276 research outputs found
Photonic integrated beam delivery in a rubidium 3D magneto-optical trap
Cold atoms are important for precision atomic applications including
timekeeping and sensing. The 3D magneto-optical trap (3D-MOT), used to produce
cold atoms, will benefit from photonic integration to improve reliability and
reduce size, weight, and cost. These traps require the delivery of multiple,
large area, collimated laser beams to an atomic vacuum cell. Yet, to date, beam
delivery using an integrated waveguide approach has remained elusive. We report
the demonstration of a 87Rb 3D-MOT using a fiber-coupled photonic integrated
circuit to deliver all beams to cool and trap > 1 x 10^6 atoms to near 200
{\mu}K. The silicon nitride photonic circuit transforms fiber-coupled 780 nm
cooling and repump light via waveguides to three mm-width non-diverging
free-space cooling and repump beams directly to the rubidium cell. This planar,
CMOS foundry-compatible integrated beam delivery is compatible with other
components, such as lasers and modulators, promising system-on-chip solutions
for cold atom applications
Long Distance Continuous-Variable Quantum Key Distribution with a Gaussian Modulation
We designed high-efficiency error correcting codes allowing to extract an
errorless secret key in a continuous-variable quantum key distribution protocol
using a Gaussian modulation of coherent states and a homodyne detection. These
codes are available for a wide range of signal-to-noise ratios on an AWGN
channel with a binary modulation and can be combined with a multidimensional
reconciliation method proven secure against arbitrary collective attacks. This
improved reconciliation procedure considerably extends the secure range of a
continuous-variable quantum key distribution with a Gaussian modulation, giving
a secret key rate of about 10^{-3} bit per pulse at a distance of 120 km for
reasonable physical parameters.Comment: 8 pages, 5 figures, 5 table
Multiple timescales in a model for DNA denaturation dynamics
The denaturation dynamics of a long double-stranded DNA is studied by means
of a model of the Poland-Scheraga type. We note that the linking of the two
strands is a locally conserved quantity, hence we introduce local updates that
respect this symmetry. Linking dissipation via untwist is allowed only at the
two ends of the double strand. The result is a slow denaturation characterized
by two time scales that depend on the chain length . In a regime up to a
first characteristic time the chain embodies an
increasing number of small bubbles. Then, in a second regime, bubbles coalesce
and form entropic barriers that effectively trap residual double-stranded
segments within the chain, slowing down the relaxation to fully molten
configurations, which takes place at . This scenario is
different from the picture in which the helical constraints are neglected.Comment: 9 pages, 5 figure
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