1,416 research outputs found
Extracting joint weak values with local, single-particle measurements
Weak measurement is a new technique which allows one to describe the
evolution of postselected quantum systems. It appears to be useful for
resolving a variety of thorny quantum paradoxes, particularly when used to
study properties of pairs of particles. Unfortunately, such nonlocal or joint
observables often prove difficult to measure weakly in practice (for instance,
in optics -- a common testing ground for this technique -- strong photon-photon
interactions would be needed). Here we derive a general, experimentally
feasible, method for extracting these values from correlations between
single-particle observables.Comment: 6 page
A catalog of radio observations of Jupiter 1961-1964
Catalog of radio observations of Jupiter 1961 to 196
X-band system performance of the very large array
The Very Large Array (VLA) is being equipped to receive telemetry from Voyager 2 during the Neptune encounter in 1989. Cryogenically cooled amplifiers are being installed on each of the 27 antennas. These amplifiers are currently a mix of field effect transistors (FETs) and high electron mobility transistors (HEMTs) and exhibit zenith system temperatures that range from 30 to 52 K. The system temperatures and aperture efficiencies determined during the past year are summarized. The nominal values of the noise diode calibration are compared with derived values made under the assumption of a uniform atmosphere over the array. Gain values are determined from observations of unresolved radio sources whose flux densities are well known. The tests suggest that the completed VLA will have a ratio of gain to system temperature that is approximately 4.4 dB above that of a single 64 m antenna of the Deep Space Network
Full characterization of a three-photon GHZ state using quantum state tomography
We have performed the first experimental tomographic reconstruction of a
three-photon polarization state. Quantum state tomography is a powerful tool
for fully describing the density matrix of a quantum system. We measured 64
three-photon polarization correlations and used a "maximum-likelihood"
reconstruction method to reconstruct the GHZ state. The entanglement class has
been characterized using an entanglement witness operator and the maximum
predicted values for the Mermin inequality was extracted.Comment: 3 pages, 3 figure
Experimental violation of a cluster state Bell inequality
Cluster states are a new type of multiqubit entangled states with
entanglement properties exceptionally well suited for quantum computation. In
the present work, we experimentally demonstrate that correlations in a
four-qubit linear cluster state cannot be described by local realism. This
exploration is based on a recently derived Bell-type inequality [V. Scarani et
al., Phys. Rev A 71, 042325 (2005)] which is tailored, by using a combination
of three- and four-particle correlations, to be maximally violated by cluster
states but not violated at all by GHZ states. We observe a cluster state Bell
parameter of , which is more than 7 standard deviations larger
than the threshold of 2 imposed by local realism.Comment: 4 pages, 2 figure
A conditional-phase switch at the single-photon level
We present an experimental realization of a two-photon conditional-phase
switch, related to the ``-'' gate of quantum computation. This gate
relies on quantum interference between photon pairs, generating entanglement
between two optical modes through the process of spontaneous parametric
down-conversion (SPDC). The interference effect serves to enhance the effective
nonlinearity by many orders of magnitude, so it is significant at the quantum
(single-photon) level. By adjusting the relative optical phase between the
classical pump for SPDC and the pair of input modes, one can impress a large
phase shift on one beam which depends on the presence or absence of a single
photon in a control mode.Comment: 8 pages, 4 figure
Mobile radio interferometric geodetic systems
Operation of the Astronomical Radio Interferometric Earth Surveying (ARIES) in a proof of concept mode is discussed. Accuracy demonstrations over a short baseline, a 180 km baseline, and a 380 km baseline are documented. Use of ARIES in the Sea Slope Experiment of the National Geodetic Survey to study the apparent differences between oceanographic and geodetic leveling determinations of the sea surface along the Pacific Coast is described. Intergration of the NAVSTAR Global Positioning System and a concept called SERIES (Satellite Emission Radio Interferometric Earth Surveying) is briefly reviewed
Experimental application of decoherence-free subspaces in a quantum-computing algorithm
For a practical quantum computer to operate, it will be essential to properly
manage decoherence. One important technique for doing this is the use of
"decoherence-free subspaces" (DFSs), which have recently been demonstrated.
Here we present the first use of DFSs to improve the performance of a quantum
algorithm. An optical implementation of the Deutsch-Jozsa algorithm can be made
insensitive to a particular class of phase noise by encoding information in the
appropriate subspaces; we observe a reduction of the error rate from 35% to
essentially its pre-noise value of 8%.Comment: 11 pages, 4 figures, submitted to PR
Violation of Bell's Inequality with Photons from Independent Sources
We report a violation of Bell's inequality using one photon from a parametric
down-conversion source and a second photon from an attenuated laser beam. The
two photons were entangled at a beam splitter using the post-selection
technique of Shih and Alley [Phys. Rev. Lett. 61, 2921 (1988)]. A quantum
interference pattern with a visibility of 91% was obtained using the photons
from these independent sources, as compared with a visibility of 99.4% using
two photons from a central parametric down-conversion source.Comment: 4 pages, 5 figures; minor change
Local Conversion of Greenberger-Horne-Zeilinger States to Approximate W States
Genuine 3-qubit entanglement comes in two different inconvertible types
represented by the Greenberger-Horne-Zeilinger (GHZ) state and the W state. We
describe a specific method based on local positive operator valued measures and
classical communication that can convert the ideal N-qubit GHZ state to a state
arbitrarily close to the ideal N-qubit W state. We then experimentally
implement this scheme in the 3-qubit case and characterize the input and the
final state using 3-photon quantum state tomography.Comment: 4 pages, 3 figure
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