Thermal Baths as Quantum Resources: More Friends than Foes?

In this article we argue that thermal reservoirs (baths) are potentially useful resources in processes involving atoms interacting with quantized electromagnetic fields and their applications to quantum technologies. One may try to suppress the bath effects by means of dynamical control, but such control does not always yield the desired results. We wish instead to take advantage of bath effects, that do not obliterate "quantumness" in the system-bath compound. To this end, three possible approaches have been pursued by us: (i) Control of a quantum system faster than the correlation time of the bath to which it couples: Such control allows us to reveal quasi-reversible/coherent dynamical phenomena of quantum open systems, manifest by the quantum Zeno or anti-Zeno effects (QZE or AZE, respectively). Dynamical control methods based on the QZE are aimed not only at protecting the quantumness of the system, but also diagnosing the bath spectra or transferring quantum information via noisy media. By contrast, AZE-based control is useful for fast cooling of thermalized quantum systems. (ii) Engineering the coupling of quantum systems to selected bath modes: This approach, based on field -atom coupling control in cavities, waveguides and photonic band structures, allows to drastically enhance the strength and range of atom-atom coupling through the mediation of the selected bath modes. More dramatically, it allows us to achieve bath-induced entanglement that may appear paradoxical if one takes the conventional view that coupling to baths destroys quantumness. (iii) Engineering baths with appropriate non-flat spectra: This approach is a prerequisite for the construction of the simplest and most efficient quantum heat machines (engines and refrigerators). We may thus conclude that often thermal baths are "more friends than foes" in quantum technologies.Comment: 27 pages, 17 figure

Quantum bistability at the interplay between collective and individual decay

We study driven collective radiation of an ensemble of atoms placed inside a cavity, accounting for individual-atom emission to free space modes. We find that the steady state exhibits a dissipative phase transition, formed by a mixture of two collective quantum states corresponding to a bistable mean-field solution. One of these states is entangled and closely resembles a coherently radiating spin state (CRSS) -- the solution obtained by neglecting individual decay (Dicke superradiance) -- allowing us to analytically find the optimally achievable spin squeezing. We predict quantum switching between the two states, verified by quantum trajectories simulations. The switching rate tends to vanish with the atom number, as the Liouvillan gap closes. Remarkably, this suggests that the system may reside in an entangled CRSS-like state associated with correlated Dicke physics, even in the presence of decorrelating individual decay. This opens a path for a systematic study of the interplay between collective and individual decay, in both experiments and theory.Comment: 7+9 pages, 4+4 figure

Data Curation from Privacy-Aware Agents

A data curator would like to collect data from privacy-aware agents. The collected data will be used for the benefit of all agents. Can the curator incentivize the agents to share their data truthfully? Can he guarantee that truthful sharing will be the unique equilibrium? Can he provide some stability guarantees on such equilibrium? We study necessary and sufficient conditions for these questions to be answered positively and complement these results with corresponding data collection protocols for the curator. Our results account for a broad interpretation of the notion of privacy awareness