AQP -seminaari: Controlled quantum systems as tools for decoherence investigation and dissipative state synthesis
Quantum systems are always subjected to dissipation and decoherence, these being not only relevant sources of errors in quantum information but also important resources in particular tasks, such as the preparation and stabilization of quantum states. In this context, here we present two recent theoretical studies [1, 2] on open systems motivated by controlled interactions in quantum technologies. In , we focused on precision studies of a superconducting circuit (left panel of Fig. 1a). By using a stochastic Liouville-von Neumann equation, we studied the dynamics and steady-state properties of a driven qubit under Ohmic dissipation and addressed, for instance, the role of the Lamb-shift (right panel of Fig. 1a) and the meltdown of the Mollow triplet. In , we used a collisional model of decoherence to build Markovian reservoirs for the vibrational mode of a single trapped ion. By taking advantage of the multilevel structure of the ion (left panel of Fig. 1b), the proposed protocol may create thermal states and speed up the generation of non-classical states (right panel of Fig. 1b). We also investigated its use in the context of quantum Otto cycles employing non-thermal states to potentially improve the performance of heat engines.
FIG. 1. Overview of the work in (a)  and (b) . The right panel of (a) shows the time-averaged fidelity between SLED and Lindblad solutions with (squares) and without (circles) Lamb-shift included as a function of the dissipation rate. The right panel of (b) shows the fidelity between the target and produced vibrational state after the N stages of the protocol. The top (bottom) panel indicates the generation of thermal states (squeezed coherent state).
 W. S. Teixeira, F. L. Semião, J. Tuorila, and M. Möttönen, New J. Phys. 24, 013005 (2021).
 W. S. Teixeira, M. Keller, and F. L. Semião, New J. Phys. 24, 023027 (2022).