Cristiano Ciuti

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Down-conversion of a single photon as a probe of many-body localization

Cristiano Ciuti

Decay of a particle into more particles is a ubiquitous phenomenon to interacting quantum systems, taking place in colliders, nuclear reactors or solids. In a nonlinear medium, even a single photon would decay by down-converting (splitting) into lower-frequency photons with the same total energy1, at a rate given by Fermi's golden rule. However, the energy-conservation condition cannot be matched precisely if the medium is finite and only supports quantized modes. In this case, the fate of the photon becomes the long-standing question of many-body localization, originally formulated as a gedanken experiment for the lifetime of a single Fermi-liquid quasiparticle confined to a quantum dot(2). Here we implement such an experiment using a superconducting multimode cavity, the nonlinearity of which was tailored to strongly violate the photon-number conservation. The resulting interaction attempts to convert a single photon excitation into a shower of low-energy photons but fails owing to the many-body localization mechanism, which manifests as a striking spectral fine structure of multiparticle resonances at the standing-wave-mode frequencies of the cavity. Each resonance was identified as a many-body state of radiation composed of photons from a broad frequency range and not obeying Fermi's golden rule theory. Our result introduces a new platform to explore the fundamentals of many-body localization without having to control many atoms or qubits(3-9).

NATURE PORTFOLIO2023

Quantum Critical Regime in a Quadratically Driven Nonlinear Photonic Lattice

Vincenzo Savona, Fabrizio Minganti, Riccardo Rota, Cristiano Ciuti

We study an array of coupled optical cavities in the presence of two-photon driving and dissipation. The system displays a critical behavior similar to that of a quantum Ising model at finite temperature. Using the corner-space renormalization method, we compute the steady-state properties of finite lattices of varying size, both in one and two dimensions. From a finite-size scaling of the average of the photon number parity, we highlight the emergence of a critical point in regimes of small dissipations, belonging to the quantum Ising universality class. For increasing photon loss rates, a departure from this universal behavior signals the onset of a quantum critical regime, where classical fluctuations induced by losses compete with long-range quantum correlations.

AMER PHYSICAL SOC2019

Down-conversion of a single photon as a probe of many-body localization

Quantum Critical Regime in a Quadratically Driven Nonlinear Photonic Lattice

Comment on "Linear Wave Dynamics Explains Observations Attributed to Dark Solitons in a Polariton Quantum Fluid"

Comment on "Linear Wave Dynamics Explains Observations Attributed to Dark Solitons in a Polariton Quantum Fluid"

Down-conversion of a single photon as a probe of many-body localization

Quantum Critical Regime in a Quadratically Driven Nonlinear Photonic Lattice