16 research outputs found
Distance growth of quantum states due to initial system--environment correlations
Intriguing features of the distance between two arbitrary states of an open
quantum system are identified that are induced by initial system-environment
correlations. As an example, we analyze a qubit dephasingly coupled to a
bosonic environment. Within tailored parameter regimes, initial correlations
are shown to substantially increase a distance between two qubit states
evolving to long-time limit states according to exact non-Markovian dynamics.
It exemplifies the breakdown of the distance contractivity of the reduced
dynamics.Comment: 4 pages, 3 figure
Sufficient conditions for the anti-Zeno effect
The ideal anti-Zeno effect means that a perpetual observation leads to an
immediate disappearance of the unstable system. We present a straightforward
way to derive sufficient conditions under which such a situation occurs
expressed in terms of the decaying states and spectral properties of the
Hamiltonian. They show, in particular, that the gap between Zeno and anti-Zeno
effects is in fact very narrow.Comment: LatEx2e, 9 pages; a revised text, to appear in J. Phys. A: Math. Ge
Distance between quantum states in presence of initial qubit-environment correlations: a comparative study
The time evolution of the trace distance between two states of an open
quantum system may increase due to initial system-environment correlations,
thus exhibiting a breakdown of distance contractivity of the reduced dynamics.
We analyze how the time evolution of the distance depends on the chosen
distance measure. Here we elucidate the behavior of the trace distance, the
Hilbert- Schmidt distance, the Bures distance, the Hellinger distance and the
quantum Jensen-Shannon divergence for two system-environment setups, namely a
qubit bi-linearly coupled to an infinite and a finite size environment with the
latter composed of harmonic oscillators
Large Deviations in the Superstable Weakly Imperfect Bose Gas
The superstable Weakly Imperfect Bose Gas {(WIBG)} was originally derived to
solve the inconsistency of the Bogoliubov theory of superfluidity. Its
grand-canonical thermodynamics was recently solved but not at {point of} the
{(first order)} phase transition. This paper proposes to close this gap by
using the large deviations formalism and in particular the analysis of the Kac
distribution function. It turns out that, as a function of the chemical
potential, the discontinuity of the Bose condensate density at the phase
transition {point} disappears as a function of the particle density. Indeed,
the Bose condensate continuously starts at the first critical particle density
and progressively grows but the free-energy per particle stays constant until
the second critical density is reached. At higher particle densities, the Bose
condensate density as well as the free-energy per particle both increase
{monotonously}
Introduction to representations of the canonical commutation and anticommutation relations
Lecture notes of a minicourse given at the Summer School on Large Coulomb
Systems - QED in Nordfjordeid, 2003, devoted to representations of the CCR and
CAR. Quasifree states, the Araki-Woods and Araki-Wyss representations, and the
lattice of von Neumenn algebras in a bosonic/fermionic Fock space are discussed
in detail