208 research outputs found
Atomic clocks: new prospects in metrology and geodesy
We present the latest developments in the field of atomic clocks and their
applications in metrology and fundamental physics. In the light of recent
advents in the accuracy of optical clocks, we present an introduction to the
relativistic modelization of frequency transfer and a detailed review of
chronometric geodesy.Comment: Proceedings of the Workshop "Relativistic Positioning Systems and
their Scientific Applications" held in Brdo near Kranj, Slovenia, 19-21
September 2012. To appear in Acta Futura
(http://www.esa.int/gsp/ACT/publications/ActaFutura/
Minimizing the Dick Effect in an Optical Lattice Clock
We discuss the minimization of the Dick effect in an optical lattice clock.
We show that optimizing the time sequence of operation of the clock can lead to
a significant reduction of the clock stability degradation by the frequency
noise of the interrogation laser. By using a non-destructive detection of the
atoms, we are able to recycle most of the atoms between cycles and consequently
to strongly reduce the time spent capturing the atoms in each cycle. With
optimized parameters, we expect a fractional Allan deviation better than
2E-16 for the lattice clock.Comment: 6 pages, 10 figures. Submitted to IEEE Transactions on Ultrasonics,
Ferroelectrics, and Frequency Contro
Tight bound on coherent states quantum key distribution with heterodyne detection
We propose a new upper bound for the eavesdropper's information in the direct
and reverse reconciliated coherent states quantum key distribution protocols
with heterodyne detection. This bound is derived by maximizing the leaked
information over the symplectic group of transformations that spans every
physical Gaussian attack on individual pulses. We exhibit four different
attacks that reach this bound, which shows that this bound is tight. Finally,
we compare the secret key rate obtained with this new bound to the homodyne
rate.Comment: 8 pages, 3 figure
Non-destructive measurement of the transition probability in a Sr optical lattice clock
We present the experimental demonstration of non-destructive probing of the
1S0-3P0 clock transition probability in an optical lattice clock with 87Sr
atoms. It is based on the phase shift induced by the atoms on a weak
off-resonant laser beam. The method we propose is a differential measurement of
this phase shift on two modulation sidebands with opposite detuning with
respect to the 1S0-1P1 transition, allowing a detection limited by the photon
shot noise. We have measured an atomic population of 10^4 atoms with a signal
to noise ratio of 100 per cycle, while keeping more than 95% of the atoms in
the optical lattice with a depth of 0.1 mK. The method proves simple and robust
enough to be operated as part of the whole clock setup. This detection scheme
enables us to reuse atoms for subsequent clock state interrogations,
dramatically reducing the loading time and thereby improving the clock
frequency stability.Comment: 4 pages, 5 figure
Observation and cancellation of the dc Stark shift in strontium optical lattice clocks
We report on the observation of a dc Stark frequency shift at the
level by comparing two strontium optical lattice clocks. This frequency shift
arises from the presence of electric charges trapped on dielectric surfaces
placed under vacuum close to the atomic sample. We show that these charges can
be eliminated by shining UV light on the dielectric surfaces, and characterize
the residual dc Stark frequency shift on the clock transition at the
level by applying an external electric field. This study shows that the dc
Stark shift can play an important role in the accuracy budget of lattice
clocks, and should be duly taken into account
Experimental implementation of non-Gaussian attacks on a continuous-variable quantum key distribution system
An intercept-resend attack on a continuous-variable quantum-key-distribution
protocol is investigated experimentally. By varying the interception fraction,
one can implement a family of attacks where the eavesdropper totally controls
the channel parameters. In general, such attacks add excess noise in the
channel, and may also result in non-Gaussian output distributions. We implement
and characterize the measurements needed to detect these attacks, and evaluate
experimentally the information rates available to the legitimate users and the
eavesdropper. The results are consistent with the optimality of Gaussian
attacks resulting from the security proofs.Comment: 4 pages, 5 figure
Lattice Induced Frequency Shifts in Sr Optical Lattice Clocks at the Level
We present a comprehensive study of the frequency shifts associated with the
lattice potential for a Sr lattice clock. By comparing two such clocks with a
frequency stability reaching after a one hour integration
time, and varying the lattice depth up to with being the
recoil energy, we evaluate lattice related shifts with an unprecedented
accuracy. We put the first experimental upper bound on the recently predicted
frequency shift due to the magnetic dipole (M1) and electric quadrupole (E2)
interactions. This upper bound is significantly smaller than the theoretical
upper limit. We also give a new upper limit on the effect of
hyperpolarizability with an improvement by more than one order of magnitude.
Finally, we report the first observation of the vector and tensor shifts in a
lattice clock. Combining these measurements, we show that all known lattice
related perturbation will not affect the clock accuracy down to the
level, even for very deep lattices, up to
Ultra-stable clock laser system development towards space applications
International audienceThe increasing performance of optical lattice clocks has made them attractive for scientific applications in space and thus has pushed the development of their components including the interrogation lasers of the clock transitions towards being suitable for space, which amongst others requires making them more power efficient, radiation hardened, smaller, lighter as well as more mechanically stable. Here we present the development towards a space-compatible interrogation laser system for a strontium lattice clock constructed within the Space Optical Clock (SOC2) project where we have concentrated on mechanical rigidity and size. The laser reaches a fractional frequency instability of 7.9 × 10−16 at 300 ms averaging time. The laser system uses a single extended cavity diode laser that gives enough power for interrogating the atoms, frequency comparison by a frequency comb and diagnostics. It includes fibre link stabilisation to the atomic package and to the comb. The optics module containing the laser has dimensions 60 × 45 × 8 cm3; and the ultra-stable reference cavity used for frequency stabilisation with its vacuum system takes 30 × 30 × 30 cm3. The acceleration sensitivities in three orthogonal directions of the cavity are 3.6 × 10−10/g, 5.8 × 10−10/g and 3.1 × 10−10/g, where g ≈ 9.8 m/s2 is the standard gravitational acceleration
Guidelines for developing optical clocks with fractional frequency uncertainty
There has been tremendous progress in the performance of optical frequency
standards since the first proposals to carry out precision spectroscopy on
trapped, single ions in the 1970s. The estimated fractional frequency
uncertainty of today's leading optical standards is currently in the
range, approximately two orders of magnitude better than that of the best
caesium primary frequency standards. This exceptional accuracy and stability is
resulting in a growing number of research groups developing optical clocks.
While good review papers covering the topic already exist, more practical
guidelines are needed as a complement. The purpose of this document is
therefore to provide technical guidance for researchers starting in the field
of optical clocks. The target audience includes national metrology institutes
(NMIs) wanting to set up optical clocks (or subsystems thereof) and PhD
students and postdocs entering the field. Another potential audience is
academic groups with experience in atomic physics and atom or ion trapping, but
with less experience of time and frequency metrology and optical clock
requirements. These guidelines have arisen from the scope of the EMPIR project
"Optical clocks with uncertainty" (OC18). Therefore, the
examples are from European laboratories even though similar work is carried out
all over the world. The goal of OC18 was to push the development of optical
clocks by improving each of the necessary subsystems: ultrastable lasers,
neutral-atom and single-ion traps, and interrogation techniques. This document
shares the knowledge acquired by the OC18 project consortium and gives
practical guidance on each of these aspects
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