17,049 research outputs found
The Lorentzian distance formula in noncommutative geometry
For almost twenty years, a search for a Lorentzian version of the well-known
Connes' distance formula has been undertaken. Several authors have contributed
to this search, providing important milestones, and the time has now come to
put those elements together in order to get a valid and functional formula.
This paper presents a historical review of the construction and the proof of a
Lorentzian distance formula suitable for noncommutative geometry.Comment: 16 pages, final form, few references adde
A pulsed Sagnac source of narrowband polarization-entangled photons
We demonstrate pulsed operation of a bidirectionally pumped polarization
Sagnac interferometric down-conversion source and its generation of narrowband,
high-visibility polarization-entangled photons. Driven by a narrowband,
mode-locked pump at 390.35 nm, the phase-stable Sagnac source with a type-II
phase-matched periodically poled KTiOPO crystal is capable of producing
0.01 entangled pair per pulse in a 0.15-nm bandwidth centered at 780.7 nm with
1 mW of average pump power at a repetition rate of 31.1 MHz. We have achieved a
mean photon-pair generation rate of as high as 0.7 pair per pulse, at which
multi-pair events dominate and significantly reduce the two-photon
quantum-interference visibility. For low generation probability , the
reduced visibility is independent of the throughput efficiency and
of the polarization analysis basis, which can be utilized to yield an accurate
estimate of the generation rate . At low we have characterized
the source entanglement quality in three different ways: average
quantum-interference visibility of 99%, the Clauser-Horne-Shimony-Holt
parameter of , and quantum state tomography with 98.85%
singlet-state fidelity. The narrowband pulsed Sagnac source of entangled
photons is suitable for use in quantum information processing applications such
as free-space quantum key distribution.Comment: 10 pages, 6 figures, accepted for publication in Phys. Rev.
Efficient and spectrally bright source of polarization-entangled photons
We demonstrate an efficient fiber-coupled source of nondegenerate
polarization entangled photons at 795 and 1609 nm using bidirectionally pumped
parametric down-conversion in bulk periodically poled lithium niobate. The
single-mode source has an inferred bandwidth of 50 GHz and a spectral
brightness of 300 pairs/s/GHz/mW of pump power that is suitable for narrowband
applications such as entanglement transfer from photonic to atomic qubits.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
Argon assisted chemical vapor deposition of CrO: an efficient process leading to high quality epitaxial films
A comparative study of the structural, microstructural and magnetic
properties of CrO thin films grown onto (110) and (100) TiO rutile
single crystal substrates by chemical vapor deposition (CVD), using CrO as
chromium precursor and either oxygen or argon as carrier gas is presented. Our
results show that growth under argon carrier gas leads to high quality CrO
epilayers with structural and magnetic properties similar to those obtained
using the more standard oxygen carrier gas. Furthermore, we interpret the
larger magnetic coercivity observed for the (110) oriented films in terms of
their microstructure, in particular of the highest strain and edge roughness of
the building structures of the CrO epilayers, which are settled by the
substrate crystallographic orientation.Comment: 27 pages, 2 tables, 8 figure
Crystal-to-crystal transition of ultrasoft colloids under shear
Ultrasoft colloids typically do not spontaneously crystallize, but rather
vitrify, at high concentrations. Combining in-situ rheo-SANS experiments and
numerical simulations we show that shear facilitates crystallization of
colloidal star polymers in the vicinity of their glass transition. With
increasing shear rate well beyond rheological yielding, a transition is found
from an initial bcc-dominated structure to an fcc-dominated one. This
crystal-to-crystal transition is not accompanied by intermediate melting but
occurs via a sudden reorganization of the crystal structure. Our results
provide a new avenue to tailor colloidal crystallization and crystal-to-crystal
transition at molecular level by coupling softness and shear
A macro-realism inequality for opto-electro-mechanical systems
We show how to apply the Leggett-Garg inequality to opto-electro-mechanical
systems near their quantum ground state. We find that by using a dichotomic
quantum non-demolition measurement (via, e.g., an additional circuit-QED
measurement device) either on the cavity or on the nanomechanical system
itself, the Leggett-Garg inequality is violated. We argue that only
measurements on the mechanical system itself give a truly unambigous violation
of the Leggett-Garg inequality for the mechanical system. In this case, a
violation of the Leggett-Garg inequality indicates physics beyond that of
"macroscopic realism" is occurring in the mechanical system. Finally, we
discuss the difficulties in using unbound non-dichotomic observables with the
Leggett-Garg inequality.Comment: 9 pages, 2 figures. Added additional figure (2b), and associated
conten
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