Research

To excite most nuclei above the ground isomeric state, energies of order keV to MeV are required. The ²²⁹Th isotope, on the other hand, is believed to possess an energy splitting of only 7.6 ± 0.5 eV, putting it in reach of tabletop UV lasers [1]. Along with the exceptional isolation of the nucleus from the outside environment, the narrow linewidth of this transition could be exploited for a new generation of high precision clocks [2]. Further applications of this nuclear transition could include enhanced sensitivity to variations in the fine structure constant [3].

In order to study the nuclear isomer, we first must produce triply ionized thorium, Th³⁺, as it is the lowest charge state of thorium that offers a convenient electronic level structure for laser cooling. Ions are created by ablating a sample of thorium with the third harmonic of a pulsed Nd:YAG laser and are subsequently confined in a linear Paul trap. We have successfully laser cooled ²³²Th³⁺ to form Coulomb crystals (below), a necessary first step towards the study of the isomer transition in ²²⁹Th³⁺ ions.

Compared to other ions commonly used in atomic physics (such as Ba⁺), Th³⁺ has a fairly short lifetime. In order to improve this, we have studied reactions involving Th³⁺ and several gases including methane (pictured below).

Recently, our collaborators in the Kuzmich lab succeeded in directly laser cooling ²²⁹Th³⁺ [4].

[1] B. R. Beck et al., Phys. Rev. Lett. 98, 142501 (2007).
[2] E. Peik and C. Tamm, Europhys. Lett. 61, 181 (2003).
[3] V. V. Flambaum, Phys. Rev. Lett. 97, 092502 (2006).
[4] C. J. Campbell, A. G. Radnaev, and A. Kuzmich, Phys Rev. Lett. 106, 223001 (2011).

Papers

• "Multiply Charged Thorium Crystals for Nuclear Laser Spectroscopy," C. J. Campbell, A. V. Steele, L. R. Churchill, M. V. DePalatis, D. E. Naylor, D. N. Matsukevich, A. Kuzmich, and M. S. Chapman, Phys. Rev. Lett. 102, 233004 (2009)
• "Charge exchange and chemical reactions with trapped Th$^{3+}$," L. R. Churchill, M. V. DePalatis, and M. S. Chapman, Phys. Rev. A 83, 012710 (2011)

Conference Proceedings

• "Multiply charged ionic crystals for nuclear laser spectroscopy," C. J. Campbell, A. V. Steele, L. R. Churchill, M. V. DePalatis, D.E. Naylor, D. N. Matsukevich, M. S. Chapman, and A. Kuzmich, DAMOP 2009, Charlottesville, VA, May 2009. (DAMOP abstract).
• "Multiply charged thorium ions for nuclear laser spectroscopy," M. V. DePalatis, C. J. Campbell, L. R. Churchill, D. E. Naylor, A. Radnaev, M. S. Chapman, and A. Kuzmich, DAMOP 2010, Houston, TX, May 2010. (DAMOP abstract).
• "Charge exchange and chemical reactions with trapped thorium ions," M. V. DePalatis, L. R. Churchill, and M. S. Chapman, DAMOP 2011, Atlanta, GA, June 2011. (DAMOP abstract).