16,620 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
Nonlinear optics with less than one photon
We demonstrate suppression and enhancement of spontaneous parametric down-
conversion via quantum interference with two weak fields from a local
oscillator (LO). Pairs of LO photons are observed to upconvert with high
efficiency for appropriate phase settings, exhibiting an effective nonlinearity
enhanced by at least 10 orders of magnitude. This constitutes a two-photon
switch, and promises to be useful for a variety of nonlinear optical effects at
the quantum level.Comment: 8 pages, 5 figure
Quantum Nonlocality in Two-Photon Experiments at Berkeley
We review some of our experiments performed over the past few years on
two-photon interference. These include a test of Bell's inequalities, a study
of the complementarity principle, an application of EPR correlations for
dispersion-free time-measurements, and an experiment to demonstrate the
superluminal nature of the tunneling process. The nonlocal character of the
quantum world is brought out clearly by these experiments. As we explain,
however, quantum nonlocality is not inconsistent with Einstein causality.Comment: 16 pages including 24 figure
Comment on "A linear optics implementation of weak values in Hardy's paradox"
A recent experimental proposal by Ahnert and Payne [S.E. Ahnert and M.C.
Payne, Phys. Rev. A 70, 042102 (2004)] outlines a method to measure the weak
value predictions of Aharonov in Hardy's paradox. This proposal contains flaws
such as the state preparation method and the procedure for carrying out the
requisite weak measurements. We identify previously published solutions to some
of the flaws.Comment: To be published in Physical Review
A low-mass faraday cup experiment for the solar wind
Faraday cups have proven to be very reliable and accurate instruments capable of making 3-D velocity distribution measurements on spinning or 3-axis stabilized spacecraft. Faraday cup instrumentation continues to be appropriate for heliospheric missions. As an example, the reductions in mass possible relative to the solar wind detection system about to be flown on the WIND spacecraft were estimated. Through the use of technology developed or used at the MIT Center for Space Research but were not able to utilize for WIND: surface-mount packaging, field-programmable gate arrays, an optically-switched high voltage supply, and an integrated-circuit power converter, it was estimated that the mass of the Faraday Cup system could be reduced from 5 kg to 1.8 kg. Further redesign of the electronics incorporating hybrid integrated circuits as well as a decrease in the sensor size, with a corresponding increase in measurement cycle time, could lead to a significantly lower mass for other mission applications. Reduction in mass of the entire spacecraft-experiment system is critically dependent on early and continual collaborative efforts between the spacecraft engineers and the experimenters. Those efforts concern a range of issues from spacecraft structure to data systems to the spacecraft power voltage levels. Requirements for flight qualification affect use of newer, lighter electronics packaging and its implementation; the issue of quality assurance needs to be specifically addressed. Lower cost and reduced mass can best be achieved through the efforts of a relatively small group dedicated to the success of the mission. Such a group needs a fixed budget and greater control over quality assurance requirements, together with a reasonable oversight mechanism
Phase Space Tomography of Classical and Nonclassical Vibrational States of Atoms in an Optical Lattice
Atoms trapped in optical lattice have long been a system of interest in the
AMO community, and in recent years much study has been devoted to both short-
and long-range coherence in this system, as well as to its possible
applications to quantum information processing. Here we demonstrate for the
first time complete determination of the quantum phase space distributions for
an ensemble of atoms in such a lattice, including a negative Wigner
function for atoms in an inverted state.Comment: Submitted to Journal of Optics B: Quantum and Semiclassical Optics.
Special issue in connection with the 9th International Conference on Squeezed
States and Uncertainty Relations, to be held in Besancon, France, on 2-6 May
200
Clock synchronization with dispersion cancellation
The dispersion cancellation feature of pulses which are entangled in
frequency is employed to synchronize clocks of distant parties. The proposed
protocol is insensitive to the pulse distortion caused by transit through a
dispersive medium. Since there is cancellation to all orders, also the effects
of slowly fluctuating dispersive media are compensated. The experimental setup
can be realized with currently available technology, at least for a proof of
principle.Comment: 4 pages, 3 figure
Observation of high-order quantum resonances in the kicked rotor
Quantum resonances in the kicked rotor are characterized by a dramatically
increased energy absorption rate, in stark contrast to the momentum
localization generally observed. These resonances occur when the scaled
Planck's constant hbar=(r/s)*4pi, for any integers r and s. However only the
hbar=r*2pi resonances are easily observable. We have observed high-order
quantum resonances (s>2) utilizing a sample of low temperature, non-condensed
atoms and a pulsed optical standing wave. Resonances are observed for
hbar=(r/16)*4pi r=2-6. Quantum numerical simulations suggest that our
observation of high-order resonances indicates a larger coherence length than
expected from an initially thermal atomic sample
Quantum nonlocality obtained from local states by entanglement purification
We have applied an entanglement purification protocol to produce a single
entangled pair of photons capable of violating a CHSH Bell inequality from two
pairs that individually could not. The initial poorly-entangled photons were
created by a controllable decoherence that introduced complex errors. All of
the states were reconstructed using quantum state tomography which allowed for
a quantitative description of the improvement of the state after purification.Comment: 4 pages, 4 figure
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