90 research outputs found
Pulse shaping with birefringent crystals: a tool for quantum metrology
A method for time differentiation based on a Babinet-Soleil-Bravais
compensator is introduced. The complex transfer function of the device is
measured using polarization spectral interferometry. Time differentiation of
both the pulse field and pulse envelope are demonstrated over a spectral width
of about 100 THz with a measured overlap with the objective mode greater than
99.8%. This pulse shaping technique is shown to be perfectly suited to time
metrology at the quantum limit
Precision measurements with photon-subtracted or photon-added Gaussian states
Photon-subtracted and photon-added Gaussian states are amongst the simplest
non-Gaussian states that are experimentally available. It is generally believed
that they are some of the best candidates to enhance sensitivity in parameter
extraction. We derive here the quantum Cram\'er-Rao bound for such states and
find that for large photon numbers photon-subtraction or -addition only leads
to a small correction of the quantum Fisher information (QFI). On the other
hand a divergence of the QFI appears for very small squeezing in the limit of
vanishing photon number in the case of photon subtraction, implying an
arbitrarily precise measurement with almost no light. However, at least for the
standard and experimentally established preparation scheme, the decreasing
success probability of the preparation in that limit exactly cancels the
divergence, leading to finite sensitivity per square root of Hertz, when the
duration of the preparation is taken into account.Comment: 19 pages, 3 figure
General Cram\'er-Rao bound for parameter estimation using Gaussian multimode quantum resources
Multimode Gaussian quantum light, including multimode squeezed and/or
multipartite quadrature entangled light, is a very general and powerful quantum
resource with promising applications to quantum information processing and
metrology involving continuous variables. In this paper, we determine the
ultimate sensitivity in the estimation of any parameter when the information
about this parameter is encoded in such Gaussian light, irrespective of the
exact information extraction protocol used in the estimation. We then show
that, for a given set of available quantum resources, the most economical way
to maximize the sensitivity is to put the most squeezed state available in a
well-defined light mode. This implies that it is not possible to take advantage
of the existence of squeezed fluctuations in other modes, nor of quantum
correlations and entanglement between different modes. We show that an
appropriate homodyne detection scheme allows us to reach this Cramr-Rao bound.
We apply finally these considerations to the problem of optimal phase
estimation using interferometric techniques
Dual-Polarised Radiometer for Road Surface Characterisation
This paper presents measurements using a dual-polarised radiometer operating at 93\ua0GHz to detect ice or water on asphalt in laboratory conditions. The brightness temperatures of both H and V polarizations were measured for a dry surface, liquid water, and ice on asphalt at observation angles of 50\ub0 and 56\ub0. The results presented in this paper demonstrate that the studied road conditions can be identified by the radiometer. The measurements are compared with a model and surface parameters, such as dielectric constant and roughness are fitted and compared to reference values. The experiments and results, described in this article, are the first steps towards the future installation of a polarimetric sensor on a moving vehicle for traffic safety
A mirrorless spinwave resonator
Optical resonance is central to a wide range of optical devices and
techniques. In an optical cavity, the round-trip length and mirror reflectivity
can be chosen to optimize the circulating optical power, linewidth, and
free-spectral range (FSR) for a given application. In this paper we show how an
atomic spinwave system, with no physical mirrors, can behave in a manner that
is analogous to an optical cavity. We demonstrate this similarity by
characterising the build-up and decay of the resonance in the time domain, and
measuring the effective optical linewidth and FSR in the frequency domain. Our
spinwave is generated in a 20 cm long Rb gas cell, yet it facilitates an
effective FSR of 83 kHz, which would require a round-trip path of 3.6 km in a
free-space optical cavity. Furthermore, the spinwave coupling is controllable
enabling dynamic tuning of the effective cavity parameters.Comment: 13 pages, 4 figure
Real-time distance measurement immune from atmospheric parameters using optical frequency combs
We propose a direct and real-time ranging scheme using an optical frequency
combs, able to compensate optically for index of refraction variations due to
atmospheric parameters. This scheme could be useful for applications requiring
stringent precision over a long distance in air, a situation where dispersion
becomes the main limitation. The key ingredient is the use of a mode-locked
laser as a precise source for multi-wavelength interferometry in a homodyne
detection scheme. By shaping temporally the local oscillator, one can directly
access the desired parameter (distance) while being insensitive to fluctuations
induced by parameters of the environment such as pressure, temperature,
humidity and CO content
Spatial mode storage in a gradient echo memory
Three-level atomic gradient echo memory (lambda-GEM) is a proposed candidate
for efficient quantum storage and for linear optical quantum computation with
time-bin multiplexing. In this paper we investigate the spatial multimode
properties of a lambda-GEM system. Using a high-speed triggered CCD, we
demonstrate the storage of complex spatial modes and images. We also present an
in-principle demonstration of spatial multiplexing by showing selective recall
of spatial elements of a stored spin wave. Using our measurements, we consider
the effect of diffusion within the atomic vapour and investigate its role in
spatial decoherence. Our measurements allow us to quantify the spatial
distortion due to both diffusion and inhomogeneous control field scattering and
compare these to theoretical models.Comment: 11 pages, 9 figure
Ultimate sensitivity of precision measurements with Gaussian quantum light : a multi-modal approach
Multimode Gaussian quantum light, which includes multimode squeezed and
multipartite quadrature entangled light, is a very general and powerful quantum
resource with promising applications in quantum information processing and
metrology. In this paper, we determine the ultimate sensitivity in the
estimation of any parameter when the information about this parameter is
encoded in such light, irrespective of the information extraction protocol used
in the estimation and of the measured observable. In addition we show that an
appropriate homodyne detection scheme allows us to reach this ultimate
sensitivity. We show that, for a given set of available quantum resources, the
most economical way to maximize the sensitivity is to put the most squeezed
state available in a well-de ned light mode. This implies that it is not
possible to take advantage of the existence of squeezed fluctuations in other
modes, nor of quantum correlations and entanglement between diff erent modes
Generation and characterization of multimode quantum frequency combs
Multimode nonclassical states of light are an essential resource in quantum
computation with continuous variables, for example in cluster state
computation. They can be generated either by mixing different squeezed light
sources using linear optical operations, or directly in a multimode optical
device. In parallel, frequency combs are perfect tools for high precision
metrological applications and for quantum time transfer. Synchronously Pumped
Optical Parametric Oscillators (SPOPOs) have been theoretically shown to
produce multimode non-classical frequency combs. In this paper, we present the
first experimental generation and characterization of a femtosecond quantum
frequency comb generated by a SPOPO. In particular, we give the experimental
evidence of the multimode nature of the generated quantum state and, by
studying the spectral noise distribution of this state, we show that at least
three nonclassical independent modes are required to describe it
- …