Quantum Control of Strongly Disordered Solid StateSystems
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shim-shiminki-bs-2026-thesis.pdf
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Author(s)
Shim, Minki
Advisor(s)
Choi, Soonwon
Date Issued
May 2026
Publisher
Massachusetts Institute of Technology
Abstract
Implementing high-fidelity quantum gates on solid-state spin ensembles is challenging in the strong-disorder regime, where the detuning spread is comparable to the maximum Rabi frequency of the control field. We address the challenges in this regime through two complementary approaches. When the hyperfine coupling produces a set of well-separated detuning peaks across subensembles of electron spins, as in ¹⁰B¹⁵N hBN V⁻_B centers, we map the problem onto quantum signal processing (QSP) with detuning as the signal variable and aim to generate different target unitaries at each peak. Averaging uniformly over all sets of four target x rotation gates, we achieved 97% gate fidelity. We furthermore uncovered an emergent low-dimensional geometric structure within a sub-family of the QSP pulses in the space of optimal control angles. When detuning is instead broadened into a regime where detuning fluctuation equals or exceeds the Rabi frequency, the QSP ansatz fails. We leverage the transformer architecture trained on “composite pulse tokenization” to address the challenge. The model effectively extract a non-perturbative disorder canceling mechanism from analytical composite pulses, and we achieved the high 99.1% average fidelity over all SU(2) gates with pulse duration of 13.1π, outperforming the state-of-the-art composite pulse optimized for the strongly disordered regime. Our work paves the way towards high-fidelity control of strongly disordered spin ensembles with limited control field strength, enabling sensitivity-limited quantum sensing on solid-state platforms and a route to electron-nuclear entangling gates in hBN that exploit, rather than suppress, the hyperfine structure.
MIT Department
Massachusetts Institute of Technology. Department of Physics
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