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arXiv:1711.10407 · Physical Review X

Frequency Measurements of Superradiance from the Strontium Clock Transition

Matthew A. Norcia, Julia R. K. Cline, Juan A. Muniz, John M. Robinson, Ross B. Hutson, Akihisa Goban, G. Edward Marti, Jun Ye, James K. Thompson

Published May 9, 2018• 123 citations
arXivHTMLPDF

Abstract

The frequency stability of superradiant light emitted from an optical clock transition in cold strontium atoms surpasses that of active microwave atomic clocks, paving the way for a next generation of high-precision optical frequency references to be used outside the laboratory environment.
DOI
10.1103/physrevx.8.021036

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Abstract Current state-of-the-art frequency standards are passive optical atomic clocks where the frequency of an optical resonator is stabilized to a narrow atomic transition. Passive clocks have achieved unprecedented stabilities of 6.6 × 10−19 over one hour of averaging time [1]. However, they face intrinsic limitations, particularly due to thermal and mechanical fluctuations of the local oscillator. To surpass the limitations of the passive clocks and go beyond the state-of-the-art, the idea of building active optical atomic clocks emerges. These clocks would be optical counterparts of hydrogen masers, with the emitted frequency defined by the atomic transition and therefore inherently stable against cavity instabilities. This paper discusses the latest developments and future prospects in the field of active optical atomic clocks.
We develop a stochastic mean-field theory to describe active frequency measurements of pulsed superradiant emission, studied in a recent experiment with strontium-87 atoms trapped in an optical lattice inside an optical cavity [M. Norcia et al., Phys. Rev. X 8, 021036 (2018)PRXHAE2160-330810.1103/PhysRevX.8.021036]. Our theory reveals the intriguing dynamics of atomic ensembles with multiple transition frequencies, and it reproduces the superradiant beats signal, noisy power spectra, and frequency uncertainty in remarkable agreement with the experiments. Moreover, using longer superradiant pulses of similar strength and shortening the experimental duty cycle, we predict a short-term frequency uncertainty 7×10^{-17}/sqrt[τ/s], which makes active frequency measurements with superradiant transitions comparable with the record performance of current frequency standards [M. Schioppo et al., Nat. Photonics 11, 48 (2017)NPAHBY1749-488510.1038/nphoton.2016.231]. Our theory combines cavity quantum electrodynamics and quantum measurement theory, and it can be readily applied to explore conditional quantum dynamics and describe frequency measurements for other processes such as steady-state superradiance and superradiant Raman lasing.
Abstract This report concerns the experiment of precision spectroscopy of cold strontium atoms in the Polish National Laboratory of Atomic, Molecular and Optical Physics in Toruń. The system is composed of a Zeeman slower and magneto-optical traps (at 461 nm and 689 nm), a frequency comb, and a narrow-band laser locked to an ultra-stable optical cavity. All parts of the experiment are prepared and the first measurements of the absolute frequency of the 1S0-3P1, 689 nm optical transition in 88Sr atoms are performed.