119 research outputs found
Stochastic Quantization of Bottomless Systems: Stationary quantities in a diffusive process
By making use of the Langevin equation with a kernel, it was shown that the
Feynman measure exp(-S) can be realized in a restricted sense in a diffusive
stochastic process, which diverges and has no equilibrium, for bottomless
systems. In this paper, the dependence on the initial conditions and the
temporal behavior are analyzed for 0-dim bottomless systems. Furthermore, it is
shown that it is possible to find stationary quantities.Comment: LaTeX2e, 10 pages with 4 eps figures, to be published in Prog. Theor.
Phys. 102; revised page layou
A Simple Scheme to Entangle Distant Qubits from a Mixed State via an Entanglement Mediator
A simple scheme to prepare an entanglement between two separated qubits from
a given mixed state is proposed. A single qubit (entanglement mediator) is
repeatedly made to interact locally and consecutively with the two qubits
through rotating-wave couplings and is then measured. It is shown that we need
to repeat this kind of process only three times to establish a maximally
entangled state directly from an arbitrary initial mixed state, with no need to
prepare the state of the qubits in advance or to rearrange the setup step by
step. Furthermore, the maximum yield realizable with this scheme is compatible
with the maximum entanglement, provided that the coupling constants are
properly tuned.Comment: 9 pages, 3 figures; the version accepted for publication (with the
new title
Typical Pure Nonequilibrium Steady States
We show that typicality holds for a class of nonequilibrium systems, i.e.,
nonequilibrium steady states (NESSs): almost all the pure states properly
sampled from a certain Hilbert space well represent a NESS and characterize its
intrinsic thermal nature. We clarify the relevant Hilbert space from which the
pure states are to be sampled, and construct practically all the typical pure
NESSs. The scattering approach leads us to the natural extension of the
typicality for equilibrium systems. Each pure NESS correctly yields the
expectation values of observables given by the standard ensemble approach. It
means that we can calculate the expectation values in a NESS with only a single
pure NESS. We provide an explicit construction of the typical pure NESS for a
model with two reservoirs, and see that it correctly reproduces the
Landauer-type formula for the current flowing steadily between the reservoirs.Comment: 6 pages, 1 figur
On the derivation of the GKLS equation for weakly coupled systems
We consider the reduced dynamics of a small quantum system in interaction
with a reservoir when the initial state is factorized. We present a rigorous
derivation of a GKLS master equation in the weak-coupling limit for a generic
bath, which is not assumed to have a bosonic or fermionic nature, and whose
reference state is not necessarily thermal. The crucial assumption is a
reservoir state endowed with a mixing property: the n-point connected
correlation function of the interaction must be asymptotically bounded by the
product of two-point functions (clustering property).Comment: 26 pages, 2 figure
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