Attaining the shot-noise-limit in the ACME measurement of the electron electric dipole moment

C. D. Panda*, C. Meisenhelder, M. Verma, D. G. Ang, J. Chow, Z. Lasner, X. Wu, D. Demille, J. M. Doyle, G. Gabrielse

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Experimental searches for the electron electric dipole moment, d e, probe new physics beyond the Standard Model. Recently, the ACME Collaboration set a new limit of |de| < 1.1 × 10-29 e · cm (ACME Collaboration 2018 Nature 562 355-60), constraining time reversal symmetry (T) violating physics in the 3-100 TeV energy scale. ACME extracts d e from the measurement of electron spin precession due to the thorium monoxide (ThO) molecule's internal electric field. This recent ACME II measurement achieved an order of magnitude increased sensitivity over ACME I by reducing both statistical and systematic uncertainties in the measurement of the electric dipole precession frequency. The ACME II statistical uncertainty was a factor of 1.7 above the ideal shot-noise limit. We have since traced this excess noise to timing imperfections. When the experimental imperfections are eliminated, we show that shot noise limit is attained by acquiring noise-free data in the same configuration as ACME II.

Original languageEnglish (US)
Article number235003
JournalJournal of Physics B: Atomic, Molecular and Optical Physics
Issue number23
StatePublished - Nov 4 2019


  • beyond the standard model
  • electron electric dipole moment
  • excess noise suppression
  • fast polarization switching
  • shot-noise limit
  • spin precession measurement

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Condensed Matter Physics


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