2,181 research outputs found
Optomechanical position detection enhanced by de-amplification using intracavity squeezing
It has been predicted and experimentally demonstrated that by injecting
squeezed light into an optomechanical device it is possible to enhance the
precision of a position measurement. Here, we present a fundamentally different
approach where the squeezing is created directly inside the cavity by a
nonlinear medium. Counterintuitively, the enhancement of the signal to noise
ratio works by de-amplifying precisely the quadrature that is sensitive to the
mechanical motion without losing quantum information. This enhancement works
for systems with a weak optomechanical coupling and/or strong mechanical
damping. This could allow for larger mechanical bandwidth of quantum limited
detectors based on optomechanical devices. Our approach can be
straightforwardly extended to Quantum Non Demolition (QND) qubit detection.Comment: references added, slight change
Correlation induced resonances in transport through coupled quantum dots
We investigate the effect of local electron correlations on transport through
parallel quantum dots. The linear conductance as a function of gate voltage is
strongly affected by the interplay of the interaction U and quantum
interference. We find a pair of novel correlation induced resonances separated
by an energy scale that depends exponentially on U. The effect is robust
against a small detuning of the dot energy levels and occurs for arbitrary
generic tunnel couplings. It should be observable in experiments on the basis
of presently existing double-dot setups.Comment: 4+ pages, 5 figures included, version accepted for publication in PR
Topological Phases of Sound and Light
Topological states of matter are particularly robust, since they exploit
global features insensitive to local perturbations. In this work, we describe
how to create a Chern insulator of phonons in the solid state. The proposed
implementation is based on a simple setting, a dielectric slab with a suitable
pattern of holes. Its topological properties can be wholly tuned in-situ by
adjusting the amplitude and frequency of a driving laser that controls the
optomechanical interaction between light and sound. The resulting chiral,
topologically protected phonon transport along the edges can be probed
completely optically. Moreover, we identify a regime of strong mixing between
photon and phonon excitations, which gives rise to a large set of different
topological phases. This would be an example of a Chern insulator produced from
the interaction between two physically very different particle species, photons
and phonons
Antiphosphatidylserine antibody as a cause of multiple dural venous sinus thromboses and ST-elevation myocardial infarction
Objective: Rare disease Background: Antiphospholipid syndrome (APS) is an autoimmune disease characterized by antibodies directed against phos-pholipids on plasma membranes. Through unclear mechanisms, APS confers hypercoagulability. APS may cause recurrent thromboses in the arterial and venous vasculature. We report a case of primary APS resulting in cerebral venous thrombosis and ST-elevation myocardial infarction (STEMI) for which only antiphosphatidylserine (aPS) IgM antibody was positive after extensive investigation. Case Report: A 48-year-old male was admitted after a witnessed generalized seizure with subsequent confusion. Imaging demonstrated thrombosis of multiple central nervous system (CNS) sinuses, including the superior sagittal sinus and bilateral transverse sinuses. The patient was heparinized with aggressive hydration, which proved inadequate, prompting endovascular thrombectomy. Three months later, despite anticoagulation therapy, the patient developed a STEMI when International Normalized Ratio (INR) was 1.8. Echocardiogram (ECHO) and PAN CT scan were normal. Initial coagulation studies demonstrated normal anticardiolipin antibody, prothrombin time, partial thromboplastin time, and platelet count. Outpatient coagulation studies revealed normal an-tithrombin III, protein C/S, hemoglobin electrophoresis, homocysteine, anti-b2 glycoprotein 1 antibodies, and D-Dimer. Factor V Leiden, JAK 2 mutation, prothrombin gene mutation, and tests for paroxysmal nocturnal he-moglobinuria (PNH) were negative. A positive phosphatidylserine IgM was detected. The patient was continued on warfarin (10 mg daily) with a target INR of 3.0–3.5 and clopidogrel (75 mg daily). Conclusions: Despite extensive investigation, this patient only showed evidence of elevated aPS IgM antibodies, likely contributing to his CNS venous sinus thromboses and STEMI. It is important to screen for antiphosphatidylserine antibodies in cases of unprovoked thrombosis when standard thrombophilia analysis is unrevealing. This will assist in identifying pathogenicity and help prevent recurrence of subsequent thromboses. © Am J Case Rep, 2018
Optomechanical creation of magnetic fields for photons on a lattice
We propose using the optomechanical interaction to create artificial magnetic
fields for photons on a lattice. The ingredients required are an optomechanical
crystal, i.e. a piece of dielectric with the right pattern of holes, and two
laser beams with the right pattern of phases. One of the two proposed schemes
