18 research outputs found
Spectral weight suppression in response functions of ultracold fermion-boson mixtures
We study the dynamical response of ultracold fermion-boson mixture in the
Bogoliubov regime, where the interactions between fermionic impurities and
bosonic excitations (phonons) are described by an effective Frohlich model
under the Bogoliubov approximation. A characteristic suppression of the
single-particle spectral weight is found in the small momentum region where the
impurity band and phonon mode intersect. Using diagrammatic technique we
compute the Bragg spectra as well as the momentum dependent force-force
correlation function. We fnd that both of them are heavily affected by the
spectral weight suppression effect at low impurity densities in both 1D and 2D
systems. We show that the the spectral weight suppression feature in Bragg
spectra, which was previously found in the quantum Monte Carlo simulations and
which cannot be recovered by the random phase approximation, can be accurately
reproduced with the help of vertex corrections.Comment: 14 pages, 10 figures. Final version with a new title, some revisions
and a new figur
Dynamical response of ultracold interacting fermion-boson mixtures
We analyze the dynamical response of a ultracold binary gas mixture in
presence of strong boson-fermion couplings. Mapping the problem onto that of
the optical response of a metal/semiconductor electronic degrees of freedom to
electromagnetic perturbation we calculate the corresponding dynamic linear
response susceptibility in the non-perturbative regimes of strong boson-fermion
coupling using diagrammatic resummation technique as well as quantum Monte
Carlo simulations. We evaluate the Bragg spectral function as well as the
optical conductivity and find a pseudogap, which forms in certain parameter
regimes.Comment: 32 pages, 13 figure
Rydberg crystallization detection by statistical means
We investigate an ensemble of atoms which can be excited into a Rydberg
state. Using a disordered quantum Ising model, we perform a numerical
simulation of the experimental procedure and calculate the probability
distribution function to create a certain number of Rydberg atoms ,
as well as their pair correlation function. Using the latter, we identify the
critical interaction strength above which the system undergoes a phase
transition to a Rydberg crystal. We then show that this phase transition can be
detected using alone.Comment: 7 pages, 9 figure
Detecting an exciton crystal by statistical means
We investigate an ensemble of excitons in a coupled quantum well excited via
an applied laser field. Using an effective disordered quantum Ising model, we
perform a numerical simulation of the experimental procedure and calculate the
probability distribution function to create excitons as well as
their correlation function. It shows clear evidence of the existence of two
phases corresponding to a liquid and a crystal phase. We demonstrate that not
only the correlation function but also the distribution is very well
suited to monitor this transition.Comment: 5 pages, 5 figure
Bosonic transport through a chain of quantum dots
The particle transport through a chain of quantum dots coupled to two bosonic
reservoirs is studied. For the case of reservoirs of non-interacting bosonic
particles, we derive an exact set of stochastic differential equations, whose
memory kernels and driving noise are characterised entirely by the properties
of the reservoirs. Going to the Markovian limit an analytically solvable case
is presented. The effect of interparticle interactions on the transient
behaviour of the system, when both reservoirs are instantaneously coupled to an
empty chain of quantum dots, is approximated by a semiclassical method, known
as the Truncated Wigner approximation. The steady-state particle flow through
the chain and the mean particle occupations are explained via the spectral
properties of the interacting system.Comment: 7 pages, 4 figure
Full counting statistics of persistent current
We develop a method for calculation of charge transfer statistics of persistent current in nanostructures in terms of the cumulant generating function (CGF) of transferred charge. We consider a simply connected one-dimensional system (a wire) and develop a procedure for the calculation of the CGF of persistent currents when the wire is closed into a ring via a weak link. For the non-interacting system we derive a general formula in terms of the two-particle Green's functions. We show that, contrary to the conventional tunneling contacts, the resulting cumulant generating function has a doubled periodicity as a function of the counting field. We apply our general formula to short tight-binding chains and show that the resulting CGF perfectly reproduces the known evidence for the persistent current. Its second cumulant turns out to be maximal at the switching points and vanishes identically at zero temperature. Furthermore, we apply our formalism for a computation of the charge transfer statistics of genuinely interacting systems. First we consider a ring with an embedded Anderson impurity and employing a self-energy approximation find an overall suppression of persistent current as well as of its noise. Finally, we compute the charge transfer statistics of a double quantum dot system in the deep Kondo limit using an exact analytical solution of the model at the Toulouse point. We analyze the behaviour of the resulting cumulants and compare them with those of a noninteracting double quantum dot system and find several pronounced differences, which can be traced back to interaction effects