arXiv subjects

Filippo Ferrari

Publications and source records attributed to Filippo Ferrari.

12 recordsLinked to original sources

arXiv2026

Dissipation-induced Sachdev-Ye-Kitaev physics in many-body cavity quantum electrodynamics

We show that cavity quantum electrodynamics (QED) devices can realize dissipative Sachdev-Ye-Kitaev (SYK) physics, a paradigmatic setting for quantum chaos in open many-body systems. Ultracold fermions with disordered, all-to-all cavity-mediated interactions provide two complementary routes: atomic spontaneous emission in a single-mode cavity and photon leakage from a multimode cavity. Strikingly, both converge to the same non-Hermitian random-matrix universality despite originating from integrable and chaotic closed-system limits, respectively. In the single-mode case, dissipation therefore creates quantum chaos from an integrable Hamiltonian. We trace this convergence to a tunable growth in dissipative rank, controlled, respectively, by the Lamb-Dicke parameter and the cavity-mode spacing. The resulting chaos leaves a dynamical fingerprint: a crossover from long-lived prethermal memory to rapid thermalization, visible in single-atom-resolved densities.

quant-ph↗

arXiv2026

Dissipative phase transitions and chaos in two-photon driven quantum optomechanics

We investigate nonequilibrium criticality and chaos in a two-photon-driven optomechanical system. The parametric drive preserves a discrete $\mathbb{Z}_2$ symmetry of the optical field, while radiation-pressure coupling transfers the resulting nonlinear dynamics to a mechanical oscillator. Combining semiclassical stability analysis, exact Liouvillian spectra, and stochastic quantum trajectories, we show that this driven-dissipative optomechanical model supports both first- and second-order dissipative phase transitions. At negative detuning a second-order transition yields spontaneous breaking of the cavity-parity symmetry in the thermodynamic limit. At positive detuning the same symmetry breaking coexists with a first-order transition, signaled by metastability and by an additional symmetric Liouvillian mode. At stronger pump power the mean-field dynamics loses all stable fixed points and develops limit cycles and chaotic attractors with positive Lyapunov exponent. Quantum trajectories in this regime display chaotic-like motion, enhanced steady-state entropy, and delocalization over many entropic Liouvillian modes. These results establish two-photon-driven optomechanics as a platform where dissipative criticality, symmetry breaking, and quantum signatures of chaos emerge within the same experimentally accessible setting.

quant-ph↗

arXiv2026

Controlling many-body quantum chaos in a dissipative optical cavity

Cavity quantum electrodynamics (QED) with ultracold fermions provides a promising platform for realizing many-body quantum chaos through disordered, photon-mediated long-range interactions. Such setups are inherently open and are therefore subject to dissipation arising from cavity photon loss and atomic spontaneous emission. In this article, we study the driven-dissipative dynamics of a typical cavity QED setting including controllable disorder and long-range interactions. We find that the two dissipation sources have qualitatively different structures. Cavity loss reduces to a single dephasing channel, whereas spontaneous emission in the experimentally relevant regime generates a collection of nonlocal dephasing channels. Cavity-induced dephasing preserves signatures distinguishing integrable from chaotic Hamiltonian dynamics in observables that depend linearly on the density matrix, while spontaneous emission suppresses these signatures. By contrast, quantities that probe the structure of the many-body state, such as the entanglement entropy, are strongly affected by both dissipation mechanisms. Assuming experimentally realistic parameters, we derive quantitative constraints for the observation and control of many-body quantum chaos in cavity-QED platforms.

quant-ph↗

arXiv2026

Bit flips are erasures in dissipative cat qubits

Autonomous quantum error correction (QEC) stabilizes a logical manifold through dissipative events that emit into output channels, which are typically accessible to measurement. These signals are often discarded, and whether they contain useful information about logical failures remains generally unclear. Using quantum trajectories, we show that in dissipatively stabilized cat qubits bit flips are not silent logical errors: each flip is accompanied by a strong, time-localized photon burst from the dissipative buffer. Photon counting and homodyne monitoring can therefore herald the loss of logical information without interrupting the autonomous stabilization: bit flips in dissipative cat qubits are erasures. More broadly, our results show that the emitted signals of engineered reservoirs can act as built-in failure monitors for autonomous QEC, turning rare logical faults into erasures available to a decoder and reducing fault-tolerance overhead. To this end, we develop a general framework, based on past quantum states and number-resolved master equations, to quantify the detectability of such logical failures in autonomous QEC from the emitted signal.

