5 research outputs found
Dissipative Landau-Zener transitions of a qubit: bath-specific and universal behavior
We study Landau-Zener transitions in a qubit coupled to a bath at zero
temperature. A general formula is derived that is applicable to models with a
non-degenerate ground state. We calculate exact transition probabilities for a
qubit coupled to either a bosonic or a spin bath. The nature of the baths and
the qubit-bath coupling is reflected in the transition probabilities. For
diagonal coupling, when the bath causes energy fluctuations of the diabatic
qubit states but no transitions between them, the transition probability
coincides with the standard LZ probability of an isolated qubit. This result is
universal as it does not depend on the specific type of bath. For pure
off-diagonal coupling, by contrast, the tunneling probability is sensitive to
the coupling strength. We discuss the relevance of our results for experiments
on molecular nanomagnets, in circuit QED, and for the fast-pulse readout of
superconducting phase qubits.Comment: 16 pages, 8 figure
Quantum Driven Dissipative Parametric Oscillator in a Blackbody Radiation Field
We consider the general open system problem of a charged quantum oscillator
confined in a harmonic trap, whose frequency can be arbitrarily modulated in
time, that interacts with both an incoherent quantized (blackbody) radiation
field and with an arbitrary coherent laser field. We assume that the oscillator
is initially in thermodynamic equilibrium with its environment, a
non-factorized initial density matrix of the system and the environment, and
that at the modulation of the frequency, the coupling to the incoherent
and the coherent radiation are switched on. The subsequent dynamics, induced by
the presence of the blackbody radiation and the laser field, is studied in the
framework of the influence functional approach. This approach allows
incorporating, in \emph{analytic closed formulae}, the non-Markovian character
of the oscillator-environment interaction at any temperature as well the
non-Markovian character of the blackbody radiation and its zero-point
fluctuations. Expressions for the time evolution of the covariance matrix
elements of the quantum fluctuations and the reduced density-operator are
obtained.Comment: 11 pages. It matches the published versio
Reduced density matrix for nonequilibrium steady states: A modified Redfield solution approach
10.1103/PhysRevE.88.052127Physical Review E - Statistical, Nonlinear, and Soft Matter Physics885-PLEE