arXiv subjects

Michael Thorwart

Publications and source records attributed to Michael Thorwart.

57 records · Page 4Linked to original sources

arXiv2007

Spin-boson dynamics: A unified approach from weak to strong coupling

We present a novel approximation scheme to describe the influence of a harmonic bath on the dynamics of a two-level particle over almost the whole regime of temperatures and coupling to the environment, for a wide class of bath spectral densities. Starting from the exact path-integral solution for the two-level system density matrix, effective intra-blip correlations are fully included, while inter-blip and blip-sojourn interactions are considered up to first order. In the proper regimes, an excellent agreement with conventional perturbative approaches and ab-initio path-integral results is found.

cond-mat.mes-hall↗

arXiv2001

Decoherence and dissipation during a quantum XOR gate operation

The dynamics of a quantum XOR gate operation in a two-qubit system being coupled to a bath of quantum harmonic oscillators is investigated. Upon applying the numerical quasiadiabatic propagator path integral method, we obtain the numerically precise time-resolved evolution of this interacting two-qubit system in presence of time-dependent external fields without further approximations. We simulate the dissipative gate operation for characteristic experimental realizations of condensed matter qubits; namely, the flux and charge qubits realized in superconducting Josephson systems and qubits formed with semiconductor quantum dots. Moreover, we study systematically the quality of the XOR gate by determining the four characteristic gate quantifiers: fidelity, purity, the quantum degree, and the entanglement capability of the gate. Two different types of errors in the qubits have been modelled, i.e., bit-flip errors and phase errors. The dependence of the quality of the gate operation on the environmental temperature, on the friction strength stemming from the system-bath interaction, and on the strength of the interqubit coupling is systematically explored: Our main finding is that the four gate quantifiers depend only weakly on temperature, but are rather sensitive to the friction strength.

cond-mat↗

arXiv2000

Iterative algorithm versus analytic solutions of the parametrically driven dissipative quantum harmonic oscillator

We consider the Brownian motion of a quantum mechanical particle in a one-dimensional parabolic potential with periodically modulated curvature under the influence of a thermal heat bath. Analytic expressions for the time-dependent position and momentum variances are compared with results of an iterative algorithm, the so-called quasiadiabatic propagator path integral algorithm (QUAPI). We obtain good agreement over an extended range of parameters for this spatially continuous quantum system. These findings indicate the reliability of the algorithm also in cases for which analytic results may not be available a priori.

cond-mat↗