An atomic fountain for measuring the fine-structure constant

The fine-structure constant α describes the strength of the electromagnetic interaction. By measuring the recoil frequency (defined as the kinetic energy gained by an atom that has been kicked by a photon), we can make an improved measurement of the fine structure constant. Such a measurement could be compared to the value of α as determined from measurements of the electron's gyromagnetic anomaly g-2. This would amount to a precision test of the theory of quantum electrodynamics (QED). Indeed, large parts of the standard model, including the physics of hadrons and the weak interaction, are tested by a comparison at the current level of precision. We may even find new physics. We seek a measurement of α with a precision of 0.25 parts-per-billion.

The phase difference accrued by an interferometer increases with the time the two arms spend apart, and with the kinetic energy of the moving atoms. To increase this energy, we use standing light waves to transfer the momentum of 8-12 photons to the atoms using Bragg transitions, and we additionally impart up to 100 photon momenta with Bloch oscillations.

En route to a precision measurement of α, we have characterized important systematic effects that enter into the interferometer's phase difference, including shifts from Bragg transitions and the Coriolis effect.

Team members

Richard Parker

Weicheng Zhong

Zachary Pagel

Past team members

Chenghui Yu

Brian Estey

Jiafeng Cui

Eric Huang

Pei-Chen Kuan

Shau-Yu Lan


  1. Measurement of the fine-structure constant as a test of the Standard Model. Richard H. Parker, Chenghui Yu, Weicheng Zhong, Brian Estey, and Holger Müller, Science 360, 191-195 (2018).

  2. Controlling the Multiport Nature of Bragg Diffraction in Atom Interferometry. Richard H. Parker, Chenghui Yu, Brian Estey, Weicheng Zhong, Eric Huang, and Holger Müller, Phys. Rev. A 94, 053618 and arXiv:1609.06344.

  3. Improved Accuracy of Atom Interferometry Using Bragg Diffraction. ith suppressed diffraction phases**. Brian Estey, Chenghui Yu, Holger Müller, Pei-Chen Kuan, and Shau-Yu Lan, Phys. Rev. Lett. 115, 083002 (2015) and arXiv:1410.8486.

  4. A clock directly linking time to a particle’s mass. Shau-Yu Lan, Pei-Chen Kuan, Brian Estey, Damon English, Justin Brown, Michael Hohensee, and Holger Müller, Science, 339, 554 (2013) with Science Perspective.