Laser cycling of resonances can remove entropy from a system via spontaneously emitted photons, with electronic resonances providing the fastest cooling timescales because of their rapid spontaneous relaxation. Although atoms are routinely laser-cooled, even simple molecules pose two interrelated challenges for cooling: every populated rotational-vibrational state requires a different laser frequency, and electronic relaxation generally excites vibrations. Here we cool trapped AlH þ molecules to their ground rotational-vibrational quantum state using an electronically exciting broadband laser to simultaneously drive cooling resonances from many different rotational levels. Undesired vibrational excitation is avoided because of vibrational-electronic decoupling in AlH þ . We demonstrate rotational cooling on the 140(20) ms timescale from room temperature to 3:8 þ 0:9 À 0:3 K, with the groundstate population increasing from B3 to 95:4 þ 1:3 À 2:1 % . This cooling technique could be applied to several other neutral and charged molecular species useful for quantum information processing, ultracold chemistry applications and precision tests of fundamental symmetries.

We study the motion of an undamped single-ion harmonic oscillator, resonantly driven with a pulsed radiation pressure force. We demonstrate that a barium ion, initially cooled to the Doppler limit, quickly phase locks to the drive and builds up coherent oscillations above the thermal distribution after scattering of order 100 photons. In our experiment, this seeded motion is subsequently amplified and then analyzed by Doppler velocimetry. Since the coherent oscillation is conditional upon the internal quantum state of the ion, this motional excitation technique could be useful in atomic or molecular single-ion spectroscopy experiments, providing a simple protocol for state readout of nonfluorescing ions with partially closed-cycle transitions.

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The system of a trapped ion translationally excited by a blue-detuned near-resonant laser, sometimes described as an instance of a phonon laser, has recently received attention as interesting in its own right and for its application to non-destructive readout of internal states of non-fluorescing ions. Previous theoretical work has been limited to cases of two-level ions. Here, we perform simulations to study the dynamics of a phonon laser involving the Λ-type + Ba 138 ion, in which coherent population trapping (CPT) effects lead to different behavior than in the previously studied cases. We explore optimization of the laser parameters to maximize amplification gain for initially seeded motion and consider the related signal-to-noise ratios for internal state readout. We find that good Doppler amplification and state readout performance can be obtained even when operating quite near the CPT dip.