49 research outputs found
Direct Production of Tripartite Pump-Signal-Idler Entanglement in the Above-Threshold Optical Parametric Oscillator
We calculate the quantum correlations existing among the three output fields
(pump, signal, and idler) of a triply resonant non-degenerate Optical
Parametric Oscillator operating above threshold. By applying the standard
criteria [P. van Loock and A. Furusawa, Phys. Rev. A 67, 052315 (2003)], we
show that strong tripartite continuous-variable entanglement is present in this
well-known and simple system. Furthermore, since the entanglement is generated
directly from a nonlinear process, the three entangled fields can have very
different frequencies, opening the way for multicolored quantum information
networks.Comment: 4 pages, 3 figure
Magnetic-field-dependent photodynamics of single NV defects in diamond: Application to qualitative all-optical magnetic imaging
Magnetometry and magnetic imaging with nitrogen-vacancy (NV) defects in
diamond rely on the optical detection of electron spin resonance (ESR).
However, this technique is inherently limited to magnetic fields that are weak
enough to avoid electron spin mixing. Here we focus on the high off-axis
magnetic field regime for which spin mixing alters the NV defect spin dynamics.
We first study in a quantitative manner the dependence of the NV defect optical
properties on the magnetic field vector B. Magnetic-field-dependent
time-resolved photoluminescence (PL) measurements are compared to a seven-level
model of the NV defect that accounts for field-induced spin mixing. The model
reproduces the decreases in (i) ESR contrast, (ii) PL intensity and (iii)
excited level lifetime with an increasing off-axis magnetic field. We next
demonstrate that those effects can be used to perform all-optical magnetic
imaging in the high off-axis magnetic field regime. Using a scanning NV defect
microscope, we map the stray field of a magnetic hard disk through both PL and
fluorescence lifetime imaging. This all-optical method for high magnetic field
imaging at the nanoscale might be of interest in the field of nanomagnetism,
where samples producing fields in excess of several tens of milliteslas are
typical
Non-linear and quantum optics of a type II OPO containing a birefringent element Part 1: Classical operation
We describe theoretically the main characteristics of the steady state regime
of a type II Optical Parametric Oscillator (OPO) containing a birefringent
plate. In such a device the signal and idler waves are at the same time
linearly coupled by the plate and nonlinearly coupled by the
crystal. This mixed coupling allows, in some well-defined range of the control
parameters, a frequency degenerate operation as well as phase locking between
the signal and idler modes. We describe here a complete model taking into
account all possible effects in the system, \emph{i.e.} arbitrary rotation of
the waveplate, non perfect phase matching, ring and linear cavities. This model
is able to explain the detailed features of the experiments performed with this
system.Comment: To be published in EPJ
Magnetic imaging with an ensemble of Nitrogen Vacancy centers in diamond
The nitrogen-vacancy (NV) color center in diamond is an atom-like system in
the solid-state which specific spin properties can be efficiently used as a
sensitive magnetic sensor. An external magnetic field induces Zeeman shifts of
the NV center levels which can be measured using Optically Detected Magnetic
Resonance (ODMR). In this work, we exploit the ODMR signal of an ensemble of NV
centers in order to quantitatively map the vectorial structure of a magnetic
field produced by a sample close to the surface of a CVD diamond hosting a thin
layer of NV centers. The reconstruction of the magnetic field is based on a
maximum-likelihood technique which exploits the response of the four intrinsic
orientations of the NV center inside the diamond lattice. The sensitivity
associated to a 1 {\mu}m^2 area of the doped layer, equivalent to a sensor
consisting of approximately 10^4 NV centers, is of the order of 2
{\mu}T/sqrt{Hz}. The spatial resolution of the imaging device is 400 nm,
limited by the numerical aperture of the optical microscope which is used to
collect the photoluminescence of the NV layer. The versatility of the sensor is
illustrated by the accurate reconstruction of the magnetic field created by a
DC current inside a copper wire deposited on the diamond sample.Comment: 11 pages, 5 figures, figure 4 added, results unchange
