1,343 research outputs found
Wafer-bonded single-crystal silicon slot waveguides and ring resonators
We fabricated horizontal Si slot waveguides with a 25 nm SiO2 slot layer by bonding thin Si-on-insulator wafers. After removing the Si substrate and buried oxide from one side of the bonded structure, grating-coupled waveguides and ring resonators were partially etched into the Si/SiO2/Si device layers. The gratings exhibit efficiencies of up to 23% at 1550 nm and the ring resonators were measured to have loaded quality factors near 42 000 for the lowest-order transverse-electric mode, corresponding to a propagation loss of 15 dB/cm. The leaky lowest-order transverse-magnetic mode was also observed with a propagation loss of 44 dB/cm
Production of heralded pure single photons from imperfect sources using cross phase modulation
Realistic single-photon sources do not generate single photons with
certainty. Instead they produce statistical mixtures of photons in Fock states
and vacuum (noise). We describe how to eliminate the noise in the
output of the sources by means of another noisy source or a coherent state and
cross phase modulation (XPM). We present a scheme which announces the
production of pure single photons and thus eliminates the vacuum contribution.
This is done by verifying a XPM related phase shift with a Mach-Zehnder
interferometer.Comment: 8 pages, 8 EPS figures, RevTeX4. Following changes have been made in
v.3: Title and abstract slightly changed; numerous minor revisions and
clarifications within the text; an appendix with three new figures has been
added. In version v4 we have included a supplementary analysis of our scheme
that takes into account absorption losses. Our analysis is heuristic and
based on a phenomenological model, which is independent of the physical
realization of the proposed scheme. We have estimated upper bounds up to
which absorption losses can be tolerated, so as our scheme to improve the
efficiency of single photon sources still works. Accepted for publication in
Phys. Rev.
Deviations from Linear Theory for Fluctuations below the Supercritical Primary Bifurcation to Electroconvection
We report measurements of thermally-induced mean-square director-angle
fluctuations below primary supercritical bifurcations to
electroconvection of the nematic liquid crystals I52 and "Merck Phase V". For
epsilon_mf = V^2/V_c,mf^2 - 1 < -0.1 (V is the amplitude of the applied
alternating voltage) we find proportional to epsilon_mf^(-gamma) with
gamma given by linear theory (LT). Closer to the bifurcation there are
deviations from LT with a smaller gamma and with V_c^2 > V_c,mf^2. For I52
measurements as a function of the conductivity sigma of above V_c^2
suggest a tricritical bifurcation at sigma_t = 4.0 x 10^(-9) Omega^(-1)m^(-1),
and (V_c^2 - V_c,mf^2)/V_c^2 increases strongly as sigma_t is approached from
above.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Finite-Temperature Fidelity-Metric Approach to the Lipkin-Meshkov-Glick Model
The fidelity metric has recently been proposed as a useful and elegant
approach to identify and characterize both quantum and classical phase
transitions. We study this metric on the manifold of thermal states for the
Lipkin-Meshkov-Glick (LMG) model. For the isotropic LMG model, we find that the
metric reduces to a Fisher-Rao metric, reflecting an underlying classical
probability distribution. Furthermore, this metric can be expressed in terms of
derivatives of the free energy, indicating a relation to Ruppeiner geometry.
This allows us to obtain exact expressions for the (suitably rescaled) metric
in the thermodynamic limit. The phase transition of the isotropic LMG model is
signalled by a degeneracy of this (improper) metric in the paramagnetic phase.
Due to the integrability of the isotropic LMG model, ground state level
crossings occur, leading to an ill-defined fidelity metric at zero temperature.Comment: 18 pages, 3 figure
Design and fabrication of chemically robust three-dimensional microfluidic valves
A current problem in microfluidics is that poly(dimethylsiloxane) (PDMS), used to fabricate many microfluidic devices, is not compatible with most organic solvents. Fluorinated compounds are more chemically robust than PDMS but, historically, it has been nearly impossible to construct valves out of them by multilayer soft lithography (MSL) due to the difficulty of bonding layers made of non-stick fluoropolymers necessary to create traditional microfluidic valves. With our new three-dimensional (3D) valve design we can fabricate microfluidic devices from fluorinated compounds in a single monolithic layer that is resistant to most organic solvents with minimal swelling. This paper describes the design and development of 3D microfluidic valves by molding of a perfluoropolyether, termed Sifel, onto printed wax molds. The fabrication of Sifel-based microfluidic devices using this technique has great potential in chemical synthesis and analysis
Heralded single-photon generation using imperfect single-photon sources and a two-photon-absorbing medium
We propose a setup for a heralded, i.e. announced generation of a pure
single-photon state given two imperfect sources whose outputs are represented
by mixtures of the single-photon Fock state with the vacuum
. Our purification scheme uses beam splitters, photodetection and a
two-photon-absorbing medium. The admixture of the vacuum is fully eliminated.
We discuss two potential realizations of the scheme.Comment: 22 pages, 8 figures (LaTeX). In version v2 we have slightly modified
our setup so as to increase the success probability of single-photon
generation by a factor of two. In addition, in an appendix we discuss
alternative realizations of single-photon generation without a Mach-Zehnder
interferometer. Three new figures have been added. Version v3 is a revised
version published in Phys. Rev. A. It contains numerous minor corrections and
clarifications. A new figure has been added in order to clarify our
convention regarding labelling the field modes. The action of the beam
splitters in the Schroedinger picture is introduced. A new reference has been
include
Low field extension for magnetometers (TinyBee) used for investigations on low-dimensional superconductors with Bc1 < 5G
In this article a simple and easy to install low magnetic field extension of
the SQUID magnetometer Quantum Design MPMS-7 is described. This has been
accomplished by complementing the MPMS-7 magnet control system with a
laboratory current supply for the low magnetic field region (B \leq 200G). This
hard- and software upgrade provides a significant gain in the magnetic field
accuracy up to an order of magnitude compared with the standard instrument's
setup and is improving the resolution to better than 0.01G below 40G. The field
control has been integrated into the Quantum Design MultiVu software for a
transparent and user-friendly operation of this extension. The improvements
achieved are especially useful, when low magnetic field strengths (B < 1G) are
required at high precision. The specific advantages of this application are
illustrated by sophisticated magnetic characterisation of lowdimensional
superconductors like Sc3CoC4 and SnSe2{Co({\eta}-C5H5)2}x.Comment: 16 pages, 7 figure
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