130 research outputs found
Crystalline phase of strongly interacting Fermi mixtures
We show that the system of weakly bound molecules of heavy and light
fermionic atoms is characterized by a long-range intermolecular repulsion and
can undergo a gas-crystal quantum transition if the mass ratio exceeds a
critical value. For the critical mass ratio above 100 obtained in our
calculations, this crystalline order can be observed as a superlattice in an
optical lattice for heavy atoms with a small filling factor. We also find that
this novel system is sufficiently stable with respect to molecular relaxation
into deep bound states and to the process of trimer formation.Comment: 4 pages, 1 color figure, published versio
Feshbach resonances in Cesium at Ultra-low Static Magnetic Fields
We have observed Feshbach resonances for 133Cs atoms in two different
hyperfine states at ultra-low static magnetic fields by using an atomic
fountain clock. The extreme sensitivity of our setup allows for high
signal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have
reproduced these resonances using coupled-channels calculations which are in
excellent agreement with our measurements. We justify that these are s-wave
resonances involving weakly-bound states of the triplet molecular Hamiltonian,
identify the resonant closed channels, and explain the observed multi-peak
structure. We also describe a model which precisely accounts for the
collisional processes in the fountain and which explains the asymmetric shape
of the observed Feshbach resonances in the regime where the kinetic energy
dominates over the coupling strength.Comment: 5 pages, 4 figures, 1 tabl
Coupled pair of one and two dimensional magneto-plasmons on electrons on helium
Electrons on the liquid helium surface form an extremely clean two
dimensional system where different plasmon-excitations can coexist. Under a
magnetic field time reversal symmetry is broken and all the bulk
magneto-plasmons become gaped at frequencies below cyclotron resonance while
chiral one dimensional edge magneto-plasmons appear at the system perimeter. We
theoretically show that the presence of a homogeneous density gradient in the
electron gas leads to the formation of a delocalized magneto-plasmon mode in
the same frequency range as the lowest frequency edge-magnetoplasmon mode. We
experimentally confirm its existence by measuring the corresponding resonance
peak in frequency dependence of the admittance of the electron gas. This allows
to realize a prototype system to investigate the coupling between a chiral
one-dimensional mode and a single delocalized bulk mode. Such a model system
can be important for the understanding of transport properties of topological
materials where states of different dimensionality can coexist
Dipolar-induced resonance for ultracold bosons in a quasi-one-dimensional optical lattice
We study the role of the dipolar-induced resonance (DIR) in a quasi-one-dimensional system of ultracold bosons. We first describe the effect of the DIR on two particles in a harmonic trap. Then, we consider a deep optical lattice loaded with ultracold dipolar bosons. In order to describe this system, we introduce a novel atom-dimer extended Bose-Hubbard model, which is the minimal model correctly accounting for the DIR. We analyze the impact of the DIR on the phase diagram at T=0 by exact diagonalization of a small-sized system. We show that the DIR strongly affects this phase diagram. In particular, we predict the mass density wave to occur in a narrow domain corresponding to weak nearest-neighbor interactions, and we predict the occurrence of a collapse phase for stronger dipolar interactions. © 2013 American Physical Society
Interaction induced decay of a heteronuclear two-atom system
Two-atom systems in small traps are of fundamental interest, first of all for
understanding the role of interactions in degenerate cold gases and for the
creation of quantum gates in quantum information processing with single-atom
traps. One of the key quantities is the inelastic relaxation (decay) time when
one of the atoms or both are in a higher hyperfine state. Here we measure this
quantity in a heteronuclear system of Rb and Rb in a micro
optical trap and demonstrate experimentally and theoretically the presence of
both fast and slow relaxation processes, depending on the choice of the initial
hyperfine states. The developed experimental method allows us to single out a
particular relaxation process and, in this sense, our experiment is a
"superclean platform" for collisional physics studies. Our results have also
implications for engineering of quantum states via controlled collisions and
creation of two-qubit quantum gates.Comment: 8 pages, 3 figure
Dipolar-Induced Resonance for Ultracold Bosons in a Quasi-1D Optical Lattice
We study the role of the Dipolar-Induced Resonance (DIR) in a
quasi-one-dimensional system of ultracold bosons. We first describe the effect
of the DIR on two particles in a harmonic trap. Then, we consider a deep
optical lattice loaded with ultracold dipolar bosons. In order to describe this
system, we introduce a novel atom-dimer extended Bose-Hubbard model, which is
the minimal model correctly accounting for the DIR. We analyze the impact of
the DIR on the phase diagram at T=0 by exact diagonalization of a small-sized
system. We show that the DIR strongly affects this phase diagram. In
particular, we predict the mass density wave to occur in a narrow domain
corresponding to weak nearest-neighbor interactions, and the occurrence of a
collapse phase for stronger dipolar interactions.Comment: 6 pages, 10 figure
Classical, non-linear, internal dynamics of large, isolated, vibrationally excited molecules
This work reports numerical experiments intended to clarify the internal
equilibration process in large molecules, following vibrational excitation. A
model of amorphous and oxygenated hydrocarbon macromolecule (about 500
atoms)--simulating interstellar dust-- is built up by means of a chemical
simulation code. Its structure is optimized, and its normal modes determined.
About 4.5 eV of potential energy is then deposited locally by perturbing one of
the C-H peripheral bonds, thus simulating the capture of a free H atom by a
dangling C bond. The ensuing relaxation of the system is followed for up to 300
ps, using a molecular mechanics code. When steady state is reached, spectra and
time correlation functions of kinetic energy and bond length fluctuations
indicate that most normal modes have been activated, but the motion remains
quasi-periodic or regular. By contrast, when the molecule is violently excited
or embedded in a thermal bath (modelled by Langevin dynamics), the same markers
clearly depict chaotic motions. Thus it appears that even such a large system
of oscillators is unable to provide the equivalent of a thermal bath to any one
of these, unless there are strong resonances between some of them. In general,
therefore, an energy of a few eV's deposited in an isolated molecule will not
be immediately thermalized. This conclusion is of consequence for the
interpretation of astronomical UIB spectra.
Key Words:IS dust--UIBs--Excitation, relaxation processes.Comment: 19 pages, 9 figures, J. of Phys. B 2002, vol 35(17
- …