Wide bandwidth instantaneous radio frequency spectrum analyzer based on nitrogen vacancy centers in diamond
We propose an original analog method to perform instantaneous and quantitative spectral analysis
of microwave signals. An ensemble of nitrogen-vacancy (NV) centers held in a diamond plate is
pumped by a 532 nm laser. Its photoluminescence is imaged through an optical microscope and
monitored by a digital camera. An incoming microwave signal is converted into a microwave field
in the area of the NV centers by a loop shaped antenna. The resonances induced by the magnetic
component of that field are detected through a decrease of the NV centers photoluminescence. A
magnetic field gradient induces a Zeeman shift of the resonances and transforms the frequency information
into spatial information, which allows for the simultaneous analysis of the microwave
signal in the entire frequency bandwidth of the device. The time dependent spectral analysis of an
amplitude modulated microwave signal is demonstrated over a bandwidth of 600 MHz, associated
to a frequency resolution of 7MHz , and a refresh rate of 4 ms. With such integration time, a field
of a few hundreds of lW can be detected. Since the optical properties of NV centers can be
maintained even in high magnetic field, we estimate that an optimized device could allow
frequency analysis in a range of 30 GHz, only limited by the amplitude of the magnetic field
gradient. In addition, an increase of the NV centers quantity could lead both to an increase of the
microwave sensitivity and to a decrease of the minimum refresh rate down to a few ls
Ultra-low threshold CW Triply Resonant OPO in the near infrared using Periodically Poled Lithium Niobate
We have operated a CW triply resonant OPO using a PPLN crystal pumped by a
Nd:YAG laser at 1.06 micron and generating signal and idler modes in the 2-2.3
micron range. The OPO was operated stably in single mode operation over large
periods of time with a pump threshold as low as 500 microwatts.Comment: 7 pages, 5 figures, submitted to JEOS
Using quantum key distribution for cryptographic purposes: a survey
The appealing feature of quantum key distribution (QKD), from a cryptographic
viewpoint, is the ability to prove the information-theoretic security (ITS) of
the established keys. As a key establishment primitive, QKD however does not
provide a standalone security service in its own: the secret keys established
by QKD are in general then used by a subsequent cryptographic applications for
which the requirements, the context of use and the security properties can
vary. It is therefore important, in the perspective of integrating QKD in
security infrastructures, to analyze how QKD can be combined with other
cryptographic primitives. The purpose of this survey article, which is mostly
centered on European research results, is to contribute to such an analysis. We
first review and compare the properties of the existing key establishment
techniques, QKD being one of them. We then study more specifically two generic
scenarios related to the practical use of QKD in cryptographic infrastructures:
1) using QKD as a key renewal technique for a symmetric cipher over a
point-to-point link; 2) using QKD in a network containing many users with the
objective of offering any-to-any key establishment service. We discuss the
constraints as well as the potential interest of using QKD in these contexts.
We finally give an overview of challenges relative to the development of QKD
technology that also constitute potential avenues for cryptographic research.Comment: Revised version of the SECOQC White Paper. Published in the special
issue on QKD of TCS, Theoretical Computer Science (2014), pp. 62-8
Engineered arrays of NV color centers in diamond based on implantation of CN- molecules through nanoapertures
We report a versatile method to engineer arrays of nitrogen-vacancy (NV)
color centers in dia- mond at the nanoscale. The defects were produced in
parallel by ion implantation through 80 nm diameter apertures patterned using
electron beam lithography in a PMMA layer deposited on a diamond surface. The
implantation was performed with CN- molecules which increased the NV defect
formation yield. This method could enable the realization of a solid-state
coupled-spin array and could be used for positioning an optically active NV
center on a photonic microstructure.Comment: 12 pages, 3 figure