907 research outputs found
Observation of Interactions between Trapped Ions and Ultracold Rydberg Atoms
We report on the observation of interactions between ultracold Rydberg atoms
and ions in a Paul trap. The rate of observed inelastic collisions, which
manifest themselves as charge transfer between the Rydberg atoms and ions,
exceeds that of Langevin collisions for ground state atoms by about three
orders of magnitude. This indicates a huge increase in interaction strength. We
study the effect of the vacant Paul trap's electric fields on the Rydberg
excitation spectra. To quantitatively describe the exhibited shape of the ion
loss spectra, we need to include the ion-induced Stark shift on the Rydberg
atoms. Furthermore, we demonstrate Rydberg excitation on a dipole-forbidden
transition with the aid of the electric field of a single trapped ion. Our
results confirm that interactions between ultracold atoms and trapped ions can
be controlled by laser coupling to Rydberg states. Adding dynamic Rydberg
dressing may allow for the creation of spin-spin interactions between atoms and
ions, and the elimination of collisional heating due to ionic micromotion in
atom-ion mixtures.Comment: 7 pages, 5 figures, including appendices. Note that the title has
been changed in version
Dynamical Diffraction Theory for Wave Packet Propagation in Deformed Crystals
We develop a theory for the trajectory of an x ray in the presence of a
crystal deformation. A set of equations of motion for an x-ray wave packet
including the dynamical diffraction is derived, taking into account the Berry
phase as a correction to geometrical optics. The trajectory of the wave packet
has a shift of the center position due to a crystal deformation. Remarkably, in
the vicinity of the Bragg condition, the shift is enhanced by a factor (: frequency of an x ray, : gap frequency
induced by the Bragg reflection). Comparison with the conventional dynamical
diffraction theory is also made.Comment: 4 pages, 2 figures. Title change
Boundary conditions for interfaces of electromagnetic (photonic) crystals and generalized Ewald-Oseen extinction principle
The problem of plane-wave diffraction on semi-infinite orthorhombic
electromagnetic (photonic) crystals of general kind is considered. Boundary
conditions are obtained in the form of infinite system of equations relating
amplitudes of incident wave, eigenmodes excited in the crystal and scattered
spatial harmonics. Generalized Ewald-Oseen extinction principle is formulated
on the base of deduced boundary conditions. The knowledge of properties of
infinite crystal's eigenmodes provides option to solve the diffraction problem
for the corresponding semi-infinite crystal numerically. In the case when the
crystal is formed by small inclusions which can be treated as point dipolar
scatterers with fixed direction the problem admits complete rigorous analytical
solution. The amplitudes of excited modes and scattered spatial harmonics are
expressed in terms of the wave vectors of the infinite crystal by closed-form
analytical formulae. The result is applied for study of reflection properties
of metamaterial formed by cubic lattice of split-ring resonators.Comment: 15 pages, 8 figures, submitted to PR
Prospects of reaching the quantum regime in Li-Yb mixtures
We perform numerical simulations of trapped Yb ions that are
buffer gas cooled by a cold cloud of Li atoms. This species combination has
been suggested to be the most promising for reaching the quantum regime of
interacting atoms and ions in a Paul trap. Treating the atoms and ions
classically, we compute that the collision energy indeed reaches below the
quantum limit for a perfect linear Paul trap. We analyze the effect of
imperfections in the ion trap that cause excess micromotion. We find that the
suppression of excess micromotion required to reach the quantum limit should be
within experimental reach. Indeed, although the requirements are strong, they
are not excessive and lie within reported values in the literature. We analyze
the detection and suppression of excess micromotion in our experimental setup.
