293 research outputs found
Quantum cryptography protocols robust against photon number splitting attacks for weak laser pulses implementations
We introduce a new class of quantum quantum key distribution protocols,
tailored to be robust against photon number splitting (PNS) attacks. We study
one of these protocols, which differs from the BB84 only in the classical
sifting procedure. This protocol is provably better than BB84 against PNS
attacks at zero error.Comment: 4 pages, 2 figure
Tight focusing of plane waves from micro-fabricated spherical mirrors
We derive a formula for the light field of a monochromatic plane wave that is
truncated and reflected by a spherical mirror. Our formula is valid even for
deep mirrors, where the aperture radius approaches the radius of curvature. We
apply this result to micro-fabricated mirrors whose size scales are in the
range of tens to hundreds of wavelengths, and show that sub-wavelength spot
sizes can be achieved. This opens up the possibility of scalable arrays of
tightly focused optical dipole traps without the need for high-performance
optical systems.Comment: 8 pages, 5 color figures, 1 .sty file; changes made in response to
referee comments; published in Optics Expres
Nondegenerate parametric down conversion in coherently prepared two-level atomic gas
We describe parametric down conversion process in a two-level atomic gas,
where the atoms are in a superposition state of relevant energy levels. This
superposition results in splitting of the phase matching condition into three
different conditions. Another, more important, peculiarity of the system under
discussion is the nonsaturability of amplification coefficients with increasing
pump wave intensity, under "sideband" generation conditions
Experimental demonstration of phase measurement precision beating standard quantum limit by projection measurement
We propose and demonstrate experimentally a projection scheme to measure the
quantum phase with a precision beating the standard quantum limit. The initial
input state is a twin Fock state proposed by Holland and Burnett [Phys.
Rev. Lett. {\bf 71}, 1355 (1993)] but the phase information is extracted by a
quantum state projection measurement. The phase precision is about for
large photon number , which approaches the Heisenberg limit of 1/N.
Experimentally, we employ a four-photon state from type-II parametric
down-conversion and achieve a phase uncertainty of beating the
standard quantum limit of for four photons.Comment: 5 figure
Bichromatic Driving of a Solid State Cavity QED System
The bichromatic driving of a solid state cavity quantum electrodynamics
system is used to probe cavity dressed state transitions and observe coherent
interaction between the system and the light field. We theoretically
demonstrate the higher order cavity-dressed states, supersplitting, and AC
stark shift in a solid state system comprised of a quantum dot strongly coupled
to a photonic crystal cavity for on- and far off-resonant cases. For the
off-resonant case, phonons mediate off-resonant coupling between the quantum
dot and the photonic resonator, a phenomenon unique to solid state cavity
quantum electrodynamics.Comment: 8 pages 6 figure
Superconducting nanowire photon number resolving detector at telecom wavelength
The optical-to-electrical conversion, which is the basis of optical
detectors, can be linear or nonlinear. When high sensitivities are needed
single-photon detectors (SPDs) are used, which operate in a strongly nonlinear
mode, their response being independent of the photon number. Nevertheless,
photon-number resolving (PNR) detectors are needed, particularly in quantum
optics, where n-photon states are routinely produced. In quantum communication,
the PNR functionality is key to many protocols for establishing, swapping and
measuring entanglement, and can be used to detect photon-number-splitting
attacks. A linear detector with single-photon sensitivity can also be used for
measuring a temporal waveform at extremely low light levels, e.g. in
long-distance optical communications, fluorescence spectroscopy, optical
time-domain reflectometry. We demonstrate here a PNR detector based on parallel
superconducting nanowires and capable of counting up to 4 photons at
telecommunication wavelengths, with ultralow dark count rate and high counting
frequency
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