Experimental simulation of a non-equilibrium quantum piston on a programmable photonic quantum computer
Govind Krishna, Rohan Yadgirkar, Balakrishnan Krishnakumar, Andrea Cataldo, Ze-Sheng Xu, Johannes W. N. Los, Val Zwiller, Ali W. Elshaari, Ali W. Elshaari
Quantum thermodynamics examines energy exchange and work in microscopic systems. These processes are difficult to investigate for identical particles because individual particles cannot be tracked separately and quantum interference affects their collective behavior. Here, we use two indistinguishable photons in a programmable photonic processor to simulate a quantum piston, in which identical bosons are confined by a moving boundary. Energy levels are represented by optical modes, and measured transitions between these modes are used to reconstruct the work distribution. The results show how driving speed and bosonic interference arising from particle indistinguishability influence work statistics and energy dissipation. This approach provides a platform for studying non-equilibrium quantum thermodynamics.
Quantum thermodynamics examines energy exchange and work in microscopic systems. These processes are difficult to investigate for identical particles because individual particles cannot be tracked separately and quantum interference affects their collective behavior. Here, we use two indistinguishable photons in a programmable photonic processor to simulate a quantum piston, in which identical bosons are confined by a moving boundary. Energy levels are represented by optical modes, and measured transitions between these modes are used to reconstruct the work distribution. The results show how driving speed and bosonic interference arising from particle indistinguishability influence work statistics and energy dissipation. This approach provides a platform for studying non-equilibrium quantum thermodynamics.
Quantum fluctuation relations provide a microscopic formulation of thermodynamics beyond equilibrium, but experimentally accessing many-body quantum work statistics remains an outstanding challenge. The quantum piston constitutes a canonical model of boundary-driven nonequilibrium dynamics, where finite-time deformation of a confining potential generates non-adiabatic transitions, dissipation and irreversibility. Here we experimentally simulate the nonequilibrium dynamics of a two-boson quantum piston on a programmable photonic quantum computer. Using two indistinguishable photons, we encode a truncated piston propagator through a quasi-unitary embedding, with an ancilla mode representing leakage into higher-energy states outside the resolved manifold. This architecture enables direct reconstruction of thermodynamic transition statistics for both expansion and compression protocols as functions of driving speed and final trap length. We observe the crossover from quasi-adiabatic to strongly non-adiabatic evolution and show that bosonic interference restructures the resulting two-particle Fock-state populations and work distributions. The measured statistics are in close agreement with theoretical predictions and satisfy the Jarzynski equality across expansion and compression protocols for cyclic driving we further quantify irreversibility through dissipated work and state overlap. Our work identifies programmable photonic quantum hardware as a powerful platform for simulating nonequilibrium quantum thermodynamics and for experimentally resolving how indistinguishability and many-body interference shape quantum work, dissipation and entropy production.
Maxwell's demon elucidates the value of information in thermodynamics, using measurement and feedback: he evolves an equilibrated gas into a nonequilibrium state, from which one might extract work. The demon can evolve the system farther from equilibrium, on average, if the particles obey Bose-Einstein statistics than if they are distinguishable. We experimentally support this decade-and-a-half-old prediction by comparing indistinguishable with distinguishable photons. We use a fully programmable linear-optics platform, whose local photon statistics were shown recently to behave thermally. Our demon nondestructively measures the number of photons in a subset of the modes. Guided by the outcome, he conditionally interchanges the measured and unmeasured modes. This interchange creates a positive temperature difference between a mode in a particular subset and a mode in the other. The temperature difference is greater, on average, if the photons are indistinguishable. This result bolsters a long-standing prediction about the interplay among thermodynamics, information, and quantum particle statistics. Additionally, this work suggests a thermodynamic means of weakly validating boson-sampling platforms.
This thesis provides a fundamental characterization of photon gases in nanostructured microcavities, investigating the underlying physics that may eventually support new forms of information processing. While the transition from electronic to photonic architectures is often motivated by the physical limits of semiconductors, such as the ’power wall’ and carrier scattering, realizing these systems requires a deep understanding of quantum dynamics. This work addresses these fundamental questions by examining collective dynamics in condensate networks, single-particle tunneling, and the thermodynamics of isolated quantum gases. The first part of this work explored the collective behavior of coupled photon Bose-Einstein condensates as a preliminary step toward building larger computational networks. By experimentally realizing a negatively coupled triplet of condensates, this study demonstrated that the system resides in a frustrated state. Although this represents only a fundamental building block, it serves as a necessary milestone for the potential scaling of these networks into larger Hamiltonian simulators. Future research in this direction will be required to implement reconfigurable coupling geometries and to determine if these analog systems can effectively compete with classical heuristic algorithms for complex optimization tasks. The second part of this research was the investigation of particle motion within classically forbidden regions. Understanding the transport mechanisms that govern phase coherence is essential for any platform where particles must move between defined sites. Using a measurement scheme based on two coupled waveguides, where population transfer acts as a clock to determine particle speed, evanescent states in a reflective potential step were analyzed. The results revealed an inverse relationship between energy and speed, where lower energy leads to higher speeds within the potential. These findings agree with the Büttiker and Landauer tunneling time framework, suggesting that the effective speed within the barrier is governed by the interaction between phase and amplitude gradients. Extending this waveguide clock methodology to more complex landscapes, such as periodic barriers or time-dependent potentials, will clarify the role of amplitude gradients in particle transport. This understanding directly supports the design of high-speed quantum electronic components, where evanescent states play a major role. The final section examined the emergence of thermodynamic behavior from an isolated quantum system. This was achieved by studying a photon gas within a gravitational wedge billiard. Experimental analysis of spatial autocorrelation functions showed that the microcanonical standard deviation decreases as the system approaches the semiclassical limit, which supports the Eigenstate Thermalization Hypothesis. Furthermore, thermodynamic phase transitions in the microcanonical density of states, surface entropy, and surface temperature were observed. Because the gas is two-dimensional, these transitions were driven entirely by the geometry of the billiard. The quantum virial theorem was also qualitatively confirmed. Future research can build on these results to investigate the transition from ergodicity to many-body localization within photon gases, and to study how dimensionality and boundary conditions dictate the macroscopic thermodynamic properties of a quantum system. In conclusion, the findings described in this thesis contribute to a broader scientific effort to understand and control light as a state of matter. By investigating the fundamental mechanisms of tunneling and thermalization, this work provides the physical insights necessary to move beyond the constraints of current electronic architectures. While the development of large-scale photonic simulators remains a long-term objective, the methodologies and theoretical frameworks established here offer a cohesive narrative on how the structural control of light can lead to the observation and utilization of complex quantum phenomena.
