307 research outputs found
All-Optical Switching Using the Quantum Zeno Effect and Two-Photon Absorption
We have previously shown that the quantum Zeno effect can be used to
implement quantum logic gates for quantum computing applications, where the
Zeno effect was produced using a strong two-photon absorbing medium. Here we
show that the Zeno effect can also be used to implement classical logic gates
whose inputs and outputs are high-intensity fields (coherent states). The
operation of the devices can be understood using a quasi-static analysis, and
their switching times are calculated using a dynamic approach. The two-photon
absorption coefficient of rubidium vapor is shown to allow operation of these
devices at relatively low power levels.Comment: 21 pages, 11 figures. Submitted to Phys. Rev.
Single Photons on Pseudo-Demand from Stored Parametric Down-Conversion
We describe the results of a parametric down-conversion experiment in which
the detection of one photon of a pair causes the other photon to be switched
into a storage loop. The stored photon can then be switched out of the loop at
a later time chosen by the user, providing a single photon for potential use in
a variety of quantum information processing applications. Although the stored
single photon is only available at periodic time intervals, those times can be
chosen to match the cycle time of a quantum computer by using pulsed
down-conversion. The potential use of the storage loop as a photonic quantum
memory device is also discussed.Comment: 8 pages, 7 Figs., RevTe
Investigation of a single-photon source based on quantum interference
We report on an experimental investigation of a single-photon source based on
a quantum interference effect first demonstrated by Koashi, Matsuoka, and
Hirano [Phys. Rev. A 53, 3621 (1996)]. For certain types of measurement-based
quantum information processing applications this technique may be useful as a
high rate, but random, source of single photons.Comment: Submitted to the New J. Phys. Focus Issue on "Measurement-based
quantum information processing
Sensitivity of entangled photon holes to loss and amplification
Energy-time entangled photon holes are shown to be relatively insensitive to
photon loss due to absorption by atoms whose coherence times are longer than
the time delays typically employed in nonlocal interferometry (a fraction of a
nanosecond). Roughly speaking, the excited atoms do not retain any significant
"which-path" information regarding the time at which a photon was absorbed.
High-intensity entangled photon holes can also be amplified under similar
conditions. Decoherence does occur from losses at beam splitters, and these
results show that photon loss cannot always be adequately modeled using a
sequence of beam splitters. These properties of entangled photon holes may be
useful in quantum communications systems where the range of the system is
limited by photon loss.Comment: 10 pages, 6 figure
Complete physical simulation of the entangling-probe attack on the BB84 protocol
We have used deterministic single-photon two qubit (SPTQ) quantum logic to
implement the most powerful individual-photon attack against the
Bennett-Brassard 1984 (BB84) quantum key distribution protocol. Our measurement
results, including physical source and gate errors, are in good agreement with
theoretical predictions for the Renyi information obtained by Eve as a function
of the errors she imparts to Alice and Bob's sifted key bits. The current
experiment is a physical simulation of a true attack, because Eve has access to
Bob's physical receiver module. This experiment illustrates the utility of an
efficient deterministic quantum logic for performing realistic physical
simulations of quantum information processing functions.Comment: 4 pages, 5 figure
All-Optical Switching Demonstration using Two-Photon Absorption and the Classical Zeno Effect
Low-contrast all-optical Zeno switching has been demonstrated in a silicon
nitride microdisk resonator coupled to a hot atomic vapor. The device is based
on the suppression of the field build-up within a microcavity due to
non-degenerate two-photon absorption. This experiment used one beam in a
resonator and one in free-space due to limitations related to device physics.
These results suggest that a similar scheme with both beams resonant in the
cavity would correspond to input power levels near 20 nW.Comment: 4 pages, 5 figure
Full Quantum Analysis of Two-Photon Absorption Using Two-Photon Wavefunction: Comparison with One-Photon Absorption
For dissipation-free photon-photon interaction at the single photon level, we
analyze one-photon transition and two-photon transition induced by photon pairs
in three-level atoms using two-photon wavefunctions. We show that the
two-photon absorption can be substantially enhanced by adjusting the time
correlation of photon pairs. We study two typical cases: Gaussian wavefunction
and rectangular wavefunction. In the latter, we find that under special
conditions one-photon transition is completely suppressed while the high
probability of two-photon transition is maintained.Comment: 6 pages, 4 figure
Haemodialysis activates phospholipase A2 enzyme
Background Clinical and experimental evidence suggest that haemodialysis (HD) procedure is an inflammatory process. For the production of proinflammatory lipid mediators in many inflammatory reactions, the release of arachidonic acid by phospholipase A2 (PLA2 enzyme is a prerequisite. Therefore, the purpose of the present investigation was to establish whether the activity of PLA2 increases during HD and whether the increase depends on the type of dialyser used. Methods We performed dialysis in eight chronic HD patients. Blood samples entering and leaving the dialyser were obtained before and at 15, 60, 120 and 180 min after the dialysis was started, on one occasion using a cuprophane and on another occasion a cellulose triacetate dialyser. PLA2 activity was assessed in crude plasma and in plasma extract. Results PLA2 activity in plasma extract exhibited similar biochemical properties to that of inflammatory human synovial fluid PLA2 enzyme which is of group II PLA2. PLA2 activity in crude plasma represents a type of PLA2 other than the synovial type. In HD patients, baseline PLA2 activities in crude plasma and plasma extract were significantly increased when compared to normal subjects. An increase in PLA2 activity was observed in crude plasma with a peak appearing at 15 min when the patients were dialysed with cuprophane and cellulose triacetate membranes. This increase was observed in both arterial and venous blood samples and was more pronounced when the patients were dialysed with cuprophane than with cellulose triacetate membranes. When PLA2 was assessed in plasma extract, the activity increased only with cuprophane but not with cellulose triacetate membranes. Conclusions PLA2 activity in plasma is increased in HD patients and increases during the dialysis procedure to a greater extent with a less biocompatible membrane. Continuous activation of PLA2 might be relevant for long-term deleterious consequences of H
Interference in dielectrics and pseudo-measurements
Inserting a lossy dielectric into one arm of an interference experiment acts
in many ways like a measurement. If two entangled photons are passed through
the interferometer, a certain amount of information is gained about which path
they took, and the interference pattern in a coincidence count measurement is
suppressed. However, by inserting a second dielectric into the other arm of the
interferometer, one can restore the interference pattern. Two of these
pseudo-measurements can thus cancel each other out. This is somewhat analogous
to the proposed quantum eraser experiments.Comment: 7 pages RevTeX 3.0 + 2 figures (postscript). Submitted to Phys. Rev.
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