RESUMEN
Optical pumping of molecules provides unique opportunities for control of chemical reactions at a wide range of rotational energies. This work reports a chemical reaction with extreme rotational excitation of a reactant and its kinetic characterization. We investigate the chemical reactivity for the hydrogen abstraction reaction SiO+ + H2 â SiOH+ + H in an ion trap. The SiO+ cations are prepared in a narrow rotational state distribution, including super-rotor states with rotational quantum number (j) as high as 170, using a broad-band optical pumping method. We show that the super-rotor states of SiO+ substantially enhance the reaction rate, a trend reproduced by complementary theoretical studies. We reveal the mechanism for the rotational enhancement of the reactivity to be a strong coupling of the SiO+ rotational mode with the reaction coordinate at the transition state on the dominant dynamical pathway.
RESUMEN
Improved optical control of molecular quantum states promises new applications including chemistry in the quantum regime, precision tests of fundamental physics, and quantum information processing. While much work has sought to prepare ground state molecules, excited states are also of interest. Here, we demonstrate a broadband optical approach to pump trapped SiO+ molecules into pure super rotor ensembles maintained for many minutes. Super rotor ensembles pumped up to rotational state N = 67, corresponding to the peak of a 9400 K distribution, had a narrow N spread comparable to that of a few-kelvin sample, and were used for spectroscopy of the previously unobserved C2Π state. Significant centrifugal distortion of super rotors pumped up to N = 230 allowed probing electronic structure of SiO+ stretched far from its equilibrium bond length.
RESUMEN
We propose an optical pumping scheme to prepare trapped AlH+ molecules in a pure state, the stretched hyperfine state of the rovibronic ground manifold |X2Σ+, v = 0, N = 0 . Our scheme utilizes linearly-polarized and circularly-polarized fields of a broadband pulsed laser to cool the rotational degree of freedom and drive the population to the hyperfine state, respectively. We simulate the population dynamics by solving a representative system of rate equations that accounts for the laser fields, blackbody radiation, and spontaneous emission. In order to model the hyperfine structure, new hyperfine constants of the A2Π excited state were computed using a RASSCF wavefunction. We find that adding an infrared laser to drive the 1-0 vibrational transition within the X2Σ+ manifold accelerates the cooling process. The results show that, under optimal conditions, the population in the target state of the rovibronic ground manifold can reach 63% after 68 µs (330 ms) and 95% after 25 ms (1.2 s) with (without) the infrared laser.
RESUMEN
We demonstrate rotational cooling of the silicon monoxide cation via optical pumping by a spectrally filtered broadband laser. Compared with diatomic hydrides, SiO^{+} is more challenging to cool because of its smaller rotational interval. However, the rotational level spacing and the large dipole moment of SiO^{+} allows for direct manipulation by microwaves, and the absence of hyperfine structure in its dominant isotopologue greatly reduces demands for pure quantum state preparation. These features make ^{28}Si^{16}O^{+} a good candidate for future applications such as quantum information processing. Cooling to the ground rotational state is achieved on a 100 ms timescale and attains a population of 94(3)%, with an equivalent temperature T=0.53(6) K. We also describe a novel spectral-filtering approach to cool into arbitrary rotational states and use it to demonstrate a narrow rotational population distribution (N±1) around a selected state.
RESUMEN
The Libbrecht-Hall circuit is a well-known, low-noise current driver for narrow-linewidth diode lasers. An important feature of the circuit is a current limit to protect the laser diode. As the current approaches the maximum limit, however, the noise in the laser current increases dramatically. This paper documents this behavior and explores simple circuit modifications to alleviate this issue.
RESUMEN
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 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.
RESUMEN
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(+) 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(+). We demonstrate rotational cooling on the 140(20) ms timescale from room temperature to 3.8(-0.3)(+0.9) K, with the ground-state population increasing from ~3 to 95.4(-2.1)(+1.3)%. 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.