70 research outputs found
Particle current, noise, and counting statistics of quantum transport in the presence of a single-particle loss
How dissipation affects transport is an important theme in quantum science.
Here we theoretically investigate an impact of a single-particle loss in
mesoscopic transport, which has been an issue in experiments of ultracold
atomic gases. By explicitly analyzing quantum point contact and quantum dot
systems, we obtain a cumulant generating function on the particle current whose
formal expression turns out to be common to two systems. In terms of this
generating function, behaviors of average current, particle loss rate, and
noises in presences of losses introduced in conduction channels are exemplified
for free fermions. It is shown that the current noise contains the component
proportional to the particle loss rate, which may be measurable in experiments.Comment: 12 pages, 8 figure
Unconventional superfluidity in quasi-one-dimensional systems
We show that an unconventional superfluid triggered by spin-orbit coupling is
realized for repulsively interacting quasi-one-dimensional fermions. A
competition between spin-singlet and -triplet pairings occurs due to the
breaking of inversion symmetry. We show that both superfluid correlations decay
algebraically with the same exponent except for special coupling constants for
which a dominant superfluid is controlled by the spin-orbit coupling. We also
discuss a possible experiment to observe such phases with cold atoms.Comment: 5 pages, 2 figure
Comparative study for two-terminal transport through a lossy one-dimensional quantum wire
Motivated by realization of the dissipative quantum point contact in
ultracold atomic gases, we investigate a two-terminal mesoscopic transport
system in which a single-particle loss is locally present in a one-dimensional
chain. By means of the Dyson equation approach in the Keldysh formalism that
can incorporate dissipative effects, we reveal analytic structures of the
particle and energy currents whose formal expressions correspond to ones in
certain three-terminal systems where the particle loss is absent. The obtained
formulas are also consistent with non-hermitian and three-terminal
Landauer-B\"{u}ttiiker analyses. The universality on the current expressions
holds regardless of quantum statistics and may be useful for understanding
lossy two-terminal transport in terms of three-terminal transport and vice
versa.Comment: 15 pages, 1 figur
Coleman-Weinberg mechanism in spinor Bose-Einstein condensates
It is argued that a continuous quantum phase transition between different
ordered phases in spinor Bose-Einstein condensates predicted by the mean-field
theory is vulnerable to quantum fluctuations. By analyzing Lee-Huang-Yang
corrections in the condensate, we demonstrate that the so-called
Coleman-Weinberg mechanism takes place in such a transition, that is, the
transition becomes of the first order by quantum fluctuations. A jump to be
expected in this first-order transition is induced by a correction from density
fluctuations despite a transition between different magnetic properties with
keeping condensation. We exemplify this with an experimentally relevant case
and show that a measurement of a condensate depletion can be utilized to
confirm the first-order transition.Comment: 6 pages, 2 figure
Universal Noise in Continuous Transport Measurements of Interacting Fermions
We propose and analyze continuous measurements of atom number and atomic
currents using dispersive probing in an optical cavity. For an atom-number
measurement in a closed system, we relate both the detection noise and the
heating rate due to measurement back-action to Tan's contact, and identify an
emergent universal quantum non-demolition (QND) regime in the good-cavity
limit. We then show that such a continuous QND measurement of atom number
serves as a quantum-limited current transducer in a two-terminal setup. We
derive a universal bound on the precision of current measurement, which results
from a tradeoff between detection noise and back-action of the atomic current
measurement. Our results apply regardless of the strength of interaction or the
state of matter and set fundamental bounds on future precision measurements of
transport properties in cold-atom quantum simulators.Comment: 13 pages, 6 figures; Accepted for publication in Phys. Rev.
- …