7,337 research outputs found
Diffractionless image propagation and frequency conversion via four-wave mixing exploiting the thermal motion of atoms
A setup to frequency-convert an arbitrary image encoded in the spatial
profile of a probe field onto a signal field using four-wave mixing in a
thermal atom vapor is proposed. The atomic motion is exploited to cancel
diffraction of both signal and probe fields simultaneously. We show that an
incoherent probe field can be used to enhance the transverse momentum bandwidth
which can be propagated without diffraction, such that smaller structures with
higher spatial resolution can be transmitted. It furthermore compensate linear
absorption with non-linear gain, to improve the four-wave mixing performance
since the propagation dynamics of the various field intensities is favorably
modified.Comment: 12 pages, 7 figure
Ground state cooling of a nanomechanical resonator in the weak-confinement regime via quantum interference
Ground state cooling of a nanomechanical resonator coupled to a
superconducting flux qubit is discussed. We show that by inducing quantum
interference to cancel detrimental carrier excitations, ground state cooling
becomes possible in the weak-confinement or non-resolved regime. The qubit is
modelled as a three-level system in lambda configuration, and the driving
fluxes are applied such that the qubit absorption spectrum exhibits
electromagnetically induced transparency, thereby cancelling the unwanted
carrier excitation. As our interference-based scheme allows to apply strong
cooling fields, fast and efficient cooling can be achieved
Four-wave mixing enhanced white-light cavity
We discuss in-medium propagation dynamics in a white light cavity that leads
to an enhancement of the cavity's bandwidth without reducing its maximum
intensity buildup. We analyze the spatiotemporal dynamics of our system with a
full simulation of the field propagation in a regime that leads to strong
absorption of the control fields. We find that an additional coherent field is
generated within the medium via four-wave mixing. This self-generated field
leads to a backaction of the medium onto the probe field. Counter intuitively,
this pronounced in-medium dynamics throughout the propagation leads to an
additional enhancement of the cavity bandwidth.Comment: 5 pages, 4 figure
Collective effects between multiple nuclear ensembles in an x-ray cavity-QED setup
The setting of Moessbauer nuclei embedded in thin-film cavities has
facilitated an aspiring platform for x-ray quantum optics as shown in several
recent experiments. Here, we generalize the theoretical model of this platform
that we developed earlier [Phys. Rev. A 88, 043828 (2013)]. The theory
description is extended to cover multiple nuclear ensembles and multiple modes
in the cavity. While the extensions separately do not lead to qualitatively new
features, their combination gives rise to cooperative effects between the
different nuclear ensembles and distinct spectral signatures in the
observables. A related experiment by Roehlsberger et al. [Nature 482, 199
(2012)] is successfully modeled, the scalings derived with semiclassical
methods are reproduced, and a microscopic understanding of the setting is
obtained with our quantum mechanical description.Comment: 18 pages, 6 figure
X-ray quantum optics with M\"ossbauer nuclei embedded in thin film cavities
A promising platform for the emerging field of x-ray quantum optics are
M\"ossbauer nuclei embedded in thin film cavities probed by near-resonant x-ray
light, as used in a number of recent experiments. Here, we develop a quantum
optical framework for the description of experimentally relevant settings
involving nuclei embedded in x-ray waveguides. We apply our formalism to two
settings of current experimental interest based on the archetype M\"ossbauer
isotope 57Fe. For present experimental conditions, we derive compact analytical
expressions and show that the alignment of medium magnetization as well as
incident and detection polarization enable the engineering advanced quantum
optical level schemes. The model encompasses non-linear and quantum effects
which could become accessible in future experiments.Comment: 13 pages, 6 figure
Spontaneous-emission suppression via multiphoton quantum interference
The spontaneous emission is investigated for an effective atomic two-level
system in an intense coherent field with frequency lower than the
vacuum-induced decay width. As this additional low-frequency field is assumed
to be intense, multiphoton processes may be induced, which can be seen as
alternative transition pathways in addition to the simple spontaneous decay.
The interplay of the various interfering transition pathways influences the
decay dynamics of the two-level system and may be used to slow down the
spontaneous decay considerably. We derive from first principles an expression
for the Hamiltonian including up to three-photon processes. This Hamiltonian is
then applied to a quantum mechanical simulation of the decay dynamics of the
two-level system. Finally, we discuss numerical results of this simulation
based on a rubidium atom and show that the spontaneous emission in this system
may be suppressed substantially.Comment: 18 pages, 7 figures, latest version with minor change
Flexible Sensor Network Reprogramming for Logistics
Besides the currently realized applications, Wireless Sensor
Networks can be put to use in logistics processes. However, doing so requires a level of flexibility and safety not provided by the current WSN software platforms. This paper discusses a logistics scenario, and presents SensorScheme, a runtime environment used to realize this scenario, based on semantics of the Scheme programming language. SensorScheme is a general purpose WSN platform, providing dynamic reprogramming, memory safety (sandboxing), blocking I/O, marshalled communication, compact code transport. It improves on the state of the art by making better use of the little available memory, thereby providing greater capability in terms of program size and complexity. We illustrate the use of our platform with some application examples, and provide experimental results to show its
compactness, speed of operation and energy efficiency
Node counting in wireless ad-hoc networks
We study wireless ad-hoc networks consisting of small microprocessors with
limited memory, where the wireless communication between the processors can be highly unreliable. For this setting, we propose a number of algorithms to estimate the number of nodes in the network, and the number of direct neighbors of each node. The algorithms are simulated, allowing comparison of their performance
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