a resource, improving energy efficiency and reliability in optical systems and potentially extending to other platforms. Our findings pave the way for computational devices utilizing ambient fluctuations as a resource.
Superfluidity—frictionless flow—has been observed in various physical systems such as liquid helium, cold atoms, and exciton polaritons. Superfluidity is usually realized by cooling and suppressing all dissipation. Here we challenge this paradigm by demonstrating signatures of superfluidity, enabled by dissipation, in the flow of light within a room-temperature oil-filled cavity. Dissipation in the oil mediates effective photon-photon interactions which are noninstantaneous and nonlocal. Such interactions were expected to severely limit the emergence of superfluidity in conservative photonic systems. Surprisingly, when launching a photon fluid with sufficiently high density and low velocity against an obstacle in our driven-dissipative cavity, we observe a record suppression of backscattering. Our experiments also reveal the reorganization dynamics of photons into a nonscattering steady state and a qualitatively changing behavior of the optical phase as light propagates around the obstacle. The phase is locked between the laser and the obstacle but evolves with the intensity in the wake of the obstacle where the density of the photon fluid and its mean-field interaction energy decrease. Using a generalized Gross–Pitaevskii equation for photons coupled to a thermal field, we model our experiments and elucidate how the noninstantaneous and nonlocal character of interactions influences the suppression of scattering associated with superfluidity. Beyond providing the first signatures of cavity photon superfluidity, and of any superfluid both at room temperature and in steady state, our results pave the way for probing photon hydrodynamics in arbitrary potential landscapes using structured mirrors. Published by the American Physical Society 2024
The idea of making photons effectively interact has attracted a lot of interest in recent years, for several reasons. Firstly, since photons do not naturally interact with each other, it is of fundamental physical interest to see what kind of medium can mediate interactions between these fundamental and non-interacting particles, and to what extent. Secondly, photonics is a major candidate for future quantum technology, due to the easy manipulation, readout, and transport of photons, which makes them ideal for quantum information processing. Finally, achieving strong and tunable interactions among photons would open up an avenue for exploring the many-body physics of a fluid of light. In this thesis, we will see how a cavity formed of subwavelength lattices of two-level atoms can confine photons to a nonlinear environment for a long time, such that emitted photons have accumulated strong correlations both among their momenta and in their temporal statistics. This speaks of a strong photon-photon interaction within the cavity. The nonlinearity originates in the saturability of individual atoms, and the lattice structure results in a strong and low-loss collective interaction with light. While a single atomic lattice has a largely linear nature, as the effect of individual atoms washes out in the collective response, the confining geometry of the cavity means the photons are exposed to the underlying saturability of the atoms for such a long time that the nonlinearity is revived. We will analyse this system both using a standard input-output formalism, where the nonlinear physics of the system is handled numerically, and a powerful Green's function-based approach that allows for exact analytical results with no additional approximations. This analytical description has the potential to lead to an exact study of the many-body physics of interacting photons in a two-dimensional setting.
In this thesis we study ultrafast all-optical switching of microcavities. We employ the electronic Kerr effect to switch the resonance frequency of microcavities operating at telecom wavelengths. We observe the fastest possible switching of a microcavity resonance within 300 fs. The switching speed is only determined by the cavity storage time; only limited by the speed of light and not by material related relaxation properties. For the first time, we derive and measure the non-degenerate three-photon absorption coefficient of GaAs. Using the measured nondegenerate two- and three-photon absorption coefficients we estimate that the trigger laser only lose 22 aJ/µm2 at each switch event, which is a record level of minimum energy loss per switch event. We achieve repeated switching of microcavities within 700 fs, corresponding to THz rates. Therefore to best of our knowledge, we have broken the THz clock rate barrier experimentally using semiconductor cavities for the first time. The THz clock rate that we achieve can be a solution for information technology that is exploring ways to meet the growth rate of the computational demand. The color of light is a main visual perception of light for humans. Indeed, a simple measure for the color of light is given by its frequency since frequency of light is invariant from one medium to another. Although the propagation of light is strongly modified using nanostructures such as photonic crystals and microcavities, the frequency of light stays constant in these structures as well. The color of light can be changed in a nonlinear process or by absorption and re-emission. Using microcavities light is conveniently confined in space and then by dynamical control the medium can be changed to act as a nonlinear medium for light. Remarkably, we show that during the switching of cavities we achieve both up and down frequency conversion of light. The frequency conversion that we observe is a result of the instantaneous refractive index change achieved using the electronic Kerr effect. We achieve repeated frequency conversion at THz rates and generate blue- and red-shifted light pulses at this rate.
In this work we give an overview on a couple of decades of theoretical and experimental research on the many-body physics of driven-dissipative quantum fluids of light in optical cavities. These systems consist of a large number of photons enclosed in a cavity device where spatial confinement induces a finite photon mass and the Kerr optical nonlinearity of the cavity material mediates finite photon-photon interactions. Differently from standard Bose gases of material particles like liquid Helium or ultracold atomic gases, photons are inevitably subject to radiative and/or non-radiative losses, which must be compensated by some pumping mechanism. As a result, the properties of the steady state are not imposed by a thermal equilibrium condition, but are determined by a dynamical interplay of pumping and losses. Among the many collective phenomena that are observed in these systems, we focus here on the collective excitations around the steady state and we characterize the impact of the driven-dissipative nature of the gas on their properties, in particular on their dispersion relation. Different pumping configurations give very different behaviors: a specific discussion is provided for the most important configurations used in the experiments. Observable consequences of the various forms of the dispersion -gapped, gapless, sonic, band-sticking, diffusive Goldstone- are illustrated with a special eye towards their consequences on the superfluidity properties. We conclude the article with a presentation of a few research avenues that we personally find most exciting for the next years, namely the osbervable consequences of the concurrently superfluid and solid nature of supersolid states of light and the collective dynamics of quantum correlated states of strongly interacting photon gases in the presence of strong nonlinearities, in particular Mott insulator states.