Improving trapped ion motional coherence for quantum simulations of molecular dynamics

The analog simulation of a quantum chemical system is challenging using conventional computers, particularly in strong vibronic (vibrational and electronic) coupling regimes when the Born-Oppenheimer approximation breaks down. We show that vibronic coupling Hamiltonians representing ultrafast molecular dynamics can be efficiently simulated on quantum systems with coupled internal states and bosonic modes [1]. Furthermore, this “mixed qudit boson” (MQB) approach can be extended to time-domain measurements used to reproduce molecular absorption spectra. We performed proof-of-principle experiments using a trapped-ion system. Time-domain measurements make our simulator susceptible to various mechanisms of decoherence. This places stringent requirements on the simulation time before the system thermalizes with the environment. We identified the limiting factor of simulation times in our system is the bosonic radial mode’s coherence time associated with technical noises within the radio-frequency trapping field. By implementing amplitude noise filtering and feedback, we improve radial mode coherence times from ~1 ms to more than ~20 ms. This enabled us to compute the 1-dimensional Franck-Condon spectra of an SO2 molecule.

[1] Analog quantum simulation of chemical dynamics. Ryan J. MacDonell, Claire E. Dickerson, Clare J. T. Birch, Alok Kumar, Claire L. Edmunds, Michael J. Biercuk, Cornelius Hempel and Ivan Kassal, Chem. Sci., 2021,12, 9794-9805