791 research outputs found
Time reversal symmetry in optics
The utilization of time reversal symmetry in designing and implementing
(quantum) optical experiments has become more and more frequent over the past
years. We review the basic idea underlying time reversal methods, illustrate it
with several examples and discuss a number of implications.Comment: 5 pages, 3 figures, typeset with revte
Practical implementation of mutually unbiased bases using quantum circuits
The number of measurements necessary to perform the quantum state
reconstruction of a system of qubits grows exponentially with the number of
constituents, creating a major obstacle for the design of scalable tomographic
schemes. We work out a simple and efficient method based on cyclic generation
of mutually unbiased bases. The basic generator requires only Hadamard and
controlled-phase gates, which are available in most practical realizations of
these systems. We show how complete sets of mutually unbiased bases with
different entanglement structures can be realized for three and four qubits. We
also analyze the quantum circuits implementing the various entanglement
classes.Comment: 5 pages, 2 color figures. Comments welcome
Continuous Variable Quantum Cryptography - beating the 3 dB loss limit
We demonstrate that secure quantum key distribution systems based on
continuous variables implementations can operate beyond the apparent 3 dB loss
limit that is implied by the beam splitting attack . The loss limit was
established for standard minimum uncertainty states such as coherent states. We
show that by an appropriate postselection mechanism we can enter a region where
Eve's knowledge falls behind the information shared between Alice and Bob even
in the presence of substantial losses.Comment: 4 pages, 2 figure
Waveguide properties of single subwavelength holes demonstrated with radially and azimuthally polarized light
We investigate the transmission of focused beams through single subwavelength
holes in a silver film. We use radially and azimuthally polarized light,
respectively, to excite higher order waveguide modes as well as to match the
radial symmetry of the aperture geometry. Remarkably, the transmission
properties can be described by a classical waveguide model even for thicknesses
of the silver film as thin as a quarter of a wavelength
Angular Distribution of Photoelectrons in Three Photon Ionisation of Sodium
Druckfehler auf Seite 54
Dielectric tuning and coupling of whispering gallery modes using an anisotropic prism
Optical whispering gallery mode (WGM) resonators are a powerful and versatile
tool used in many branches of science. Fine tuning of the central frequency and
line width of individual resonances is however desirable in a number of
applications including frequency conversion, optical communications and
efficient light-matter coupling. To this end we present a detailed theoretical
analysis of dielectric tuning of WGMs supported in axisymmetric resonators.
Using the Bethe-Schwinger equation and adopting an angular spectrum field
representation we study the resonance shift and mode broadening of high
WGMs when a planar dielectric substrate is brought close to the resonator.
Particular focus is given to use of a uniaxial substrate with an arbitrarily
aligned optic axis. Competing red and blue resonance shifts ( MHz),
deriving from generation of a near field material polarisation and back action
from the radiation continuum respectively, are found. Anomalous resonance
shifts can hence be observed depending on the substrate material, whereas mode
broadening on the order of MHz can also be simply realised.
Furthermore, polarisation selective coupling with extinction ratios of
can be achieved when the resonator and substrate are of the same composition
and their optic axes are chosen correctly. Double refraction and properties of
out-coupled beams are also discussed
Nonlinear cross-Kerr quasiclassical dynamics
We study the quasiclassical dynamics of the cross-Kerr effect. In this
approximation, the typical periodical revivals of the decorrelation between the
two polarization modes disappear and they remain entangled. By mapping the
dynamics onto the Poincare space, we find simple conditions for polarization
squeezing. When dissipation is taken into account, the shape of the states in
such a space is not considerably modified, but their size is reduced.Comment: 16 pages, 5 figure
Squeezed state purification with linear optics and feed forward
A scheme for optimal and deterministic linear optical purification of mixed
squeezed Gaussian states is proposed and experimentally demonstrated. The
scheme requires only linear optical elements and homodyne detectors, and allows
the balance between purification efficacy and squeezing degradation to be
controlled. One particular choice of parameters gave a ten-fold reduction of
the thermal noise with a corresponding squeezing degradation of only 11%. We
prove optimality of the protocol, and show that it can be used to enhance the
performance of quantum informational protocols such as dense coding and
entanglement generation.Comment: 4 pages, 3 figure
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