6,513 research outputs found
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.
The molecular environment of massive star forming cores associated with Class II methanol maser emission
Methanol maser emission has proven to be an excellent signpost of regions
undergoing massive star formation (MSF). To investigate their role as an
evolutionary tracer, we have recently completed a large observing program with
the ATCA to derive the dynamical and physical properties of molecular/ionised
gas towards a sample of MSF regions traced by 6.7 GHz methanol maser emission.
We find that the molecular gas in many of these regions breaks up into multiple
sub-clumps which we separate into groups based on their association
with/without methanol maser and cm continuum emission. The temperature and
dynamic state of the molecular gas is markedly different between the groups.
Based on these differences, we attempt to assess the evolutionary state of the
cores in the groups and thus investigate the role of class II methanol masers
as a tracer of MSF.Comment: 5 pages, 1 figure, IAU Symposium 242 Conference Proceeding
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
Electromagnetic Transition in Waveguide with Application to Lasers
The electromagnetic transition of two-level atomic systems in a waveguide is
calculated. Compared with the result in free space, the spontaneous emission
rate decrease because the phase space is smaller, and meanwhile, some resonance
appears in some cases. Moreover, the influence of non-uniform electromagnetic
field in a waveguide on absorption and stimulated emission is considered.
Applying the results to lasers, a method to enhance the laser power is
proposed.Comment: 4 pages, 2 figure
Overcoming phonon-induced dephasing for indistinguishable photon sources
Reliable single photon sources constitute the basis of schemes for quantum
communication and measurement based quantum computing. Solid state single
photon sources based on quantum dots are convenient and versatile but the
electronic transitions that generate the photons are subject to interactions
with lattice vibrations. Using a microscopic model of electron-phonon
interactions and a quantum master equation, we here examine phonon-induced
decoherence and assess its impact on the rate of production, and
indistinguishability, of single photons emitted from an optically driven
quantum dot system. We find that, above a certain threshold of desired
indistinguishability, it is possible to mitigate the deleterious effects of
phonons by exploiting a three-level Raman process for photon production
Two-atom dark states in electromagnetic cavities
The center-of-mass motion of two two-level atoms coupled to a single damped
mode of an electromagnetic resonator is investigated. For the case of one atom
being initially excited and the cavity mode in the vacuum state it is shown
that the atomic time evolution is dominated by the appearance of dark states.
These states, in which the initial excitation is stored in the internal atomic
degrees of freedom and the atoms become quantum mechanically entangled, are
almost immune against photon loss from the cavity. Various properties of the
dark states within and beyond the Raman-Nath approximation of atom optics are
worked out.Comment: 8 pages, 4 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
Magnetic field induced lattice anomaly inside the superconducting state of CeCoIn: evidence of the proposed Fulde-Ferrell-Larkin-Ovchinnikov state
We report high magnetic field linear magnetostriction experiments on
CeCoIn single crystals. Two features are remarkable: (i) a sharp
discontinuity in all the crystallographic axes associated with the upper
superconducting critical field that becomes less pronounced as the
temperature increases; (ii) a distinctive second order-like feature observed
only along the c-axis in the high field (10 T ) low
temperature ( 0.35 K) region. This second order transition is
observed only when the magnetic field lies within 20 of the ab-planes and
there is no signature of it above , which raises questions regarding
its interpretation as a field induced magnetically ordered phase. Good
agreement with previous results suggests that this anomaly is related to the
transition to the Fulde-Ferrel-Larkin-Ovchinnikov superconducting state.Comment: 3 figures, 5 page
Luminescence Spectra of Quantum Dots in Microcavities. I. Bosons
We provide a unified theory of luminescence spectra of coupled light-matter
systems realized with semiconductor heterostructures in microcavities,
encompassing: i) the spontaneous emission case, where the system decays from a
prepared (typically pure) initial state, and ii) luminescence in the presence
of a continuous, incoherent pump. While the former case has been amply
discussed in the literature (albeit mainly for the case of resonance), no
consideration has been given to the influence of the incoherent pump. We show
how, by provoking a self-consistent quantum state, the pump considerably alters
the emission spectra, even at vanishing intensities. The main outcome of our
analysis is to unambiguously identify strong-coupling in situations where it
appears in disguise or only seems to appear. Here, we consider bosonic matter
fields, in which case fully analytical solutions can be obtained. This
describes the case of quantum wells or large quantum dots, or the limit of low
excitation where the average populations remain much smaller than one
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