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Blue-sky bifurcation of ion energies and the limits of neutral-gas sympathetic cooling of trapped ions

Steven J. Schowalter, Alexander J. Dunning, Kuang Chen, Prateek Puri, Christian Schneider & Eric R. Hudson

Nature Communications 7, Article number: 12448 (2016)

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Atomic and molecular collision processesUltracold gases

Received: 26 January 2016 Accepted: 05 July 2016 Published online: 11 August 2016


Sympathetic cooling of trapped ions through collisions with neutral buffer gases is critical to a variety of modern scientific fields, including fundamental chemistry, mass spectrometry, nuclear and particle physics, and atomic and molecular physics. Despite its widespread use over four decades, there remain open questions regarding its fundamental limitations. To probe these limits, here we examine the steady-state evolution of up to 10 barium ions immersed in a gas of three-million laser-cooled calcium atoms. We observe and explain the emergence of nonequilibrium behaviour as evidenced by bifurcations in the ion steady-state temperature, parameterized by ion number. We show that this behaviour leads to the limitations in creating and maintaining translationally cold samples of trapped ions using neutral-gas sympathetic cooling. These results may provide a route to studying non-equilibrium thermodynamics at the atomic level.


This work was supported by National Science Foundation (PHY-1205311) and Army Research Office (W911NF-15-1-0121 and W911NF-14-1-0378) grants.

Author information


Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA

Steven J. Schowalter, Alexander J. Dunning, Kuang Chen, Prateek Puri, Christian Schneider & Eric R. Hudson


E.R.H. and K.C. conceived the theoretical concept. E.R.H., S.J.S. and A.J.D. conceived the experiment and measurement protocol. C.S. and S.J.S. built the apparatus. S.J.S., A.J.D. and P.P. acquired and analysed all of the data. K.C. developed the MD software and A.J.D. performed all of the simulations presented. S.J.S. wrote the manuscript and S.J.S., A.J.D. and C.S. prepared all of the figures with input from all authors.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Steven J. Schowalter.

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