Quantum state preparation of homonuclear molecular ions enabled via a cold buffer gas: An ab initio study for the H2+ and the D2

Abstract

Precision vibrational spectroscopy of the molecular hydrogen ions is of significant interest for determining fundamental constants, for searching for new forces, and for testing quantum electrodynamics calculations. Future experiments can profit from the ability of preparing molecular hydrogen ions at ultralow kinetic energy and in preselected internal states, with respect to vibration, rotation, and spin degrees of freedom. For the homonuclear ions (H 2 + , D 2 + ), direct laser cooling of the rotational degree of freedom is not feasible. We show by quantum calculations that rotational cooling by cold He buffer gas is an effective approach. For this purpose we have computed the energy-dependent cross sections for rotationally elastic and inelastic collisions, h 2 + (v = 0, N) + He → h 2 + (v = 0, N ) + He (where h = H, D), using ab initio coupled-channel calculations. We find that rotational cooling to the lowest rotational state is possible within tens of seconds under experimentally realistic conditions. We furthermore describe possible protocols for the preparation of a single quantum state, where also the spin state is well defined.

Modeling Quantum Kinetics in Ion Traps: State‐changing Collisions for OH+() Ions with He as a Buffer Gas

“…It is interesting to note that the population changes with temperature produce, at each T value, results which essentially coincide with the Boltzmann's distribution at that temperature. This result agrees with what we had already verified in our earlier studies ,. In those papers we had also made use of another useful indicator for assessing the efficiency of the time‐dependence of the process under study.…”

“…These asymptotic solutions correspond to the steady‐state conditions in the trap and can be obtained by solving the corresponding homogeneous form of eq 10 given as: . We solved the homogeneous equations by using the singular‐value decomposition technique (SVD), already employed by us in previous studies ,. The non‐homogeneous equations 10, starting from our t initial of 400 K, were solved using the Runge‐Kutta method for different translational temperatures of the trap.…”

Rotationally inelastic cross sections, rates and cooling times for para-H2 +, ortho-D2 + and HD+ in cold helium gas

“…As discussed elsewhere [25] we may consider this time to be around 1 s for all three systems, so that the density is approximately 1 × 10 9 cm −3 . Under this condition, the calculations indicate for all three systems mean cooling times between 4 s and 7 s, which is a reasonable request for the trap's experimental conditions.…”

Fundamental Transitions and Ionization Energies of the Hydrogen Molecular Ions with Few ppt Uncertainty

“…As was pointed out already some time ago [3], and recently discussed more extensively [4], if the theory would be sufficiently precise, the spectroscopy of HMI may be used for determining of the fundamental physical constants such as the protonto-electron mass ratio. The ionization energy of HMI is also of high importance for the determination of ionization and dissociation energies of the hydrogen molecule from spectroscopic studies [5][6][7] as well as for the determination of atomic masses of light nuclei [8][9][10].On the experimental side there are many new projects started, which are now oriented towards Doppler-free spectroscopy with accuracy targeted to 1 ppt (one part per trillion) or better [4,[11][12][13]. These perspectives bring strong motivation for theory.…”

“…On the experimental side there are many new projects started, which are now oriented towards Doppler-free spectroscopy with accuracy targeted to 1 ppt (one part per trillion) or better [4,[11][12][13]. These perspectives bring strong motivation for theory.…”