9 research outputs found
Pseudomodes and the corresponding transformation of the temperature-dependent bath correlation function
In open system approaches with non-Markovian environments, the process of
inserting an individual mode (denoted as "pseudomode") into the bath or
extracting it from the bath is widely employed. This procedure, however, is
typically performed on basis of the spectral density (SD) and does not
incorporate temperature. Here, we show how the - temperature-dependent - bath
correlation function (BCF) transforms in such a process. We present analytic
formulae for the transformed BCF and numerically study the differences between
factorizing initial state and global thermal (correlated) initial state of mode
and bath, respectively. We find that in the regime of strong coupling of the
mode to both system and bath, the differences in the BCFs give rise to
pronounced differences in the dynamics of the system.Comment: 12 pages, 4 figure
Coherent versus incoherent excitation dynamics in dissipative many-body Rydberg systems
We study the impact of dephasing on the excitation dynamics of a cloud of
ultracold two-level Rydberg atoms for both resonant and off-resonant laser
excitation, using the wave function Monte Carlo (MCWF) technique. We find that
while for resonant laser driving, dephasing mainly leads to an increase of the
Rydberg population and a decrease of the Mandel Q parameter, at off-resonant
driving strong dephasing toggles between direct excitation of pairs of atoms
and subsequent excitation of single atoms, respectively. These two excitation
mechanisms can be directly quantified via the pair correlation function, which
shows strong suppression of the two-photon resonance peak for strong dephasing.
Consequently, qualitatively different dynamics arise in the excitation
statistics for weak and strong dephasing in off-resonant excitation. Our
findings show that time-resolved excitation number measurements can serve as a
powerful tool to identify the dominating process in the system's excitation
dynamics.Comment: 10 pages, 10 figure
Collective excitation of Rydberg-atom ensembles beyond the enhancement
In an ensemble of laser-driven atoms involving strongly interacting Rydberg
states, the excitation probability is usually strongly suppressed. In contrast,
here we identify a regime in which the steady-state Rydberg excited fraction is
enhanced by the interaction. This effect is associated with the build-up of
many-body coherences, induced by coherent multi-photon excitations between
collective states. The excitation enhancement should be observable under
currently-existing experimental conditions, and may serve as a direct probe for
the presence of coherent multi-photon dynamics involving collective quantum
states.Comment: 7 pages, 4 figure