Trapped Ion Chain Thermometry and Mass Spectrometry through Imaging
  We demonstrate a spatial-imaging thermometry technique for ions in a one-dimensional Coulomb crystal by relating their imaged spatial extent along the linear radiofrequency ion trap axis to normal modes of vibration of coupled oscillators in a harmonic potential. We also use the thermal spatial spread of bright ions in the case of a two-species mixed chain to measure the center-of-mass (COM) resonance frequency of the entire chain and infer the molecular composition of the co-trapped dark ions. These non-destructive techniques create new possibilities for better understanding of sympathetic cooling in mixed-ion chains, improving few-ion mass spectrometry, and trapped-ion thermometry without requiring a scan of Doppler cooling parameters. 
V. Rajagopal, J.P. Marler, M.G. Kokish, B.C. Odom
physics.atom-ph quant-ph