Letter | Published:

Michelson–Morley analogue for electrons using trapped ions to test Lorentz symmetry

Nature volume 517, pages 592595 (29 January 2015) | Download Citation

Abstract

All evidence so far suggests that the absolute spatial orientation of an experiment never affects its outcome. This is reflected in the standard model of particle physics by requiring all particles and fields to be invariant under Lorentz transformations. The best-known tests of this important cornerstone of physics are Michelson–Morley-type experiments verifying the isotropy of the speed of light1,2,3. For matter, Hughes–Drever-type experiments4,5,6,7,8,9,10,11 test whether the kinetic energy of particles is independent of the direction of their velocity, that is, whether their dispersion relations are isotropic. To provide more guidance for physics beyond the standard model, refined experimental verifications of Lorentz symmetry are desirable. Here we search for violation of Lorentz symmetry for electrons by performing an electronic analogue of a Michelson–Morley experiment. We split an electron wave packet bound inside a calcium ion into two parts with different orientations and recombine them after a time evolution of 95 milliseconds. As the Earth rotates, the absolute spatial orientation of the two parts of the wave packet changes, and anisotropies in the electron dispersion will modify the phase of the interference signal. To remove noise, we prepare a pair of calcium ions in a superposition of two decoherence-free states, thereby rejecting magnetic field fluctuations common to both ions12. After a 23-hour measurement, we find a limit of h × 11 millihertz (h is Planck’s constant) on the energy variations, verifying the isotropy of the electron’s dispersion relation at the level of one part in 1018, a 100-fold improvement on previous work9. Alternatively, we can interpret our result as testing the rotational invariance of the Coulomb potential. Assuming that Lorentz symmetry holds for electrons and that the photon dispersion relation governs the Coulomb force, we obtain a fivefold-improved limit on anisotropies in the speed of light2,3. Our result probes Lorentz symmetry violation at levels comparable to the ratio between the electroweak and Planck energy scales13. Our experiment demonstrates the potential of quantum information techniques in the search for physics beyond the standard model.

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Acknowledgements

This work was supported by the NSF CAREER programme grant no. PHY 0955650 and NSF grants no. PHY 1212442 and no. PHY 1404156, and was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. We thank H. Müller for critical reading of the manuscript.

Author information

Affiliations

  1. Department of Physics, University of California, Berkeley, California 94720, USA

    • T. Pruttivarasin
    • , M. Ramm
    • , M. A. Hohensee
    •  & H. Häffner
  2. Quantum Metrology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan

    • T. Pruttivarasin
  3. Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA

    • S. G. Porsev
    •  & M. S. Safronova
  4. Petersburg Nuclear Physics Institute, Gatchina, Leningrad District 188300, Russia

    • S. G. Porsev
  5. Department of Physics, St Petersburg State University, Ulianovskaya 1, Petrodvorets, St Petersburg 198504, Russia

    • I. I. Tupitsyn
  6. Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, College Park, Maryland 20742, USA

    • M. S. Safronova
  7. Lawrence Livermore National Laboratory, Livermore, California 94550, USA

    • M. A. Hohensee

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Contributions

H.H., M.A.H. and T.P. had the idea for the experiment. T.P. and M.R. carried out the measurements. S.G.P., I.I.T. and M.S.S. calculated the sensitivity of the energy to Lorentz violation. T.P., M.A.H. and H.H. wrote the main part of the manuscript. S.G.P., I.I.T. and M.S.S. wrote the Methods section on calculating the energy shift. All authors contributed to the discussions of the results and manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to T. Pruttivarasin or H. Häffner.

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https://doi.org/10.1038/nature14091

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