Towards an electrically controlled spin-valley quantum dot qubit in silicon*

Electrical control of electron spins in semiconductor quantum dot qubits requires some form of spin-electric field interaction, typically as a micromagnet-induced field gradient. However, electron spins are known to couple to valley states in silicon [1], which could afford a new method for spin control without the need of a micromagnet or native spin-orbit interaction. Building on our recent result of electrical control of a valley qubit in a Si/SiGe double quantum dot [2], we show that the valley splitting can be tuned by 32 μeV with modest voltages on local gates. Using real-time spin relaxation measurements on a single electron in this device with a variable external field, we see evidence of spin-valley mixing signified by a “hot spot” with high spin relaxation below 500 mT. Additionally, we show our progress on implementing valley-mediated spin qubit operations.
[1] X. Hao, R. Ruskov, M. Xiao, C. Tahan, and H. W. Jiang, "Electron Spin Resonance and Spin-Valley Physics in a Silicon Double Quantum Dot", Nat. Comm. 5, 3860 (2014).
[2] N. E. Penthorn, J. S. Schoenfield, J. D. Rooney, L. F. Edge, and H. W. Jiang, “Two-axis quantum control of a fast valley qubit in silicon”, npj Quant. Inform., in press (2019).