12,406 research outputs found
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
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
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
Diagnosis, prescription and prognosis of a Bell-state filter by quantum process tomography
Using a Hong-Ou-Mandel interferometer, we apply the techniques of quantum
process tomography to characterize errors and decoherence in a prototypical
two-photon operation, a singlet-state filter. The quantum process tomography
results indicate a large asymmetry in the process and also the required
operation to correct for this asymmetry. Finally, we quantify errors and
decoherence of the filtering operation after this modification.Comment: 4 pages, 4 figure
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
Sub-femtosecond determination of transmission delay times for a dielectric mirror (photonic bandgap) as a function of angle of incidence
Using a two-photon interference technique, we measure the delay for
single-photon wavepackets to be transmitted through a multilayer dielectric
mirror, which functions as a ``photonic bandgap'' medium. By varying the angle
of incidence, we are able to confirm the behavior predicted by the group delay
(stationary phase approximation), including a variation of the delay time from
superluminal to subluminal as the band edge is tuned towards to the wavelength
of our photons. The agreement with theory is better than 0.5 femtoseconds (less
than one quarter of an optical period) except at large angles of incidence. The
source of the remaining discrepancy is not yet fully understood.Comment: 5 pages and 5 figure
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
Diel Vertical Distribution Patterns of Zooplankton along the Western Antarctic Peninsula
The Western Antarctic Peninsula (WAP) is a region that has undergone significant change over the past several decades due to unprecedented increases sea surface temperature and decreases in sea ice cover. The ongoing Palmer Antarctica Long-Term Ecological Research (PAL LTER) study shows that these environmental changes are significantly affecting the marine pelagic ecosystem along the WAP. The goal of this study was to analyze diel vertical distribution patterns of zooplankton along the WAP
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