Comparison of two Yb+ single-ion clocks yields improved limits on spacetime symmetry violation PTB has carried out a comparison of two ytterbium single-ion clocks over half a year, which demonstrated a relative deviation of less than 3 x 10-18, consistent with the clocks’ estimated combined systematic uncertainty of 4 x 10-18. The upper level of the employed electric-octupole clock reference transition exhibits a distinctly elongated electron wavefunction whose orientation was set to be approximately orthogonal in both clocks (see figure). Therefore one expects that violations of the Lorentz symmetry for electrons would lead to a periodic frequency difference between the clocks that is coupled with the Earth’s rotation, but no such difference was observed. In a theoretical analysis of the atomic structure of Yb+ and of the experimental data performed in collaboration with scientists from the University of Delaware (USA), the previous limits on Lorentz symmetry violations could be reduced drastically by a factor of 100, as described in this paper published in Nature. OC18 M36 progress meeting The month-36 progress meeting was held at VTT, Finland on Monday 8th – Tuesday 9th April, 2019. Dr Ekkehard Peik wins two prestigious awards Project consortium member and Work Package 2 leader, Dr. Ekkehard Peik (PTB) has received two awards whilst working on this project:• He was elected Distinguished Lecturer by the IEEE Ultrasonics Ferroelectrics and Frequency Control Society. Distinguished Lecturers are recognised for their personal stature, contribution to, and broad knowledge of, a particular field.• He received the European Frequency and Time Award 2018. This award recognises outstanding contributions in the field of time and frequency.Congratulations to Ekkehard! School on Optical Clocks A very successful School on Optical Clocks for PhD students was held 10th – 14th September, 2018 in Aosta Valley, Italy. Tutorial lectures and photos from the event are now also available. OC18 M27 progress meeting The month-27 progress meeting was held at CMI, Prague on Monday 16th – Tuesday 17th July, 2018. Public engagement Members of the consortium participated in the Royal Society Summer Science Exhibition, 2nd – 8th July 2018. This was a chance to present atomic clocks in a hands-on way to the public as part of an outreach activity celebrating the redefinition of the SI base units. Two Researcher Mobility Grants – successful first year Carmen Vélez López and Héctor Álvarez Martinez, both from ROA (Real Instituto y Observatorio de la Armada in San Fernando, Spain) have completed their first year of visits hosted by INRIM and OBSPARIS, funded with Researcher Mobility Grants. Their experience in optical clocks and frequency transfer will help ROA strengthen its expertise and enable a first optical atomic clock to be built in Spain. Carmen has been acquiring knowledge and practical experience of operating optical lattice clocks. She has developed a new laser system at 399 nm for cooling and trapping ytterbium atoms, and has delivered clock-stabilised light to the optical frequency comb. She is pictured here making adjustments to the alignment of the optical setup. Héctor has been working with a long Fabry-Pérot cavity to build a new ultra-stable laser at 1542 nm, and is pictured here with the team putting the cavity under vacuum. This laser will be a key piece of equipment in the laboratory over the next few years, opening the way towards laser frequency stabilities at the level of 10-16 at 1 s. OC18 M18 progress meeting The month-18 progress meeting was held at SYRTE on Monday 13th – Tuesday 14th November, 2017. It was a great opportunity to catch up with colleagues and discuss scientific progress. Laser stabilisation using atoms in cavities KU are working on a new approach to laser stabilisation that uses narrow linewidth atoms inside optical cavities. Such an approach may ultimately outperform the traditional optical cavities. In this paper, KU investigates the phase shift arising from the atom-light coupling, and how this can be optimised for laser frequency locking. Updated frequency values for Consultative Committee for Time and Frequency (CCTF) New absolute frequencies and optical frequency ratio measurements involving the clocks in OC18 were submitted to the Frequency Standards Working Group (CCL-CCTF-WGFS) in June 2017. These enable optimised frequency values for the secondary representations of the SI second to be updated. Record-breaking laser frequency instabilities PTB and JILA