Rosario Lo Franco

We study an optomechanical Otto engine whose working medium is a single-mode cavity driven by beams of coherently prepared three-level phaseonium atoms. The atoms are not thermal reservoirs in the Gibbs sense; rather, their populations and ground-state coherence set the detailed-balance ratio of the cavity collision map, so that the field relaxes to a Gibbs state at an operational apparent temperature. We combine the finite-time collision-model dynamics with radiation-pressure work extraction and compare three reservoir preparations: a thermal reference at the same apparent temperatures, an incoherent atomic beam with the same populations, and the coherent phaseonium beam. We show that the phaseonium isochore charges the cavity passively: the cavity ergotropy and energy-basis coherence remain zero up to numerical precision, while the state converges to the Gibbs fixed point selected by the apparent detailed balance. We further estimate lower bounds on the cost of preparing the atomic populations and coherence, showing that the relevant advantage of phaseonium is a resource-preparation tradeoff rather than a cost-free enhancement over a thermal bath at the same temperature. Finally, we assess the finite-time performance of a two-cavity cascade with additive mechanical work accounting. Over the investigated coherence-phase range, the cascade produces approximately 47 % – 52 % more power than the single-cavity engine while requiring only 65 % – 68 % of the hot and cold phaseonium atoms needed by two independent engines, resulting in a 9 % – 15 % enhancement of power per injected atom over a complete cycle.

Relativistic motion introduces decoherence that limits quantum parameter estimation. Earlier treatments of bipartite Unruh–DeWitt detectors have often restricted the reduced state to the X-state form. We consider single-qubit and isolated-ancilla two-qubit probes whose reduced state is not restricted to this form, moving along a trajectory that combines uniform acceleration with a transverse velocity. The quantum Fisher information for an initially encoded phase and for a charging time across the three velocity regimes is investigated. The two parameters respond to acceleration in distinct ways, and the isolated ancilla improves both estimations over different portions of the parameter space. Phase estimation remains nearly unaffected by the transverse velocity of the probe, whereas at short drive durations, the charging-time QFI reverses with acceleration. The separable regime that follows entanglement loss is not devoid of metrological value: both parameters can still be estimated, and the discord of the reduced state remains nonzero. These results point to quantum correlations beyond entanglement as a resource for parameter estimation in accelerated probes.

Phys. Rev. A 114, 049902 (2026)

Quantum coherence is a key resource underpinning quantum technologies, yet it is highly susceptible to environmental decoherence, especially in thermal settings. While frequency modulation (FM) has shown promise in preserving coherence at zero temperature, its effectiveness in realistic, noisy thermal environments remains unclear. In this work, we investigate a single frequency‐modulated qubit interacting with a thermal phase‐covariant reservoir composed of dissipative and dephasing channels. We demonstrate that FM significantly preserves coherence in the presence of thermal dissipation while being ineffective under thermal pure‐dephasing noise due to commutation between system and interaction Hamiltonians. When both noise channels are present, FM offers protection only for weak dephasing coupling. Our findings clarify the limitations and potential of FM‐based coherence protection under thermal noise, supplying practical insights into designing robust quantum systems for quantum applications.

We present a microscopic derivation of a master equation for two-component bosons (bosonic qubits) which tunnel between spatially separated modes under local dephasing noise. Starting from the full system-bath Hamiltonian with Lorentzian coupling distributions, we analytically obtain a time-local master equation whose structure reveals intrinsic non-Markovian features and recovers the standard phenomenological dephasing model in the short-time limit. Comparison with exact pseudomode simulations confirms its validity beyond weak-coupling and Markovian regimes. We identify a resonance condition between tunneling and bath frequencies for which dephasing drives the system toward correlated steady states, stabilizing coherence and entanglement instead of suppressing them. These results establish a rigorous microscopic foundation for dephasing models in bosonic tunneling systems and reveal a noise-induced mechanism for steady-state entanglement.

We present a quantum thermometric protocol for the estimation of multiple temperatures within the collisional model framework. Employing the formalism of multiparameter quantum metrology, we develop a systematic strategy to estimate the temperatures of several thermal reservoirs with minimal estimation error. We prove a necessary and sufficient condition for the singularity of the Fisher information matrix for a bi-parametrized qubit state. By using controlled rotations of ancillary systems between successive interaction stages, we eliminate parameter interdependencies, thereby rendering the quantum Fisher information matrix non-singular. Remarkably, we demonstrate that precision enhancement in the joint estimation of multiple temperatures can be achieved even in the absence of correlations among the ancillas, surpassing the corresponding thermal Fisher information limits. Exploiting correlations within the ancillary system yields additional enhancement of Fisher information. Finally, we identify the dimensionality of the ancillary systems as a key factor governing the efficiency of multiparameter temperature estimation.

The principle that heat spontaneously flows from higher temperature to lower temperature is a cornerstone of classical thermodynamics, often assumed to be independent of the sequence of interactions. While this holds true for macroscopic systems at equilibrium, here we show that, when the order of interactions between two identical thermalization channels is indefinite, an anomalous heat flow emerges, whereby heat can sometime flow from a colder entity to a hotter one. Taking advantage of this anomalous heat flow, we design a quantum Otto cycle with indefinite causal order, which not only achieves refrigeration but also generates work. The anomalous heat flow and the quantum Otto cycle are experimentally simulated in a photonic quantum setup, which provides a proof-of-principle demonstration of the theory.