4,718 research outputs found
Average fidelity between random quantum states
We analyze mean fidelity between random density matrices of size N, generated
with respect to various probability measures in the space of mixed quantum
states: Hilbert-Schmidt measure, Bures (statistical) measure, the measures
induced by partial trace and the natural measure on the space of pure states.
In certain cases explicit probability distributions for fidelity are derived.
Results obtained may be used to gauge the quality of quantum information
processing schemes.Comment: 15 revtex pages with 4 figures; Ver. 2: another distribution derived,
an extra figure included, Ver. 3: comments in introduction and conclusion
added ver 4. minor improvment
Electron gun for diffraction experiments off controlled molecules
A dc electron gun, generating picosecond pulses with up to
electrons per pulse, was developed. Its applicability for future
time-resolved-diffraction experiments on state- and conformer-selected
laser-aligned or oriented gaseous samples was characterized. The focusing
electrodes were arranged in a velocity-map imaging spectrometer configuration.
This allowed to directly measure the spatial and velocity distributions of the
electron pulses emitted from the cathode. The coherence length and pulse
duration of the electron beam were characterized by these measurements combined
with electron trajectory simulations. Electron diffraction data off a thin
aluminum foil illustrated the coherence and resolution of the electron-gun
setup
Locking entanglement measures with a single qubit
We study the loss of entanglement of bipartite state subjected to discarding
or measurement of one qubit. Examining the behavior of different entanglement
measures, we find that entanglement of formation, entanglement cost, and
logarithmic negativity are lockable measures in that it can decrease
arbitrarily after measuring one qubit. We prove that any convex and
asymptotically non-continuous measure is lockable. As a consequence, all the
convex roof measures can be locked. Relative entropy of entanglement is shown
to be a non-lockable measure.Comment: 5 pages, RevTex
Truncations of Random Orthogonal Matrices
Statistical properties of non--symmetric real random matrices of size ,
obtained as truncations of random orthogonal matrices are
investigated. We derive an exact formula for the density of eigenvalues which
consists of two components: finite fraction of eigenvalues are real, while the
remaining part of the spectrum is located inside the unit disk symmetrically
with respect to the real axis. In the case of strong non--orthogonality,
const, the behavior typical to real Ginibre ensemble is found. In the
case with fixed , a universal distribution of resonance widths is
recovered.Comment: 4 pages, final revised version (one reference added, minor changes in
Introduction
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