1,346 research outputs found
A Bell-type test of energy-time entangled qutrits
We have performed a Bell-type test for energy-time entangled qutrits. A
method of inferring the Bell violation in terms of an associated interference
visibility is derived. Using this scheme we obtained a Bell value of , representing a violation of above the limit for local
variables. The scheme has been developed for use at telecom wavelengths and
using proven long distance quantum communication architecture to optimize the
utility of this high dimensional entanglement resource.Comment: replaced lost acknowledement
Cyclic networks of quantum gates
In this article initial steps in an analysis of cyclic networks of quantum
logic gates is given. Cyclic networks are those in which the qubit lines are
loops. Here we have studied one and two qubit systems plus two qubit cyclic
systems connected to another qubit on an acyclic line. The analysis includes
the group classification of networks and studies of the dynamics of the qubits
in the cyclic network and of the perturbation effects of an acyclic qubit
acting on a cyclic network. This is followed by a discussion of quantum
algorithms and quantum information processing with cyclic networks of quantum
gates, and a novel implementation of a cyclic network quantum memory. Quantum
sensors via cyclic networks are also discussed.Comment: 14 pages including 11 figures, References adde
Imperfect Detectors in Linear Optical Quantum Computers
We discuss the effects of imperfect photon detectors suffering from loss and
noise on the reliability of linear optical quantum computers. We show that for
a given detector efficiency, there is a maximum achievable success probability,
and that increasing the number of ancillary photons and detectors used for one
controlled sign flip gate beyond a critical point will decrease the probability
that the computer will function correctly. We have also performed simulations
of some small logic gates and estimate the efficiency and noise levels required
for the linear optical quantum computer to function properly.Comment: 13 pages, 5 figure
No-hidden-variables proof for two spin-1/2 particles preselected and postselected in unentangled states
It is a well-known fact that all the statistical predictions of quantum
mechanics on the state of any physical system represented by a two-dimensional
Hilbert space can always be duplicated by a noncontextual hidden-variables
model. In this paper, I show that, in some cases, when we consider an
additional independent (unentangled) two-dimensional system, the quantum
description of the resulting composite system cannot be reproduced using
noncontextual hidden variables. In particular, a no-hidden-variables proof is
presented for two individual spin-1/2 particles preselected in an uncorrelated
state AB and postselected in another uncorrelated state aB, B being the same
state for the second particle in both preselection and postselection.Comment: LaTeX, 8 page
Generalized quantum measurements and local realism
The structure of a local hidden variable model for experiments involving
sequences of measurements rigorously is analyzed. Constraints imposed by local
realism on the conditional probabilities of the outcomes of such measurement
schemes are explicitly derived. The violation of local realism in the case of
``hidden nonlocality'' is illustrated by an operational example.Comment: Revtex, 12 pages; Some modifications of introduction has been made; a
note stating that part of results had been obtained earlier by other authors,
has been added; one postscript figure available at request from
[email protected]
Status of SuperSpec: A Broadband, On-Chip Millimeter-Wave Spectrometer
SuperSpec is a novel on-chip spectrometer we are developing for multi-object,
moderate resolution (R = 100 - 500), large bandwidth (~1.65:1) submillimeter
and millimeter survey spectroscopy of high-redshift galaxies. The spectrometer
employs a filter bank architecture, and consists of a series of half-wave
resonators formed by lithographically-patterned superconducting transmission
lines. The signal power admitted by each resonator is detected by a lumped
element titanium nitride (TiN) kinetic inductance detector (KID) operating at
100-200 MHz. We have tested a new prototype device that is more sensitive than
previous devices, and easier to fabricate. We present a characterization of a
representative R=282 channel at f = 236 GHz, including measurements of the
spectrometer detection efficiency, the detector responsivity over a large range
of optical loading, and the full system optical efficiency. We outline future
improvements to the current system that we expect will enable construction of a
photon-noise-limited R=100 filter bank, appropriate for a line intensity
mapping experiment targeting the [CII] 158 micron transition during the Epoch
of ReionizationComment: 16 pages, 10 figures, Proceedings of the SPIE Astronomical Telescopes
+ Instrumentation 2014 Conference, Vol 9153, Millimeter, Submillimeter, and
Far-Infrared Detectors and Instrumentation for Astronomy VI
Preparation of polarization entangled mixed states of two photons
We propose a scheme for preparing arbitrary two photons polarization
entangled mixed states via controlled location decoherence. The scheme uses
only linear optical devices and single-mode optical fibers, and may be feasible
in experiment within current optical technology.Comment: 3 pages, 5 figs. The article has been rewritten. Discussion about
experiment are added. To appear in Phys. Rev.
Good Quantum Convolutional Error Correction Codes And Their Decoding Algorithm Exist
Quantum convolutional code was introduced recently as an alternative way to
protect vital quantum information. To complete the analysis of quantum
convolutional code, I report a way to decode certain quantum convolutional
codes based on the classical Viterbi decoding algorithm. This decoding
algorithm is optimal for a memoryless channel. I also report three simple
criteria to test if decoding errors in a quantum convolutional code will
terminate after a finite number of decoding steps whenever the Hilbert space
dimension of each quantum register is a prime power. Finally, I show that
certain quantum convolutional codes are in fact stabilizer codes. And hence,
these quantum stabilizer convolutional codes have fault-tolerant
implementations.Comment: Minor changes, to appear in PR
Effects and Propositions
The quantum logical and quantum information-theoretic traditions have exerted
an especially powerful influence on Bub's thinking about the conceptual
foundations of quantum mechanics. This paper discusses both the quantum logical
and information-theoretic traditions from the point of view of their
representational frameworks. I argue that it is at this level, at the level of
its framework, that the quantum logical tradition has retained its centrality
to Bub's thought. It is further argued that there is implicit in the quantum
information-theoretic tradition a set of ideas that mark a genuinely new
alternative to the framework of quantum logic. These ideas are of considerable
interest for the philosophy of quantum mechanics, a claim which I defend with
an extended discussion of their application to our understanding of the
philosophical significance of the no hidden variable theorem of Kochen and
Specker.Comment: Presented to the 2007 conference, New Directions in the Foundations
of Physic
Collective tests for quantum nonlocality
Pairs of spin-1/2 particles are prepared in a Werner state (namely, a mixture
of singlet and random components). If the random component is large enough, the
statistical results of spin measurements that may be performed on each pair
separately can be reproduced by an algorithm involving local ``hidden''
variables. However, if several such pairs are tested simultaneously, a
violation of the Clauser-Horne-Shimony-Holt inequality may occur, and no local
hidden variable model is compatible with the results.Comment: 14 pages, LaTeX, 1 figure on separate pag
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