Energy distributions of an ion in a radiofrequency trap immersed in a buffer gas under the influence of additional external forces

Abstract

An ion held in a radiofrequency trap interacting with a uniform buffer gas of neutral atoms develops a steady-state energy distribution characterised by a power-law tail at high energies instead of the exponential decay characteristic of thermal equilibrium. We have previously shown that the Tsallis statistics frequently used as an empirical model for this distribution is a good approximation when the ion is heated due to a combination of micromotion interruption and exchange of kinetic energy with the buffer gas [I. Rouse and S. Willitsch, Phys. Rev. Lett. 118, 143401 (2017)]. Here, we extend our treatment to include the heating due to additional motion of the ion caused by external forces, including the "excess micromotion" induced by uniform electric fields and rf phase offsets. We show that this also leads to a Tsallis distribution with a potentially different power-law exponent from that observed in the absence of this additional forced motion, with the difference increasing as the ratio of the mass of the neutral atoms to that of the ion decreases. Our results indicate that unless the excess micromotion is minimised to a very high degree, then even a system with very light neutrals and a heavy ion does not exhibit a thermal distribution.

arXiv comment16 pages, 9 figures

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Cited by in corpus (8)

• Cold hybrid ion-atom systems
• Cold trapped molecular ions and hybrid platforms for ions and neutral particles
• Effect of ion-trap parameters on energy distributions of ultra-cold atom-ion mixtures
• Experimental setup for studying an ultracold mixture of trapped Yb${}^{+}$-${}^6$Li
• Far-from-equilibrium noise heating and laser cooling dynamics in radio-frequency Paul traps
• Minimizing rf-induced excess micromotion of a trapped ion with the help of ultracold atoms
• Tuning nonthermal distributions to thermal ones in time-dependent Paul traps
• The energy distribution of an ion in a radiofrequency trap interacting with a nonuniform neutral buffer gas