A fast and robust cooling method for trapped-ion qubits: phonon rapid adiabatic passage

In the quantum computing ‘QCCD’ architecture, circuit time is dominated by sideband cooling operations that limit operational fidelity via memory error. Some motional modes of a multi-species crystal cool inefficiently due to small Lamb-Dicke factors, resulting in order-of-magnitude differences in the cooling times needed to address all motional modes. Previous work has shown that quanta can be transferred between modes by high-frequency modulation of local electric fields, opening the possibility of transferring phonons out of problematic modes [1,2,3]. However, these techniques are hindered by the voltage noise suppression filters commonly employed on ion traps and are furthermore sensitive to drift in both mode frequency and drive amplitude. Here we present a technique that overcomes these limitations, which we call phonon rapid adiabatic passage (phrap). Analogous to adiabatic rapid passage, we quasi-statically couple harder-to-cool modes with easier ones, using a DC electric field. Nearly complete phonon population exchange results when the crystal is adiabatically driven through the resulting avoided crossing. We demonstrate this technique on two-ion crystals by the indirect ground-state cooling of all radial modes, achieving an order of magnitude speedup in cooling times as compared with traditional sideband cooling.

[1] D. J. Gorman, P. Schindler, S. Selvarajan, N. Daniilidis, and H. H ̈affner, Two-mode coupling in a single-ion oscillator via parametric resonance, Physical Review A 89,062332 (2014).

[2] P.-Y. Hou, J. J. Wu, S. D. Erickson, D. C. Cole, G. Zaran-tonello, A. D. Brandt, A. C. Wilson, D. H. Slichter, and D. Leibfried, Coherently coupled mechanical oscillators in the quantum regime, arXiv preprint arXiv:2205.14841 (2022).

[3] P.-Y. Hou, J. J. Wu, S. D. Erickson, G. Zarantonello,A. D. Brandt, D. C. Cole, A. C. Wilson, D. H. Slichter, and D. Leibfried, Indirect cooling of weakly coupled trapped-ion mechanical oscillators, arXiv preprint arXiv:2308.05158 (2023).