242 research outputs found
Switching Exciton Pulses Through Conical Intersections
Exciton pulses transport excitation and entanglement adiabatically through
Rydberg aggregates, assemblies of highly excited light atoms, which are set
into directed motion by resonant dipole-dipole interaction. Here, we
demonstrate the coherent splitting of such pulses as well as the spatial
segregation of electronic excitation and atomic motion. Both mechanisms exploit
local nonadiabatic effects at a conical intersection, turning them from a
decoherence source into an asset. The intersection provides a sensitive knob
controlling the propagation direction and coherence properties of exciton
pulses. The fundamental ideas discussed here have general implications for
excitons on a dynamic network.Comment: Letter with 4 pages and 4 figures. Supplemental material with 4 pages
and 4 figure
On-chip quantum tomography of mechanical nano-scale oscillators with guided Rydberg atoms
Nano-mechanical oscillators as well as Rydberg-atomic waveguides hosted on
micro-fabricated chip surfaces hold promise to become pillars of future quantum
technologies. In a hybrid platform with both, we show that beams of Rydberg
atoms in waveguides can quantum-coherently interrogate and manipulate
nanomechanical elements, allowing full quantum state tomography. Central to the
tomography are quantum non-demolition measurements using the Rydberg atoms as
probes. Quantum coherent displacement of the oscillator is also made possible,
by driving the atoms with external fields while they interact with the
oscillator. We numerically demonstrate the feasibility of this fully integrated
on-chip control and read-out suite for quantum nano-mechanics, taking into
account noise and error sources.Comment: 11 pages, 5 figures, 1 tabl
Quantum dynamics of long-range interacting systems using the positive-P and gauge-P representations
We provide the necessary framework for carrying out stochastic positive-P and
gauge-P simulations of bosonic systems with long range interactions. In these
approaches, the quantum evolution is sampled by trajectories in phase space,
allowing calculation of correlations without truncation of the Hilbert space or
other approximations to the quantum state. The main drawback is that the
simulation time is limited by noise arising from interactions.
We show that the long-range character of these interactions does not further
increase the limitations of these methods, in contrast to the situation for
alternatives such as the density matrix renormalisation group. Furthermore,
stochastic gauge techniques can also successfully extend simulation times in
the long-range-interaction case, by making using of parameters that affect the
noise properties of trajectories, without affecting physical observables.
We derive essential results that significantly aid the use of these methods:
estimates of the available simulation time, optimized stochastic gauges, a
general form of the characteristic stochastic variance and adaptations for very
large systems. Testing the performance of particular drift and diffusion gauges
for nonlocal interactions, we find that, for small to medium systems, drift
gauges are beneficial, whereas for sufficiently large systems, it is optimal to
use only a diffusion gauge.
The methods are illustrated with direct numerical simulations of interaction
quenches in extended Bose-Hubbard lattice systems and the excitation of Rydberg
states in a Bose-Einstein condensate, also without the need for the typical
frozen gas approximation. We demonstrate that gauges can indeed lengthen the
useful simulation time.Comment: 19 pages, 11 appendix, 3 figure
Conical intersections in an ultracold gas
We find that energy surfaces of more than two atoms or molecules interacting
via dipole-dipole po- tentials generically possess conical intersections (CIs).
Typically only few atoms participate strongly in such an intersection. For the
fundamental case, a circular trimer, we show how the CI affects adiabatic
excitation transport via electronic decoherence or geometric phase
interference. These phe- nomena may be experimentally accessible if the trimer
is realized by light alkali atoms in a ring trap, whose dipole-dipole
interactions are induced by off-resonant dressing with Rydberg states. Such a
setup promises a direct probe of the full many-body density dynamics near a
conical intersection.Comment: 4 pages, 4 figures, replacement to add archive referenc
Newton's cradle and entanglement transport in a flexible Rydberg chain
In a regular, flexible chain of Rydberg atoms, a single electronic excitation
localizes on two atoms that are in closer mutual proximity than all others. We
show how the interplay between excitonic and atomic motion causes electronic
excitation and diatomic proximity to propagate through the Rydberg chain as a
combined pulse. In this manner entanglement is transferred adiabatically along
the chain, reminiscent of momentum transfer in Newton's cradle.Comment: 4 pages, 3 figures. Revised versio
Excitation transport through Rydberg dressing
We show how to create long range interactions between alkali-atoms in
different hyper-fine ground states, allowing coherent electronic quantum state
migration. The scheme uses off resonant dressing with atomic Rydberg states,
exploiting the dipole-dipole excitation transfer that is possible between
those. Actual population in the Rydberg state is kept small. Dressing offers
large advantages over the direct use of Rydberg levels: It reduces ionisation
probabilities and provides an additional tuning parameter for life-times and
interaction-strengths. We present an effective Hamiltonian for the ground-state
manifold and show that it correctly describes the full multi-state dynamics for
up to 5 atoms.Comment: 22 pages + 6 pages appendices, 8 figures, replaced with revised
version, added journal referenc
Phonon background versus analogue Hawking radiation in Bose-Einstein condensates
We determine the feasibility of detecting analogue Hawking radiation in a
Bose-Einstein condensate in the presence of atom loss induced heating. We find
that phonons created by three-body losses overshadow those due to analogue
Hawking radiation. To overcome this problem, three-body losses may have to be
suppressed, for example as proposed by Search et al. [Phys. Rev. Lett. 92
140401 (2004)]. The reduction of losses to a few percent of their normal rate
is typically sufficient to suppress the creation of loss phonons on the time
scale of a fast analogue Hawking phonon detection.Comment: 4 pages, no figures, revised versio
Quantum-field dynamics of expanding and contracting Bose-Einstein condensates
We analyze the dynamics of quantum statistics in a harmonically trapped
Bose-Einstein condensate, whose two-body interaction strength is controlled via
a Feshbach resonance. From an initially non-interacting coherent state, the
quantum field undergoes Kerr squeezing, which can be qualitatively described
with a single mode model. To render the effect experimentally accessible, we
propose a homodyne scheme, based on two hyperfine components, which converts
the quadrature squeezing into number squeezing. The scheme is numerically
demonstrated using a two-component Hartree-Fock-Bogoliubov formalism.Comment: 9 pages, 4 figure
Dipole-dipole induced global motion of Rydberg-dressed atom clouds
We consider two clouds of ground state alkali atoms in two distinct hyperfine
ground states. Each level is far off-resonantly coupled to a Rydberg state,
which leads to dressed ground states with a weak admixture of the Rydberg state
properties. Due to this admixture, for a proper choice of the Rydberg states,
the atoms experience resonant dipole-dipole interactions that induce mechanical
forces acting on all atoms within both clouds. This behavior is in contrast to
the dynamics predicted for bare dipole-dipole interactions between Rydberg
superatoms, where only a single atom per cloud is subject to dipole-dipole
induced motion [Phys. Rev. A {\bf 88} 012716 (2013)].Comment: 15 pages, 2 figure
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