Thermal management of atomic and photonic systems

Recent years have seen tremendous progress in developing quantum technologies that rely on the physical systems' quantum features, such as quantum coherence and entanglement. In principle, these quantum systems are not isolated and interact with the environment, which leads to decoherence in which quantum correlations weaken or vanish entirely. The mathematical formulation which describes the system's dynamics in the environment's presence generally requires several approximations. One example is the quantum Markovian master equation based on the perturbative approach in weak system-bath interaction. Typically, a phenomenological approach is adopted in deriving the master equation in which inter-system interactions are ignored, which results in the ``local" dissipation terms in the master equation. We show that such an approach is inconsistent with the laws of thermodynamics in the case of nonlinearly coupled resonators. Instead, the master equation derived from the first principles is consistent, usually termed the ``global" master equation. The heat flow put serious restrictions on the miniaturization of quantum-based technologies. One promising direction can be to power these devices with heat rather than considering the heat flow as a noise source. Accordingly, it is desirable to have efficient models of quantum thermal heat managers which can assist in controlling the heat flow. Following this direction, here, we propose an efficient quantum thermal diode and transistor model that can provide perfect rectification and very large tunable heat amplification, respectively. The dynamics of the system are described by the global master equation, which assists in uncovering the underlying mechanism in these thermal devices. In addition, we show that our model of the quantum thermal transistor, based on two coupled qubits, can also be used as a quantum absorption refrigerator, which is in variance with previous proposals of refrigerators that generally require three-body interaction. It is often required to cool finite quantum systems rather than classical reservoirs. For instance, cooling mechanical resonators to the ground state is a prerequisite for most applications based on mechanical systems in quantum information and quantum communication. However, cooling multiple resonators to the ground state is challenging using typical laser and feedback cooling schemes. To overcome this challenge, we propose a scheme by which simultaneous cooling of multiple resonators is possible. Unlike previous proposals, external control or work input is not required; instead, incoherent thermal drives can cool the resonators. Finally, we investigate the possibility of generating entanglement between uncoupled mechanical resonators, which are only driven by incoherent thermal baths. We show that it is possible to generate significant entanglement between the resonators by judicious choice of thermal baths spectra. The suppression of undesired dissipation and favoring the desired effective two-mode squeezing-like interactions generated by the incoherent interaction with the baths leads to entanglement between the resonators.