47 research outputs found
Quantum Monte Carlo simulation of overpressurized liquid 4He
A diffusion Monte Carlo simulation of superfluid He at zero temperature
and pressures up to 275 bar is presented. Increasing the pressure beyond
freezing ( 25 bar), the liquid enters the overpressurized phase in a
metastable state. In this regime, we report results of the equation of state
and the pressure dependence of the static structure factor, the condensate
fraction, and the excited-state energy corresponding to the roton. Along this
large pressure range, both the condensate fraction and the roton energy
decrease but do not become zero. The roton energies obtained are compared with
recent experimental data in the overpressurized regime.Comment: 5 pages, accepted for publication in Phys. Rev. Let
Universality in molecular halo clusters
Ground state of weakly bound dimers and trimers with a radius extending well
into the classically forbidden region is explored, with the goal to test the
predicted universality of quantum halo states. The focus of the study are
molecules consisting of T, D, He, He and alkali
atoms, where interaction between particles is much better known than in the
case of nuclei, which are traditional examples of quantum halos. The study of
realistic systems is supplemented by model calculations in order to analyze how
low-energy properties depend on the interaction potential. The use of
variational and diffusion Monte Carlo methods enabled very precise calculation
of both size and binding energy of the trimers. In the quantum halo regime, and
for large values of scaled binding energies, all clusters follow almost the
same universal line. As the scaled binding energy decreases, Borromean states
separate from tango trimers.Comment: 5 pages, 3 figures, accepted for publication in Phys. Rev. Let
One Dimensional 1H, 2H and 3H
The ground-state properties of one-dimensional electron-spin-polarized
hydrogen H, deuterium H, and tritium H are obtained by means of
quantum Monte Carlo methods. The equations of state of the three isotopes are
calculated for a wide range of linear densities. The pair correlation function
and the static structure factor are obtained and interpreted within the
framework of the Luttinger liquid theory. We report the density dependence of
the Luttinger parameter and use it to identify different physical regimes:
Bogoliubov Bose gas, super-Tonks-Girardeau gas, and quasi-crystal regimes for
bosons; repulsive, attractive Fermi gas, and quasi-crystal regimes for
fermions. We find that the tritium isotope is the one with the richest
behaviour. Our results show unambiguously the relevant role of the isotope mass
in the properties of this quantum system.Comment: 19 pages, 7 figures, contribution to special issue in NJP in memory
of Marvin Girardea
Ultradilute quantum liquid drops
Using quantum Monte Carlo methods we have studied dilute Bose-Bose mixtures
with attractive interspecies interaction in the limit of zero temperature. The
calculations are exact within some statistical noise and thus go beyond
previous perturbative estimations. By tuning the intensity of the attraction,
we observe the evolution of an -particle system from a gas to a self-bound
liquid drop. This observation agrees with recent experimental findings and
allows for the study of an ultradilute liquid never observed before in Nature.Comment: 5 pages, 5 figure
Trapped Bose-Bose mixtures at finite temperature: a quantum Monte Carlo approach
We study thermal properties of a trapped Bose-Bose mixture in a dilute regime
using quantum Monte Carlo methods. Our main aim is to investigate the
dependence of the superfluid density and the condensate fraction on
temperature, for the mixed and separated phases. To this end, we use the
diffusion Monte Carlo method, in the zero-temperature limit, and the
path-integral Monte Carlo method for finite temperatures. The results obtained
are compared with solutions of the coupled Gross-Pitaevskii equations for the
mixture at zero temperature. We notice the existence of an anisotropic
superfluid density in some phase-separated mixtures. Our results also show that
the temperature evolution of the superfluid density and condensate fraction is
slightly different, showing noteworthy situations where the superfluid fraction
is smaller than the condensate fraction.Comment: accepted for publication in Phys. Rev.
Ground state of small mixed helium and spin-polarized tritium clusters: a quantum Monte Carlo stud
We report results for the ground-state energy and structural properties of
small He-T clusters consisting of up to 4 T and 8
He atoms. These results have been obtained using very well-known
He-He and T-T interaction potentials and
several models for the He-T interatomic potential. All the
calculations have been performed with variational and diffusion Monte Carlo
methods. It takes at least three atoms to form a mixed bound state. In
particular, for small clusters the binding energies are significantly affected
by the precise form of the He-T interatomic potential but the
stability limits remain unchanged. The only exception is the
HeT trimer whose stability in the case of the weakest
He-T interaction potential is uncertain, while it seems stable
for other potentials. The mixed trimer He(T), a candidate
for Borromean state, is not bound. All other studied clusters are stable. Some
of the weakest bound clusters can be classified as quantum halos, as a
consequence of having high probability of being in a classically forbidden
region.Comment: 20 pages, accepted for publication in J. Chem. Phy
Spin-polarized hydrogen and its isotopes: a rich class of quantum phases (Review Article)
We review the recent activity in the theoretical description of spin-polarized atomic hydrogen and its isotopes at very low temperatures. Spin-polarized hydrogen is the only system in nature that remains stable in the gas phase even in the zero temperature limit due to its small mass and weak interatomic interaction. Hydrogen and its heavier isotope tritium are bosons, the heavier mass of tritium producing a self-bound (liquid) system at zero temperature. The other isotope, deuterium, is a fermion with nuclear spin one making possible the study of three different quantum systems depending on the population of the three degenerate spin states. From the theoretical point of view, spin-polarized hydrogen is specially appealing because its interatomic potential is very accurately known making possible its precise quantum many-body study. The experimental study of atomic hydrogen has been very difficult due to its high recombination rate, but it finally led to its Bose–Einstein condensate state in 1998. Degeneracy has also been observed in thin films of hydrogen adsorbed on the ⁴He surface allowing for thepossibility of observing the Berezinskii–Kosterlitz–Thouless superfluid transition
Quantum virial expansion approach to thermodynamics of He adsorbates in carbon nanotube materials: Interacting Bose gas in one dimension
I demonstrate that He adsorbates in carbon nanotube materials can be
treated as one-dimensional interacting gas of spinless bosons for temperatures
below 8 K and for coverages such that all the adsorbates are in the groove
positions of the carbon nanotube bundles. The effects of adsorbate-adsorbate
interactions are studied within the scheme of virial expansion approach. The
theoretical predictions for the specific heat of the interacting adsorbed gas
are given.Comment: 5 PS figure