Ultimate stability of active optical frequency standards

Abstract

Active optical frequency standards provide interesting alternatives to their passive counterparts. Particularly, such a clock alone continuously generates highly-stable narrow-line laser radiation. Thus a local oscillator is not required to keep the optical phase during a dead time between interrogations as in passive clocks, but only to boost the active clock's low output power to practically usable levels with the current state of technology. Here we investigate the spectral properties and the stability of active clocks, including homogeneous and inhomogeneous broadening effects. We find that for short averaging times the stability is limited by photon shot noise from the limited emitted laser power and at long averaging times by phase diffusion of the laser output. Operational parameters for best long-term stability were identified. Using realistic numbers for an active clock with ${}^{87}$Sr we find that an optimized stability of ${\sigma }_y(\tau )\approx 4\times 10^{-18}/\sqrt{\tau [\mathrm{s}]}$ is achievable.

15 pages

References in corpus (6)

• Resolving the gravitational redshift within a millimeter atomic sample
• Ultra-stable optical clock with two cold-atom ensembles
• Real-time geopotentiometry with synchronously linked optical lattice clocks
• Nuclear Spin Effects in Optical Lattice Clocks
• Active optical frequency standard using sequential coupling of atomic ensembles
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• Superradiant active optical atomic clocks: motivations and current challenges