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Integrated Quantum Clock

Periodic Reporting for period 1 - iqClock (Integrated Quantum Clock)

Reporting period: 2018-10-01 to 2020-03-31

Optical clocks are amazingly stable frequency standards, which would be off by only one second over the age of the universe. This precision is orders of magnitude better than the one of commercial frequency standards, which operate at microwave frequencies, and is enabled by the interrogation of ultranarrow optical transitions in atoms that are cooled to near standstill. So far these clocks are complex, fragile and maintenance intensive devices, built by researchers and only usable with their experience. Bringing those clocks from the laboratory into a robust, compact and easy to use form will have a large impact on telecommunication and navigation (e.g. network synchronization, increased traffic bandwidth, GPS spoofing and outage resilience, terrestrial navigation with cm precision), geology (e.g. underground exploration, monitoring of water tables, volcanoes or ice sheets), astronomy and space (e.g. low-frequency gravitational wave detection, radio telescope synchronization, deep space navigation) and other fields. Likewise, techniques developed for robust clocks will improve laboratory clocks, potentially leading to physics beyond the standard model.

To make this a reality, we have founded the iqClock consortium, assembling leading experts from academia, strong industry partners, and relevant end users. We will seize on recent developments in clock concepts and technology to start-up a clock development pipeline along the technology readiness level (TRL) scale. Our consortium represents a nucleus for a European optical clock ecosystem, which will continuously deliver competitive products and foster the development of clock applications.

The objectives of iqClock are arranged in four scientific work packages along the TRL scale and one outreach work package. Each scientific work package has the goal to push a certain aspect of clock development two points up the TRL scale. The largest work package (WP3) addresses the most resource intensive challenge: building an industrial prototype of a field-ready, compact and robust optical lattice clock. The University of Birmingham’s (UoB’s) Quantum Sensing Hub is guiding our industry partners (Toptica (laser systems), Teledyne e2v (vacuum chamber and control electronics), NKT Photonics (multicolour optical fibres), Acktar (internal black coating of vacuum chamber for stray light suppression)) in the development and production of the components of this clock. The components will be tested at UoB and integrated into a clock, which will be benchmarked in a real use case, the synchronization of a network node of British Telecom (BT), using test equipment developed by Chronos.

Three smaller scientific work packages are developing a new type of optical clock, which promises enhanced robustness, reduced complexity and potentially better performance than existing types. Existing optical clocks reference their frequency to atomic transitions by shining laser light onto atoms and detecting how strongly the atoms get excited. A slightly off clock frequency leads to detectably less excitation, which serves as signal to correct the clock frequency and thereby keep it stable. This scheme leads to complications that could be circumvented if the atoms would not be passively interrogated, but be teased to actively emit light on the optical clock transition, forming a laser beam. Our goal is to build for the first time a continuously operating laser of this type, a “superradiant” laser. In WP4 we are building the simplest version of such a device, operating on a kHz-linewidth transition, which has the prospect to result in commercial frequency references that could compete with hydrogen masers. In WP5 we will push the technology to the ultimate level, continuous superradiant lasing on mHz-linewidth transitions. In WP6 we theoretically and experimentally explore the foundations of superradiant lasing. These work packages are executed jointly by partners from the Universities in Copenhagen (UCPH), Torun (UMK), Amsterdam (UvA), Vienna (TUW) and Innsbruck (UIBK).

In order to increase our impact and to broaden our industry base we reach out to all clock stakeholders, train the next generation of quantum engineers, educate and listen to end users, and enrich the exchange of scientific ideas (WP2 Outreach).
WP3
Optical lattice clock testbed assembled at UoB. This testbed will first test industry components and later be used as reference clock for integrated clock. Toptica has first laser systems ready to ship and will deliver all till August. NKT’s first multi-color optical fibres under test at UoB. Acktar coated testbed clock vacuum chamber black and benchmarked it successfully. Teledyne e2v finalizing design of industry vacuum chamber and control system. Chronos and BT preparing test of integrated clock at TRL 6.

WP4
UCPH experimentally and theoretically studied pulsed superradiant lasing. Numerical simulations of continuous kHz superradiance clarified that µK beam is needed. Design of clock in advanced stage. Many systems built or being machined.

WP5
Two complementary approaches pursued jointly at UMK and UvA. Both designs mature; most components ordered or being machined. UvA demonstrated continuous source high phase-space density 87Sr beam and augmented flux of existing source by an order of magnitude. TUW theoretically explored conditions for continuous mHz superradiance, guiding machine design.

WP6
TUW and UIBK studied influences of real-life effects on superradiant lasing with focus on our experimental implementations. Open-source programming package for simulation of superradiant lasers and other quantum optical systems created and online. TUW and UMK benchmarked theoretical model by reproducing pulsed Ca superradiance experiments, increasing confidence in model predictions for Sr. Novel implementations of superradiant lasing theoretically developed. UvA used increased µK Sr flux to create first Bose-Einstein condensate of ultracold atoms in steady-state, which paves way to continuous atom laser with applications in quantum sensing.

WP2 Outreach
Highlights: www.iqClock.eu iqClock YouTube video, research school on clocks.
Expected status at end of first Flagship period:

WP3
Integrated optical lattice clock prototype tested in a network node of BT, reaching TRL 6. This clock is largely built by industry, bringing an optical lattice clock product much closer to reality. If cheap and reliable enough this product could lead to the applications outlined in Sec. 1.1. Industry partners made advances that can also be exploited in other contexts or sold as products.

WP4
We demonstrated a continuous kHz superradiant clock or we gained detailed insights into which modifications to our machines are needed to demonstrate one. During the later years of the Flagship this can lead to products replacing hydrogen masers.

WP5
We have demonstrated a continuous superradiant mHz clock or gained detailed insights into which modifications to our machines are needed to demonstrate one. This can lead to more compact and robust optical clocks towards end of Quantum Flagship.

WP6
Real-life effects influencing performance of superradiant clocks are much better understood. New superradiant lasing schemes have been invented. Flexible apparatus enables study of foundations of superradiant lasing. We provide open-source tools to conveniently simulate quantum optical systems.
iqClock lab
iqClock lab, Volkskrant
iqClock lab