quant-ph↗

arXiv2026

Density Wave Ordering with Disordered Ultracold Fermions in Optical Cavities

We investigate the interplay between cavity-induced density-wave ordering and controllable disorder in a trapped two-dimensional gas of ultracold fermions. The atoms are dispersively coupled to an optical cavity and transversely driven by a pump beam, while an additional speckle beam spatially modulates the atom-light coupling through an AC-Stark shift of the atomic transition. In momentum space, this disorder converts the usual coupling between the cavity mode and a discrete set of density-wave Fourier components into a coupling to a continuum of fermionic density modes, weighted by the spectrum of the speckle pattern. Using linear response theory, we derive the superradiant threshold and show that the disordered interaction renormalizes the effective light-matter coupling, lowering the critical pump strength on average, with the threshold becoming self-averaging for short speckle correlation lengths. We complement this analysis with a numerical mean-field treatment that gives access to the intracavity photon number and to the real-space fermion density across the transition. These results confirm that the disorder shifts the photonic phase boundary and, above threshold, distorts the density-wave crystal by populating Fourier components beyond those selected by the clean cavity geometry. Our findings identify both the emitted cavity light and in situ density images as probes of engineered disorder in fermionic matter coupled to optical cavities.

cond-mat.quant-gas↗

arXiv2026

Bit flips, saturation, and quantum chaos in dissipative cat qubits

Bosonic cat qubits promise hardware-efficient quantum error correction because their logical bit-flip rate is exponentially suppressed with the photon number of the cat state. However, several experiments report a saturation of this suppression at large photon numbers, thus limiting the achievable protection. Combining quantum-trajectory simulations, semiclassical analysis, and Liouvillian spectral methods, we investigate the properties of bit flips in realistic dissipative cat qubits, where a memory mode hosting quantum information interacts with a dissipative buffer cavity. We show that bit flips are dynamical processes inherently involving both the memory and buffer, and therefore cannot be captured by single-mode approximate descriptions. We identify a reflection symmetry, resulting in a phase-locking condition at the semiclassical level and for quantum trajectories, as the main requirement for regular bit-flip dynamics. Its breakdown is the origin of the saturation, and we find that it occurs when two conditions are met. First, the adiabatic approximation, where the state of the buffer instantaneously follows that of the memory, must not be valid, which typically happens at large photon numbers. Second, key parameters such as the cross-Kerr interaction and dephasing must be present, leading to irregular dynamics in which memory fluctuations are amplified by the buffer during bit flips. In this regime, we find that bit flips manifest as chaotic bursts within otherwise regular dynamics, as evidenced by both changes in the topology of quantum trajectories and in the Liouvillian spectrum and its associated eigenmodes involved in these switching events. Finally, we verify our predictions against experimental data, highlighting the detrimental role of dissipative chaotic behavior in bosonic error-correcting codes.

quant-ph↗

arXiv2026

Floquet Dissipative Phase Transitions

Dissipative phase transitions (DPTs) are traditionally characterized through the spectrum of a time-independent Liouvillian superoperator. However, this definition does not apply to time-periodic (Floquet) systems that cannot be exactly recast as time-independent problems. Here, we develop a general framework to characterize DPTs in time-periodic open quantum systems through the spectrum of the Floquet propagator. We first study driven-dissipative Kerr resonators, known to display a DPT, showing that counter-rotating terms in the drive shift the critical point and significantly change the time scales associated with the transition. We then investigate DPTs in the driven quantum Rabi model and its time-independent approximation, the driven Jaynes-Cummings model, finding that the Rabi model exhibits distinct critical features as the ultrastrong coupling regime is approached. Moreover, our Floquet analysis unveils the disappearance of the DPT in the deep strong coupling regime, due to light-matter decoupling. Our approach sets the stage for the study of dissipative criticality in a broad class of time-dependent open quantum systems.

quant-ph↗

arXiv2025

Chaos and quantum regimes in $n$-photon driven, dissipative bosonic chains

We investigate the steady-state dynamical regimes of boundary-driven, dissipative bosonic chains subjected to $n$-photon drives. Using the truncated Wigner approximation, we explore how multi-photon drives shape the interplay between quantum fluctuations, nonlinear interactions, and dissipative processes in such quantum systems. We identify two main regimes: a chaotic hydrodynamic regime characterized by the restoration of a local $\mathbb{U}(1)$ symmetry, photon saturation due to Kerr nonlinearity, and spatial prethermalization effects; and a non-chaotic resonant nonlinear wave (RNW) regime exhibiting sub-Poissonian photon statistics, persistent $\mathbb{Z}_n$ symmetry, and quantum-driven phase decoherence. Our findings reveal the universal nature of the hydrodynamic regime and highlight the RNW regime's sensitivity to boundary driving conditions, suggesting novel routes for quantum state engineering in driven-dissipative quantum devices. These results are experimentally relevant for state-of-the-art circuit quantum electrodynamics platforms.

