Transportable Optical Lattice Clock with7×10−17Uncertainty

Abstract

We present a transportable optical clock (TOC) with 87 Sr. Its complete characterization against a stationary lattice clock resulted in a systematic uncertainty of 7.4 × 10 −17 which is currently limited by the statistics of the determination of the residual lattice light shift. The measurements confirm that the systematic uncertainty is reduceable to below the design goal of 1 × 10 −17 . The instability of our TOC is 1.3 × 10 −15 / √ τ . Both, the systematic uncertainty and the instability are to our best knowledge currently the best achieved with any type of transportable clock. For autonomous operation the TOC is installed in an air-conditioned car-trailer. It is suitable for chronometric leveling with sub-meter resolution as well as intercontinental cross-linking of optical clocks, which is essential for a redefiniton of the SI second. In addition, the TOC will be used for high precision experiments for fundamental science that are commonly tied to precise frequency measurements and it is a first step to space borne optical clocks. PACS numbers:The best clocks in the world reach a fractional systematic uncertainty at the low 10 −18 level [1-4] and instabilities near or even below 10 2,[4][5][6], surpassing the clocks realizing the SI second in both by two orders of magnitude. This has triggered a discussion about a redefinition of the SI second [7,8], pushes the frontiers of precision spectroscopy and tests fundamental physics [9][10][11][12][13][14], and enables chronometric leveling [15][16][17][18][19], where gravitational redshifts are exploited to measure height differences.So far, the operation of optical clocks has been constrained to laboratories. However, transportable clocks are required for the necessary flexibility in the choice of measurement sites for applications like chronometric leveling. Also, they are highly interesting for frequency metrology and time keeping in creating a consistent worldwide network of the next-generation ultraprecise clocks. Although comparisons at the full performance level of state-of-the-art optical clocks are possible on a continental scale [18,19] through a few specialized optical fiber links [20][21][22], intercontinental links are so far restricted to satellite-based methods that cannot fully exploit the clock performance [23]. A transfer standard enables world-wide interconnections between optical clocks and will thus benefit the efforts towards a redefinition of the SI second.Making laboratory setups compact and robust for transport is also the first step towards granting a wide community of users access to these devices [24][25][26]. Furthermore, transportability is a first step towards applications of optical clocks in space. Developments in these directions are ongoing for optical lattice clocks (OLCs) with strontium [27,28]; however, to our knowledge the single-ion clock reported recently [29] is the only other transportable clock with uncertainty below 10 −16 .The requirements on such a TOC are challenging indeed: To enable comparisons of other optical cl...

Seconds-scale coherence on an optical clock transition in a tweezer array

“…Here, we use a Ramsey interrogation sequence with 150 ms dark evolution time and 1.5 ms π pulses, 90 ms of dead time per cycle, and either 300 or 750 ms to load a new ensemble of atoms. These load times reflect our current value, and a somewhat longer value reflecting constraints on atomic flux and laser power that may be associated with a portable system [43]. With these assumptions, the contributions to total noise from Dick noise aliasing and QPN are comparable, even at our current atom number, and both improve with repeated imaging.…”

The unit of time: Present and future directions

“…First proof-of-concept experiments used coherent optical fiber links between laboratories with already existing state-of-the-art optical frequency metrology programs [137] [62]. Over the years, transportable optical frequency standards were developed and currently achieve uncertainties in the 10 −17 range [192] [193] [194], also with the aim to increase technology readiness for space. Recently, one of these devices was used for another proofof-concept experiment [195] again in conjunction with coherent optical fiber link.…”

Combining fiber Brillouin amplification with a repeater laser station for fiber-based optical frequency dissemination over 1400 km

“…The fiber-based transfer of optical frequencies reaches uncertainties 10 -18 over continental distances [1][2][3] and is currently the only means enabling comparison of remote state-of-the art optical clocks [4][5][6][7] without significant uncertainty contributions of the link [8]. Such a low remote clock comparison uncertainty is neither achievable through the alternative of microwave-based satellite connections [9] nor by exchanging transportable optical clocks [10,11]. Besides supporting the roadmap towards the redefinition of the SI-second [12], fiberbased comparisons of distant optical clocks enables high-resolution measurements of height differences by chronometric levelling [13][14][15] or tests of non-local relativistic effects [16].…”