Sideband cooling of small ion Coulomb crystals in a Penning trap

Journal article

We have recently demonstrated the laser cooling of a single 40Ca+ ion to the motional ground state in a Penning trap using the resolved-sideband cooling technique on the electric quadrupole transition S1/2 ↔ D5/2. Here we report on the extension of this technique to small ion Coulomb crystals made of two or three 40Ca+ ions. Efficient cooling of the axial motion is achieved outside the Lamb-Dicke regime on a two-ion string along the magnetic field axis as well as on two- and three-ion planar crystals. Complex sideband cooling sequences are required in order to cool both axial degrees of freedom simultaneously. We measure a mean excitation after cooling of n¯COM = 0.30(4) for the centre of mass (COM) mode and n¯B = 0.07(3) for the breathing mode of the two-ion string with corresponding heating rates of 11(2) s−1 and 1(1)s−1 at a trap frequency of 162 kHz. The occupation of the ground state of the axial modes (ntilt = nCOM = 0) is above 75% for the two-ion planar crystal and the associated heating rates 0.8(5)s−1 at a trap frequency of 355 kHz.

Authors: Stutter, G; Hrmo, P; Jarlaud, V; Joshi, MK; Goodwin, JF

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Taylor and Francis
• Journal: Journal of Modern Optics
• Volume: 65
• Issue: 5-6
• Pages: 64-74
• Publication date: 2017-10-24
• Acceptance date: 2017-08-25
• DOI: 10.1080/09500340.2017.1376719
• EISSN: 1362-3044
• ISSN: 0950-0340
• Keywords: sideband cooling; trapped ions; Penning trap; ion Coulomb crystals