489 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
Nonlinearity in Single Photon Detection: Modeling and Quantum Tomography
Single Photon Detectors are integral to quantum optics and quantum
information. Superconducting Nanowire based detectors exhibit new levels of
performance, but have no accepted quantum optical model that is valid for
multiple input photons. By performing Detector Tomography, we improve the
recently proposed model [M.K. Akhlaghi and A.H. Majedi, IEEE Trans. Appl.
Supercond. 19, 361 (2009)] and also investigate the manner in which these
detectors respond nonlinearly to light, a valuable feature for some
applications. We develop a device independent model for Single Photon Detectors
that incorporates this nonlinearity
Classical dispersion-cancellation interferometry
Even-order dispersion cancellation, an effect previously identified with
frequency-entangled photons, is demonstrated experimentally for the first time
with a linear, classical interferometer. A combination of a broad bandwidth
laser and a high resolution spectrometer was used to measure the intensity
correlations between anti-correlated optical frequencies. Only 14% broadening
of the correlation signal is observed when significant material dispersion,
enough to broaden the regular interferogram by 4250%, is introduced into one
arm of the interferometer.Comment: 4 pages, 3 figure
Optimal experiment design revisited: fair, precise and minimal tomography
Given an experimental set-up and a fixed number of measurements, how should
one take data in order to optimally reconstruct the state of a quantum system?
The problem of optimal experiment design (OED) for quantum state tomography was
first broached by Kosut et al. [arXiv:quant-ph/0411093v1]. Here we provide
efficient numerical algorithms for finding the optimal design, and analytic
results for the case of 'minimal tomography'. We also introduce the average
OED, which is independent of the state to be reconstructed, and the optimal
design for tomography (ODT), which minimizes tomographic bias. We find that
these two designs are generally similar. Monte-Carlo simulations confirm the
utility of our results for qubits. Finally, we adapt our approach to deal with
constrained techniques such as maximum likelihood estimation. We find that
these are less amenable to optimization than cruder reconstruction methods,
such as linear inversion.Comment: 16 pages, 7 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
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