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The pursuit of fundamental limits in frequency metrology has historically motivated the development of groundbreaking techniques such as laser cooling and spin-squeezing. Our research focuses on the use of trapped ions for optical frequency metrology and the development of quantum-limited techniques for high-accuracy measurements. We target applications from atomic clocks to tests of fundamental physics and relativistic geodesy.

Below are descriptions of our experiments and links to some key publications. Contact information for any current member of the group is available in the Time and Frequency Division Staff Listing.


Computer-generated image showing a cross-shaped gold metal cutout on a red mount in between two metal posts, with an inset magnifying the cutout to show blue and yellow balls at the center.
Illustration of the ion trap that forms the heart of NIST’s quantum logic clock. The trap is the gold structure with the cross-shaped cutout. The inset shows the aluminum ion (blue), the source of the clock’s “ticks,” and the partner magnesium ion (yellow).
Credit: S. Burrows/JILA

This project uses techniques from quantum information science to enable precision metrology.  We use the dipole-forbidden 1S0 - 3P0 transition in singly-ionized aluminum as an stable frequency reference (natural linewidth ~8 mHz), which we detect using quantum logic spectroscopy with a second ion held in the same trap [1]. Current efforts focus on reducing systematic effects, such as relativistic shifts due to time dilation, and increasing clock stability by use of quantum entanglement and classical correlations. For example, probing two separate clocks in a correlated manner enables clock interrogation beyond the coherence limits of the probe laser and approaching the lifetime limit of the clock transition [2-3].  These clocks have demonstrated state-of-the-art accuracy for optical clock measurements worldwide [4], with the current generation reaching fractional uncertainty below 1x10-18 [5].

[1] P. O. Schmidt et al., "Spectroscopy using quantum logic", Science 309, 749-752 (2005) 

[2] E. R. Clements et al., "Lifetime-limited interrogation of two independent 27Al+ clocks using correlation spectroscopy", Phys. Rev. Lett. 125, 243602 (2020)

[3] M. E. Kim et al., "Improved interspecies optical clock comparisons through differential spectroscopy", Nat. Phys. 19, 25 (2022)

[4] Beloy et al. (BACON Collaboration), "Frequency Ratio Measurements at 18-digit accuracy using an optical clock network", Nature 591, 564 (2021) 

[5] S. M. Brewer et al., "27Al+ quantum-logic clock with systematic uncertainty below 10-18", Phys. Rev. Lett. 123, 033201 (2019)


Permanent staff: David Hume, Chin-Wen (James) Chou

Postdocs: Mason Marshall

Graduate student: Daniel Rodriguez Castillo, Jose Valencia

Created April 7, 2023, Updated May 2, 2023