3,283 research outputs found
Quantum entanglement enhances the capacity of bosonic channels with memory
The bosonic quantum channels have recently attracted a growing interest,
motivated by the hope that they open a tractable approach to the generally hard
problem of evaluating quantum channel capacities. These studies, however, have
always been restricted to memoryless channels. Here, it is shown that the
classical capacity of a bosonic Gaussian channel with memory can be
significantly enhanced if entangled symbols are used instead of product
symbols. For example, the capacity of a photonic channel with 70%-correlated
thermal noise of one third the shot noise is enhanced by about 11% when using
3.8-dB entangled light with a modulation variance equal to the shot noise.Comment: 4 pages, 4 figure
Artificial Rheotaxis
Motility is a basic feature of living microorganisms, and how it works is
often determined by environmental cues. Recent efforts have focused on develop-
ing artificial systems that can mimic microorganisms, and in particular their
self-propulsion. Here, we report on the design and characterization of syn-
thetic self-propelled particles that migrate upstream, known as positive rheo-
taxis. This phenomenon results from a purely physical mechanism involving the
interplay between the polarity of the particles and their alignment by a
viscous torque. We show quantitative agreement between experimental data and a
simple model of an overdamped Brownian pendulum. The model no- tably predicts
the existence of a stagnation point in a diverging flow. We take advantage of
this property to demonstrate that our active particles can sense and
predictably organize in an imposed flow. Our colloidal system represents an
important step towards the realization of biomimetic micro-systems withthe
ability to sense and respond to environmental changesComment: Published in Science Advances [Open access journal of Science
Magazine
Comparative Legal Responses to Terrorism: Lessons from Europe
After September 11, 2001, the U.S. Congress and President initiated legal changes to combat terrorism. In the late 20th century, Europe also experienced terrorist attacks on its soil and initiated legal adaptations. Europe\u27s legal history with terrorism shows that harsh procedure-stripping rules do not stop terrorism and come at great costs in civil liberties and legal clout. More procedural safeguards would bring the U.S. legal response back in line with its traditional legal values while still providing a way to fight terrorism. This note investigates the European legal response to its terrorist attacks-measuring successes and gauging costs where possible-and evaluates the the prudence of the current U.S. legal response to terrorism in this light. It compares and contrasts the past legal reactions in Western European countries to the current legal reaction in the United States, focusing on Irish Republican Army (IRA) terrorism in England, Basque terrorism in Spain, and Islamic terrorism in France
Resolving Phonon Fock States in a Multimode Cavity with a Double-Slit Qubit
We resolve phonon number states in the spectrum of a superconducting qubit
coupled to a multimode acoustic cavity. Crucial to this resolution is the sharp
frequency dependence in the qubit-phonon interaction engineered by coupling the
qubit to surface acoustic waves in two locations separated by acoustic
wavelengths. In analogy to double-slit diffraction, the resulting
self-interference generates high-contrast frequency structure in the
qubit-phonon interaction. We observe this frequency structure both in the
coupling rate to multiple cavity modes and in the qubit spontaneous emission
rate into unconfined modes. We use this sharp frequency structure to resolve
single phonons by tuning the qubit to a frequency of destructive interference
where all acoustic interactions are dispersive. By exciting several detuned yet
strongly-coupled phononic modes and measuring the resulting qubit spectrum, we
observe that, for two modes, the device enters the strong dispersive regime
where single phonons are spectrally resolved.Comment: 9 pages, 8 figures; revised arguments in paragraphs 3 and 8, added
Hamiltonian description, and corrected typo
Photonic crystal fibre source of photon pairs for quantum information processing
We demonstrate two key components for optical quantum information processing:
a bright source of heralded single photons; and a bright source of entangled
photon pairs. A pair of pump photons produces a correlated pair of photons at
widely spaced wavelengths (583 nm and 900 nm), via a four-wave
mixing process. We demonstrate a non-classical interference between heralded
photons from independent sources with a visibility of 95%, and an entangled
photon pair source, with a fidelity of 89% with a Bell state.Comment: 4 pages, 3 figure
Effects of muscle dynamics and proprioceptive feedback on the kinematics and CPG activity of salamander stepping
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