Efficient motional-mode characterization for high-fidelity trapped-ion quantum computing

Abstract

To achieve high-fidelity operations on a large-scale quantum computer, the parameters of the physical system must be efficiently characterized with high accuracy. For trapped ions, the entanglement between qubits are mediated by the motional modes of the ion chain, and thus characterizing the motional-mode parameters becomes essential. In this paper, we develop and explore physical models that accurately predict both magnitude and sign of the Lamb-Dicke parameters when the modes are probed in parallel. We further devise an advanced characterization protocol that shortens the characterization time by more than an order of magnitude, when compared to that of the conventional method that only uses mode spectroscopy. We discuss potential ramifications of our results to the development of a scalable trapped-ion quantum computer, viewed through the lens of system-level resource trade offs.

Pulse optimization for high-precision motional-mode characterization in trapped-ion quantum computers

“…This necessitates gate pulse design methods to construct solutions that are robust to parameter offsets, albeit at the cost of a significantly higher power or longer pulse length [5, 6, 24-26, 34, 35]. Despite much effort, readily available rough theoretical estimates of the mode parameters, calculated using minimal knowledge of the system configurations such as the voltages applied to the trap [36], have been proven to be insufficient for high-fidelity quantum operations, as evidenced in [5] (see also footnote [35] of [1]).…”

“…In this paper, we aim to address this challenge for a trapped-ion quantum computer. In particular, our focus is to enhance the accuracy of motional-mode parameter estimation [1], as these parameters are essential for designing and performing high-fidelity two-qubit operations [2][3][4][5][6][7]. An accurate characterization of mode parameters can provide several additional benefits as well.…”

“…In a characterization experiment, a model is used to predict the physical parameters being characterized via fitting to some measured quantities. A major bottleneck to achieving high-accuracy characterization is the mismatch between the model's predictions and experimental outcomes [1], resulting from various sources of experimental imperfections and/or model violations. [1] presents improved fitting models as well as parallelized characterization protocols to address some of these mismatches.…”

“…A major bottleneck to achieving high-accuracy characterization is the mismatch between the model's predictions and experimental outcomes [1], resulting from various sources of experimental imperfections and/or model violations. [1] presents improved fitting models as well as parallelized characterization protocols to address some of these mismatches. To achieve further improvement in the accuracy of mode-parameter characterization, here, we investigate a complementary approach to the characterization tools developed in [1] by leveraging the control degrees of freedom that are already readily available for the quantum gate implementation on the hardware level.…”

“…[1] presents improved fitting models as well as parallelized characterization protocols to address some of these mismatches. To achieve further improvement in the accuracy of mode-parameter characterization, here, we investigate a complementary approach to the characterization tools developed in [1] by leveraging the control degrees of freedom that are already readily available for the quantum gate implementation on the hardware level.…”