2,306 research outputs found
Charge sensitivity of radio frequency single-electron transistor (RF-SET)
A theoretical analysis of the charge sensitivity of the RF-SET is presented.
We use the ``orthodox'' approach and consider the case when the carrier
frequency is much less than where is the typical current through
RF-SET. The optimized noise-limited sensitivity is determined by the
temperature , and at low it is only 1.4 times less than the sensitivity
of conventional single-electron transistor.Comment: 3 pages, 4 figure
Future Measurements of Deeply Virtual Compton Scattering at HERMES
Prospects for future measurements of Deeply Virtual Compton Scattering at
HERMES are studied using different simple models for parameterizations of
generalized parton distributions (GPDs). Measurements of the lepton charge and
lepton beam helicity asymmetry will yield important input for theoretical
models towards the future extraction of GPDs.Comment: 12 pages, 7 figure
Nonideal quantum detectors in Bayesian formalism
The Bayesian formalism for a continuous measurement of solid-state qubits is
derived for a model which takes into account several factors of the detector
nonideality. In particular, we consider additional classical output and
backaction noises (with finite correlation), together with quantum-limited
output and backaction noises, and take into account possible asymmetry of the
detector coupling. The formalism is first derived for a single qubit and then
generalized to the measurement of entangled qubits.Comment: 10 page
Spectrum of qubit oscillations from Bloch equations
We have developed a formalism suitable for calculation of the output spectrum
of a detector continuously measuring quantum coherent oscillations in a
solid-state qubit, starting from microscopic Bloch equations. The results
coincide with that obtained using Bayesian and master equation approaches. The
previous results are generalized to the cases of arbitrary detector response
and finite detector temperature.Comment: 8 page
Transversity Distribution and Polarized Fragmentation Function from Semi-inclusive Pion Electroproduction
A method is discussed to determine the hitherto unknown u-quark transversity
distribution from a planned HERMES measurement of a single-spin asymmetry in
semi-inclusive pion electroproduction off a transversely polarized target.
Assuming u-quark dominance, the measurement yields the shapes of the
transversity distribution and of the ratio of a polarized and the unpolarized
u-quark fragmentation functions. The unknown relative normalization can be
obtained by identifying the transversity distribution with the well-known
helicity distribution at large x. The systematic uncertainty of the method is
dominated by the assumption of u-quark dominance.Comment: 5 pages, 5 figures, revised version as will be published in EPJ
Violating the Modified Helstrom Bound with Nonprojective Measurements
We consider the discrimination of two pure quantum states with three allowed
outcomes: a correct guess, an incorrect guess, and a non-guess. To find an
optimum measurement procedure, we define a tunable cost that penalizes the
incorrect guess and non-guess outcomes. Minimizing this cost over all
projective measurements produces a rigorous cost bound that includes the usual
Helstrom discrimination bound as a special case. We then show that
nonprojective measurements can outperform this modified Helstrom bound for
certain choices of cost function. The Ivanovic-Dieks-Peres unambiguous state
discrimination protocol is recovered as a special case of this improvement.
Notably, while the cost advantage of the latter protocol is destroyed with the
introduction of any amount of experimental noise, other choices of cost
function have optima for which nonprojective measurements robustly show an
appreciable, and thus experimentally measurable, cost advantage. Such an
experiment would be an unambiguous demonstration of a benefit from
nonprojective measurements.Comment: 5 pages, 2 figure
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