quant-ph↗

arXiv2025

Chaos and thermalization in open quantum systems

The eigenstate thermalization hypothesis (ETH) provides a cornerstone for understanding thermalization in isolated quantum systems, linking quantum chaos with statistical mechanics. In this work, we extend the ETH framework to open quantum systems governed by Lindblad dynamics. We introduce the concept of Liouvillian stripe (spectral subset of the non-Hermitian Liouvillian superoperator) which enables the definition of effective pseudo-Hermitian Hamiltonians. This construction allows us to conjecture a Liouvillian version of ETH, whereby local superoperators exhibit statistical properties akin to ETH in closed systems. We substantiate our hypothesis using both random Liouvillians and a driven-dissipative quantum spin chain, showing that thermalization manifests through the suppression of coherent oscillations and the emergence of structureless local dynamics. These findings have practical implications for the control and measurement of many-body open quantum systems, highlighting how chaotic dissipative dynamics can obscure the system response to external probes.

quant-ph↗

arXiv2024

Chaotic and quantum dynamics in driven-dissipative bosonic chains

Thermalization in quantum many-body systems typically unfolds over timescales governed by intrinsic relaxation mechanisms. Yet, its spatial aspect is less understood. We investigate this phenomenon in the nonequilibrium steady state (NESS) of a Bose-Hubbard chain subject to coherent driving and dissipation at its boundaries, a setup inspired by current designs in circuit quantum electrodynamics. The dynamical fingerprints of chaos in this NESS are probed using semiclassical out-of-time-order correlators (OTOCs) within the truncated Wigner approximation (TWA). At intermediate drive strengths, we uncover a two-stage thermalization along the spatial dimension: phase coherence is rapidly lost near the drive, while amplitude relaxation occurs over much longer distances. This separation of scales gives rise to an extended hydrodynamic regime exhibiting anomalous temperature profiles, which we designate as a ``prethermal'' domain. At stronger drives, the system enters a nonthermal, non-chaotic finite-momentum condensate characterized by sub-Poissonian photon statistics and a spatially modulated phase profile, whose stability is undermined by quantum fluctuations. We explore the conditions underlying this protracted thermalization in space and argue that similar mechanisms are likely to emerge in a broad class of extended driven-dissipative systems.

quant-ph↗

arXiv2024

Landau-Zener without a Qubit: Unveiling Multiphoton Interference, Synthetic Floquet Dimensions, and Dissipative Quantum Chaos

Landau-Zener-St\"uckelberg-Majorana (LZSM) interference occurs when qubit parameters are periodically modulated across avoided level crossings. We explore this phenomenon in nonlinear multilevel bosonic systems, where interference is influenced by multiple energy levels. We fabricate two superconducting resonators with flux-tunable Josephson junction arrays. The first device, exhibiting weak nonlinearity, behaves like a linear resonator under weak driving but shows LZSM interference akin to two-level systems. With stronger driving, nonlinear effects alter the interference pattern. We theoretically demonstrate that merging LZSM peaks can lead to dissipative quantum chaos. In the second device, where nonlinearity exceeds photon-loss rates, we observe additional LZSM peaks from Kerr multiphoton resonances. Under Floquet theory, these resonances represent synthetic modes of coupled nonlinear cavities, revealing effective coupling as modulation parameters vary. Our findings advance the understanding of LZSM physics and emphasize the control of nonlinear Floquet states and the emergence of chaos in engineered systems, with significant implications for novel applications in quantum dynamics and quantum control.

quant-ph↗

arXiv2023

Dissipative Quantum Chaos unveiled by Stochastic Quantum Trajectories

We define quantum chaos and integrability in open quantum many-body systems as a dynamical property of single stochastic realizations, referred to as quantum trajectories. This definition relies on the predictions of random matrix theory applied to the subset of the Liouvillian spectrum involved in each quantum trajectory. Our approach, which we name spectral statistics of quantum trajectories (SSQT), enables a natural distinction between transient and steady-state quantum chaos as general phenomena in open setups. We test the generality and reliability of the SSQT criterion on several dissipative systems, further showing that an open system with a chaotic structure can evolve towards either a chaotic or integrable steady state. We apply our theoretical framework to two driven-dissipative bosonic systems. First, we study the driven-dissipative Bose-Hubbard model, an example of quantum simulator, clarifying the interplay of integrability, transient, and steady-state chaos across its phase diagram. Our analysis shows the existence of an emergent dissipative quantum chaotic phase, whereas the classical and semi-classical limits display integrable behavior. In this regime, chaos arises from the quantum and classical fluctuations associated with the dissipation mechanisms. Second, we investigate dissipative quantum chaos in the dispersive readout of a transmon qubit: a measurement technique ubiquitous in superconducting-based quantum hardware. Through the SSQT, we distinguish regimes where the performance of the measurement instrument can be connected to the integrable or chaotic nature of the underlying driven-dissipative bosonic system. Our work offers a general understanding of the integrable and chaotic dynamics of open quantum systems and paves the way for the investigation of dissipative quantum chaos and its consequences on state-of-the-art noisy intermediate-scale quantum devices.

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