Randomized Benchmarking in a Si/SiGe Triple-Dot Decoherence-Free Subsystem

We demonstrate single-qubit randomized benchmarking of an exchange-only quantum-dot qubit. The qubit is implemented using an array of three electron spins in three undoped accumulation-mode quantum dots fabricated from an isotopically enhanced Si/SiGe heterostructure [1]. The three spins form a decoherence-free subsystem with encoded universal control using the exchange interaction [2], for which Clifford operators are composed of 1 to 4 sequential, voltage-controlled exchange evolutions of calibrated strength. Symmetric pulsing using an inter-dot exchange gate reduces sensitivity to charge noise [3]. We find that at zero magnetic field, charge noise nevertheless contributes significantly to gate errors, with additional errors due to pulse imperfections and spurious magnetic field gradients. Errors as low as 1\% have been obtained for single qubit randomized benchmarking using only the exchange interaction for qubit rotations. \newline [1] M.G. Borselli et al., Nanotechnology 26, 375202 (2015)\newline [2] K. Eng et al., Sci. Adv. 1, e1500214 (2015)\newline [3] M.D. Reed et al., Phys. Rev. Lett. 116B, 110402 (2016)