Systematic evaluation of an atomic clock at 2 × 10−18 total uncertainty

Abstract

The pursuit of better atomic clocks has advanced many research areas, providing better quantum state control, new insights in quantum science, tighter limits on fundamental constant variation and improved tests of relativity. The record for the best stability and accuracy is currently held by optical lattice clocks. Here we take an important step towards realizing the full potential of a many-particle clock with a state-of-the-art stable laser. Our 87Sr optical lattice clock now achieves fractional stability of 2.2 × 10−16 at 1 s. With this improved stability, we perform a new accuracy evaluation of our clock, reducing many systematic uncertainties that limited our previous measurements, such as those in the lattice ac Stark shift, the atoms' thermal environment and the atomic response to room-temperature blackbody radiation. Our combined measurements have reduced the total uncertainty of the JILA Sr clock to 2.1 × 10−18 in fractional frequency units.

Gravitational wave detection with optical lattice atomic clocks

“…Taking N ¼ 7 × 10 6 atoms yields a minimum detectable fractional frequency difference of σ min ¼ 1.1 × 10 −20 = ffiffiffiffiffiffi Hz p . Although this represents a 4 order of magnitude improvement over demonstrated clock stability [14], the use of correlated noise spectroscopy, along with anticipated large improvements in the atom number, coherence time, and improved laser linewidth, helps realize this gain. Note that because σ min can only be achieved using measurements with optimal Ramsey precession time T max ¼ 160 s, our detector is spectrally narrow band and thus is not well suited for the detection of short burst GWs.…”

“…The culmination of a century-long search [1][2][3][4][5][6][7][8][9][10], GW detection is now emerging as a new tool with which to study the Universe, illuminating previously invisible astrophysical phenomena. In parallel, the developments of laser cooling and the laser frequency comb have given rise to optical atomic clocks with accuracies and stabilities at the 10 −18 level [11][12][13][14][15]. As clock precision continues to improve, there is growing interest in the prospect of using optical atomic clocks for GW detection [10,16,17].…”

“…An important advantage of the atomic clock scheme over other Doppler tracking methods is that one has full control over the frequency references. As a result, synchronized measurement sequences can be applied at both ends of the baseline to cancel laser frequency noise [21,[27][28][29][30]: thus the atomic clock technique requires only two spacecraft, not three, and the differential measurement is entirely limited by the internal atomic transition, not the stability of the local oscillator used to probe it [10][11][12][13][14][15]. Furthermore, dynamical decoupling (DD) control sequences can be applied to the internal states of the atoms [31,32], extending the range of GW frequencies to which the detector can be maximally sensitive, from milliHertz to tens of Hertz, without requiring any physical changes to the detector.…”

“…In addition, quantum techniques such as atomic spin squeezing and entangled states [33][34][35] offer the potential for future improvements in sensitivity, detection bandwidth, and spectral range. Finally, because optical atomic clocks are currently the most accurate frequency references [11][12][13][14][15], and can provide improved sensitivity to beyond-standard-model phenomena that may couple to atomic properties such as mass, charge, and spin [36][37][38][39], there is already considerable motivation to develop spacehardy optical clocks, and to integrate them with other proposed GW detectors.…”

Probing beyond the laser coherence time in optical clock comparisons

“…Optical clock measurements are the most stable measurements of any kind [1][2][3], driven largely by recent progress in ultrastable lasers [4][5][6]. Still, laser frequency noise limits the stability of frequency comparisons well short of the limits imposed by atomic coherence [7], and has so far prevented the use of Heisenberg-limited measurements that realize a quantum enhancement in measurement stability [8,9].…”