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arXiv:2607.06789

Microsecond-Scale Coherent Control of a Forbidden Clock Transition with Doppler-Free Multiphoton Excitations

Guglielmo Panelli, Erik J. Porter, V. Rose Knight, S. C. Burd, Mark A. Kasevich

Published Jul 7, 2026• 0 citations
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Abstract

We demonstrate two Doppler-free (DF) excitation schemes for coherent manipulation of the ${}^1\!S_0 - {}^3\!P_0$ clock transition in $^{88}$Sr that achieve microsecond-scale excitation times. The first approach uses three-photon excitation with distinct phase-coherent spectral components to couple the ground and clock states while canceling the first-order Doppler shift. The second approach is a sequential protocol that combines a single-photon excitation with a two-photon Raman excitation, reducing coherent clock transition manipulation times to below a microsecond. With both methods, we perform high-contrast Ramsey spectroscopy on thermal ensembles of $3 \times 10^{6}$ atoms in free space. We observe three orders of magnitude suppression of Doppler dephasing compared to single-photon excitation, relaxing the need for tight confinement or ultra-low temperatures. These broadly applicable techniques enable fast, coherent manipulation of narrow-line transitions, with implications for optical atomic clocks, matter-wave interferometers, quantum-enhanced metrology, and quantum information processing.

DOI
10.48550/arxiv.2607.06789

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Optical clocks and atom interferometers provide complementary ways to measure time, motion and gravity. Combining these capabilities requires matter-wave beam splitters that manipulate different clock states in the same way, so that optical internal energy becomes a controlled degree of freedom rather than a source of systematic phase shifts. Here we realized a dual matter-wave interferometer operating simultaneously on the two states of the 88^{88}88Sr optical clock transition, 1S0^1S_01S0​ and 3P0^3P_03P0​. The interferometer is driven by Bragg pulses at the 813 nm magic wavelength, for which the two clock states experience the same optical coupling strength. This realizes a common matter-wave beam splitter for atoms whose internal energies differ by an optical excitation. With a sensitivity of 30 mrad, our measurement is consistent with a zero differential phase shift between the two clock-state Mach-Zehnder interferometers, translating to an absence of state-dependent acceleration in free fall at the level of 10−510^{-5}10−5. We further used the same interferometer to measure state-dependent optical dipole forces and determine a tune-out wavelength of the metastable 3P0^3P_03P0​ state to be 478.95(8) nm. These results establish magic-wavelength clock-state interferometry as a platform for differential force sensing, excited-state polarizability metrology and future quantum-clock tests of gravity.
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