17,623 research outputs found
Propagation of temporal entanglement
The equations that govern the temporal evolution of two photons in the
Schr{\"o}dinger picture are derived, taking into account the effects of loss,
group-velocity dispersion, temporal phase modulation, linear coupling among
different optical modes, and four-wave mixing. Inspired by the formalism, we
propose the concept of quantum temporal imaging, which uses dispersive elements
and temporal phase modulators to manipulate the temporal correlation of two
entangled photons. We also present the exact solution of a two-photon vector
soliton, in order to demonstrate the ease of use and intuitiveness of the
proposed formulation.Comment: 8 pages, 4 figure
Finite momentum condensation in a pumped microcavity
We calculate the absorption spectra of a semiconductor microcavity into which
a non-equilibrium exciton population has been pumped. We predict strong peaks
in the spectrum corresponding to collective modes analogous to the Cooper modes
in superconductors and fermionic atomic gases. These modes can become unstable,
leading to the formation of off-equilibrium quantum condensates. We calculate a
phase diagram for condensation, and show that the dominant instabilities can be
at a finite momentum. Thus we predict the formation of inhomogeneous
condensates, similar to Fulde-Ferrel-Larkin-Ovchinnikov states.Comment: 7 pages, 4 figures, updated to accepted versio
Comparison of the INRIM and PTB lattice-spacing standards
To base the kilogram definition on the atomic mass of the silicon 28 atom,
the present relative uncertainty of the silicon 28 lattice parameter must
lowered to 3E-9. To achieve this goal, a new experimental apparatus capable of
a centimetre measurement-baseline has been made at the INRIM. The comparison
between the determinations of the lattice parameter of crystals MO*4 of INRIM
and WASO4.2a of PTB is intended to verify the measurement capabilities and to
assess the limits of this experiment.Comment: 10 pages, 8 figures, submitted to Metrologi
Purely transmitting integrable defects
Some aspects of integrable field theories possessing purely transmitting
defects are described. The main example is the sine-Gordon model and several
striking features of a classical field theory containing one or more defects
are pointed out. Similar features appearing in the associated quantum field
theory are also reviewed briefly.Comment: 6 pages, to appear in Proceedings of the XVth International
Colloquium on Integrable Systems and Quantum Symmetries, Prague, June 200
Adventures in Invariant Theory
We provide an introduction to enumerating and constructing invariants of
group representations via character methods. The problem is contextualised via
two case studies arising from our recent work: entanglement measures, for
characterising the structure of state spaces for composite quantum systems; and
Markov invariants, a robust alternative to parameter-estimation intensive
methods of statistical inference in molecular phylogenetics.Comment: 12 pp, includes supplementary discussion of example
Data transmission with variable-redundancy error control over a high-frequency channel
Results of computations and field tests on a binary-data-transmission system, operating at 1 kbaud over an h.f. channel, are presented. Error correction is effected by means of error detection and automatic request for repeat, via a feedback channel (a Post Office private line). A set of short, fixed-block-length cyclic codes is available, a code of appropriate redundancy being automatically selected to match the varying channel conditions. The decision about which code to use is made at the receiver, and the transmitter is informed via the feedback channel. The results show that relatively simple, reliable, and efficient data communication can be realised by this means
Transition temperature of a dilute homogeneous imperfect Bose gas
The leading-order effect of interactions on a homogeneous Bose gas is
theoretically predicted to shift the critical temperature by an amount
\Delta\Tc = # a_{scatt} n^{1/3} T_0 from the ideal gas result T_0, where
a_{scatt} is the scattering length and n is the density. There have been
several different theoretical estimates for the numerical coefficient #. We
claim to settle the issue by measuring the numerical coefficient in a lattice
simulation of O(2) phi^4 field theory in three dimensions---an effective theory
which, as observed previously in the literature, can be systematically matched
to the dilute Bose gas problem to reproduce non-universal quantities such as
the critical temperature. We find # = 1.32 +- 0.02.Comment: 4 pages, submitted to Phys. Rev. Lett; minor changes due to
improvement of analysis in the longer companion pape
Activation-induced deoxycytidine deaminase (AID) co-transcriptional scanning at single-molecule resolution
Activation-induced deoxycytidine deaminase (AID) generates antibody diversity in B cells by initiating somatic hypermutation (SHM) and class-switch recombination (CSR) during transcription of immunoglobulin variable (IgV) and switch region (IgS) DNA. Using single-molecule FRET, we show that AID binds to transcribed dsDNA and translocates unidirectionally in concert with RNA polymerase (RNAP) on moving transcription bubbles, while increasing the fraction of stalled bubbles. AID scans randomly when constrained in an 8 nt model bubble. When unconstrained on single-stranded (ss) DNA, AID moves in random bidirectional short slides/hops over the entire molecule while remaining bound for ~5 min. Our analysis distinguishes dynamic scanning from static ssDNA creasing. That AID alone can track along with RNAP during transcription and scan within stalled transcription bubbles suggests a mechanism by which AID can initiate SHM and CSR when properly regulated, yet when unregulated can access non-Ig genes and cause cancer
Radio-wave propagation through a medium containing electron-density fluctuations described by an anisotropic Goldreich-Sridhar spectrum
We study the propagation of radio waves through a medium possessing density
fluctuations that are elongated along the ambient magnetic field and described
by an anisotropic Goldreich-Sridhar power spectrum. We derive general formulas
for the wave phase structure function, visibility, angular broadening,
diffraction-pattern length scales, and scintillation time scale for arbitrary
distributions of turbulence along the line of sight, and specialize these
formulas to idealized cases.Comment: 25 pages, 3 figures, submitted to Ap
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