4,624 research outputs found
Quantum Degenerate Systems
Degenerate dynamical systems are characterized by symplectic structures whose
rank is not constant throughout phase space. Their phase spaces are divided
into causally disconnected, nonoverlapping regions such that there are no
classical orbits connecting two different regions. Here the question of whether
this classical disconnectedness survives quantization is addressed. Our
conclusion is that in irreducible degenerate systems --in which the degeneracy
cannot be eliminated by redefining variables in the action--, the
disconnectedness is maintained in the quantum theory: there is no quantum
tunnelling across degeneracy surfaces. This shows that the degeneracy surfaces
are boundaries separating distinct physical systems, not only classically, but
in the quantum realm as well. The relevance of this feature for gravitation and
Chern-Simons theories in higher dimensions cannot be overstated.Comment: 18 pages, no figure
PPLN Waveguide for Quantum Communication
We report on energy-time and time-bin entangled photon-pair sources based on
a periodically poled lithium niobate (PPLN) waveguide. Degenerate twin photons
at 1314 nm wavelength are created by spontaneous parametric down-conversion and
coupled into standard telecom fibers. Our PPLN waveguide features a very high
conversion efficiency of about 10^(-6), roughly 4 orders of magnitude more than
that obtained employing bulk crystals. Even if using low power laser diodes,
this engenders a significant probability for creating two pairs at a time - an
important advantage for some quantum communication protocols. We point out a
simple means to characterize the pair creation probability in case of a pulsed
pump. To investigate the quality of the entangled states, we perform
photon-pair interference experiments, leading to visibilities of 97% for the
case of energy-time entanglement and of 84% for the case of time-bin
entanglement. Although the last figure must still be improved, these tests
demonstrate the high potential of PPLN waveguide based sources to become a key
element for future quantum communication schemesComment: 11 pages, 9 figures, submitted to the European Physical Journal D
(special issue of the Quick conference
Broadband integrated beam splitter using spatial adiabatic passage
Light routing and manipulation are important aspects of integrated optics.
They essentially rely on beam splitters which are at the heart of
interferometric setups and active routing. The most common implementations of
beam splitters suffer either from strong dispersive response (directional
couplers) or tight fabrication tolerances (multimode interference couplers). In
this paper we fabricate a robust and simple broadband integrated beam splitter
based on lithium niobate with a splitting ratio achromatic over more than 130
nm. Our architecture is based on spatial adiabatic passage, a technique
originally used to transfer entirely an optical beam from a waveguide to
another one that has been shown to be remarkably robust against fabrication
imperfections and wavelength dispersion. Our device shows a splitting ratio of
0.520.03 and 0.480.03 from 1500\,nm up to 1630\,nm. Furthermore, we
show that suitable design enables the splitting in output beams with relative
phase 0 or . Thanks to their independence to material dispersion, these
devices represent simple, elementary components to create achromatic and
versatile photonic circuits
A quantum relay chip based on telecommunication integrated optics technology
We investigate an integrated optical circuit on lithium niobate designed to
implement the teleportation-based quantum relay scheme for one-way quantum
communication at a telecom wavelength. Such an advanced quantum circuit merges
for the first time, both optical-optical and electro-optical non-linear
functions necessary to implement the desired on-chip single qubit
teleportation. On one hand, spontaneous parametric down-conversion is used to
produce entangled photon-pairs. On the other hand, we take advantage of two
photon routers, consisting of electro-optically controllable couplers, to
separate the paired photons and to perform a Bell state measurement,
respectively. After having validated all the individual functions in the
classical regime, we have performed a Hong-Ou-Mandel (HOM) experiment to mimic
a one-way quantum communication link. Such a quantum effect, seen as a
prerequisite towards achieving teleportation, has been obtained, at one of the
routers, when the chip was coupled to an external single photon source. The
two-photon interference pattern shows a net visibility of 80%, which validates
the proof of principle of a "quantum relay circuit" for qubits carried by
telecom photons. In case of optimized losses, such a chip could increase the
maximal achievable distance of one-way quantum key distribution links by a
factor 1.8. Our approach and results emphasize the high potential of integrated
optics on lithium niobate as a key technology for future reconfigurable quantum
information manipulation.Comment: 16 pages, 8 figure
Polarization entangled photon-pair source based on quantum nonlinear photonics and interferometry
We present a versatile, high-brightness, guided-wave source of polarization
entangled photons, emitted at a telecom wavelength. Photon-pairs are generated
using an integrated type-0 nonlinear waveguide, and subsequently prepared in a
polarization entangled state via a stabilized fiber interferometer. We show
that the single photon emission wavelength can be tuned over more than 50 nm,
whereas the single photon spectral bandwidth can be chosen at will over more
than five orders of magnitude (from 25 MHz to 4 THz). Moreover, by performing
entanglement analysis, we demonstrate a high degree of control of the quantum
state via the violation of the Bell inequalities by more than 40 standard
deviations. This makes this scheme suitable for a wide range of quantum optics
experiments, ranging from fundamental research to quantum information
applications. We report on details of the setup, as well as on the
characterization of all included components, previously outlined in F. Kaiser
et al. (2013 Laser Phys. Lett. 10, 045202).Comment: 16 pages, 7 figure
The strong coupling constant at small momentum as an instanton detector
We present a study of at small p computed from the lattice.
It shows a dramatic law which can be understood within an
instanton liquid model. In this framework the prefactor gives a direct measure
of the instanton density in thermalised configurations. A preliminary result
for this density is 5.27(4) fm^{-4}.Comment: 12 pages, 4 figure
Spitzer Observations of Interstellar Object 1I/`Oumuamua
1I/`Oumuamua is the first confirmed interstellar body in our Solar System.
Here we report on observations of `Oumuamua made with the Spitzer Space
Telescope on 2017 November 21--22 (UT). We integrated for 30.2~hours at 4.5
micron (IRAC channel 2). We did not detect the object and place an upper limit
on the flux of 0.3 uJy (3sigma). This implies an effective spherical diameter
less than [98, 140, 440] meters and albedo greater than [0.2, 0.1, 0.01] under
the assumption of low, middle, or high thermal beaming parameter eta,
respectively. With an aspect ratio for `Oumuamua of 6:1, these results
correspond to dimensions of [240:40, 341:57, 1080:180] meters, respectively. We
place upper limits on the amount of dust, CO, and CO2 coming from this object
that are lower than previous results; we are unable to constrain the production
of other gas species. Both our size and outgassing limits are important because
`Oumuamua's trajectory shows non-gravitational accelerations that are sensitive
to size and mass and presumably caused by gas emission. We suggest that
`Oumuamua may have experienced low-level post-perihelion volatile emission that
produced a fresh, bright, icy mantle. This model is consistent with the
expected eta value and implied high albedo value for this solution, but, given
our strict limits on CO and CO2, requires another gas species --- probably H2O
--- to explain the observed non-gravitational acceleration. Our results extend
the mystery of `Oumuamua's origin and evolution
Domain kinetics during polarization reversal in 36o Y-cut CLN
The equipment of the Ural Center for Shared Use “Modern nanotechnology” Ural Federal University was used
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