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Measurement system for in situ application of strain in silicon and silicon–germanium quantum dots, A
Rash, Davis B.
Rash, Davis B.
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2025
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Abstract
Engineering tunable valley splitting in silicon/silicon–germanium quantum-dot spin qubits is a central route to suppressing spin–valley leakage, minimizing charge-noise sensitivity, and extending coherence times to the fault-tolerant regime. Here we develop and characterize a cryogenic measurement platform to engineer this valley splitting via uniaxial strain applied in situ to foundry-fabricated Tunnel Falls qubit chips. Strain is transferred through commercial longitudinal piezoelectric actuators and calibrated with four-wire measurement and a temperature-compensated Wheatstone bridge employing modified-Karma nickel–chromium gauges. Four-wire resistance and balanced-bridge readouts enable microstrain resolution from a room-temperature environment down to cryogenic temperatures.
Thermal and mechanical anchoring of the actuators to a stage presents challenges to prevent restriction of the actuator stroke and hence the applied strain. We design a two-piece stage that allows for easy loading of the actuators into a dilution refrigerator while providing the required anchoring. Finite-element simulations of the stage predict suppression of stray electrostatic fields by more than one order of magnitude at the device surface, helping to ensure that gate-defined potentials remain unperturbed while the crystal lattice is distorted.
Our platform enables quantitative tests of deformation-potential and interface-roughness theories that predict how strain modifies the valley–orbit coupling parameter and, consequently, the spin relaxation and coherence times. Utilizing electrically driven strain therefore opens a path toward large, tunable valley splitting, important for future large-scale CMOS-compatible quantum processors.
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