2,332 research outputs found
Absence of Long-Range Coherence in the Parametric Emission from Photonic Wires
We analytically investigate the spatial coherence properties of the signal
emission from one-dimensional optical parametric oscillators. Because of the
reduced dimensionality, quantum fluctuations are able to destroy the long-range
phase coherence even far above threshold. The spatial decay of coherence is
exponential and, for realistic parameters of semiconductor photonic wires in
the strong exciton-photon coupling regime, it is predicted to occur on an
experimentally accessible length scale.Comment: 6 pages, 3 figure
Probing few-particle Laughlin states of photons via correlation measurements
We propose methods to create and observe Laughlin-like states of photons in a
strongly nonlinear optical cavity. Such states of strongly interacting photons
can be prepared by pumping the cavity with a Laguerre-Gauss beam, which has a
well-defined orbital angular momentum per photon. The Laughlin-like states
appear as sharp resonances in the particle-number-resolved transmission
spectrum. Power spectrum and second-order correlation function measurements
yield unambiguous signatures of these few-particle strongly-correlated states.Comment: 11 pages including appendice
Controlling the pair momentum of the FFLO state in a 3D Fermi gas through a 1D periodic potential
The question whether a spin-imbalanced Fermi gas can accommodate the
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been the subject of intense
study. This state, in which Cooper pairs obtain a nonzero momentum, has
hitherto eluded experimental observation. Recently, we demonstrated that the
FFLO state can be stabilized in a 3D Fermi gas, by adding a 1D periodic
potential. Until now it was assumed that the FFLO wave vector always lies
parallel to this periodic potential (FFLO-P). In this contribution we show
that, surprisingly, the FFLO wave vector can also lie skewed with respect to
the potential (FFLO-S). Starting from the partition sum, the saddle-point free
energy of the system is derived within the path-integral formalism. Minimizing
this free energy allows us to study the different competing ground states of
the system. To qualitatively understand the underlying pairing mechanism, we
visualize the Fermi surfaces of the spin up and spin down particles. From this
visualization, we find that tilting the FFLO wave vector with respect to the
direction of the periodic potential, can result in a larger overlap between the
pairing bands of both spin species. This skewed FFLO state can provide an
additional experimental signature for observing FFLO superfluidity in a 3D
Fermi gas.Comment: 19 pages, 3 figure
The association of technology-based ageism with using digital technology in physical therapy for older persons
Integrating digital technologies in healthcare for older adults can enhance their independence and quality of life. Nevertheless, ageism among healthcare professionals impacts treatment decisions and may deprive older patients of technology-based treatment. This study explores whether technology-specific ageism influenced physiotherapists’ use of technology-based healthcare with older patients. Seventy-eight physiotherapists in Luxembourg filled out an online survey. Participants filled out the Attitudes Towards Older Adults Using Technology (ATOAUT-11) scale, Expectations Regarding Aging, attitudes towards technology use in the work environment, and whether they had not offered technology-based treatment in the past because of a patient’s age. Using logistic regression, negative ATOAUT was found to predict not offering technology-based treatment, such that participants with more negative attitudes (1 standard deviation) were two times more likely not to offer treatment. Positive attitudes towards using technology in the work environment were also found to be a significant predictor. All other characteristics (gender, age, experience and percentage of patients over 50) were not predictive of not offering treatment. This study demonstrates that technology-specific ageism may lead to discrimination and deprive older persons of optimal treatment. More research is needed to identify the magnitude of ageism in using technology-based treatment and develop interventions to overcome it
A practical guide to density matrix embedding theory in quantum chemistry
Density matrix embedding theory (DMET) provides a theoretical framework to
treat finite fragments in the presence of a surrounding molecular or bulk
environment, even when there is significant correlation or entanglement between
the two. In this work, we give a practically oriented and explicit description
of the numerical and theoretical formulation of DMET. We also describe in
detail how to perform self-consistent DMET optimizations. We explore different
embedding strategies with and without a self-consistency condition in hydrogen
rings, beryllium rings, and a sample S2 reaction. The source code
for the calculations in this work can be obtained from
\url{https://github.com/sebwouters/qc-dmet}.Comment: 41 pages, 10 figure
Observation of long-lived polariton states in semiconductor microcavities across the parametric threshold
The excitation spectrum around the pump-only stationary state of a polariton
optical parametric oscillator (OPO) in semiconductor microcavities is
investigated by time-resolved photoluminescence. The response to a weak pulsed
perturbation in the vicinity of the idler mode is directly related to the
lifetime of the elementary excitations. A dramatic increase of the lifetime is
observed for a pump intensity approaching and exceeding the OPO threshold. The
observations can be explained in terms of a critical slowing down of the
dynamics upon approaching the threshold and the following onset of the soft
Goldstone mode
A cyclic-olefin-copolymer microfluidic immobilized-enzyme reactor for rapid digestion of proteins from dried blood spots
Unstable and stable regimes of polariton condensation
Modulational instabilities play a key role in a wide range of nonlinear
optical phenomena, leading e.g. to the formation of spatial and temporal
solitons, rogue waves and chaotic dynamics. Here we experimentally demonstrate
the existence of a modulational instability in condensates of cavity
polaritons, arising from the strong coupling of cavity photons with quantum
well excitons. For this purpose we investigate the spatiotemporal coherence
properties of polariton condensates in GaAs-based microcavities under
continuous-wave pumping. The chaotic behavior of the instability results in a
strongly reduced spatial and temporal coherence and a significantly
inhomogeneous density. Additionally we show how the instability can be tamed by
introducing a periodic potential so that condensation occurs into negative mass
states, leading to largely improved coherence and homogeneity. These results
pave the way to the exploration of long-range order in dissipative quantum
fluids of light within a controlled platform.Comment: 7 pages, 5 figure
Many-body physics of a quantum fluid of exciton-polaritons in a semiconductor microcavity
Some recent results concerning nonlinear optics in semiconductor
microcavities are reviewed from the point of view of the many-body physics of
an interacting photon gas. Analogies with systems of cold atoms at thermal
equilibrium are drawn, and the peculiar behaviours due to the non-equilibrium
regime pointed out. The richness of the predicted behaviours shows the
potentialities of optical systems for the study of the physics of quantum
fluids.Comment: Proceedings of QFS2006 conference to appear on JLT
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