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FACT Period 1 – Publishable Summary

The Marie Curie Initial Training Network Future Atomic Clock Technology (FACT) is training a cohort of 14 ESRs. It is coordinated by The University of Birmingham (UoB), UK, with 13 academic and industrial Partners: Heinrich-Heine Universitaet Duesseldorf (HHUD), Germany; Instituto Nazionale Di Ricerca Metrologica (INRIM), Italy; Kayser Italia (KI), Italy; Gottfried Wilhelm Leibniz Universitaet Hannover (LUH), Germany; National Physical Laboratory (NPL), UK; Observatoire de Paris (OP), France; Physikalisch-Technische Bundesanstalt (PTB), Germany; Universite de Neuchatel (UNINE), Switzerland; Universita Degli Studi di Firenze (UNIFI), Italy; Ecole Polytechnique Federale de Lausanne (EPFL), Switzerland; OHB System, Germany (formerly Kayser Threde); The University of Nottingham (UNott), UK; Menlo Systems, Germany. In addition there is one Associated Partner, Entanglement Technologies (ET) from the USA.
The main objectives of the research programme are as follows:
• To overcome the technology bottleneck in bringing cold atom systems to market applications and demonstrate a mobile optical frequency standard.
• To develop the technology for robust laser systems for cold atom cooling, state preparation and clock interrogation with narrow and stable line widths relevant to their functionality,
• To foster technology making the superior performance of optical clocks available to end users and applications.
• To demonstrate feasibility with a commercial concept for an optical clock system.

The FACT programme promotes international and inter-sector collaboration for the advancement of science and the development of innovation in the area of atomic clocks based on cold atom quantum sensors. In particular it fosters a shared culture of research and innovation that turns the Nobel-prize winning ideas of cold atom research and precision measurement (Nobel prizes 1997 and 2005) into innovation and future expertise. The FACT programme pursues a holistic approach to the atomic clock sector at the cutting edge of research, innovation and training. The programme includes leading expertise across Europe from academia, national metrological institutes and industry. It targets advanced systems for terrestrial as well as space applications, involves industry right from the start and has a vision for the market and the end users. We are developing two advanced systems based on Sr and Yb in order to explore a wide variety of operational parameters, and minimise the risk associated. The targeted frequency stability and accuracy are on the order of 5 in 1017. There has already been a tremendous progress on various fronts. For Sr, a transportable system has been developed. It comprises an advanced atomics package consisting of a low energy, compact and high flux atom source, a small compact and zero power Zeeman slower (by NPL) with permanent magnets, very low power magnetic coils and an advanced vacuum chamber with arrangements for minimising thermal gradients leading to black body radiation contribution; a compact frequency distribution module acting as an interface between the atomics package and laser sources, a frequency stabilising system (FSS, developed jointly by HHUD and NPL) acting a single unit in order phase stabilise cooling and lattice lasers, laser systems and a computer control based on an FPGA. The apparatus (vacuum system and lasers) is now enclosed in a 163×99×60 cm3 transportable rack.
Up to 3×107 strontium atoms have been trapped in the 1st stage MOT. The atoms have been transferred into the 2nd stage MOT reaching a temperature below 2 μK there. Finally, robust preparation of cold 88Sr atoms in an optical lattice was achieved.

In June 2015, the atomic package together with the laser system has been moved from UoB to PTB (Braunschweig) where the integration of the transportable clock laser from OP and the final characterization of the clock is being performed. After the journey by van from Birmingham to PTB and all the necessary loading/unloading procedures, no changes have been noticed in the performance of the system: this demonstrates the robustness of the apparatus.
Another advanced system based on Yb has been developed at INRIM. The preliminary measurements on its performance have been carried out. In fact in addition to the above mentioned two systems, one stationary Sr optical lattice clock at NPL, one stationary Sr optical lattice clock at PTB, one transportable Sr optical lattice clock at PTB and two stationary Sr optical lattice clocks at OP have been used to train the ESRs.

A frequency comb is a device that enables us to go from optical frequency domain to radio frequency domain. In this programme, we are following both fiber based combs and micro-combs. Fibers based combs reach a high degree of reliability and achieve continuous 24 h/7 days per week operation. They are commercially available and come on an easily transportable breadboard, fully automated, hands off and with network control software (MENLO) Specification for the commercial combs is 10-14, in this programme we are developing subsystems with performance at the 10-18 level. Keeping an eye on space as well, we have tested a fiber comb on board a sounding rocket (German Space Agency’s TEXUS 51) attaining 6 minutes of microgravity at an altitude of 260 km. The Menlo Systems Optical Frequency Comb was used to compare two different species of thermal atomic clocks. Second types of combs based on micro-resonators are a new and very intriguing way to generate frequency combs. These combs are generated using only a low-power continuous-wave telecom type laser. This new technology is in principle extremely attractive for future use in space since it is potentially capable of being implemented as an integrated-optics element. Raman induced soliton self-frequency shift in microresonator Kerr frequency combs based on SiN have been observed by the EPFL group and are relevant to the fundamental timing jitter of microresonator solitons.

Metrological applications of frequency combs require the carrier-envelope offset frequency to be stabilized, which is normally achieved through the standard f-to-2f scheme. At UNINE it has been shown that it is possible to characterize the carrier-envelope offset in an optical frequency comb without traditional f-to-2f interferometry, which constitutes an attractive method for initial investigations on novel frequency combs for which the f-to-2f method is not yet applicable.

For portable and space systems, it is extremely important to focus on compactification, energy efficiency and robustness. For space systems, the additional requirement is radiation hardness, in this respect a lot of work is going on at OHB and KI as both have vast experience in space systems. At the UNott, Laser cooling of rubidium-87 atoms has been demonstrated in two setups with combinations of an atom chip, mm-cm scale copper wire structures, miniature copper-ribbon coils and printed circuit boards.
At the LUH, Bloch band spectroscopy as a new method to determine the magic wavelength of an optical lattice has been investigated in a Mg optical lattice clock setup. At the UNIFI, technique of Large-momentum-transfer Bragg interferometer has been explored using Sr88 atoms, achieving up to 8 photon recoils. Among other things, the technique has implications in precision metrology.

The expected outcome of the project is to aid the development of optical clocks and frequency standards from the laboratory stage to commercially viable systems. This project is focussing on the technological developments enhancing the technology readiness level of new optical atomic clocks by implementing a training programme covering all aspects from the atomic reference and ultrastable lasers to frequency comb synthesis, precision frequency distribution and commercial system technology. Initially, it is expected that these devices will be used in space technology.

As part of its dissemination strategy, among other routes, it has already published 6 articles in the international renowned journals, 10 oral presentations and more than 20 posters in conferences/schools/invited. As part of its outreach, FACT has taken up a wide range of outreach activities including science festivals, public lectures, and lectures/visits to schools.

FACT Network Coordinator, Professor Kai Bongs, +44 121 4148278
The FACT Website can be accessed at

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