Recent developments in quantum technology have allowed us to control system-environment interactions and engineer the spectral properties of the environment. The weak coupling Lindblad approach has been widely used as a standard tool for modeling the open quantum systems dynamics of quantum devices. However, the approximations made in deriving the Lindblad equation limit its applicability. In-depth studies and precise theoretical predictions require modeling beyond the weak coupling approach. In this thesis, we study open quantum system dynamics of quantum devices beyond the Lindblad model. This work has been carried out in two parts. In the first part, we study fast dynamics and control of a transmon without being limited to the two-level subspace. We analyze the decay of a transmon coupled to a bosonic bath using numerically exact stochastic Liouville equations. We find that there is considerable short-time leakage during the decay of a transmon due to universal decoherence, which is more significant for transmons that are strongly interacting with the environment. We further investigate the influence of the higher energy states and dissipation in the coherent driving of qubits, especially in single-qubit gate operations. Finally, we demonstrate the elimination of leakage errors with derivative removal adiabatic gate control for a transmon in the presence of a dissipative environment. In the second part, we study the role of system-environment correlations in open quantum dynamics. The explicit dependence of the dynamics on correlation and information about correlation is masked in most existing methods, including the standard weak-coupling Lindblad equations. We resolve this by introducing a new dynamical picture called a correlation picture, which enables us to derive a universal dynamical equation for reduced dynamics with a Lindblad-like mathematical form. We also develop a weak-correlation expansion that offers systematic perturbative master equations that defeat existing weak-coupling techniques. We further investigate the hidden correlations in master equations with the correlation picture formalism. We unfold system-environment correlations in master equations by rewriting them into a universal form in which the system-bath correlation operator appears.
|Julkaisun otsikon käännös||Dissipative dynamics of quantum devices beyond Lindblad model|
|Tila||Julkaistu - 2021|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|