4,936 research outputs found
Optomechanical self-structuring in cold atomic gases
The rapidly developing field of optomechanics aims at the combined control of
optical and mechanical (solid-state or atomic) modes. In particular, laser
cooled atoms have been used to exploit optomechanical coupling for
self-organization in a variety of schemes where the accessible length scales
are constrained by a combination of pump modes and those associated to a second
imposed axis, typically a cavity axis. Here, we consider a system with many
spatial degrees of freedom around a single distinguished axis, in which two
symmetries - rotations and translations in the plane orthogonal to the pump
axis - are spontaneously broken. We observe the simultaneous spatial
structuring of the density of a cold atomic cloud and an optical pump beam. The
resulting patterns have hexagonal symmetry. The experiment demonstrates the
manipulation of matter by opto-mechanical self-assembly with adjustable length
scales and can be potentially extended to quantum degenerate gases.Comment: 20 pages, 6 figure
The theory of parametrically amplified electron-phonon superconductivity
The ultrafast optical manipulation of ordered phases in strongly correlated
materials is a topic of significant theoretical, experimental, and
technological interest. Inspired by a recent experiment on light-induced
superconductivity in fullerenes [Mitrano et al., Nature 530, 2016], we develop
a comprehensive theory of light-induced superconductivity in driven
electron-phonon systems with lattice nonlinearities. In analogy with the
operation of parametric amplifiers, we show how the interplay between the
external drive and lattice nonlinearities lead to significantly enhanced
effective electron-phonon couplings. We provide a detailed and unbiased study
of the nonequilibrium dynamics of the driven system using the real-time Green's
function technique. To this end, we develop a Floquet generalization of the
Migdal-Eliashberg theory and derive a numerically tractable set of quantum
Floquet-Boltzmann kinetic equations for the coupled electron-phonon system. We
study the role of parametric phonon generation and electronic heating in
destroying the transient superconducting state. Finally, we predict the
transient formation of electronic Floquet bands in time- and angle-resolved
photo-emission spectroscopy experiments as a consequence of the proposed
mechanism.Comment: 42 pages, 17 figure
Control of microwave signals using circuit nano-electromechanics
Waveguide resonators are crucial elements in sensitive astrophysical
detectors [1] and circuit quantum electrodynamics (cQED) [2]. Coupled to
artificial atoms in the form of superconducting qubits [3, 4], they now provide
a technologically promising and scalable platform for quantum information
processing tasks [2, 5-8]. Coupling these circuits, in situ, to other quantum
systems, such as molecules [9, 10], spin ensembles [11, 12], quantum dots [13]
or mechanical oscillators [14, 15] has been explored to realize hybrid systems
with extended functionality. Here, we couple a superconducting coplanar
waveguide resonator to a nano-coshmechanical oscillator, and demonstrate
all-microwave field controlled slowing, advancing and switching of microwave
signals. This is enabled by utilizing electromechanically induced transparency
[16-18], an effect analogous to electromagnetically induced transparency (EIT)
in atomic physics [19]. The exquisite temporal control gained over this
phenomenon provides a route towards realizing advanced protocols for storage of
both classical and quantum microwave signals [20-22], extending the toolbox of
control techniques of the microwave field.Comment: 9 figure
On the origins of the compressive cochlear nonlinearity
Various simple mathematical models of the dynamics of the organ of Corti in the mammalian cochlea are analysed. The models are assessed against their ability to explain the compressive nonlinear response of the basilar membrane. The speci fic models considered are: phenomenological Hopf and cusp normal forms, a recently-proposed description combining active hair-bundle motility and somatic motility, a reduction thereof, and finally a new model highlighting the importance of the coupling between the nonlinear transduction current and somatic motility. The overall conclusion is that neither a Hopf bifurcation nor cusp bifurcation are necessary for realistic compressive nonlinearity. Moreover, two physiological models are discussed showing compressive nonlinearities similar to experimental observations without the need for tuning near any bifurcation
Cooling of a micro-mechanical oscillator using radiation pressure induced dynamical back-action
Cooling of a 58 MHz micro-mechanical resonator from room temperature to 11 K
is demonstrated using cavity enhanced radiation pressure. Detuned pumping of an
optical resonance allows enhancement of the blue shifted motional sideband
(caused by the oscillator's Brownian motion) with respect to the red-shifted
sideband leading to cooling of the mechanical oscillator mode. The reported
cooling mechanism is a manifestation of the effect of radiation pressure
induced dynamical backaction. These results constitute an important step
towards achieving ground state cooling of a mechanical oscillator.Comment: accepted for publication (Phys. Rev. Lett.
Fluctuation conductivity in superconductors in strong electric fields
We study the effect of a strong electric field on the fluctuation
conductivity within the time-dependent Ginzburg-Landau theory for the case of
arbitrary dimension. Our results are based on the analytical derivation of the
velocity distribution law for the fluctuation Cooper pairs, from the Boltzmann
equation. Special attention is drawn to the case of small nonlinearity of
conductivity, which can be investigated experimentally. We obtain a general
relation between the nonlinear conductivity and the temperature derivative of
the linear Aslamazov-Larkin conductivity, applicable to any superconductor. For
the important case of layered superconductors we derive an analogous relation
between the small nonlinear correction for the conductivity and the
fluctuational magnetoconductivity. On the basis of these relations we provide
new experimental methods for determining both the lifetime constant of
metastable Cooper pairs above T_c and the coherence length. A systematic
investigation of the 3rd harmonic of the electric field generated by a harmonic
current can serve as an alternative method for the examination of the
metastable Cooper-pair relaxation time.Comment: 18 pages, REVTeX, submitted to Phys. Rev.
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