Quantum many-body systems coupling photonic and matter degrees of freedom are ideal for the realization of driven open quantum dynamics at the intersection of quantum optics and condensed matter. They offer the possibility to address unresolved issues regarding a variety of non-equilibrium phenomena. In such open systems, the substructure of the reservoir then introduces further timescales that may enter into competition with rapid system processes, raising long-standing questions about the influence of non-Markovian effects on dynamics and equilibration out of equilibrium. \n \nThe central result of this thesis is a general pseudo-particle technique that can be applied to a large class of models of interacting light and matter and allows for realistic and efficient simulations of the full non-equilibrium dynamics of these systems. Since organic molecules, as used in experiments with photon condensates, which provide the main area of application for this thesis, possess an electronic transition coupled to vibrational phonon modes, we construct a representation where an auxiliary boson is assigned to each vibrational state of the molecule. An operator constraint then enforces single occupation across all of these states. We emphasize that we implement the operator constraint exactly and that we are the first to apply a faithful auxiliary-boson representation to open quantum systems. \n \nAs a contribution to bridging the gap between well-understood equilibrium and less explored non-equilibrium phenomena, we investigate photon condensates as they are driven away from equilibrium. The earliest signs of the non-equilibrium character of the driven-dissipative photon gas do not manifest in the spectrally resolved intensity distribution but in the time dependence of the intensity fluctuations. The energy flow through the system renders it {non-Hermitian} and induces a novel driven-dissipative transition in the second-order correlations characterized by the appearance of exceptional points. If only the static intensity spectrum is monitored, this transition remains unnoticed, as does the fact that the system is not truly in equilibrium. Non-Markovian effects due to the non-separability of system and reservoir timescales are shown to become important far away from equilibrium. Furthermore, we derive a novel photon-condensate Gross-Pitaevskii equation, which is capable of describing photo-molecular coherence. Such effects cannot be captured by existing theories and hence serve as a validation of our auxiliary-boson method. These results provide a building block to understanding the properties of the photon condensates in stationary operation where they act as fluctuating light sources. In the future, lattice systems of coupled photon condensates may lead to the appearance of novel driven-dissipative phases of light.
Quantum-mechanical particles in a confining potential interfere with each other while undergoing thermodynamic processes far from thermal equilibrium. By evaluating the corresponding transition probabilities between many-particle eigenstates we obtain the quantum work distribution function for identical bosons and fermions, which we compare with the case of distinguishable particles. We find that the quantum work distributions for bosons and fermions significantly differ at low temperatures, while, as expected, at high temperatures the work distributions converge to the classical expression. These findings are illustrated with two analytically solvable examples, namely the time-dependent infinite square well and the parametric harmonic oscillator.
This dissertation explores the use of single photons in integrated photonic circuits as a platform for quantum computation and quantum simulation. In the noisy intermediate-scale quantum (NISQ) era, photonic implementations of boson sampling provide one of the most promising routes to demonstrating quantum advantage, while also enabling insight-driven experiments that probe many-body interference and computational complexity. The first part of the thesis is devoted to the hardware development and characterization of programmable silicon nitride photonic processors. We demonstrate large-scale multi-photon interference in a 20-mode universal processor, establishing the potential of integrated photonics for scaling up boson sampling experiments. In parallel, we introduce a validation protocol based on detector binning, implemented on a 12-mode predecessor of the device. Together, these studies advance the photonic platform itself, focusing on scalability, versatility, and benchmarking, rather than direct applications. The second part turns to quantum simulation. We first present a photonic simulation of a spin-foam amplitude from loop quantum gravity, illustrating how multi-photon interference can provide a testbed for problems in fundamental physics. We then implement a particle-number-difference Maxwell demon using conditional operations on photon subsets in a multi-mode interferometer. This experiment probes the link between thermodynamics and information theory, showing how a photonic platform with single-photon resolution and quantum interference can be used to explore information-driven control of physical systems. The final part addresses quantum computation, where we demonstrate a boson-sampling-accelerated Monte Carlo integrator. This hybrid quantum–classical algorithm represents one of the few proposals to extend boson sampling toward practical applications while plausibly retaining its computational hardness. We validate the method in a proof-of-principle experiment reproducing perturbative corrections in a model inspired by Efimov physics. Altogether, the results presented in this thesis position integrated photonics as both a scalable hardware platform for multi-photon experiments and a versatile tool for advancing quantum simulation and computation.