41,604 research outputs found
Multimode analysis of the light emitted from a pulsed optical parametric oscillator
We present a multimode treatment of the optical parametric oscillator, which
is valid for both pulsed and continuous-wave pump fields. The two-time
correlation functions of the output field are derived, and we apply the theory
to analyze a scheme for heralded production of non-classical field states that
may be subsequently stored in an atomic quantum memory.Comment: 11 pages, 6 figure
High purity bright single photon source
Using cavity-enhanced non-degenerate parametric downconversion, we have built
a frequency tunable source of heralded single photons with a narrow bandwidth
of 8 MHz, making it compatible with atomic quantum memories. The photon state
is 70% pure single photon as characterized by a tomographic measurement and
reconstruction of the quantum state, revealing a clearly negative Wigner
function. Furthermore, it has a spectral brightness of ~1,500 photons/s per MHz
bandwidth, making it one of the brightest single photon sources available. We
also investigate the correlation function of the down-converted fields using a
combination of two very distinct detection methods; photon counting and
homodyne measurement.Comment: 9 pages, 4 figures; minor changes, added referenc
Time gating of heralded single photons for atomic memories
We demonstrate a method for time gating the standard heralded continuous-
wave (cw) spontaneous parametric down-converted (SPDC) single photon source by
using pulsed pumping of the optical parametric oscillator (OPO) below
threshold. The narrow bandwidth, high purity, high spectral brightness and the
pseudo-deterministic character make the source highly suitable for light-atom
interfaces with atomic memories.Comment: Accepted for publication in Optics Letter
Investigating the tetraquark structure of the new mesons
Using the QCD sum rule approach we investigate the possible four-quark
structure of the recently observed mesons , firstly observed
by BaBaR, X(3872), firstly observed by BELLE and observed by
BELLE. We use diquark-antidiquark currents and work in full QCD, without
relying on expansion. Our results indicate that a four-quark structure
is acceptable for these mesons.Comment: 4 pages 1 eps figure, proceedings of the XVIII Workshop on Hadronic
Interactions (RETINHA-18) Sao Paulo-S
Error Analysis For Encoding A Qubit In An Oscillator
In the paper titled "Encoding A Qubit In An Oscillator" Gottesman, Kitaev,
and Preskill [quant-ph/0008040] described a method to encode a qubit in the
continuous Hilbert space of an oscillator's position and momentum variables.
This encoding provides a natural error correction scheme that can correct
errors due to small shifts of the position or momentum wave functions (i.e.,
use of the displacement operator). We present bounds on the size of correctable
shift errors when both qubit and ancilla states may contain errors. We then use
these bounds to constrain the quality of input qubit and ancilla states.Comment: 5 pages, 8 figures, submitted to Physical Review
Overcoming a limitation of deterministic dense coding with a non-maximally entangled initial state
Under two-party deterministic dense-coding, Alice communicates (perfectly
distinguishable) messages to Bob via a qudit from a pair of entangled qudits in
pure state |Psi>. If |Psi> represents a maximally entangled state (i.e., each
of its Schmidt coefficients is sqrt(1/d)), then Alice can convey to Bob one of
d^2 distinct messages. If |Psi> is not maximally entangled, then Ji et al.
[Phys. Rev. A 73, 034307 (2006)] have shown that under the original
deterministic dense-coding protocol, in which messages are encoded by unitary
operations performed on Alice's qudit, it is impossible to encode d^2-1
messages. Encoding d^2-2 is possible; see, e.g., the numerical studies by Mozes
et al. [Phys. Rev. A 71, 012311 (2005)]. Answering a question raised by Wu et
al. [Phys. Rev. A 73, 042311 (2006)], we show that when |Psi> is not maximally
entangled, the communications limit of d^2-2 messages persists even when the
requirement that Alice encode by unitary operations on her qudit is weakened to
allow encoding by more general quantum operators. We then describe a
dense-coding protocol that can overcome this limitation with high probability,
assuming the largest Schmidt coefficient of |Psi> is sufficiently close to
sqrt(1/d). In this protocol, d^2-2 of the messages are encoded via unitary
operations on Alice's qudit, and the final (d^2-1)-th message is encoded via a
(non-trace-preserving) quantum operation.Comment: 18 pages, published versio
Assessing Relative Volatility/Intermittency/Energy Dissipation
We introduce the notion of relative volatility/intermittency and demonstrate
how relative volatility statistics can be used to estimate consistently the
temporal variation of volatility/intermittency when the data of interest are
generated by a non-semimartingale, or a Brownian semistationary process in
particular. This estimation method is motivated by the assessment of relative
energy dissipation in empirical data of turbulence, but it is also applicable
in other areas. We develop a probabilistic asymptotic theory for realised
relative power variations of Brownian semistationary processes, and introduce
inference methods based on the theory. We also discuss how to extend the
asymptotic theory to other classes of processes exhibiting stochastic
volatility/intermittency. As an empirical application, we study relative energy
dissipation in data of atmospheric turbulence.Comment: 25 pages, 4 figures, v3: major revision, this version contains an
application to electricity prices that was omitted from the published versio
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A comparison of in-sample forecasting methods
In-sample forecasting is a recent continuous modification of well-known forecasting methods based on aggregated data. These aggregated methods are known as age-cohort methods in demography, economics, epidemiology and sociology and as chain ladder in non-life insurance. Data is organized in a two-way table with age and cohort as indices, but without measures of exposure. It has recently been established that such structured forecasting methods based on aggregated data can be interpreted as structured histogram estimators. Continuous in-sample forecasting transfers these classical forecasting models into a modern statistical world including smoothing methodology that is more efficient than smoothing via histograms. All in-sample forecasting estimators are collected and their performance is compared via a finite sample simulation study. All methods are extended via multiplicative bias correction. Asymptotic theory is being developed for the histogram-type method of sieves and for the multiplicatively corrected estimators. The multiplicative bias corrected estimators improve all other known in-sample forecasters in the simulation study. The density projection approach seems to have the best performance with forecasting based on survival densities being the runner-up
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