Collinear Three-Photon Excitation of a Strongly Forbidden Optical Clock Transition

TL;DR

This paper demonstrates a novel three-photon excitation method to coherently excite a forbidden optical clock transition in bosonic strontium, enabling more precise atomic clocks and quantum sensors with reduced systematic errors.

Contribution

It introduces a collinear three-photon process for exciting the $^{1} ext{S}_0$-$^{3} ext{P}_0$ transition in bosonic ${}^{88}$Sr, overcoming previous limitations.

Findings

Achieved Rabi oscillations at 50 kHz frequency.

Enabled excitation in bosonic isotopes with low magnetic fields.

Facilitated interrogation of spatially separated ensembles.

Abstract

The ${{^1\mathrm{S}_0}\!-\!{^3\mathrm{P}_0}}$ clock transition in strontium serves as the foundation for the world's best atomic clocks and for gravitational wave detector concepts in clock atom interferometry. This transition is weakly allowed in the fermionic isotope $^{87}$Sr but strongly forbidden in bosonic isotopes. Here, we demonstrate coherent excitation of the clock transition in bosonic ${}^{88}$Sr using a novel collinear three-photon process in a weak magnetic field. We observe Rabi oscillations with frequencies of up to $50~\text{kHz}$ using $\text{W}/\text{cm}^{2}$ laser intensities and Gauss-level magnetic field amplitudes. The absence of nuclear spin in bosonic isotopes offers decreased sensitivity to magnetic fields and optical lattice light shifts, enabling atomic clocks with reduced systematic errors. The collinear propagation of the laser fields permits the interrogation of spatially separated atomic ensembles with common laser pulses, a key requirement for dark matter searches and gravitational wave detection with next-generation quantum sensors.