453 research outputs found
Strong Optomechanical Squeezing of Light
We create squeezed light by exploiting the quantum nature of the mechanical
interaction between laser light and a membrane mechanical resonator embedded in
an optical cavity. The radiation pressure shot noise (fluctuating optical force
from quantum laser amplitude noise) induces resonator motion well above that of
thermally driven motion. This motion imprints a phase shift on the laser light,
hence correlating the amplitude and phase noise, a consequence of which is
optical squeezing. We experimentally demonstrate strong and continuous
optomechanical squeezing of 1.7 +/- 0.2 dB below the shot noise level. The peak
level of squeezing measured near the mechanical resonance is well described by
a model whose parameters are independently calibrated and that includes thermal
motion of the membrane with no other classical noise sources.Comment: 12 pages, 8 figure
Tuning p-wave interactions in an ultracold Fermi gas of atoms
We have measured a p-wave Feshbach resonance in a single-component, ultracold
Fermi gas of potassium atoms. We have used this resonance to enhance the
normally suppressed p-wave collision cross-section to values larger than the
background s-wave cross-section between potassium atoms in different
spin-states. In addition to the modification of two-body elastic processes, the
resonance dramatically enhances three-body inelastic collisional loss.Comment: 4 pages, 5 figure
Control of Material Damping in High-Q Membrane Microresonators
We study the mechanical quality factors of bilayer aluminum/silicon-nitride
membranes. By coating ultrahigh-Q Si3N4 membranes with a more lossy metal, we
can precisely measure the effect of material loss on Q's of tensioned resonator
modes over a large range of frequencies. We develop a theoretical model that
interprets our results and predicts the damping can be reduced significantly by
patterning the metal film. Using such patterning, we fabricate Al-Si3N4
membranes with ultrahigh Q at room temperature. Our work elucidates the role of
material loss in the Q of membrane resonators and informs the design of hybrid
mechanical oscillators for optical-electrical-mechanical quantum interfaces
Cavity optomechanics with Si3N4 membranes at cryogenic temperatures
We describe a cryogenic cavity-optomechanical system that combines Si3N4
membranes with a mechanically-rigid Fabry-Perot cavity. The extremely high
quality-factor frequency products of the membranes allow us to cool a MHz
mechanical mode to a phonon occupation of less than 10, starting at a bath
temperature of 5 kelvin. We show that even at cold temperatures
thermally-occupied mechanical modes of the cavity elements can be a limitation,
and we discuss methods to reduce these effects sufficiently to achieve ground
state cooling. This promising new platform should have versatile uses for
hybrid devices and searches for radiation pressure shot noise.Comment: 19 pages, 5 figures, submitted to New Journal of Physic
Dilute Fermi gas: kinetic and interaction energies
A dilute homogeneous 3D Fermi gas in the ground state is considered for the
case of a repulsive pairwise interaction. The low-density (dilution) expansions
for the kinetic and interaction energies of the system in question are
calculated up to the third order in the dilution parameter. Similar to the
recent results for a Bose gas, the calculated quantities turn out to depend on
a pairwise interaction through the two characteristic lengths: the former, ,
is the well-known s-wave scattering length, and the latter, , is related to
by , where stands for the fermion mass.
To take control of the results, calculations are fulfilled in two independent
ways. The first involves the Hellmann-Feynman theorem, taken in conjunction
with a helpful variational theorem for the scattering length. This way is used
to derive the kinetic and interaction energies from the familiar low-density
expansion of the total system energy first found by Huang and Yang. The second
way operates with the in-medium pair wave functions. It allows one to derive
the quantities of interest``from the scratch'', with no use of the total
energy. An important result of the present investigation is that the pairwise
interaction of fermions makes an essential contribution to their kinetic
energy. Moreover, there is a complicated and interesting interplay of these
quantities
Improving broadband displacement detection with quantum correlations
Interferometers enable ultrasensitive measurement in a wide array of
applications from gravitational wave searches to force microscopes. The role of
quantum mechanics in the metrological limits of interferometers has a rich
history, and a large number of techniques to surpass conventional limits have
been proposed. In a typical measurement configuration, the tradeoff between the
probe's shot noise (imprecision) and its quantum backaction results in what is
known as the standard quantum limit (SQL). In this work we investigate how
quantum correlations accessed by modifying the readout of the interferometer
can access physics beyond the SQL and improve displacement sensitivity.
Specifically, we use an optical cavity to probe the motion of a silicon nitride
membrane off mechanical resonance, as one would do in a broadband displacement
or force measurement, and observe sensitivity better than the SQL dictates for
our quantum efficiency. Our measurement illustrates the core idea behind a
technique known as \textit{variational readout}, in which the optical readout
quadrature is changed as a function of frequency to improve broadband
displacement detection. And more generally our result is a salient example of
how correlations can aid sensing in the presence of backaction.Comment: 17 pages, 5 figure
Gap solitons in superfluid boson-fermion mixtures
Using coupled equations for the bosonic and fermionic order parameters, we
construct families of gap solitons (GSs) in a nearly one-dimensional Bose-Fermi
mixture trapped in a periodic optical-lattice (OL) potential, the boson and
fermion components being in the states of the BEC and BCS superfluid,
respectively. Fundamental GSs are compact states trapped, essentially, in a
single cell of the lattice. Full families of such solutions are constructed in
the first two bandgaps of the OL-induced spectrum, by means of variational and
numerical methods, which are found to be in good agreement. The families
include both intra-gap and inter-gap solitons, with the chemical potentials of
the boson and fermion components falling in the same or different bandgaps,
respectively.Nonfundamental states, extended over several lattice cells, are
constructed too. The GSs are stable against strong perturbations.Comment: 9 pages, 14 figure
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