7,945 research outputs found
Resonator-Aided Single-Atom Detection on a Microfabricated Chip
We use an optical cavity to detect single atoms magnetically trapped on an
atom chip. We implement the detection using both fluorescence into the cavity
and reduction in cavity transmission due to the presence of atoms. In
fluorescence, we register 2.0(2) photon counts per atom, which allows us to
detect single atoms with 75% efficiency in 250 microseconds. In absorption, we
measure transmission attenuation of 3.3(3)% per atom, which allows us to count
small numbers of atoms with a resolution of about 1 atom.Comment: 4.1 pages, 5 figures, and submitted to Physical Review Letter
DC field induced enhancement and inhibition of spontaneous emission in a cavity
We demonstrate how spontaneous emission in a cavity can be controlled by the
application of a dc field. The method is specially suitable for Rydberg atoms.
We present a simple argument for the control of emission.Comment: 3-pages, 2figure. accepted in Phys. Rev.
Importance of an Astrophysical Perspective for Textbook Relativity
The importance of a teaching a clear definition of the ``observer'' in
special relativity is highlighted using a simple astrophysical example from the
exciting current research area of ``Gamma-Ray Burst'' astrophysics. The example
shows that a source moving relativistically toward a single observer at rest
exhibits a time ``contraction'' rather than a ``dilation'' because the light
travel time between the source and observer decreases with time. Astrophysical
applications of special relativity complement idealized examples with real
applications and very effectively exemplify the role of a finite light travel
time.Comment: 5 pages TeX, European Journal of Physics, in pres
Maximizing the quality factor to mode volume ratio for ultra-small photonic crystal cavities
Small manufacturing-tolerant photonic crystal cavities are systematically
designed using topology optimization to enhance the ratio between quality
factor and mode volume, Q/V. For relaxed manufacturing tolerance, a cavity with
bow-tie shape is obtained which confines light beyond the diffraction limit
into a deep-subwavelength volume. Imposition of a small manufacturing tolerance
still results in efficient designs, however, with diffraction-limited
confinement. Inspired by numerical results, an elliptic ring grating cavity
concept is extracted via geometric fitting. Numerical evaluations demonstrate
that for small sizes, topology-optimized cavities enhance the Q/V-ratio by up
to two orders of magnitude relative to standard L1 cavities and more than one
order of magnitude relative to shape-optimized L1 cavities. An increase in
cavity size can enhance the Q/V-ratio by an increase of the Q-factor without
significant increase of V. Comparison between optimized and reference cavities
illustrates that significant reduction of V requires big topological changes in
the cavity
A simple derivation of the electromagnetic field of an arbitrarily moving charge
The expression for the electromagnetic field of a charge moving along an
arbitrary trajectory is obtained in a direct, elegant, and Lorentz invariant
manner without resorting to more complicated procedures such as differentiation
of the Lienard-Wiechert potentials. The derivation uses arguments based on
Lorentz invariance and a physically transparent expression originally due to
J.J.Thomson for the field of a charge that experiences an impulsive
acceleration.Comment: The following article has been accepted by the American Journal of
Physics. After it is published, it will be found at
http://scitation.aip.org/ajp; 12 pages, 1 figur
Improved qubit bifurcation readout in the straddling regime of circuit QED
We study bifurcation measurement of a multi-level superconducting qubit using
a nonlinear resonator biased in the straddling regime, where the resonator
frequency sits between two qubit transition frequencies. We find that
high-fidelity bifurcation measurements are possible because of the enhanced
qubit-state-dependent pull of the resonator frequency, the behavior of
qubit-induced nonlinearities and the reduced Purcell decay rate of the qubit
that can be realized in this regime. Numerical simulations find up to a
threefold improvement in qubit readout fidelity when operating in, rather than
outside of, the straddling regime. High-fidelity measurements can be obtained
at much smaller qubit-resonator couplings than current typical experimental
realizations, reducing spectral crowding and potentially simplifying the
implementation of multi-qubit devices.Comment: 9 pages, 6 figure
Decays in Quantum Hierarchical Models
We study the dynamics of a simple model for quantum decay, where a single
state is coupled to a set of discrete states, the pseudo continuum, each
coupled to a real continuum of states. We find that for constant matrix
elements between the single state and the pseudo continuum the decay occurs via
one state in a certain region of the parameters, involving the Dicke and
quantum Zeno effects. When the matrix elements are random several cases are
identified. For a pseudo continuum with small bandwidth there are weakly damped
oscillations in the probability to be in the initial single state. For
intermediate bandwidth one finds mesoscopic fluctuations in the probability
with amplitude inversely proportional to the square root of the volume of the
pseudo continuum space. They last for a long time compared to the non-random
case
Color Fields on the Light-Shell
We study the classical color radiation from very high energy collisions that
produce colored particles. In the extreme high energy limit, the classical
color fields are confined to a light-shell expanding at and are associated
with a non-linear -model on the 2D light-shell with specific symmetry
breaking terms. We argue that the quantum version of this picture exhibits
asymptotic freedom and may be a useful starting point for an effective
light-shell theory of the structure between the jets at a very high energy
collider.Comment: 11 pages, no figure
Squeezed single-atom laser in a photonic crystal
We study non-classical and spectral properties of a strongly driven
single-atom laser engineered within a photonic crystal that facilitates a
frequency-dependent reservoir. In these studies, we apply a dressed atom model
approach to derive the master equation of the system and study the properties
of the dressed laser under the frequency dependent transition rates. By going
beyond the secular approximation in the dressed-atom cavity field interaction,
we find that if, in addition, the non-secular terms are included into the
dynamics of the system, then non-linear processes can occur that lead to
interesting new aspects of cavity field behavior. We calculate variances of the
quadrature phase amplitudes and the incoherent part of the spectrum of the
cavity field and show that they differ qualitatively from those observed under
the secular approximation. In particular, it is found that the non-linear
processes lead to squeezing of the fluctuations of the cavity field below the
quantum shot noise limit. The squeezing depends on the relative population of
the dressed states of the system and is found only if there is no population
inversion between the dressed states. Furthermore, we find a linewidth
narrowing below the quantum limit in the spectrum of the cavity field that is
achieved only when the secular approximation is not made. An interpretation of
the linewidth narrowing is provided in terms of two phase dependent noise
(squeezing) spectra that make up the incoherent spectrum. We establish that the
linewidth narrowing is due squeezing of the fluctuations in one quadrature
phase components of the cavity field.Comment: 12 pages, 6 figure
Two-particle Aharonov-Bohm effect and Entanglement in the electronic Hanbury Brown Twiss setup
We analyze a Hanbury Brown Twiss geometry in which particles are injected
from two independent sources into a mesoscopic electrical conductor. The set-up
has the property that all partial waves end in different reservoirs without
generating any single particle interference. There is no single particle
Aharonov-Bohm effect. However, exchange effects lead to two-particle
Aharonov-Bohm oscillations in current correlations. We demonstrate that the
two-particle Aharonov-Bohm effect is connected to orbital entanglement which
can be used for violation of a Bell Inequality.Comment: 4 pages, 2 figures, discussion of postselected electron-electron
entanglement adde
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