have demonstrated laser frequency instabilities that go beyond the previous state-of-the-art. By stabilising lasers to silicon Fabry-Pérot cavities, operated at 124 K, they have reached a flicker noise floor at the level of 4 parts in 1017. Find out more in their publication. EURAMET TC-TF meeting 2017 Progress on the OC18 project was presented at the annual meeting of the EURAMET Technical Committee for Time and Frequency, held at the Spanish Royal Naval Institute and Observatory (ROA – Real Instituto y Observatorio de la Armada) in San Fernando on 8th – 9th March 2017. Reducing frequency instability in optical clocks with optimised probing LUH has carried out a theoretical investigation to establish the optimum atom-laser interaction times for running an optical clock with the lowest instability. Results are given for different noise types in the local oscillator and as a function of clock atom number. See the publication for full details. Optical atomic clock searches for dark matterUMK has demonstrated how optical atomic clocks can be used to address fundamental physics questions concerning the nature of dark matter and its coupling to atoms. Their paper has been published in the high-impact journal, Nature Astronomy, and received widespread coverage with press releases and articles in the popular press. Beyond its gravitational interactions at the galactic scale, little is known about the nature of dark matter. The paper reports that a single optical atomic clock can be used as a detector for the hypothetical dark matter in the form of stable topological defects, slight variations on the quantum field created at the birth of the universe, containing energy. In the presence of such a defect, the fine-structure constant should be slightly modified. The reported experiment has exploited differences in the susceptibilities to the fine-structure constant of essential parts of an optical atomic clock, i.e. the atoms and the cavity. The level of constraint on the strength of atomic coupling to hypothetical dark-matter cosmic objects was found to exceed the previously reported limits by more than three orders of magnitude. OC18 M9 progress meeting The month-9 progress meeting was held at PTB on Monday 13th – Tuesday 14th February, 2017. Representatives from all 12 partners were present and it was a very productive meeting, discussing progress so far and planning future activities. School on Optical Clocks 2018 Following a successful summer school in 2015, we are pleased to announce a second School on Optical Clocks to be held 10th – 14th September 2018 in Aosta Valley, Italy. The school will be hosted by INRIM and the other OC18 partners, and will be aimed at PhD students, post-docs, young scientists and engineers in the field with a strong focus on training and education. The scope will include tutorials and the latest advances in frequency metrology and atomic frequency standards. We welcome applications from anyone interested in learning more about optical clocks and their developments through lectures from international experts in the field. Ion-trap exhibited at Quantum Technologies Showcase A prototype single-ion trap, being developed at NPL in conjunction with OC18, was exhibited at the UK’s 2016 National Quantum Technologies Showcase on 3rd November 2016. This was a one-day event highlighting quantum technologies that have the potential for the creation of new markets and economic benefit. Two Researcher Mobility Grants awarded Congratulations to two researchers from ROA (Royal Observatory of the Spanish Navy), Spain on their successful applications for Researcher Mobility Grants in the 2016 call. Héctor Álvarez Martínez will be hosted by OBSPARIS at SYRTE for 18 months to investigate an alternative approach to clock laser stabilisation, using a cavity with several resonators bored in the same spacer. María del Carmen Vélez López will be a guest worker at INRIM for 13 months, developing laser systems for a second ytterbium optical lattice clock, and carrying out frequency comparisons between different atomic clocks. OC18 kick-off meeting The kick-off meeting for the OC18 project was held at NPL on 15th – 16th June, 2016, with representatives from NPL, CMI, INRIM, LNE, OSBPARIS PTB, TUBITAK, VTT, LUH, UMK and CNRS present. EURAMET TC-TF meeting 2016An introduction to the OC18 project was presented at the annual meeting of “EURAMET Technical Committee for Time and Frequency”, held at MIKES Metrology, VTT Technical Research Centre of Finland on 1st – 2nd March, 2016.