241 research outputs found
Collisional stability of a three-component degenerate Fermi gas
We report on the creation of a degenerate Fermi gas consisting of a balanced
mixture of atoms in three different hyperfine states of Li. This new system
consists of three distinguishable Fermions with different and tunable
interparticle scattering lengths , and . We are able
to prepare samples containing atoms in each state at a
temperature of about nK, which corresponds to . We
investigated the collisional stability of the gas for magnetic fields between 0
and 600 G and found a prominent loss feature at 130 G. From lifetime
measurements we determined three-body loss coefficients, which vary over nearly
three orders of magnitude
Efficient and robust initialization of a qubit register with fermionic atoms
We show that fermionic atoms have crucial advantages over bosonic atoms in
terms of loading in optical lattices for use as a possible quantum computation
device. After analyzing the change in the level structure of a non-uniform
confining potential as a periodic potential is superimposed to it, we show how
this structure combined with the Pauli principle and fermion degeneracy can be
exploited to create unit occupancy of the lattice sites with very high
efficiency.Comment: 4 pages, 3 figure
Fermionization of two distinguishable fermions
In this work we study a system of two distinguishable fermions in a 1D
harmonic potential. This system has the exceptional property that there is an
analytic solution for arbitrary values of the interparticle interaction. We
tune the interaction strength via a magnetic offset field and compare the
measured properties of the system to the theoretical prediction. At the point
where the interaction strength diverges, the energy and square of the wave
function for two distinguishable particles are the same as for a system of two
identical fermions. This is referred to as fermionization. We have observed
this phenomenon by directly comparing two distinguishable fermions with
diverging interaction strength with two identical fermions in the same
potential. We observe good agreement between experiment and theory. By adding
one or more particles our system can be used as a quantum simulator for more
complex few-body systems where no theoretical solution is available
Collective excitations of a degenerate gas at the BEC-BCS crossover
We study collective excitation modes of a fermionic gas of Li atoms in
the BEC-BCS crossover regime. While measurements of the axial compression mode
in the cigar-shaped trap close to a Feshbach resonance confirm theoretical
expectations, the radial compression mode shows surprising features. In the
strongly interacting molecular BEC regime we observe a negative frequency shift
with increasing coupling strength. In the regime of a strongly interacting
Fermi gas, an abrupt change in the collective excitation frequency occurs,
which may be a signature for a transition from a superfluid to a collisionless
phase.Comment: Feshbach resonance position updated, few minor change
Bloch oscillations in Fermi gases
The possibility of Bloch oscillations for a degenerate and superfluid Fermi
gas of atoms in an optical lattice is considered. For a one-component
degenerate gas the oscillations are suppressed for high temperatures and band
fillings. For a two-component gas the Landau criterion is used for specifying
the regime where Bloch oscillations of the superfluid may be observed. We show
how the amplitude of Bloch oscillations varies along the BCS-BEC crossover.Comment: 4 pages, 2 figures. explanations adde
Truncated-Determinant Diagrammatic Monte Carlo for Fermions with Contact Interaction
For some models of interacting fermions the known solution to the notorious
sign-problem in Monte Carlo (MC) simulations is to work with macroscopic
fermionic determinants; the price, however, is a macroscopic scaling of the
numerical effort spent on elementary local updates. We find that the {\it
ratio} of two macroscopic determinants can be found with any desired accuracy
by considering truncated (local in space and time) matices. In this respect, MC
for interacting fermionic systems becomes similar to that for the
sign-problem-free bosonic systems with system-size independent update cost. We
demonstrate the utility of the truncated-determinant method by simulating the
attractive Hubbard model within the MC scheme based on partially summed Feynman
diagrams. We conjecture that similar approach may be useful in other
implementations of the sign-free determinant schemes.Comment: results of the actual Hubbard model simulations are adde
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