Daniele Nicolodi

Optical to microwave clock frequency ratios with a nearly continuous strontium optical lattice clock

Optical lattice clocks are at the forefront of frequency metrology. Both the instability and systematic uncertainty of these clocks have been reported to be two orders of magnitude smaller than the best microwave clocks. For this reason, a redefinition of the SI second based on optical clocks seems possible in the near future. However, the operation of optical lattice clocks has not yet reached the reliability that microwave clocks have achieved so far. In this paper, we report on the operation of a strontium optical lattice clock that spans several weeks, with more than 80% uptime. We make use of this long integration time to demonstrate a reproducible measurement of frequency ratios between the strontium clock transition and microwave Cs primary and Rb secondary frequency standards.

A clock network for geodesy and fundamental science.

Leveraging the unrivalled performance of optical clocks as key tools for geo-science, for astronomy and for fundamental physics beyond the standard model requires comparing the frequency of distant optical clocks faithfully. Here, we report on the comparison and agreement of two strontium optical clocks at an uncertainty of 5 × 10−17 via a newly established phase-coherent frequency link connecting Paris and Braunschweig using 1,415 km of telecom fibre. The remote comparison is limited only by the instability and uncertainty of the strontium lattice clocks themselves, with negligible contributions from the optical frequency transfer. A fractional precision of 3 × 10−17 is reached after only 1,000 s averaging time, which is already 10 times better and more than four orders of magnitude faster than any previous long-distance clock comparison. The capability of performing high resolution international clock comparisons paves the way for a redefinition of the unit of time and an all-optical dissemination of the SI-second.

Photonic microwave signals with zeptosecond-level absolute timing noise

Ultralow-noise microwave signals are generated at 12 GHz by a low-noise fibre-based frequency comb and cutting-edge photodetection techniques. The microwave signals have a fractional frequency stability below 6.5 × 10–16 at 1 s and a timing noise floor below 41 zs Hz–1/2. Photonic synthesis of radiofrequency (RF) waveforms revived the quest for unrivalled microwave purity because of its ability to convey the benefits of optics to the microwave world1,2,3,4,5,6,7,8,9,10,11. In this work, we perform a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-noise fibre-based frequency comb and cutting-edge photodetection techniques. We demonstrate the generation of the purest microwave signal with a fractional frequency stability below 6.5 × 10−16 at 1 s and a timing noise floor below 41 zs Hz−1/2 (phase noise below −173 dBc Hz−1 for a 12 GHz carrier). This outperforms existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved through a heterodyne cross-correlation scheme with the lowermost detection noise. This unprecedented level of purity can impact domains such as radar systems12, telecommunications13 and time–frequency metrology2,14. The measurement methods developed here can benefit the characterization of a broad range of signals.

Quantum cascade laser frequency stabilization at the sub-Hz level

Quantum Cascade Lasers (QCL) are increasingly being used to probe the mid-infrared “molecular fingerprint” region. This prompted efforts towards improving their spectral performance, in order to reach ever-higher resolution and precision. Here, we report the stabilisation of a QCL onto an optical frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and 10-14, respectively. The comb is stabilised to a remote near-infrared ultra-stable laser referenced to frequency primary standards, whose signal is transferred via an optical fibre link. The stability and frequency traceability of our QCL exceed those demonstrated so far by two orders of magnitude. As a demonstration of its capability, we then use it to perform high-resolution molecular spectroscopy. We measure absorption frequencies with an 8x10-13 relative uncertainty. This confirms the potential of this setup for ultra-high precision measurements with molecules, such as our ongoing effort towards testing the parity symmetry by probing chiral species.

Spectral purity transfer between optical wavelengths at the 10 −18 level

We present an optical frequency comb-based scheme that transfers 4.5 × 10-16 fractional frequency stability from a 1062 nm wavelength laser to a 1542 nm laser. We demonstrate that this scheme does not hinder the transfer down to 3 × 10-18 at 1 s, one order of magnitude better than previous reported result. This exceeds, by more than one order of magnitude, the stability of any optical oscillator demonstrated to date, and satisfies the stability requirement for quantum projection noise-limited optical lattice clocks. We will finally describe our latest efforts to apply this technique for improving the performance the LNE-SYRTE Sr-based optical lattice clocks.

Mid-infrared laser phase-locking to a remote near-infrared frequency reference for high-precision molecular spectroscopy

We present a method for accurate mid-infrared frequency measurements and stabilization to a near-infrared ultra-stable frequency reference, transmitted with a long-distance fibre link and continuously monitored against state-of-the-art atomic fountain clocks. As a first application, we measure the frequency of an OsO4 rovibrational molecular line around 10 μm with an uncertainty of 8 × 10−13. We also demonstrate the frequency stabilization of a mid-infrared laser with fractional stability better than 4 × 10−14 at 1 s averaging time and a linewidth below 17 Hz. This new stabilization scheme gives us the ability to transfer frequency stability in the range of 10−15 or even better, currently accessible in the near infrared or in the visible, to mid-infrared lasers in a wide frequency range.

Comparing a mercury optical lattice clock with microwave and optical frequency standards

In this paper we report the evaluation of an optical lattice clock based on neutral mercury with a relative uncertainty of

Ultra-stable long distance optical frequency distribution using the Internet fiber network and application to high-precision molecular spectroscopy

1.7\times {10}^{-16}

Accurate control of optoelectronic amplitude to phase noise conversion in photodetection of ultra-fast optical pulses

. Comparing this characterized frequency standard to a 133Cs atomic fountain we determine the absolute frequency of the

Phase noise characterization of sub-hertz linewidth lasers via digital cross correlation

{}^{1}{{\rm{S}}}_{0}\to {}^{3}{{\rm{P}}}_{0}