432 research outputs found
Response of the Higgs amplitude mode of superfluid Bose gases in a three dimensional optical lattice
We study the Higgs mode of superfluid Bose gases in a three dimensional
optical lattice, which emerges near the quantum phase transition to the Mott
insulator at commensurate fillings. Specifically, we consider responses of the
Higgs mode to temporal modulations of the onsite interaction and the hopping
energy. In order to calculate the response functions including the effects of
quantum and thermal fluctuations, we map the Bose-Hubbard model onto an
effective pseudospin-one model and use a perturbative expansion based on the
imaginary-time Green's function theory. We also include the effects of an
inhomogeneous trapping potential by means of a local density approximation. We
find that the response function for the hopping modulation is equal to that for
the interaction modulation within our approximation. At the unit filling rate
and in the absence of a trapping potential, we show that the Higgs mode can
exist as a sharp resonance peak in the dynamical susceptibilities at typical
temperatures. However, the resonance peak is significantly broadened due to the
trapping potential when the modulations are applied globally to the entire
system. We suggest that the Higgs mode can be detected as a sharp resonance
peak by partial modulations around the trap center.Comment: 22 pages, 9 figure
Bose-Einstein Condensation of an Ytterbium Isotope
We report the observation of a Bose Einstein condensate in a bosonic isotope
of ytterbium (170Yb). More than 10^6 atoms are trapped in a crossed optical
dipole trap and cooled by evaporation. Condensates of approximately 10^4 atoms
have been obtained. From an expansion of the condensate, we have extracted the
scattering length a=3.6(9) nm.Comment: 4 pages, 3 figure
All-Optical Formation of Quantum Degenerate Mixtures
We report the realization of quantum degenerate mixed gases of ytterbium (Yb)
isotopes using all-optical methods. We have succeeded in cooling attractively
interacting 176Yb atoms via sympathetic cooling down to below the Bose-Einstein
transition temperature, coexisting with a stable condensate of 174Yb atoms with
a repulsive interaction. We have observed a rapid atom loss in 176Yb atoms
after cooling down below the transition temperature, which indicates the
collapse of a 176Yb condensate. The sympathetic cooling technique has been
applied to cool a 173Yb-174Yb Fermi-Bose mixture to the quantum degenerate
regime.Comment: 4 pages, 3 figure
Degenerate Fermi Gases of Ytterbium
An evaporative cooling was performed to cool the fermionic 173Yb atoms in a
crossed optical dipole trap. The elastic collision rate, which is important for
the evaporation, turns out to be large enough from our study. This large
collision rate leads to efficient evaporation and we have successfully cooled
the atoms below 0.6 of the Fermi temperature, that is to say, to a quantum
degenerate regime. In this regime, a plunge of evaporation efficiency is
observed as the result of the Fermi degeneracy.Comment: 4 pages, 3figure
Bose-Einstein condensate in gases of rare atomic species
We report on the successful extension of production of Bose-Einstein
Condensate (BEC) to rare species. Despite its low natural abundance of 0.13%,
Yb is directly evaporatively cooled down to BEC. Our successful
demonstration encourages attempts to obtain quantum gases of radioactive atoms,
which extends the possibility of quantum many-body physics and precision
measurement. Moreover, a stable binary mixture of Yb BEC and Yb
BEC is successfully formed.Comment: 5 pages, 3 figures. Accepted for Phys. Rev.
Effect of Nozzle Length on Breakup Length of Liquid Jet
Although the stability of Newtonian liquid jet has been investigated experimentally and theoretically, many problems has remained unsolved. Especially, the stability of liquid jets in immiscible liquid systems has been little studied. Furthermore, one has to point out that the stability of jets may be influenced by the turbulence in the nozzle and the velocity profile. This work presents the experimental result about the effect of the nozzle length on the breakup length of liquid jets in the air and in the immiscible liquid, as the beginning of a systematic investigation of the influence by these factors on the
breakup of jet. The dependence of the initial amplitude of surface disturbances on the nozzle geometry is presented for evaluating the effect of the nozzle length on the breakup length of laminar liquid jet in the air and in the
immiscible liquid
Observation of the Mott Insulator to Superfluid Crossover of a Driven-Dissipative Bose-Hubbard System
Dissipation is ubiquitous in nature and plays a crucial role in quantum
systems such as causing decoherence of quantum states. Recently, much attention
has been paid to an intriguing possibility of dissipation as an efficient tool
for preparation and manipulation of quantum states. Here we report the
realization of successful demonstration of a novel role of dissipation in a
quantum phase transition using cold atoms. We realize an engineered dissipative
Bose-Hubbard system by introducing a controllable strength of two-body
inelastic collision via photo-association for ultracold bosons in a
three-dimensional optical lattice. In the dynamics subjected to a slow
ramp-down of the optical lattice, we find that strong on-site dissipation
favors the Mott insulating state: the melting of the Mott insulator is delayed
and the growth of the phase coherence is suppressed. The controllability of the
dissipation is highlighted by quenching the dissipation, providing a novel
method for investigating a quantum many-body state and its non-equilibrium
dynamics.Comment: 26 pages, 17 figure
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