2,506 research outputs found
Enhancing Light-Atom Interactions via Atomic Bunching
There is a broad interest in enhancing the strength of light-atom
interactions to the point where injecting a single photon induces a nonlinear
material response. Here, we show theoretically that sub-Doppler-cooled,
two-level atoms that are spatially organized by weak optical fields give rise
to a nonlinear material response that is greatly enhanced beyond that
attainable in a homogeneous gas. Specifically, in the regime where the
intensity of the applied optical fields is much less than the off-resonant
saturation intensity, we show that the third-order nonlinear susceptibility
scales inversely with atomic temperature and, due to this scaling, can be two
orders of magnitude larger than that of a homogeneous gas for typical
experimental parameters. As a result, we predict that spatially bunched
two-level atoms can exhibit single-photon nonlinearities. Our model is valid
for all atomic temperature regimes and simultaneously accounts for the
back-action of the atoms on the optical fields. Our results agree with previous
theoretical and experimental results for light-atom interactions that have
considered only a limited range of temperatures. For lattice beams tuned to the
low-frequency side of the atomic transition, we find that the nonlinearity
transitions from a self-focusing type to a self-defocusing type at a critical
intensity. We also show that higher than third-order nonlinear optical
susceptibilities are significant in the regime where the dipole potential
energy is on the order of the atomic thermal energy. We therefore find that it
is crucial to retain high-order nonlinearities to accurately predict
interactions of laser fields with spatially organized ultracold atoms. The
model presented here is a foundation for modeling low-light-level nonlinear
optical processes for ultracold atoms in optical lattices
A pseudo-matched filter for chaos
A matched filter maximizes the signal-to-noise ratio of a signal. In the
recent work of Corron et al. [Chaos 20, 023123 (2010)], a matched filter is
derived for the chaotic waveforms produced by a piecewise-linear system.
Motivated by these results, we describe a pseudo-matched filter, which removes
noise from the same chaotic signal. It consists of a notch filter followed by a
first-order, low-pass filter. We compare quantitatively the matched filter's
performance to that of our pseudo-matched filter using correlation functions in
a simulated radar application. On average, the pseudo-matched filter performs
with a correlation signal-to-noise ratio that is 2.0 dB below that of the
matched filter. Our pseudo-matched filter, though somewhat inferior in
comparison to the matched filter, is easily realizable at high speed (> 1 GHz)
for potential radar applications
Effect of L-methionine-DL-sulfoximine on acetylene reduction and vesicle formation in derepressed cultures of Frankia strain D 11
Synchronization of Coupled Boolean Phase Oscillators
We design, characterize, and couple Boolean phase oscillators that include
state-dependent feedback delay. The state-dependent delay allows us to realize
an adjustable coupling strength, even though only Boolean signals are
exchanged. Specifically, increasing the coupling strength via the range of
state-dependent delay leads to larger locking ranges in uni- and bi-directional
coupling of oscillators in both experiment and numerical simulation with a
piecewise switching model. In the unidirectional coupling scheme, we unveil
asymmetric triangular-shaped locking regions (Arnold tongues) that appear at
multiples of the natural frequency of the oscillators. This extends
observations of a single locking region reported in previous studies. In the
bidirectional coupling scheme, we map out a symmetric locking region in the
parameter space of frequency detuning and coupling strength. Because of large
scalability of our setup, our observations constitute a first step towards
realizing large-scale networks of coupled oscillators to address fundamental
questions on the dynamical properties of networks in a new experimental
setting.Comment: 8 pages, 8 figure
High Speed Chaos in Optical Feedback System with Flexible Timescales
We describe a new opto-electronic device with time-delayed feedback that uses
a Mach-Zehnder interferometer as passive nonlinearity and a semiconductor laser
as a current-to-optical-frequency converter. Bandlimited feedback allows tuning
of the characteristic time scales of both the periodic and high dimensional
chaotic oscillations that can be generated with the device. Our implementation
of the device produces oscillations in the frequency range of tens to hundreds
of MHz. We develop a model and use it to explore the experimentally observed
Andronov-Hopf bifurcation of the steady state and to estimate the dimension of
the chaotic attractor.Comment: 7 pages, 6 figures, to be published in IEEE J. Quantum Electro
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