Y. Le Coq

Sr Lattice Clock at 1 x 10-16 Fractional Uncertainty by Remote Optical Evaluation with a Ca Clock

Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies. Rigorous evaluations of these clocks require direct comparisons between them. We have realized a high-performance remote comparison of optical clocks over kilometer-scale urban distances, a key step for development, dissemination, and application of these optical standards. Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1 × 10–16 fractional level, surpassing the current best evaluations of cesium (Cs) primary standards. We also report on the observation of density-dependent effects in the spin-polarized fermionic sample and discuss the current limiting effect of blackbody radiation–induced frequency shifts.

Ultrastable lasers based on vibration insensitive cavities

We present two ultrastable lasers based on two vibration insensitive cavity designs, one with vertical optical axis geometry, the other horizontal. Ultrastable cavities are constructed with fused silica mirror substrates, shown to decrease the thermal noise limit, in order to improve the frequency stability over previous designs. Vibration sensitivity components measured are equal to or better than

Ultralow noise microwave generation with fiber-based optical frequency comb and application to atomic fountain clock

1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}/\text{m}\text{ }{\text{s}}^{\ensuremath{-}2}

Experimental realization of an optical second with strontium lattice clocks

for each spatial direction, which shows significant improvement over previous studies. We have tested the very low dependence on the position of the cavity support points, in order to establish that our designs eliminate the need for fine tuning to achieve extremely low vibration sensitivity. Relative frequency measurements show that at least one of the stabilized lasers has a stability better than

Ultra-low-noise microwave extraction from fiber-based optical frequency comb

5.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}

Optical-fiber pulse rate multiplier for ultralow phase-noise signal generation

at 1 s, which is the best result obtained for this length of cavity.

A clock network for geodesy and fundamental science.

We demonstrate the use of a fiber-based femtosecond laser locked onto an ultrastable optical cavity to generate a low-noise microwave reference signal. Comparison with both a cryogenic sapphire oscillator (CSO) and a titanium-sapphire-based optical frequency comb system exhibit a stability of about 3×10−15 between 1 and 10 s. The microwave signal from the fiber system is used to perform Ramsey spectroscopy in a state-of-the-art cesium fountain clock. The resulting clock is compared to the CSO and exhibits a stability of 3.5×10−14τ−1/2.

Amplitude to phase conversion of InGaAs pin photo-diodes for femtosecond lasers microwave signal generation

Progress in realizing the SI second had multiple technological impacts and enabled further constraint of theoretical models in fundamental physics. Caesium microwave fountains, realizing best the second according to its current definition with a relative uncertainty of 2-4 × 10(-16), have already been overtaken by atomic clocks referenced to an optical transition, which are both more stable and more accurate. Here we present an important step in the direction of a possible new definition of the second. Our system of five clocks connects with an unprecedented consistency the optical and the microwave worlds. For the first time, two state-of-the-art strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.5 × 10(-16). Their comparison with three independent caesium fountains shows a degree of accuracy now only limited by the best realizations of the microwave-defined second, at the level of 3.1 × 10(-16).

Sub-100 attoseconds stability optics-to-microwave synchronization

In conclusion, we have used two FOFC based optical to microwave division frequency synthesizers referenced to a common optically source to create 11.55 GHz microwave signals with a relative frequency stability of 1.6×10-16 at 1 s. The relative phase noise spectral density at a 1 Hz offset from the 11.55 GHz carrier is measured at 111 dBrad2/Hz, limited by the readout system noise floor. Long term stability and accuracy down to 3×10-19 at 65536 s was also demonstrated from a set of 3 days continuous measurement. These results are obtained with classical double balanced mixers measurement scheme. By using a noise measurement system based on the carrier suppression method and advanced noise reduction techniques we are able to improve the results down to a phase noise spectral density at a 1 Hz of 117 dBrad2/Hz and a FFS is of 1.5×10-19 at 1000s (for a single system).

Doppler-free spectroscopy of the 1S0-3P0 optical clock transition in laser-cooled fermionic isotopes of neutral mercury.

In this Letter we report on an all optical-fiber approach to the synthesis of ultralow-noise microwave signals by photodetection of femtosecond laser pulses. We use a cascade of Mach-Zehnder fiber interferometers to realize stable and efficient repetition rate multiplication. This technique increases the signal level of the photodetected microwave signal by close to 18 dB. That in turn allows us to demonstrate a residual phase-noise level of -118 dBc/Hz at 1 Hz and -160 dBc/Hz at 10 MHz from a 12 GHz signal. The residual noise floor of the fiber multiplier and photodetection system alone is around -164 dBc/Hz at the same offset frequency, which is very close to the fundamental shot-noise floor.