Comparison of Two Independent Sr Optical Clocks with 1e-17 Stability at 10^3 s

TL;DR

This paper demonstrates two independent Sr optical clocks achieving a fractional instability of 1e-17 at 1000 seconds, approaching quantum projection noise limits, and evaluates their systematic uncertainties.

Contribution

It reports the first realization of two independent Sr optical clocks with stability near quantum limits, using improved oscillators and systematic uncertainty analysis.

Findings

Achieved 1e-17 fractional instability at 1000 s

Demonstrated stability close to quantum projection noise limit

Evaluated systematic uncertainties including atomic interactions

Abstract

Many-particle optical lattice clocks have the potential for unprecedented measurement precision and stability due to their low quantum projection noise. However, this potential has so far never been realized because clock stability has been limited by frequency noise of optical local oscillators. By synchronously probing two 87Sr lattice systems using a laser with a thermal noise floor of 1e-15, we remove classically correlated laser noise from the intercomparison, but this does not demonstrate independent clock performance. With an improved optical oscillator that has a 1e-16 thermal noise floor, we demonstrate an order of magnitude improvement over the best reported stability of any independent clock, achieving a fractional instability of 1e-17 in 1000 s of averaging time for synchronous or asynchronous comparisons. This result is within a factor of 2 of the combined quantum projection noise limit for a 160 ms probe time with ~10^3 atoms in each clock. We further demonstrate that even at this high precision, the overall systematic uncertainty of our clock is not limited by atomic interactions. For the second Sr clock, which has a cavity-enhanced lattice, the atomic-density-dependent frequency shift is evaluated to be -3.11e-17 with an uncertainty of 8.2e-19.