11,746 research outputs found
Some remarks on 'superradiant' phase transitions in light-matter systems
In this paper we analyze properties of the phase transition that appears in a
set of quantum optical models; Dicke, Tavis-Cummings, quantum Rabi, and finally
the Jaynes-Cummings model. As the light-matter coupling is increased into the
deep strong coupling regime, the ground state turns from vacuum to become a
superradiant state characterized by both atomic and photonic excitations. It is
pointed out that all four transitions are of the mean-field type, that quantum
fluctuations are negligible, and hence these fluctuations cannot be responsible
for the corresponding vacuum instability. In this respect, these are not
quantum phase transitions. In the case of the Tavis-Cummings and
Jaynes-Cummings models, the continuous symmetry of these models implies that
quantum fluctuations are not only negligible, but strictly zero. However, all
models possess a non-analyticity in the ground state in agreement with a
continuous quantum phase transition. As such, it is a matter of taste whether
the transitions should be termed quantum or not. In addition, we also consider
the modifications of the transitions when photon losses are present. For the
Dicke and Rabi models these non-equilibrium steady states remain critical,
while the criticality for the open Tavis-Cummings and Jaynes-Cummings models is
completely lost, i.e. in realistic settings one cannot expect a true critical
behaviour for the two last models.Comment: 25 pages (single column), 6 figure
The assessment of long-term orbital debris models
Existing long-term orbital debris models are assessed as a first step in the Air Force's effort to develop an Air Force long-term orbital debris model which can perform the following functions: (1) operate with the necessary accuracy at the relevant altitudes and orbital parameters; (2) benefit from new Air Force and non-Air Force debris measurements; and (3) accommodate current and future Air Force space scenarios. Model assessment results are shown for the NASA engineering model. The status of the NASA EVOLVE model assessment is discussed
Some local--global phenomena in locally finite graphs
In this paper we present some results for a connected infinite graph with
finite degrees where the properties of balls of small radii guarantee the
existence of some Hamiltonian and connectivity properties of . (For a vertex
of a graph the ball of radius centered at is the subgraph of
induced by the set of vertices whose distance from does not
exceed ). In particular, we prove that if every ball of radius 2 in is
2-connected and satisfies the condition for
each path in , where and are non-adjacent vertices, then
has a Hamiltonian curve, introduced by K\"undgen, Li and Thomassen (2017).
Furthermore, we prove that if every ball of radius 1 in satisfies Ore's
condition (1960) then all balls of any radius in are Hamiltonian.Comment: 18 pages, 6 figures; journal accepted versio
Could any black holes be produced at the LHC?
We introduce analytical quantum gravity modifications of the production cross
section for terascale black holes by employing an effective ultraviolet cut off
. We find the new cross sections approach the usual "black disk" form at
high energy, while they differ significantly near the fundamental scale from
the standard increase with respect to . We show that the heretofore
discontinuous step function used to represent the cross section threshold can
realistically be modeled by two functions representing the incoming and final
parton states in a high energy collision. The growth of the cross section with
collision energy is thus a unique signature of and number of spatial
dimensions . Contrary to the classical black disk result, our cross section
is able to explain why black holes might not be observable in LHC experiments
while they could be still at the reach of ultra-high energy cosmic ray events.Comment: v1: 10 pages, 1 figure; v2: 11 pages, 1 figure, additional
references, minor modifications; v3: new title, expanded discussion with
updated production estimates, additional references, 4 figures, 19 pages,
version accepted for publication on Physical Review
Noise Properties of Superconducting Coplanar Waveguide Microwave Resonators
We have measured noise in thin-film superconducting coplanar waveguide
resonators. This noise appears entirely as phase noise, equivalent to a jitter
of the resonance frequency. In contrast, amplitude fluctuations are not
observed at the sensitivity of our measurement. The ratio between the noise
power in the phase and amplitude directions is large, in excess of 30 dB. These
results have important implications for resonant readouts of various devices
such as detectors, amplifiers, and qubits. We suggest that the phase noise is
due to two-level systems in dielectric materials.Comment: 4 pages, 3 figures, accepted for publication in Applied Physics
Letter
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