Jason Chadwick
Jason D. Chadwick
Quantum computing Ph.D. student
University of Chicago
jchadwick@uchicago.edu

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Spin qubits in silicon quantum dot arrays are a promising quantum computation platform for long-term scalability due to their small qubit footprint and compatibility with advanced semiconductor manufacturing. However, spin qubit devices face a key architectural bottleneck: the large physical footprint of readout components relative to qubits prevents a dense layout where all qubits can be measured simultaneously, complicating the implementation of quantum error correction. This challenge is offset by the platform’s unique rapid shuttling capability. In this work, we explore the design constraints and capabilities of spin qubits in silicon and propose the SNAQ (Shuttling-capable Narrow Array of spin Qubits) surface code architecture, which relaxes the 1:1 readout-to-qubit assumption by leveraging spin shuttling to time-multiplex ancilla qubit initialization and readout. Our analysis shows that, given sufficiently-high (experimentally demonstrated) qubit coherence times, this tradeoff achieves an orders-of-magnitude reduction in chip area per logical qubit. Additionally, using a denser grid of physical qubits, SNAQ enables fast transversal logic for short-distance logical operations, achieving 2.0-14.6x improvement in local logical clock speed while still supporting global operations via lattice surgery. This translates to a 60-64% reduction in spacetime cost of 15-to-1 magic state distillation, a key fault-tolerant subroutine. Our work demonstrates the architectural consequences of this new tradeoff, pinpoints critical hardware metrics, and provides a compelling path toward high-performance fault-tolerant computation on near-term-manufacturable spin qubit arrays.