11,224 research outputs found
Correlator expansion approach to stationary states of weakly coupled cavity arrays
We introduce a method for calculating the stationary state of a translation
invariant array of weakly coupled cavities in the presence of dissipation and
coherent as well as incoherent drives. Instead of computing the full density
matrix our method directly calculates the correlation functions which are
relevant for obtaining all local quantities of interest. It considers an
expansion of the correlation functions and their equations of motion in powers
of the photon tunneling rate between adjacent cavities, leading to an exact
second order solution for any number of cavities. Our method provides a
controllable approximation for weak tunneling rates applicable to the strongly
correlated regime that is dominated by nonlinearities in the cavities and thus
of high interest.Comment: contribution to J. Phys. B special issue celebrating Jaynes-Cummings
physic
Lasing in Strong Coupling
An almost ideal thresholdless laser can be realized in the strong-coupling
regime of light-matter interaction, with Poissonian fluctuations of the field
at all pumping powers and all intensities of the field. This ideal scenario is
thwarted by quantum nonlinearities when crossing from the linear to the
stimulated emission regime, resulting in a universal jump in the second order
coherence, which measurement could however be used to establish a standard of
lasing in strong coupling.Comment: 5 pages, 2 figure
Photon correlations from ultra-strong optical nonlinearities
We study the full field and frequency filtered output photon statistics of a
resonator in thermal equilibrium with a bath and containing an arbitrarily
large quartic nonlinearity. According to the general theory of photodetection,
we derive general input-output relations valid for the ultra-anharmonic regime,
where the nonlinearity becomes comparable to the energy of the resonator, and
show how the emission properties are modified as compared to the generally
assumed simple anharmonic regime. We analyse the impact of the nonlinearity on
the full statistics of the emission and its spectral properties. In particular
we derive a semi-analytical expression for the frequency resolved two-photon
correlations or two-photon spectrum of the system in terms of the master
equation coefficients and density matrix. This provides a very clear insight
into the level structure and emission possibilities of the system.Comment: 10 pages, 7 figure
The Effects of Inlet Flow Modification on Cavitating Inducer Performance
This paper explores the effect of inlet flow modification on the cavitating and noncavitating performance of two cavitating inducers, one of simple helical design and the other a model of the low-pressure LOX pump in the Space Shuttle Main Engine. The modifications were generated by sections of honeycomb, both uniform and nonuniform. Significant improvement in the performance over a wide range of flow coefficients resulted from the use of either honeycomb section. Measurements of the axial and swirl velocity profiles of the flows entering the inducers were made in order to try to understand the nature of the inlet flow and the manner in which it is modified by the honeycomb sections
Solving the One-Dimensional Time-Independent Schr\"odinger Equation with High Accuracy: The LagrangeMesh Mathematica Package
In order to find the spectrum associated with the one-dimensional
Schr\"oodinger equation, we discuss the Lagrange Mesh method (LMM) and its
numerical implementation for bound states. After presenting a general overview
of the theory behind the LMM, we introduce the LagrangeMesh package: the
numerical implementation of the LMM in Mathematica. Using few lines of code,
the package enables a quick home-computer computation of the spectrum and
provides a practical tool to study a large class of systems in quantum
mechanics. The main properties of the package are (i) the input is basically
the potential function and the interval on which is defined; and (ii) the
accuracy in calculations and final results is controllable by the user. As
illustration, a highly accurate spectrum of some relevant quantum systems is
obtained by employing the commands that the package offers. In fact, the
present work can be regarded as a user guide based on worked examples.Comment: File LagrangeMesh.wl can be provided to the interested reader, just
contact the author via email. Alternatively, it can be found at
https://github.com/JuanCarlosdelValle/LagrangeMesh-Packag
Production and decays of supersymmetric Higgs bosons in spontaneously broken R-parity
We study the mass spectra, production and decay properties of the lightest
supersymmetric CP-even and CP-odd Higgs bosons in models with spontaneously
broken R-parity (SBRP). We compare the resulting mass spectra with expectations
of the Minimal Supersymmetric Standard Model (MSSM), stressing that the model
obeys the upper bound on the lightest CP-even Higgs boson mass. We discuss how
the presence of the additional scalar singlet states affects the Higgs
production cross sections, both for the Bjorken process and the "associated
production". The main phenomenological novelty with respect to the MSSM comes
from the fact that the spontaneous breaking of lepton number leads to the
existence of the majoron, denoted J, which opens new decay channels for
supersymmetric Higgs bosons. We find that the invisible decays of CP-even
Higgses can be dominant, while those of the CP-odd bosons may also be sizeable.Comment: 21 pages, 8 figures; minor changes, final version for publicatio
Spontaneous, collective coherence in driven, dissipative cavity arrays
We study an array of dissipative tunnel-coupled cavities, each interacting
with an incoherently pumped two-level emitter. For cavities in the lasing
regime, we find correlations between the light fields of distant cavities,
despite the dissipation and the incoherent nature of the pumping mechanism.
These correlations decay exponentially with distance for arrays in any
dimension but become increasingly long ranged with increasing photon tunneling
between adjacent cavities. The interaction-dominated and the
tunneling-dominated regimes show markedly different scaling of the correlation
length which always remains finite due to the finite photon trapping time. We
propose a series of observables to characterize the spontaneous build-up of
collective coherence in the system.Comment: 9 pages, 4 figures, including supplemental material (with 4 pages, 1
figure). This is a shorter version with some modifications in the
supplemental material (a gap in the proof was closed and calculations
significantly generalized and improved
Strong-coupling of quantum dots in microcavities
We show that strong-coupling (SC) of light and matter as it is realized with
quantum dots (QDs) in microcavities differs substantially from the paradigm of
atoms in optical cavities. The type of pumping used in semiconductors yields
new criteria to achieve SC, with situations where the pump hinders, or on the
contrary, favours it. We analyze one of the seminal experimental observation of
SC of a QD in a pillar microcavity [Reithmaier et al., Nature (2004)] as an
illustration of our main statements.Comment: Substantially revised version. The major change is in the analysis of
one of the seminal experiment of the field, that shows the excellent
quantitative agreement with the theory. Full details, especially all
concerning Fermi statistics (still present in previous versions), are now to
be presented elsewhere. To be published in Phys. Rev. Lett. 101 (2008
Effective penetration length and interstitial vortex pinning in superconducting films with regular arrays of defects
In order to compare magnetic and non-magnetic pinning we have nanostructured
two superconducting films with regular arrays of pinning centers: Cu
(non-magnetic) dots in one case, and Py (magnetic) dots in the other. For low
applied magnetic fields, when all the vortices are pinned in the artificial
inclusions, magnetic dots prove to be better pinning centers, as has been
generally accepted. Unexpectedly, when the magnetic field is increased and
interstitial vortices appear, the results are very different: we show how the
stray field generated by the magnetic dots can produce an effective reduction
of the penetration length. This results in strong consequences in the transport
properties, which, depending on the dot separation, can lead to an enhancement
or worsening of the transport characteristics. Therefore, the election of the
magnetic or non-magnetic character of the pinning sites for an effective
reduction of dissipation will depend on the range of the applied magnetic
field.Comment: 10 pages, 3 figure
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