We use Si/SiGe triple quantum dots to operate two and three spin qubits with high fidelities. For the two qubit we speed up the single qubit and exchange control to achieve the fault tolerance threshold fidelity of $> 99$ %. For the three qubits we control two exchange couplings to generate a three-spin entangled state.We use Si/SiGe triple quantum dots to operate two and three spin qubits with high fidelities. For the two qubit we speed up the single qubit and exchange control to achieve the fault tolerance threshold fidelity of$> 99$%. For the three qubits we control two exchange couplings to generate a three-spin entangled state.

Technical digest - International Electron Devices Meeting/Technical digestDec 11, 20211 citation

Fast Exchange Oscillations in Quantum Dot Spin Qubits

Shannon P. Harvey, Michael Shulman, Oliver Dial +3 more

Bulletin of the American Physical SocietyFeb 28, 20120 citations

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

Holly G. Stemp, Harry Hanlim Kang, Chih Hwan Yang +6 more

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 $T_2^*=1.17\pm0.02~μ$ s to $T_2^{\mathrm{CPMG}}=74.8\pm1.8~μ$ 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.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 $T_2^*=1.17\pm0.02~μ$s to $T_2^{\mathrm{CPMG}}=74.8\pm1.8~μ$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.

cond-mat.mes-hallCross-listedarXiv:2608.31093Sep 1, 20260 citations

> 99

%. For the three qubits we control two exchange couplings to generate a three-spin entangled state.

Device characterization of Si

/

SiGe double quantum dots using exchange oscillations in Earth's magnetic field

T_2^*=1.17\pm0.02~μ

s to

T_2^{\mathrm{CPMG}}=74.8\pm1.8~μ

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.