Description
Portable optical-frequency atomic clocks have reached a maturity level that allows them to be used outside of a laboratory setting. Specifically, portable optical clocks have been demonstrated in sea trials [1], in urban deployments [2], and clock sub-systems have even been operated on-orbit [3]. Portable optical clocks will be integral in advancing fundamental physics including tests of General Relativity; conducting novel geoscience using chronometric geodesy; enhancing national security through secure remote synchronization; and likely form the backbone of next-generation global navigation satellite systems [4].
However, many of the above-mentioned applications require timescale comparison with a precision better than the stability of the clocks. Where this involves moving optical clocks, this can only be achieved using Doppler-compensated free-space optical frequency transfer [6].
Here we report work from June 2026, on the timescale comparison between two clocks on a helicopter; and over a point-to-point, free-space link between a stationary clock and one carried on a moving platform. The two portable optical clocks used for this work are capable of achieving stabilities of 1.5×10−14 per √τ, reaching 3×10−15 at 100s of integration [1]. This is accomplished in a 25kg, 3U package, with 100W power draw. The optical-frequency transfer system (1U package) has a stability of 4×10−18 at 1s and 4×10−18 at 100s, as demonstrated over a 2.4km free-space link [7]. The active optical terminals used in this work have a mass of 4.7kg, a 10.9L volume, and a 43W power draw. All systems are portable and field-deployable in additional novel scenarios.
[1] Hilton, Nat.Commun. 15, 6063 (2025)
[2] Takamoto, Nat.Photonics 14, 411 (2020)
[3] Xia, Rev.Sci.Instrum. 96, 093201 (2025)
[4] Dix-Matthews, Nat.Commun. 12, 515 (2021)
[5] Dix-Matthews, Nat.Commun. 12, 515 (2021)
[6] McSorley, Phys.Rev.Appl. 23, L021003 (2025)
[7] Gozzard, Phys.Rev.Lett. 128, 020801 (2022)
| I am the presenting author | Yes |
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