Quantum Nondemolition Detection for Strontium Optical Lattice Clock

SummaryThe short-term frequency instability of the best optical atomic clock lies in the mid 10
⁻¹⁷
. However, the Dick effect is still an obstacle for a single operational clock closely followed by the quantum projection noise. To improve the frequency stability of the strontium optical lattice clock, we present a quantum non-demolition detection scheme based on the cavity mediated interaction between the atoms and a probe light that has a large-frequency detuning to the atomic resonance, aiming to bring the detection scheme proposed in [1] to the quantum regime. We obtained a rather small photon scattering rate, measured to be less than 0.1 photon/μs/atom, which allows us to not only preserve the atoms in the lattice but also the atomic wave function as long as the total probe time is on the order of a few microseconds. The detection noise for the number of atoms is 48/√photons atoms, implying that the frequency stability can surpass the standard quantum limit when the number of trapped atoms is larger than 2.3×10
⁴
with spin squeezing protocols.