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.

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We perform ab initio calculations needed to predict the cross-section of an experimentally accessible (1 + 1 ′ ) resonance-enhanced multiphoton dissociation (REMPD) pathway in AlH + . Experimenting on AlH + ions held in a radiofrequency Paul trap, we confirm dissociation via this channel with analysis performed using time-of-flight mass spectrometry. We demonstrate the use of REMPD for rotational state analysis, and we measure the rotational distribution of trapped AlH + to be consistent with the expected thermal distribution. AlH + is a particularly interesting species for ion trap work because of its electronic level structure, which makes it amenable to proposals for rotational optical pumping, direct Doppler cooling, and single-molecule fluorescence detection. Potential applications of trapped AlH + include searches for time-varying constants, quantum information processing, and ultracold chemistry studies.

Abstract:Vector diffraction theory is applied to the case of focused TEM 00 Gaussian beams passing through a spatially limiting aperture in order to investigate the propagation of these clipped focused-Gaussian beams. Beam distributions at different axial distances show that a traditional M 2 propagation model cannot be used for the propagation of clipped focus-Gaussian beams. Using Luneberg's vector diffraction theory and Fresnel approximations, an analytical model for the on-axis transverse and longitudinal electric fields and intensity distributions is presented including predictions of the maximum obtainable intensity. In addition, an analytical expression is provided for the longitudinal component of the electric field of a TEM 00 mode unperturbed Gaussian beam. Experimental results are also presented and compared to the model's predictions.

To date, individual addressing of ion qubits has relied primarily on local Rabi or transition frequency differences between ions created via electromagnetic field spatial gradients or via ion transport operations. Alternatively, it is possible to synthesize arbitrary local one-qubit gates by leveraging local phase differences in a global driving field. Here we report individual addressing of 40 Ca + ions in a two-ion crystal using axial potential modulation in a global gate laser field. We characterize the resulting gate performance via one-qubit randomized benchmarking, applying different random sequences to each co-trapped ion. We identify the primary error sources and compare the results with single-ion experiments to better understand our experimental limitations. These experiments form a foundation for the universal control of two ions, confined in the same potential well, with a single gate laser beam.