is based on optomechanical modulation of the links between optical modes, while
the other is an lattice extension of optomechanical wavelength-conversion
setups. We illustrate the resulting optical spectrum, photon transport in the
presence of an artificial Lorentz force, edge states, and the photonic
Aharonov-Bohm effect. Moreover, wWe also briefly describe the gauge fields
acting on the synthetic dimension related to the phonon/photon degree of
freedom. These can be generated using a single laser beam impinging on an
optomechanical array
Quantum Signatures of the Optomechanical Instability
In the past few years, coupling strengths between light and mechanical motion
in optomechanical setups have improved by orders of magnitude. Here we show
that, in the standard setup under continuous laser illumination, the steady
state of the mechanical oscillator can develop a non-classical, strongly
negative Wigner density if the optomechanical coupling is large at the
single-photon level. Because of its robustness, such a Wigner density can be
mapped using optical homodyne tomography. These features are observed near the
onset of the instability towards self-induced oscillations. We show that there
are also distinct signatures in the photon-photon correlation function
in that regime, including oscillations decaying on a time scale
not only much longer than the optical cavity decay time, but even longer than
the \emph{mechanical} decay time.Comment: 6 pages including 1 appendix. 6 Figures. Correcte
The Standard Quantum Limit of Coherent Beam Combining
Coherent beam combining refers to the process of generating a bright output
beam by merging independent input beams with locked relative phases. We report
the first quantum mechanical noise limit calculations for coherent beam
combining and compare our results to quantum-limited amplification. Our
coherent beam combining scheme is based on an optical Fourier transformation
which renders the scheme compatible with integrated optics. The scheme can be
layed out for an arbitrary number of input beams and approaches the shot noise
limit for a large number of inputs
Fermionic Mach-Zehnder interferometer subject to a quantum bath
We study fermions in a Mach-Zehnder interferometer, subject to a
quantum-mechanical environment leading to inelastic scattering, decoherence,
renormalization effects, and time-dependent conductance fluctuations. Both the
loss of interference contrast as well as the shot noise are calculated, using
equations of motion and leading order perturbation theory. The full dependence
of the shot-noise correction on setup parameters, voltage, temperature and the
bath spectrum is presented. We find an interesting contribution due to
correlations between the fluctuating renormalized phase shift and the output
current, discuss the limiting behaviours at low and high voltages, and compare
with simpler models of dephasing.Comment: 5 pages, 3 figure
Dimensional Crossover of the Dephasing Time in Disordered Mesoscopic Rings: From Diffusive through Ergodic to 0D Behavior
We analyze dephasing by electron interactions in a small disordered quasi-one
dimensional (1D) ring weakly coupled to leads, where we recently predicted a
crossover for the dephasing time \tPh(T) from diffusive or ergodic 1D
(\tPh^{-1} \propto T^{2/3}, T^{1}) to behavior (\tPh^{-1} \propto
T^{2}) as drops below the Thouless energy \ETh. We provide a detailed
derivation of our results, based on an influence functional for quantum Nyquist
noise, and calculate all leading and subleading terms of the dephasing time in
the three regimes. Explicitly taking into account the Pauli blocking of the
Fermi sea in the metal allows us to describe the regime on equal footing
as the others. The crossover to , predicted by Sivan, Imry and Aronov for
3D systems, has so far eluded experimental observation. We will show that for
T \ll \ETh, dephasing governs not only the -dependence for the smooth
part of the magnetoconductivity but also for the amplitude of the
Altshuler-Aronov-Spivak oscillations, which result only from electron paths
winding around the ring. This observation can be exploited to filter out and
eliminate contributions to dephasing from trajectories which do not wind around
the ring, which may tend to mask the behavior. Thus, the ring geometry
holds promise of finally observing the crossover to experimentally.Comment: in "Perspectives of Mesoscopic Physics - Dedicated to Yoseph Imry's
70th Birthday", edited by Amnon Aharony and Ora Entin-Wohlman (World
Scientific, 2010), chap. 20, p. 371-396, ISBN-13 978-981-4299-43-
Self-learning Machines based on Hamiltonian Echo Backpropagation
A physical self-learning machine can be defined as a nonlinear dynamical system that can be trained on data (similar to artificial neural networks), but where the update of the internal degrees of freedom that serve as learnable parameters happens autonomously. In this way, neither external processing and feedback nor knowledge of (and control of) these internal degrees of freedom is required. We introduce a general scheme for self-learning in any time-reversible Hamiltonian system. We illustrate the training of such a self-learning machine numerically for the case of coupled nonlinear wave fields
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