236 research outputs found
Robustness of spatial Penning trap modes against environment-assisted entanglement
The separability of the spatial modes of a charged particle in a Penning trap
in the presence of an environment is studied by means of the positive partial
transpose (PPT) criterion. Assuming a weak Markovian environment, described by
linear Lindblad operators, our results strongly suggest that the environmental
coupling of the axial and cyclotron degrees of freedom does not lead to
entanglement at experimentally realistic temperatures. We therefore argue that,
apart from unavoidable decoherence, the presence of such an environment does
not alter the effectiveness of recently suggested quantum information protocols
in Penning traps, which are based on the combination of a spatial mode with the
spin of the particle.Comment: 11 pages, 2 figure
Source of entangled atom pairs on demand, using the Rydberg blockade
Two ultracold atom clouds, each separately in a dipole-blockade regime,
realize a source of entangled atom pairs that can be ejected on demand.
Entanglement generation and ejection is due to resonant dipole-dipole
interactions, while van-der-Waals interactions are predominantly responsible
for the blockade that ensures the ejection of a single atom per cloud. A source
of entangled atoms using these effects can operate with a 10 kHz repetition
rate producing ejected atoms with velocities of about 0.5 m/s.Comment: 7 pages, 4 figure
Non-Markovian Dynamics in Ultracold Rydberg Aggregates
We propose a setup of an open quantum system in which the environment can be
tuned such that either Markovian or non-Markovian system dynamics can be
achieved. The implementation uses ultracold Rydberg atoms, relying on their
strong long-range interactions. Our suggestion extends the features available
for quantum simulators of molecular systems employing Rydberg aggregates and
presents a new test bench for fundamental studies of the classification of
system-environment interactions and the resulting system dynamics in open
quantum systems.Comment: 13 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
Quantum simulation of energy transport with embedded Rydberg aggregates
We show that an array of ultracold Rydberg atoms embedded in a laser driven
background gas can serve as an aggregate for simulating exciton dynamics and
energy transport with a controlled environment. Spatial disorder and
decoherence introduced by the interaction with the background gas atoms can be
controlled by the laser parameters. This allows for an almost ideal realization
of a Haken-Reineker-Strobl type model for energy transport. Physics can be
monitored using the same mechanism that provides control over the environment.
The degree of decoherence is traced back to information gained on the
excitation location through the monitoring, turning the setup into an
experimentally accessible model system for studying the effects of quantum
measurements on the dynamics of a many-body quantum system.Comment: 5 pages, 4 figures, 3 pages supp. in
Optical absorption of non-interacting tight-binding electrons in a Peierls-distorted chain at half band-filling
In this first of three articles on the optical absorption of electrons in
half-filled Peierls-distorted chains we present analytical results for
non-interacting tight-binding electrons. We carefully derive explicit
expressions for the current operator, the dipole transition matrix elements,
and the optical absorption for electrons with a cosine dispersion relation of
band width and dimerization parameter . New correction
(``''-)terms to the current operator are identified. A broad band-to-band
transition is found in the frequency range whose shape
is determined by the joint density of states for the upper and lower Peierls
subbands and the strong momentum dependence of the transition matrix elements.Comment: 17 pages REVTEX 3.0, 2 postscript figures; hardcopy versions before
May 96 are obsolete; accepted for publication in The Philosophical Magazine
Monitoring of downloads of Belgorod State University (Russia) scientists' publications by scientists from other countries
The article presents a review on the functioning of the ResearchGate network and the growth of its popularity both from the literary data and from the experiments in the Google Scholar search engine. It describes a unique weekly monitoring experiments of downloads of Belgorod State University (Russia) scientists' publications by scientists from other countries (starting on 11.01.2015 through 20.12.2015), and it is shown that scientists from the United States (about 10,000 downloads in 2015) and China (about 6,000 downloads in 2015) are most interested in these publication
Fano resonances in quantum transport with vibrations
Quantum-mechanical scattering involving continuum states coupled to a scatterer with a discrete spectrum gives rise to Fano resonances. Here we consider scatterers that possess internal vibrational degrees of freedom in addition to discrete states. Entanglement between the scattered excitation and vibrational modes complicates analytical and numerical calculations considerably. For the example of one-dimensional scattering we develop a multichannel quantum scattering approach which can determine reflection and transmission probabilities in the presence of vibrations. Application to a linear chain coupled to a control unit containing vibrating sites shows that vibrational degrees of freedom can have a profound effect on quantum transport. For suitable parameters, spectral regions which are opaque in the static case can be rendered transparent when vibrations are included. The formalism is general enough to be applicable to a variety of platforms for quantum transport including molecular aggregates, cold atom chains, quantum-dot arrays and molecular wires based on conjugated polymers
Surface superconducting states in a polycrystalline MgB sample
We report results of dc magnetic and ac linear low-frequency study of a
polycrystalline MgB sample. AC susceptibility measurements at low
frequencies, performed under dc fields parallel to the sample surface, provide
a clear evidence for surface superconducting states in MgB.Comment: 4 pages and 5 figure
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