Using the obtained experimental parameters in our simulation, we calculate
collision energies that are a factor 2-11 larger than the quantum limit,
indicating that improvements in micromotion detection and compensation are
needed there. We also analyze the buffer-gas cooling of linear and
two-dimensional ion crystals. We find that the energy stored in the eigenmodes
of ion motion may reach 10-100 K after buffer-gas cooling under realistic
experimental circumstances. Interestingly, not all eigenmodes are buffer-gas
cooled to the same energy. Our results show that with modest improvements of
our experiment, studying atom-ion mixtures in the quantum regime is in reach,
allowing for buffer-gas cooling of the trapped ion quantum platform and to
study the occurrence of atom-ion Feshbach resonances.Comment: 39 pages, 22 figure
Two-Dimensional Wigner Crystal in Anisotropic Semiconductor
We investigate the effect of mass anisotropy on the Wigner crystallization
transition in a two-dimensional (2D) electron gas. The static and dynamical
properties of a 2D Wigner crystal have been calculated for arbitrary 2D Bravais
lattices in the presence of anisotropic mass, as may be obtainable in Si
MOSFETs with (110) surface. By studying the stability of all possible lattices,
we find significant change in the crystal structure and melting density of the
electron lattice with the lowest ground state energy.Comment: 4 pages, revtex, 4 figure
Recommended from our members
Evolutionary bi-stability in pathogen transmission mode
Many pathogens transmit to new hosts by both infection (horizontal transmission) and transfer to the
infected host's offspring (vertical transmission). These two transmission modes require speci®c adap-
tations of the pathogen that can be mutually exclusive, resulting in a trade-off between horizontal and
vertical transmission. We show that in mathematical models such trade-offs can lead to the simultaneous
existence of two evolutionary stable states (evolutionary bi-stability) of allocation of resources to the two
modes of transmission. We also show that jumping between evolutionary stable states can be induced by
gradual environmental changes. Using quantitative PCR-based estimates of abundance in seed and vege-
tative parts, we show that the pathogen of wheat, Phaeosphaeria nodorum, has jumped between two
distinct states of transmission mode twice in the past 160 years, which, based on published evidence,
we interpret as adaptation to environmental change. The ®nding of evolutionary bi-stability has impli-
cations for human, animal and other plant diseases. An ill-judged change in a disease control
programme could cause the pathogen to evolve a new, and possibly more damaging, combination of
transmission modes. Similarly, environmental changes can shift the balance between transmission
modes, with adverse effects on human, animal and plant health
Buffer gas cooling of a trapped ion to the quantum regime
Great advances in precision quantum measurement have been achieved with
trapped ions and atomic gases at the lowest possible temperatures. These
successes have inspired ideas to merge the two systems. In this way one can
study the unique properties of ionic impurities inside a quantum fluid or
explore buffer gas cooling of the trapped ion quantum computer. Remarkably, in
spite of its importance, experiments with atom-ion mixtures remained firmly
confined to the classical collision regime. We report a collision energy of
1.15(0.23) times the -wave energy (or 9.9(2.0)~K) for a trapped
ytterbium ion in an ultracold lithium gas. We observed a deviation from
classical Langevin theory by studying the spin-exchange dynamics, indicating
quantum behavior in the atom-ion collisions. Our results open up numerous
opportunities, such as the exploration of atom-ion Feshbach resonances, in
analogy to neutral systems.Comment: 8 pages, 6 figures including appendice
Laughlin-Jastrow-correlated Wigner crystal in a strong magnetic field
We propose a new ground state trial wavefunction for a two-dimensional Wigner
crystal in a strong perpendicular magnetic field. The wavefunction includes
Laughlin-Jastrow correlations between electron pairs, and may be interpreted as
a crystal state of composite fermions or composite bosons. Treating the power
of the Laughlin-Jastrow factor as a variational parameter, we use quantum
Monte Carlo simulations to compute the energy of these new states. We find that
our wavefunctions have lower energy than existing crystalline wavefunctions in
the lowest Landau level. Our results are consistent with experimental
observations of the filling factor at which the transition between the
fractional quantum Hall liquid and the Wigner crystal occurs for electron
systems. Exchange contributions to the wavefunctions are estimated
quantitatively and shown to be negligible for sufficiently small filling
factors
Group classification of the Sachs equations for a radiating axisymmetric, non-rotating, vacuum space-time
We carry out a Lie group analysis of the Sachs equations for a time-dependent
axisymmetric non-rotating space-time in which the Ricci tensor vanishes. These
equations, which are the first two members of the set of Newman-Penrose
equations, define the characteristic initial-value problem for the space-time.
We find a particular form for the initial data such that these equations admit
a Lie symmetry, and so defines a geometrically special class of such
spacetimes. These should additionally be of particular physical interest
because of this special geometric feature.Comment: 18 Pages. Submitted to Classical and Quantum Gravit
Considerations on rescattering effects for threshold photo- and electro-production of on deuteron
We show that for the S-state -production in processes and the rescattering effects due to the
transition: (or are cancelled
out due to the Pauli principle. The large values for these effects predicted in
the past may result from the fact that the spin structure of the corresponding
matrix element and the necessary antisymmetrization induced by the presence of
identical protons (or neutrons) in the intermediate state was not taken into
account accurately. One of the important consequences of these considerations
is that photo- and electro-production on deuteron near threshold can
bring direct information about elementary neutron amplitudes.Comment: Add a new sectio
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