A record-breaking result reveals the precision achievable by atomic clocks, letting researchers detect slightly faster ticking over a tiny height change.

Read the full article at: https://www.sciencenews.org/article/atomic-clock-general-relativity-time-warp-millimeter-physics# Lab News

# A brand new flavor of optical lattice atomic clock: Xin and Jack’s paper posted to the arXiv!

Congratulations to Xin and Jack, as well as Kolkowitz group alums Brett, Haoran, and Varun, on the posting of their new paper “High precision differential clock comparisons with a multiplexed optical lattice clock” to the arXiv! You can find it here: http://arxiv.org/abs/2109.12237.

This paper describes the experimental realization of a new kind of optical atomic clock that consists of multiple clocks in one, and enables comparisons between these clocks at new levels of performance. For example, the paper includes a measurement of the fractional frequency difference between two clocks separated by ~6 mm at a precision below one part in 10^{19}, or in other words at 20 digits of precision. This is a world record for the most precise frequency difference ever measured*, and represents a new regime of clock comparison stability and precision. To give a sense of scale, this corresponds to measuring a difference in the rate the two clocks are ticking at that would result in them disagreeing with each other by only 1 second after 300 billion years. This unprecedented metrological precision offers sensitivity to new and exotic physics. For example, this corresponds to the difference in the ticking rate between two otherwise identical clocks separated in height by only 1 millimeter due to general relativistic time dilation from Earth’s gravity field. The Kolkowitz group is currently hard at work measuring this effect!

You can read a lot more about these and other exciting results in the paper, but one thing you can’t do on the physics arXiv is watch cool movies! So here are some animated GIFs composed of actual camera images taken with our multiplexed optical lattice clock showing the procedure for preparing 2 clocks (left) and 6 clocks (right), which each clock (or ball) composed hundreds of strontium atoms trapped in an optical lattice at temperatures of just 1 millionth of a degree above absolute zero.

* Sadly this record was short lived, thanks to very exciting complementary results from our good friends in the Ye group, which were posted to the arXiv in coordination with ours. I strongly encourage you to read about them here: http://arxiv.org/abs/2109.12238.

# Aedan, Ishita, Matt, and Sam’s paper on charge dynamics in diamond published in Nano Letters!

Congratulations to Aedan, Ishita, Matt, and Sam, whose paper on imaging and controlling charge carrier dynamics in diamond with a single color center has now been published online in *Nano Letters*!

Here’s a link to the paper: http://pubs.acs.org/articlesonrequest/AOR-AHFGVMFTPSMKYF3BGCAD.

This paper was a collaboration with Dr. Vincenzo Lordi at Lawrence Livermore National Lab, Dr. Ariel Norambuena and Dr. Hossein Dinani at Universidad Mayor, and Prof. Jero Maze at Pontificia Universidad Catolica in Santiago, Chile.

# Aedan, Ishita, Matt, and Sam’s paper on charge dynamics in diamond posted to the arXiv!

Congratulations to Aedan, Ishita, Matt, and Sam, whose paper “Probing charge dynamics in diamond with an individual color center” has now been posted to the arXiv!

# Congrats to Aedan on passing his prelim exam!

# MSPQC student Jacques Van Damme publishes first-author paper with WQI faculty

Congrats to Jacques Van Damme, a member of the first class of MSPQC students who graduated this past August, on his first-author publication! The study, published in Physical Review A, is titled, “Impacts of random …

Read the full article at: https://wqi.wisc.edu/2021/02/11/mspqc-student-jacques-van-damme-publishes-first-author-paper-with-wqi-faculty/# Matt, Aedan, and Sam’s paper published in Physical Review Research!

Congratulations to Matt, Aedan, and Sam, whose paper “State-dependent phonon-limited spin relaxation of nitrogen-vacancy centers” has just been published online in Physical Review Research! The paper describes experimental results shedding light on the physical processes limiting the “coherence times” of defects in diamond that are used as quantum sensors and qubits. (Physical Review Research is an open access online journal, so click on through if you’re interested in learning more!)

# Shimon Kolkowitz awarded two grants to push optical atomic clocks past the standard quantum limit

Optical atomic clocks are already the gold standard for precision timekeeping, keeping time so accurately that they would only lose one second every 14 billion years. Still, they could be made to be even more …

Read the full article at: https://www.physics.wisc.edu/2020/12/22/shimon-kolkowitz-awarded-two-grants-to-push-optical-atomic-clocks-past-the-standard-quantum-limit/# Going up?

Today Xin, Jack, Brett, and Haoran achieved a major milestone in the development of a multiplexed optical lattice clock and its use for new tests of relativity. The animated GIF below shows strontium atoms in an “atomic elevator” made of light, rising with respect to gravity (which is pointing down in this image) at a rate of ~3 mm/second.

The second image below, also taken today shows the preparation and simultaneous imaging of two ensembles of strontium atoms in our vacuum chamber, spatially separated by ~1 mm, a critical component of our new “multiplexed optical lattice clock” design.

This is a major step towards measuring the “gravitational redshift” due to earth’s gravity at a new length scale. In a gravitational field such as Earth’s, a clock that is elevated with respect to gravity will tick faster than a lower clock. This effect of general relativity is called the gravitational redshift, and it has previously been observed at the ~30 cm scale, but has not yet been observed at the cm or mm scale.

As shown in A in the diagram below, the Einstein equivalence principle, a foundational tenet of the theory of relativity, states that an observer cannot distinguish between being inside an elevator on the surface of earth and experiencing an acceleration due to gravity *g* (panel I), and being in an elevator accelerating through space with an acceleration *a=g *(panel II)*. *As shown in B, by combining our multiplexed optical lattice clock with the ability to accelerate atoms as in the “atomic elevator” shown above, we will be able perform a novel and direct test of the Einstein equivalence principle in our lab.

# WQI team named winners in international quantum research competition

A WQI faculty team was one of 18 winners in the Innovare Advancement Center’s “Million Dollar International Quantum U Tech Accelerator” competition, which awarded a total of $1.35 million last week. The winning teams, including …

Read the full article at: https://wqi.wisc.edu/2020/09/08/wqi-team-named-winners-in-international-quantum-research-competition/