166 research outputs found
Ionic polaron in a Bose-Einstein condensate
The ground state properties of a degenerate bosonic gas doped with an ion are
investigated by means of quantum Monte Carlo simulations in three dimensions.
The system features competing length and energy scales, which result in vastly
different polaronic properties compared to neutral quantum impurities.
Depending on whether a two-body bound state is supported or not by the atom-ion
potential, we identify a transition between a polaron regime amenable to a
perturbative treatment in the limit of weak atom-ion interactions and a
many-body bound state with vanishing quasi-particle residue composed of
hundreds of atoms. In order to analyze the structure of the corresponding
states we examine the atom-ion and atom-atom correlation functions. Our
findings are directly relevant to experiments using hybrid atom-ion setups that
have recently attained the ultracold regime.Comment: 11 pages, 6 figures, 1 tabl
A bosonic Josephson junction controlled by a single trapped ion
We theoretically investigate the properties of a double-well bosonic
Josephson junction coupled to a single trapped ion. We find that the coupling
between the wells can be controlled by the internal state of the ion, which can
be used for studying mesoscopic entanglement between the two systems and to
measure their interaction with high precision. As a particular example we
consider a single Rb atom and a small Bose-Einstein condensate
controlled by a single Yb ion. We calculate inter-well coupling
rates reaching hundreds of Hz, while the state dependence amounts to tens of Hz
for plausible values of the currently unknown s-wave scattering length between
the atom and the ion. The analysis shows that it is possible to induce either
the self-trapping or the tunneling regime, depending on the internal state of
the ion. This enables the generation of large scale ion-atomic wavepacket
entanglement within current technology.Comment: 6 pages and 5 figures, including additional material. Accepted for
publication in Phys. Rev. Let
Asymmetric double-well potential for single atom interferometry
We consider the evolution of a single-atom wavefunction in a time-dependent
double-well interferometer in the presence of a spatially asymmetric potential.
We examine a case where a single trapping potential is split into an asymmetric
double well and then recombined again. The interferometer involves a
measurement of the first excited state population as a sensitive measure of the
asymmetric potential. Based on a two-mode approximation a Bloch vector model
provides a simple and satisfactory description of the dynamical evolution. We
discuss the roles of adiabaticity and asymmetry in the double-well
interferometer. The Bloch model allows us to account for the effects of
asymmetry on the excited state population throughout the interferometric
process and to choose the appropriate splitting, holding and recombination
periods in order to maximize the output signal. We also compare the outcomes of
the Bloch vector model with the results of numerical simulations of the
multi-state time-dependent Schroedinger equation.Comment: 9 pages, 6 figure
Nonlinearity-assisted quantum tunneling in a matter-wave interferometer
We investigate the {\em nonlinearity-assisted quantum tunneling} and
formation of nonlinear collective excitations in a matter-wave interferometer,
which is realised by the adiabatic transformation of a double-well potential
into a single-well harmonic trap. In contrast to the linear quantum tunneling
induced by the crossing (or avoided crossing) of neighbouring energy levels,
the quantum tunneling between different nonlinear eigenstates is assisted by
the nonlinear mean-field interaction. When the barrier between the wells
decreases, the mean-field interaction aids quantum tunneling between the ground
and excited nonlinear eigenstates. The resulting {\em non-adiabatic evolution}
depends on the input states. The tunneling process leads to the generation of
dark solitons, and the number of the generated dark solitons is highly
sensitive to the matter-wave nonlinearity. The results of the numerical
simulations of the matter-wave dynamics are successfully interpreted with a
coupled-mode theory for multiple nonlinear eigenstates.Comment: 11 pages, 6 figures, accept for publication in J. Phys.
Decision making and management of gliomas: practical considerations
Over the last decade, diagnostic options and introduction of novel treatments have expanded the armamentarium in the management of malignant glioma. Combined chemoradiotherapy has become the standard of care in glioblastoma up to the age of 70 years, while treatment in elderly patients or with lower grade glioma is less well defined. Molecular markers define different disease subtypes and allow for adapted treatment selection. This review focuses on simple questions arising in the daily management of patient
Theoretical analysis of the implementation of a quantum phase gate with neutral atoms on atom chips
We present a detailed, realistic analysis of the implementation of a proposal
for a quantum phase gate based on atomic vibrational states, specializing it to
neutral rubidium atoms on atom chips. We show how to create a double--well
potential with static currents on the atom chips, using for all relevant
parameters values that are achieved with present technology. The potential
barrier between the two wells can be modified by varying the currents in order
to realize a quantum phase gate for qubit states encoded in the atomic external
degree of freedom. The gate performance is analyzed through numerical
simulations; the operation time is ~10 ms with a performance fidelity above
99.9%. For storage of the state between the operations the qubit state can be
transferred efficiently via Raman transitions to two hyperfine states, where
its decoherence is strongly inhibited. In addition we discuss the limits
imposed by the proximity of the surface to the gate fidelity.Comment: 9 pages, 5 color figure
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