18 research outputs found
Quantum Optomagnetics in Graphene
Graphene can be magnetized through nonlinear response of its orbital angular
momentum to an intense circularly polarized light. This optomagnetic effect can
be well exemplified by the Inverse Faraday Effect (IFE) where an
optically-generated DC magnetization leads to graphene's optical activity. We
provide a single-particle quantum mechanical model of an IFE in graphene by
solving Schr\"odinger's equation in the presence of a renormalized Hamiltonian
near a Dirac point in the presence of circularly polarized monochromatic light.
We derive an analytical expression for DC magnetization based on
non-perturbative and dressed states of quasi-electrons where their energy
spectrum is isotropically gapped by the circularly polarized light. Optical
rotatory power is then computed through the gyroelectric birefringence where a
measurable polarization rotation angle under moderate and intense optical
radiations is predicted.Comment: 7 pages, 7 figures; general typos corrected, 1 typo in equation
correct, 2 typos in notation corrected, introduction extended, original
magnetization expression integrated over k, figure added for comparison,
figures slightly changed and plotted in lower intensity range
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
Stimulated quantum phase slips from weak electromagnetic radiations in superconducting nanowires
We study the rate of quantum phase slips in an ultranarrow superconducting
nanowire exposed to weak electromagnetic radiations. The superconductor is in
the dirty limit close to the superconducting-insulating transition, where
fluxoids move in strong dissipation. We use a semiclassical approach and show
that external radiation stimulates a significant enhancement in the probability
of quantum phase slips. This can help to outline a new type of detector for
microwave to submillimetre radiations based on stimulated quantum phase slip
phenomenon.Comment: 10 pages, 9 figure
Quantum Key Distribution over Probabilistic Quantum Repeaters
A feasible route towards implementing long-distance quantum key distribution
(QKD) systems relies on probabilistic schemes for entanglement distribution and
swapping as proposed in the work of Duan, Lukin, Cirac, and Zoller (DLCZ)
[Nature 414, 413 (2001)]. Here, we calculate the conditional throughput and
fidelity of entanglement for DLCZ quantum repeaters, by accounting for the DLCZ
self-purification property, in the presence of multiple excitations in the
ensemble memories as well as loss and other sources of inefficiency in the
channel and measurement modules. We then use our results to find the generation
rate of secure key bits for QKD systems that rely on DLCZ quantum repeaters. We
compare the key generation rate per logical memory employed in the two cases of
with and without a repeater node. We find the cross-over distance beyond which
the repeater system outperforms the non-repeater one. That provides us with the
optimum inter-node distancing in quantum repeater systems. We also find the
optimal excitation probability at which the QKD rate peaks. Such an optimum
probability, in most regimes of interest, is insensitive to the total distance.Comment: 12 pages, 6 figures; Fig. 5(a) is replace
Efficient Single Photon Absorption by Optimized Superconducting Nanowire Geometries
We report on simulation results that shows optimum photon absorption by
superconducting nanowires can happen at a fill-factor that is much less than
100%. We also present experimental results on high performance of our
superconducting nanowire single photon detectors realized using NbTiN on
oxidized silicon.Comment: \copyright 2013 IEEE. Submitted to "Numerical Simulation of
Optoelectronic Devices - NUSOD 2013" on 19-April-201
New Journal of Physics Controlling a superconducting nanowire single-photon detector using tailored bright illumination
Abstract. We experimentally demonstrate that a superconducting nanowire single-photon detector is deterministically controllable by bright illumination. We found that bright light can temporarily make a large fraction of the nanowire length normally conductive, can extend deadtime after a normal photon detection, and can cause a hotspot formation during the deadtime with a highly nonlinear sensitivity. As a result, although based on different physics, the superconducting detector turns out to be controllable by virtually the same techniques as avalanche photodiode detectors. As demonstrated earlier, when such detectors are used in a quantum key distribution system, this allows an eavesdropper to launch a detector control attack to capture the full secret key without this being revealed by too many errors in the key