Applications of quantum metrology and thermodynamics in emerging quantum technologies

The emerging field of quantum technologies is poised to revolutionize various aspects of science, engineering, and computing. One of the most promising branches of quantum information sciences is quantum metrology, which plays a pivotal role in modern quantum technologies by enabling ultra-precise measurements that underpin their functionality and performance. At the heart of quantum metrology lies the exploitation of quantum resources such as entanglement which allow for unprecedented levels of sensitivity and resolution. Additionally, optimal design of quantum devices makes it necessary to study the fundamental principles governing energy transfer, work extraction, and entropy production in quantum systems. Hence, quantum thermodynamics offers profound insights into the efficiency limits of energy conversion processes, ultimately shaping the design of quantum technologies. In this thesis, I review my five manuscripts, three of which are on optical quantum metrology and two of which are on thermodynamics of engineered quantum devices, which are presented in chapter 2 to chapter 6. In chapter 2, we calculate the precision bounds of Fock state optical probes for extracting information from an artificial neural network, which mimics the behavior of the retinal network. We shown that Fock state probes yield higher sensitivity than their coherent and thermal counterparts. In chapter 3 we investigate the precision bounds of polarization entangled Bell state for a polarimetric task. Theoretical calculations are accompanied by experimental data. We show that although entanglement provides quantum advantage in terms of precision, environmental noise introduces bias in the estimated values of the parameters which limits the mentioned advantage. In chapter 4 we calculate the precision bounds on estimation of rotation angle due to a birefringent medium in a general polarimetric setup. In our study we take into account several models of depolarization and ordering of polarimetric channels and include the effect of optical losses. Our results show that NOON state probes provide superior metrological performance compared with coherent and anticoherent states as depolarization as diattenuation of the probe is not strong. Even for relatively high depolarization rates, NOON state with small mean photon numbers yield a better precision bound compared with the coherent and anticoherent states. In chapter 5 we investigate the effect of coupling strengths and coherence within a structured environment on the steady-state heat transfer in an engineered biomimetic system, using collision model for simulating the open quantum dynamics. We show that interaction with the environment modulates the energy levels of the system and decreases the transition energy between certain eigenstates, making these transitions more accessible to the hot thermal bath. In chapter 6 we implement counterdiabatic drive to accelerate adiabatic and hot isochoric branches of a quantum Otto engine. Our results for a single cycle show that, taking the control costs into consideration, the heat engine with both adiabatic and isochoric controlled branches reaches a higher power output, albeit with slightly reduced efficiency compared with the engine with counterdiabatic drive only implemented on its adiabatic strokes. However, in limit cycle, it is possible to allocate stroke durations such that the engine with both controlled adiabatic and isochoric branches operates with higher efficiency and power output. Finally, a detailed analysis and discussion of the results for all chapters is given in the conclusions section.