192 research outputs found
Quantum Interference of Force
We show that a quantum particle subjected to a positive force in one path of
a Mach-Zehnder interferometer and a null force in the other path may receive a
negative average momentum transfer when it leaves the interferometer by a
particular exit. In this scenario, an ensemble of particles may receive an
average momentum in the opposite direction of the applied force due to quantum
interference, a behavior with no classical analogue. We discuss some
experimental schemes that could verify the effect with current technology, with
electrons or neutrons in Mach-Zehnder interferometers in free space and with
atoms from a Bose-Einstein condensate.Comment: 5 figures. Accepted in Quantum on 2018-12-0
Spin and rotational symmetries in unrestricted Hartree Fock states of quantum dots
Ground state energies are obtained using the unrestricted Hartree Fock method
for up to four interacting electrons parabolically confined in a quantum dot
subject to a magnetic field. Restoring spin and rotational symmetries we
recover Hund first rule. With increasing magnetic field, crossovers between
ground states with different quantum numbers are found for fixed electron
number that are not reproduced by the unrestricted Hartree Fock approximation.
These are consistent with the ones obtained with more refined techniques. We
confirm the presence of a spin blockade due to a spin mismatch in the ground
states of three and four electrons.Comment: 16 Pages, 2 figures, accepted for publication on New Journal of
Physic
Functional approach to the electromagnetic response function: the Longitudinal Channel
In this paper we address the (charge) longitudinal electromagnetic response
for a homogeneous system of nucleons interacting via meson exchanges in the
functional framework. This approach warrants consistency if the calculation is
carried on order-by-order in the mesonic loop expansion with RPA-dressed
mesonic propagators. At the 1-loop order and considering pion, rho and omega
exchanges we obtain a quenching of the response, in line with the experimental
results.Comment: RevTeX, 18 figures available upon request - to be published in
Physical Review
Connecting scaling with short-range correlations
We reexamine several issues related to the physics of scaling in electron
scattering from nuclei. A basic model is presented in which an assumed form for
the momentum distribution having both long- and short-range contributions is
incorporated in the single-particle Green function. From this one can obtain
saturation of nuclear matter for an NN interaction with medium-range attraction
and short-range repulsion, and can obtain the density-density polarization
propagator and hence the electromagnetic response and scaling function. For the
latter, the shape of the scaling function and how it approaches scaling as a
function of momentum transfer are both explored.Comment: 24 pages, 15 figures. A reference has been corrected and update
Fermion propagators in space-time
The one- and the two-particle propagators for an infinite non-interacting
Fermi system are studied as functions of space-time coordinates. Their
behaviour at the origin and in the asymptotic region is discussed, as is their
scaling in the Fermi momentum. Both propagators are shown to have a divergence
at equal times. The impact of the interaction among the fermions on their
momentum distribution, on their pair correlation function and, hence, on the
Coulomb sum rule is explored using a phenomenological model. Finally the
problem of how the confinement is reflected in the momentum distribution of the
system's constituents is briefly addressed.Comment: 26 pages, 9 figures, accepted for publication on Phys. Rev.
The many levels pairing Hamiltonian for two pairs
We address the problem of two pairs of fermions living on an arbitrary number
of single particle levels of a potential well (mean field) and interacting
through a pairing force. The associated solutions of the Richardson's equations
are classified in terms of a number , which reduces to the seniority
in the limit of large values of the pairing strength and yields the number
of pairs not developing a collective behaviour, their energy remaining finite
in the limit. We express analytically, through the moments of the
single particle levels distribution, the collective mode energy and the two
critical values and of the coupling which can
exist on a single particle level with no pair degeneracy. Notably and merge when the number of single particle levels
goes to infinity, where they coincide with the (when it exists) of
a one pair system, not envisioned by the Richardson theory. In correspondence
of the system undergoes a transition from a mean field to a
pairing dominated regime. We finally explore the behaviour of the excitation
energies, wave functions and pair transfer amplitudes finding out that the
former, for , come close to the BCS predictions, whereas the
latter display a divergence at , signaling the onset of a long
range off-diagonal order in the system.Comment: 35 pages, 6 figures, 2 tables, to be published in EPJ
Bath-induced correlations lead to sub-shot-noise thermometry precision
We study the role of bath-induced correlations in temperature estimation of
cold Bosonic baths. Our protocol includes multiple probes, that are not
interacting, nor are they initially correlated to each other. They interact
with a Bosonic sample and reach a non-equilibrium steady state, which is
measured to estimate the temperature of the sample. It is well-known that in
the steady state such non-interacting probes may get correlated to each other
and even entangled. Nonetheless, the impact of these correlations in metrology
has not been deeply investigated yet. Here, we examine their role for
thermometry of cold Bosonic gases and show that, although being classical,
bath-induced correlations can indeed lead to sub-shot-noise precision for
thermometry at low temperatures; e.g., for a probe of non-interacting
impurities they can enhance the quantum Fisher information by two orders of
magnitude. The proposed thermometry scheme here does not require precise
dynamical control of the probes and tuning the parameters, as it is build upon
the non-equilibrium steady state of a non-interacting system. Our results put
forward new possibilities in thermometry at low temperatures, of relevance for
instance in cold gases and Bose--Einstein condensates.Comment: Comments are welcome
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