In our toolbox of quantum gates for spin qubits, the SWAP-family gates based on Heisenberg exchange coupling are quite versatile: the SWAP gate can help solve the connectivity problem by realizing both short- and long-range spin state transfer, while the (Formula presented) gate is a basic two-qubit entangling gate. Here we demonstrate a SWAP gate in a double quantum dot in isotopically enriched silicon in the presence of a micromagnet. We achieve a two-orders-of-magnitude adjustable ratio between the exchange coupling J and the Zeeman energy difference ΔEz, overcoming a major obstacle for a high-fidelity SWAP gate. We also calibrate the single-qubit local phases, evaluate the logical-basis fidelity of the SWAP gate, and further analyze the dominant error sources. These results pave the way for high-fidelity SWAP gates and processes based on them, such as quantum communication on chip and quantum simulation. ... Read more

Synthesized spin–orbit coupling (SSOC) is crucial for the operation of spin qubits in silicon quantum dot, as it address the challenge posed by the inherently weak intrinsic spin–orbit coupling in silicon. Here, we investigate the anisotropic properties of single spin qubit in silicon metal-oxide-semiconductor (Si-MOS) quantum dot and provide experimental evidence for the control of SSOC. Additionally, we experimentally demonstrate that tuning the operating point away from the conventional configuration can enhance the quality factor of the spin qubit. These findings lay a foundation for the realization of high-quality tunable spin–orbit qubits. ... Read more