Optical coherence between atomic species at the second scale: improved clock comparisons via differential spectroscopy

Abstract

Comparisons of high-accuracy optical atomic clocks [1] are essential for precision tests of fundamental physics [2], relativistic geodesy [3][4][5], and the anticipated redefinition of the SI second [6]. The scientific reach of these applications is restricted by the statistical precision of interspecies comparison measurements. The instability of individual clocks is limited by the finite coherence time of the optical local oscillator (OLO), which bounds the maximum atomic interrogation time. In this letter, we experimentally demonstrate differential spectroscopy [7], a comparison protocol that enables interrogating beyond the OLO coherence time. By phase-coherently linking a zero-dead-time (ZDT) [8] Yb optical lattice clock with an Al + single-ion clock via an optical frequency comb and performing synchronised Ramsey spectroscopy, we show an improvement in comparison instability relative to our previous result [9] of nearly an order of magnitude. To our knowledge, this result represents the most stable interspecies clock comparison to date. II. MAIN

Prospects of a thousand-ion Sn$^{2+}$ Coulomb-crystal clock with sub-$10^{-19}$ inaccuracy

“…duration in seconds, assuming a conservative 1 s probe duration and 80 % duty cycle. This is nearly two orders of magnitude better than the best clock-comparison stability achieved with an ion clock [6,39] and one order of magnitude better than the best stability comparison of independent lattice clocks [40]. At this level, it is possible to perform frequency measurements with a total uncertainty of 10 −19 in under three hours, measure the time-dependent gravitational effects of solid-Earth tides with high signal-to-noise ratio [41], and search for ultralight bosonic dark matter (DM) candidates over a broad range of particle masses [42].…”

“…Recently, a wide variety of new optical clock platforms, which overcome some of the limitations of conventional lattice and ion clocks, have been proposed and demonstrated. Composite optical clocks combining an ensemble of lattice-trapped atoms that provides high stability, together with a single trapped ion that provides high accuracy, have been proposed [4,5], and the fundamental building blocks have been demonstrated [6]. Ion trap arrays have been built and shown to be capable of supporting clock operation with around 100 ions and sub-10 −18 FIG.…”

New Horizons: Scalar and Vector Ultralight Dark Matter

“…Very recently, an extension of correlation spectroscopy called differential spectroscopy has been proposed [637] and demonstrated [638] that enables frequency difference measurements of optical quantum clocks based on different transitions with probe durations longer than the laser coherence time. In Ref.…”

“…In Ref. [638], the precision of a frequency difference measurement between an aluminum-ion clock and a ytterbium optical lattice clock was improved by a factor of 7 with respect to incoherent comparisons [331]. With technical improvements, it is anticipated that the precision of future frequency ratio measurements between a wide variety of quantum clocks can be improved by orders of magnitude using differential spectroscopy, making coherent clock comparisons a very powerful technique for UDM searches.…”

High precision differential clock comparisons with a multiplexed optical lattice clock

“…However, frequency noise in the clock lasers used to interrogate the atoms results in reduced atom-laser coherence times, and also prevents the clock stability from reaching the QPN limit for larger atom numbers due to the Dick effect [24][25][26], an aliasing of frequency noise from the non-continuous laser interrogation. This motivates the use of simultaneous differential comparisons [4,27], also known as correlated noise spectroscopy [28], for applications involving clock comparisons [6,11]. Common-mode rejection of Dick noise and 10-second-scale atomatom coherence times well beyond that of the clock laser have recently been demonstrated between two independent ion-clocks [29], between sub-ensembles in a three-dimensional Fermidegenerate OLC [2], and between sub-ensembles in a tweezer-array clock [30].…”