2,911 research outputs found
Necessary and Sufficient Classicality Conditions on Photon Number Distributions
We exploit results on the classical Stieltjes moment problem to obtain
completely explicit necessary and sufficient conditions for the photon number
distribution p(n) of a radiation field mode to be classical. These conditions
are given in two forms - respectively local and global in the individual photon
number probabilities. Central to the first approach is the recognition of the
important fact that the quantities n!p(n) are moments of a quasiprobability
distribution, notwithstanding the fact that p(n)'s can by themselves be
considered as a probability distribution over the nonnegative integers. This
leads to local classicality conditions involving p(n)'s for only a small number
of values of n. This local approach enables us to present detailed quantitative
statements on the connection between nonclassicality and oscillations in the
photon number distribution. The second approach is in terms of the traditional
factorial moments of p(n). Equivalence of the two approaches is established.Comment: 12-pages in revtex with three ps figure included using eps
The Sampling Theorem and Coherent State Systems in Quantum Mechanics
The well known Poisson Summation Formula is analysed from the perspective of
the coherent state systems associated with the Heisenberg--Weyl group. In
particular, it is shown that the Poisson summation formula may be viewed
abstractly as a relation between two sets of bases (Zak bases) arising as
simultaneous eigenvectors of two commuting unitary operators in which geometric
phase plays a key role. The Zak bases are shown to be interpretable as
generalised coherent state systems of the Heisenberg--Weyl group and this, in
turn, prompts analysis of the sampling theorem (an important and useful
consequence of the Poisson Summation Formula) and its extension from a coherent
state point of view leading to interesting results on properties of von Neumann
and finer lattices based on standard and generalised coherent state systems.Comment: 20 pages, Late
Nonclassicality and the concept of local constraints on the photon number distribution
We exploit results from the classical Stieltjes moment problem to bring out
the totality of all the information regarding phase insensitive nonclassicality
of a state as captured by the photon number distribution p_n. Central to our
approach is the realization that n !p_n constitutes the sequence of moments of
a (quasi) probability distribution, notwithstanding the fact that p_n can by
itself be regarded as a probability distribution. This leads to classicality
restrictions on p_n that are local in n involving p_n's for only a small number
of consecutive n's, enabling a critical examination of the conjecture that
oscillation in p_n is a signature of nonclassicality.Comment: Five pages in revtex with one ps figure included using eps
Facile fabrication of lateral nanowire wrap-gate devices with improved performance
We present a simple fabrication technique for lateral nanowire wrap-gate
devices with high capacitive coupling and field-effect mobility. Our process
uses e-beam lithography with a single resist-spinning step, and does not
require chemical etching. We measure, in the temperature range 1.5-250 K, a
subthreshold slope of 5-54 mV/decade and mobility of 2800-2500 --
significantly larger than previously reported lateral wrap-gate devices. At
depletion, the barrier height due to the gated region is proportional to
applied wrap-gate voltage.Comment: 3 pages, 3 figure
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