207 research outputs found
100 MHz Amplitude and Polarization Modulated Optical Source for Free-Space Quantum Key Distribution at 850 nm
We report on an integrated photonic transmitter of up to 100 MHz repetition
rate, which emits pulses centered at 850 nm with arbitrary amplitude and
polarization. The source is suitable for free space quantum key distribution
applications. The whole transmitter, with the optical and electronic components
integrated, has reduced size and power consumption. In addition, the
optoelectronic components forming the transmitter can be space-qualified,
making it suitable for satellite and future space missions.Comment: 6 figures, 2 table
Experimental Quantum Coin Tossing
In this letter we present the first implementation of a quantum coin tossing
protocol. This protocol belongs to a class of ``two-party'' cryptographic
problems, where the communication partners distrust each other. As with a
number of such two-party protocols, the best implementation of the quantum coin
tossing requires qutrits. In this way, we have also performed the first
complete quantum communication protocol with qutrits. In our experiment the two
partners succeeded to remotely toss a row of coins using photons entangled in
the orbital angular momentum. We also show the experimental bounds of a
possible cheater and the ways of detecting him
Shaping the waveform of entangled photons
We demonstrate experimentally the tunable control of the joint spectrum, i.e.
waveform and degree of frequency correlations, of paired photons generated in
spontaneous parametric downconversion. This control is mediated by the spatial
shape of the pump beam in a type-I noncollinear configuration. We discuss the
applicability of this technique to other sources of frequency entangled
photons, such as electromagnetically induced Raman transitions.Comment: 5 Pages, 4 Figure
Scattering in Multilayered Structures: Diffraction from a Nanohole
The spectral expansion of the Green's tensor for a planar multilayered
structure allows us to semi analytically obtain the angular spectrum
representation of the field scattered by an arbitrary dielectric perturbation
present in the structure. In this paper we present a method to find the
expansion coefficients of the scattered field, given that the electric field
inside the perturbation is available. The method uses a complete set of
orthogonal vector wave functions to solve the structure's vector wave equation.
In the two semi-infinite bottom and top media, those vector wave functions
coincide with the plane-wave basis vectors, including both propagating and
evanescent components. The technique is used to obtain the complete angular
spectrum of the field scattered by a nanohole in a metallic film under Gaussian
illumination. We also show how the obtained formalism can easily be extended to
spherically and cylindrically multilayered media. In those cases, the expansion
coefficients would multiply the spherical and cylindrical vector wave
functions.Comment: 9 pages, 5 figure
Vortices in atomic-molecular Bose-Einstein condensates
The structure and stability of vortices in hybrid atomic-molecular
Bose-Einstein condensates is analyzed in the framework of a two-component
Gross-Pitaevskii-type model that describes the stimulated Raman-induced
photoassociation process. New types of topological vortex states are predicted
to exist in the coherently coupled two-component condensates even without a
trap, and their nontrivial dynamics in the presence of losses is demonstrated.Comment: 7 pages, 6 figure
Structural instability of vortices in Bose-Einstein condensates
In this paper we study a gaseous Bose-Einstein condensate (BEC) and show
that: (i) A minimum value of the interaction is needed for the existence of
stable persistent currents. (ii) Vorticity is not a fundamental invariant of
the system, as there exists a conservative mechanism which can destroy a vortex
and change its sign. (iii) This mechanism is suppressed by strong interactions.Comment: 4 pages with 3 figures. Submitted to Phys. Rev. Let
Experimental estimation of the dimension of classical and quantum systems
An overwhelming majority of experiments in classical and quantum physics make
a priori assumptions about the dimension of the system under consideration.
However, would it be possible to assess the dimension of a completely unknown
system only from the results of measurements performed on it, without any extra
assumption? The concept of a dimension witness answers this question, as it
allows one to bound the dimension of an unknown classical or quantum system in
a device-independent manner, that is, only from the statistics of measurements
performed on it. Here, we report on the experimental demonstration of dimension
witnesses in a prepare and measure scenario. We use pairs of photons entangled
in both polarization and orbital angular momentum to generate ensembles of
classical and quantum states of dimensions up to 4. We then use a dimension
witness to certify their dimensionality as well as their quantum nature. Our
results open new avenues for the device-independent estimation of unknown
quantum systems and for applications in quantum information science.Comment: See also similar, independent and jointly submitted work of J. Ahrens
et al., quant-ph/1111.127
Triggered qutrits for Quantum Communication protocols
A general protocol in Quantum Information and Communication relies in the
ability of producing, transmitting and reconstructing, in general, qunits. In
this letter we show for the first time the experimental implementation of these
three basic steps on a pure state in a three dimensional space, by means of the
orbital angular momentum of the photons. The reconstruction of the qutrit is
performed with tomographic techniques and a Maximum-Likelihood estimation
method. In this way we also demonstrate that we can perform any transformation
in the three dimensional space
Kerker Conditions Upon Lossless, Absorption, and Optical Gain Regimes
The directionality and polarization of light show peculiar properties when
the scattering by a dielectric sphere can be described exclusively by electric
and magnetic dipolar modes. Particularly, when these modes oscillate in-phase
with equal amplitude, at the so-called first Kerker condition, the zero optical
backscattering condition emerges for non-dissipating spheres. However, the role
of absorption and optical gain in the first Kerker condition remains
unexplored. In this work, we demonstrate that either absorption or optical gain
precludes the first Kerker condition and, hence, the absence of backscattered
radiation light, regardless of the size of the particle, incident wavelength,
and incoming polarization. Finally, we derive the necessary prerequisites of
the second Kerker condition of the zero forward light scattering, finding that
optical gain is a compulsory requirement
The role of angular momentum in the construction of electromagnetic multipolar fields
Multipolar solutions of Maxwell's equations are used in many practical
applications and are essential for the understanding of light-matter
interactions at the fundamental level. Unlike the set of plane wave solutions
of electromagnetic fields, the multipolar solutions do not share a standard
derivation or notation. As a result, expressions originating from different
derivations can be difficult to compare. Some of the derivations of the
multipolar solutions do not explicitly show their relation to the angular
momentum operators, thus hiding important properties of these solutions. In
this article, the relation between two of the most common derivations of this
set of solutions is explicitly shown and their relation to the angular momentum
operators is exposed.Comment: 13 pages, 2 figure
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