Bosonic statistics enhance Maxwell's demon in photonic experiment

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.

💡 Research Summary

The paper presents the first experimental verification of a long‑standing theoretical prediction that bosonic (indistinguishable) particles enable a Maxwell‑demon–type protocol to generate larger non‑equilibrium gradients than distinguishable particles. The authors use a fully programmable linear‑optics platform based on a reconfigurable silicon‑nitride photonic processor. Single photons are generated by spontaneous parametric down‑conversion; three photons are injected into an M‑mode interferometer that implements a Haar‑random unitary transformation. By controlling the relative arrival times of the photons, the experiment toggles between a regime of perfect indistinguishability (bosons) and a regime where the photons are rendered distinguishable (classical statistics).

The theoretical background rests on the quantum version of Maxwell’s demon, originally formulated by Szilard and later quantified by Kim et al. (2011). In that framework, a demon measures a particle‑number imbalance between two halves of a box and, conditioned on the outcome, swaps the halves. Because bosons tend to bunch, the expected particle‑number gradient (and thus the temperature difference) is larger for bosons than for distinguishable particles; fermions would produce the smallest gradient. The authors extend the two‑particle analysis of Kim et al. to arbitrary particle numbers and embed it in the context of linear‑optical quantum thermodynamics, where Haar‑averaged linear optics drives a multimode system into a locally thermal state with an effective temperature (T = \frac{E_{\nu}}{k_B}\big