Device characterization of Si$/$SiGe double quantum dots using exchange oscillations in Earth's magnetic field

Abstract:Exchange-based semiconductor qubits encompass a broad family of encodings constructed from singlet- and triplet-like spin states, several of which are compatible with operation at zero applied magnetic field. Their reliable operation requires characterization of environmental noise, residual idle interactions, and exchange-dependent decay, but this characterization often relies on multi-axis control calibration or deliberately engineered magnetic-field gradients. A simpler zero-applied-field diagnostic is particularly valuable for hybrid semiconductor-superconductor systems, in which magnetic fields can degrade superconducting components. Here, we use the intrinsic magnetic-field gradient produced by residual nuclear spins in isotopically enriched Si/SiGe to implement exchange oscillations between two quantum dots as a characterization tool without a micromagnet, dynamic nuclear polarization, or prior multi-axis calibration. Using Carr-Purcell-Meiboom-Gill exchange sequences, we extend the singlet coherence from $T_2^*=1.17\pm0.02~\mu$s to $T_2^{\mathrm{CPMG}}=74.8\pm1.8~\mu$s with $N=70$ refocusing pulses. The oscillation phase resolves residual exchange in the tens-of-kilohertz regime and enables it to be mapped across the $(1,1)$ charge cell. These results establish intrinsic-gradient exchange oscillations as a simple, more relevant zero-field diagnostic for exchange-only and related semiconductor qubit encodings that is amenable to rapid, high-throughput device characterization.

Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

arXiv:2608.31093 [cond-mat.mes-hall]

(or arXiv:2608.31093v1 [cond-mat.mes-hall] for this version)

https://doi.org/10.48550/arXiv.2608.31093 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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