7,882 research outputs found
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
Is the number of Photons a Classical Invariant?
We describe an apparent puzzle in classical electrodynamics and its
resolution. It is concerned with the Lorentz invariance of the classical analog
of the number of photons.Comment: Revised version, 3 figure
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
Schiff moment of the Mercury nucleus and the proton dipole moment
We calculated the contribution of internal nucleon electric dipole moments to
the Schiff moment of Hg. The contribution of the proton electric dipole
moment was obtained via core polarization effects that were treated in the
framework of random phase approximation with effective residual forces. We
derived a new upper bound cm of the proton
electric dipole moment.Comment: 4 pages, 2 figures, RevTex
Quadrupole transitions near interface: general theory and application to atom inside a planar cavity
Quadrupole radiation of an atom in an arbitrary environment is investigated
within classical as well as quantum electrodynamical approaches. Analytical
expressions for decay rates are obtained in terms of Green function of Maxwell
equations. The equivalence of both approaches is shown. General expressions are
applied to analyze the quadrupole decay rate of an atom placed between two half
spaces with arbitrary dielectric constant. It is shown that in the case when
the atom is close to the surface, the total decay rate is inversely
proportional to the fifth power of distance between an atom and a plane
interface.Comment: 18 pages, 7 figure
Simple modeling of self-oscillation in Nano-electro-mechanical systems
We present here a simple analytical model for self-oscillations in
nano-electro-mechanical systems. We show that a field emission self-oscillator
can be described by a lumped electrical circuit and that this approach is
generalizable to other electromechanical oscillator devices. The analytical
model is supported by dynamical simulations where the electrostatic parameters
are obtained by finite element computations.Comment: accepted in AP
Inertial Focusing of Particles in Curved Micro-channels
Inertial focusing is the migration of particles in flow laterally across a channel into well-defined equilibrium positions. In microfluidic channels, inertial focusing takes advantage of hydrodynamic interactions even at high flow speeds. Particle isolation through inertial focusing is a high throughput method of processing biological samples for point-of-care diagnostics. While photos provide qualitative analyses of inertial focusing, we desired quantitative characterization of these systems. In this study, we ran flow experiments, first with fluorescent polystyrene beads and later with cells in solution, through curved micro-channels at controlled rates using a syringe pump. Our results from polystyrene bead experiments confirmed previous studies on flow through curved micro-channels, in which particles are focused along both sides of the channel at low flow rates and transition towards the center of the channel as the flow rate increases. FWHM analysis also showed that the streamline width is minimized at an intermediate flow rate, indicating inertial focusing is optimized under that condition. As this method of analysis was confirmed with polystyrene beads, we further used this analysis method to characterize the focusing of cells in solution. To maximize both throughput and purity, microfluidic devices must be designed to operate at the highest flow rate at which effective separation from bulk fluid can occur. The device presented in this report indeed isolates the desired target cells to be studied in downstream characterization.http://deepblue.lib.umich.edu/bitstream/2027.42/169578/1/Honors_Capstone_Anna_Kaehr.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/169578/2/Kaehr_Anna_Capstone_Poster.pptxhttp://deepblue.lib.umich.edu/bitstream/2027.42/169578/3/Capstone_Presentation_Video_Anna_Kaehr.mp
Interaction between Foxc1 and Fgf8 during Mammalian Jaw Patterning and in the Pathogenesis of Syngnathia
Syngnathia (bony fusion of the upper and lower jaw) is a rare human congenital condition, with fewer than sixty cases reported in the literature. Syngnathia typically presents as part of a complex syndrome comprising widespread oral and maxillofacial anomalies, but it can also occur in isolation. Most cartilage, bone, and connective tissue of the head and face is derived from neural crest cells. Hence, congenital craniofacial anomalies are often attributed to defects in neural crest cell formation, survival, migration, or differentiation. The etiology and pathogenesis of syngnathia however remains unknown. Here, we report that Foxc1 null embryos display bony syngnathia together with defects in maxillary and mandibular structures, and agenesis of the temporomandibular joint (TMJ). In the absence of Foxc1, neural crest cell derived osteogenic patterning is affected, as osteoblasts develop ectopically in the maxillary prominence and fuse with the dentary bone. Furthermore, we observed that the craniofacial musculature is also perturbed in Foxc1 null mice, which highlights the complex tissue interactions required for proper jaw development. We present evidence that Foxc1 and Fgf8 genetically interact and that Fgf8 dosage is associated with variation in the syngnathic phenotype. Together our data demonstrates that Foxc1 – Fgf8 signaling regulates mammalian jaw patterning and provides a mechanistic basis for the pathogenesis of syngnathia. Furthermore, our work provides a framework for understanding jaw patterning and the etiology of other congenital craniofacial anomalies, including temporomandibular joint agenesis
Surface-induced heating of cold polar molecules
We study the rotational and vibrational heating of diatomic molecules placed
near a surface at finite temperature on the basis of macroscopic quantum
electrodynamics. The internal molecular evolution is governed by transition
rates that depend on both temperature and position. Analytical and numerical
methods are used to investigate the heating of several relevant molecules near
various surfaces. We determine the critical distances at which the surface
itself becomes the dominant source of heating and we investigate the transition
between the long-range and short-range behaviour of the heating rates. A simple
formula is presented that can be used to estimate the surface-induced heating
rates of other molecules of interest. We also consider how the heating depends
on the thickness and composition of the surface.Comment: 17 pages, 7 figure
Electrostatic internal energy using the method of images
For several configurations of charges in the presence of conductors, the
method of images permits us to obtain some observables associated with such a
configuration by replacing the conductors with some image charges. However,
simple inspection shows that the potential energy associated with both systems
does not coincide. Nevertheless, it can be shown that for a system of a
grounded or neutral conductor and a distribution of charges outside, the
external potential energy associated with the real charge distribution embedded
in the field generated by the set of image charges is twice the value of the
internal potential energy associated with the original system. This assertion
is valid for any size and shape of the conductor, and regardless of the
configuration of images required. In addition, even in the case in which the
conductor is not grounded nor neutral, it is still possible to calculate the
internal potential energy of the original configuration through the method of
images. These results show that the method of images could also be useful for
calculations of the internal potential energy of the original system.Comment: 5 pages, 3 figures. New discussions added. Minor change
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