304 research outputs found
Investigation of a single-photon source based on quantum interference
We report on an experimental investigation of a single-photon source based on
a quantum interference effect first demonstrated by Koashi, Matsuoka, and
Hirano [Phys. Rev. A 53, 3621 (1996)]. For certain types of measurement-based
quantum information processing applications this technique may be useful as a
high rate, but random, source of single photons.Comment: Submitted to the New J. Phys. Focus Issue on "Measurement-based
quantum information processing
Pulsed squeezed vacuum characterization without homodyning
Direct photon detection is experimentally implemented to measure the
squeezing and purity of a single-mode squeezed vacuum state without an
interferometric homodyne detection. Following a recent theoretical proposal
[arXiv quant-ph/0311119], the setup only requires a tunable beamsplitter and a
single-photon detector to fully characterize the generated Gaussian states. The
experimental implementation of this procedure is discussed and compared with
other reference methods.Comment: 8 pages, 7 figure
Coherent excitation of a single atom to a Rydberg state
We present the coherent excitation of a single Rubidium atom to the Rydberg
state (58d3/2) using a two-photon transition. The experimental setup is
described in detail, as well as experimental techniques and procedures. The
coherence of the excitation is revealed by observing Rabi oscillations between
ground and Rydberg states of the atom. We analyze the observed oscillations in
detail and compare them to numerical simulations which include imperfections of
our experimental system. Strategies for future improvements on the coherent
manipulation of a single atom in our settings are given
Entanglement of two individual atoms using the Rydberg blockade
We report on our recent progress on the manipulation of single rubidium atoms
trapped in optical tweezers and the generation of entanglement between two
atoms, each individually trapped in neighboring tweezers. To create an
entangled state of two atoms in their ground states, we make use of the Rydberg
blockade mechanism. The degree of entanglement is measured using global
rotations of the internal states of both atoms. Such internal state rotations
on a single atom are demonstrated with a high fidelity.Comment: Proceeding of the 19th International Conference on Laser Spectroscopy
ICOLS 2009, 7-13 June 2009, Hokkaido, Japa
High performance guided-wave asynchronous heralded single photon source
We report on a guided wave heralded photon source based on the creation of
non-degenerate photon pairs by spontaneous parametric down conversion in a
Periodically Poled Lithium Niobate waveguide. Using the signal photon at 1310
nm as a trigger, a gated detection process permits announcing the arrival of
single photons at 1550 nm at the output of a single mode optical fiber with a
high probability of 0.38. At the same time the multi-photon emission
probability is reduced by a factor of 10 compared to poissonian light sources.
Relying on guided wave technologies such as integrated optics and fiber optics
components, our source offers stability, compactness and efficiency and can
serve as a paradigm for guided wave devices applied to quantum communication
and computation using existing telecom networks
Design of metallic nanoparticles gratings for filtering properties in the visible spectrum
Plasmonic resonances in metallic nanoparticles are exploited to create
efficient optical filtering functions. A Finite Element Method is used to model
metallic nanoparticles gratings. The accuracy of this method is shown by
comparing numerical results with measurements on a two-dimensional grating of
gold nanocylinders with elliptic cross section. Then a parametric analysis is
performed in order to design efficient filters with polarization dependent
properties together with high transparency over the visible range. The behavior
of nanoparticle gratings is also modelled using the Maxwell-Garnett
homogenization theory and analyzed by comparison with the diffraction by a
single nanoparticle. The proposed structures are intended to be included in
optical systems which could find innovative applications.Comment: submitted to Applied Optic
Energy distribution and cooling of a single atom in an optical tweezer
We investigate experimentally the energy distribution of a single rubidium
atom trapped in a strongly focused dipole trap under various cooling regimes.
Using two different methods to measure the mean energy of the atom, we show
that the energy distribution of the radiatively cooled atom is close to
thermal. We then demonstrate how to reduce the energy of the single atom, first
by adiabatic cooling, and then by truncating the Boltzmann distribution of the
single atom. This provides a non-deterministic way to prepare atoms at low
microKelvin temperatures, close to the ground state of the trapping potential.Comment: 9 pages, 6 figures, published in PR
Multidimensional reconciliation for continuous-variable quantum key distribution
We propose a method for extracting an errorless secret key in a
continuous-variable quantum key distribution protocol, which is based on
Gaussian modulation of coherent states and homodyne detection. The crucial
feature is an eight-dimensional reconciliation method, based on the algebraic
properties of octonions. Since the protocol does not use any postselection, it
can be proven secure against arbitrary collective attacks, by using
well-established theorems on the optimality of Gaussian attacks. By using this
new coding scheme with an appropriate signal to noise ratio, the distance for
secure continuous-variable quantum key distribution can be significantly
extended.Comment: 8 pages, 3 figure
Test of the quantumness of atom-atom correlations in a bosonic gas
It is shown how the quantumness of atom-atom correlations in a trapped
bosonic gas can be made observable. Application of continuous feedback control
of the center of mass of the atomic cloud is shown to generate oscillations of
the spatial extension of the cloud, whose amplitude can be directly used as a
characterization of atom-atom correlations. Feedback parameters can be chosen
such that the violation of a Schwarz inequality for atom-atom correlations can
be tested at noise levels much higher than the standard quantum limit
Continuous variable quantum cryptography using coherent states
We propose several methods for quantum key distribution (QKD) based upon the
generation and transmission of random distributions of coherent or squeezed
states, and we show that they are are secure against individual eavesdropping
attacks. These protocols require that the transmission of the optical line
between Alice and Bob is larger than 50 %, but they do not rely on
"non-classical" features such as squeezing. Their security is a direct
consequence of the no-cloning theorem, that limits the signal to noise ratio of
possible quantum measurements on the transmission line. Our approach can also
be used for evaluating various QKD protocols using light with gaussian
statistics.Comment: 5 pages, 1 figure. In v2 minor rewriting for clarity, references
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