13 research outputs found
Quantum dynamics and statistics of two coupled down-conversion processes
In the framework of Heisenberg-Langevin theory the dynamical and statistical
effects arising from the linear interaction of two nondegenerate
down-conversion processes are investigated. Using the strong-pumping
approximation the analytical solution of equations of motion is calculated. The
phenomena reminiscent of Zeno and anti-Zeno effects are examined. The
possibility of phase-controlled and mismatch-controlled switching is
illustrated.Comment: 17 pages, 7 figure
Experimental test of strongly non-classical character of a noisy squeezed single-photon state
We experimentally verify the quantum non-Gaussian character of a
conditionally generated noisy squeezed single-photon state with positive Wigner
function. Employing an optimized witness based on probabilities of squeezed
vacuum and squeezed single-photon states we prove that the state cannot be
expressed as a mixture of Gaussian states. In our experiment, the non-Gaussian
state is generated by conditional subtraction of a single photon from squeezed
vacuum state. The state is probed with a homodyne detector and the witness is
determined by averaging a suitable pattern function over the measured homodyne
data. Our experimental results are in good agreement with a theoretical fit
obtained from a simple yet realistic model of the experimental setup.Comment: 10 pages, 8 figures, REVTeX
Statistics of light in Raman and Brillouin nonlinear couplers
Statistical properties of optical fields in nonlinear couplers composed of
two waveguides in which Raman or Brillouin processes (with classical pumping)
are in operation and which are mutually connected through the Stokes and/or
anti-Stokes linear interactions are investigated within the framework of
generalized superposition of coherent fields and quantum noise. Heisenberg
equations describing the couplers are solved both analytically under special
conditions and numerically in general cases. Regimes for nonclassical
properties of optical fields, such as sub-Poissonian photon-number statistics,
negative reduced moments of integrated intensity and squeezing of quadrature
fluctuations are discussed for the cases of single and compound fields. General
results are compared with those from short-length approximation.Comment: LATEX, 20 pages, 19 PostScript figure
Local observables for entanglement witnesses
We present an explicit construction of entanglement witnesses for depolarized
states in arbitrary finite dimension. For infinite dimension we generalize the
construction to twin-beams perturbed by Gaussian noises in the phase and in the
amplitude of the field. We show that entanglement detection for all these
families of states requires only three local measurements. The explicit form of
the corresponding set of local observables (quorom) needed for entanglement
witness is derived.Comment: minor corrections, title change
Joint system quantum descriptions arising from local quantumness
Bipartite correlations generated by non-signalling physical systems that
admit a finite-dimensional local quantum description cannot exceed the quantum
limits, i.e., they can always be interpreted as distant measurements of a
bipartite quantum state. Here we consider the effect of dropping the assumption
of finite dimensionality. Remarkably, we find that the same result holds
provided that we relax the tensor structure of space-like separated
measurements to mere commutativity. We argue why an extension of this result to
tensor representations seems unlikely
Realization of a minimal disturbance quantum measurement
We report the first experimental realization of an "optimal" quantum device able to perform a minimal disturbance measurement on polarization encoded qubits saturating the theoretical boundary established between the classical knowledge acquired of any input state, i.e., a "classical guess," and the fidelity of the same state after disturbance due to measurement. The device has been physically realized by means of a linear optical qubit manipulation, postselection measurement, and a classical feed-forward process
Entanglement Creation by Locally Splitting a Discordant State
We introduce and experimentally implement counter-intuitive entanglement creation by locally splitting a classical mode that is part of a larger discordant state. Possible applications are quantum advantage in information encoding and assisted dense coding. (C) 2014 Optical Society of Americ