1,328 research outputs found
Measurement of the separation between atoms beyond diffraction limit
Precision measurement of small separations between two atoms or molecules has
been of interest since the early days of science. Here, we discuss a scheme
which yields spatial information on a system of two identical atoms placed in a
standing wave laser field. The information is extracted from the collective
resonance fluorescence spectrum, relying entirely on far-field imaging
techniques. Both the interatomic separation and the positions of the two
particles can be measured with fractional-wavelength precision over a wide
range of distances from bout lambda/550 to lambda/2.Comment: v2: Revised version for publicatio
Microcavities coupled to multilevel atoms
A three-level atom in the -configuration coupled to a microcavity is
studied. The two transitions of the atom are assumed couple to different
counterpropagating mode pairs in the cavity. We analyze the dynamics both, in
the strong-coupling and the bad cavity limit. We find that compared to a
two-level setup, the third atomic state and the additional control field modes
crucially modify the system dynamics and enable more advanced control schemes.
All results are explained using appropriate dressed state and eigenmode
representations. As potential applications, we discuss optical switching and
turnstile operations and detection of particles close to the resonator surface.Comment: 14 pages, 9 figure
Two-mode single-atom laser as a source of entangled light
A two-mode single-atom laser is considered, with the aim of generating
entanglement in macroscopic light. Two transitions in the four-level gain
medium atom independently interact with the two cavity modes, while two other
transitions are driven by control laser fields. Atomic relaxation as well as
cavity losses are taken into account. We show that this system is a source of
macroscopic entangled light over a wide range of control parameters and initial
states of the cavity field
Nuclear quantum optics with x-ray laser pulses
The direct interaction of nuclei with super-intense laser fields is studied.
We show that present and upcoming high-frequency laser facilities, especially
together with a moderate acceleration of the target nuclei, do allow for
resonant laser-nucleus interaction. These direct interactions may be utilized
for the optical measurement of nuclear properties such as the transition
frequency and the dipole moment, thus opening the field of nuclear quantum
optics. As ultimate goal, one may hope that direct laser-nucleus interactions
could become a versatile tool to enhance preparation, control and detection in
nuclear physics.Comment: 5 pages, 3 eps figures, revised versio
Conductance of 1D quantum wires with anomalous electron-wavefunction localization
We study the statistics of the conductance through one-dimensional
disordered systems where electron wavefunctions decay spatially as for , being a constant. In
contrast to the conventional Anderson localization where and the conductance statistics is determined by a single
parameter: the mean free path, here we show that when the wave function is
anomalously localized () the full statistics of the conductance is
determined by the average and the power . Our theoretical
predictions are verified numerically by using a random hopping tight-binding
model at zero energy, where due to the presence of chiral symmetry in the
lattice there exists anomalous localization; this case corresponds to the
particular value . To test our theory for other values of
, we introduce a statistical model for the random hopping in the tight
binding Hamiltonian.Comment: 6 pages, 8 figures. Few changes in the presentation and references
updated. Published in PRB, Phys. Rev. B 85, 235450 (2012
Light propagation through closed-loop atomic media beyond the multiphoton resonance condition
The light propagation of a probe field pulse in a four-level double-lambda
type system driven by laser fields that form a closed interaction loop is
studied. Due to the finite frequency width of the probe pulse, a
time-independent analysis relying on the multiphoton resonance assumption is
insufficient. Thus we apply a Floquet decomposition of the equations of motion
to solve the time-dependent problem beyond the multiphoton resonance condition.
We find that the various Floquet components can be interpreted in terms of
different scattering processes, and that the medium response oscillating in
phase with the probe field in general is not phase-dependent. The phase
dependence arises from a scattering of the coupling fields into the probe field
mode at a frequency which in general differs from the probe field frequency. We
thus conclude that in particular for short pulses with a large frequency width,
inducing a closed loop interaction contour may not be advantageous, since
otherwise the phase-dependent medium response may lead to a distortion of the
pulse shape. Finally, using our time-dependent analysis, we demonstrate that
both the closed-loop and the non-closed loop configuration allow for sub- and
superluminal light propagation with small absorption or even gain. Further, we
identify one of the coupling field Rabi frequencies as a control parameter that
allows to conveniently switch between sub- and superluminal light propagation.Comment: 10 pages, 8 figure
Role of THBS1, WHSC1, ADAMTS1 and RBFOX2 genes in the radiation-induced Dna double strand break repair in Hela tumor cell line
It is well known that inter-individual differences of radiosensitivity have genetic causes, such as variations in the level of DNA or expression of DNA repair genes. However, differentially expressed genes which could lead to inter-individual differences in the level of DNA damage remain largely unidentified. In our study we have induced knock-out of THBS1, WHSC1, ADAMTS1 and RBFOX2 genes in HeLa cell line to clarify the effects of these genes on DNA repair and radiosensitivity
Quasiclassical magnetotransport in a random array of antidots
We study theoretically the magnetoresistance of a
two-dimensional electron gas scattered by a random ensemble of impenetrable
discs in the presence of a long-range correlated random potential. We believe
that this model describes a high-mobility semiconductor heterostructure with a
random array of antidots. We show that the interplay of scattering by the two
types of disorder generates new behavior of which is absent for
only one kind of disorder. We demonstrate that even a weak long-range disorder
becomes important with increasing . In particular, although
vanishes in the limit of large when only one type of disorder is present,
we show that it keeps growing with increasing in the antidot array in the
presence of smooth disorder. The reversal of the behavior of is
due to a mutual destruction of the quasiclassical localization induced by a
strong magnetic field: specifically, the adiabatic localization in the
long-range Gaussian disorder is washed out by the scattering on hard discs,
whereas the adiabatic drift and related percolation of cyclotron orbits
destroys the localization in the dilute system of hard discs. For intermediate
magnetic fields in a dilute antidot array, we show the existence of a strong
negative magnetoresistance, which leads to a nonmonotonic dependence of
.Comment: 21 pages, 13 figure
Group velocity control in the ultraviolet domain via interacting dark-state resonances
The propagation of a weak probe field in a laser-driven four-level atomic
system is investigated. We choose mercury as our model system, where the probe
transition is in the ultraviolet region. A high-resolution peak appears in the
optical spectra due to the presence of interacting dark resonances. We show
that this narrow peak leads to superluminal light propagation with strong
absorption, and thus by itself is only of limited interest. But if in addition
a weak incoherent pump field is applied to the probe transition, then the peak
structure can be changed such that both sub- and superluminal light propagation
or a negative group velocity can be achieved without absorption, controlled by
the incoherent pumping strength
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