A programmable two-qubit quantum processor in silicon*

Building small-scale quantum computers where initialisation, readout, single and two-qubit gates are combined to perform computation result in new challenges such as qubit cross talk, state leakage, and calibration. Here, we overcome these challenges to demonstrate a programmable two-qubit quantum processor using single electron spins in silicon [1]. In the natural Si/SiGe double quantum dot device, single qubit gates (2 MHz) with fidelities > 98% are achieved using electric dipole spin resonance [2] while a two-qubit gate (5-20 MHz) is realised using the exchange coupling between the two electron spins [3]. We characterise entanglement in our processor by performing quantum state tomography on Bell states where we achieve state fidelities between 85-90% and concurrences between 73-80%. Finally, we demonstrate the programmability of the processor by successfully running both the Deutsch-Jozsa and the Grover search algorithms.
[1] T. F. Watson et al., arxiv: 1708.04214 (2017)
[2] E. Kawakami et al., Nature Nanotechnology 9, 666 (2014)
[3] M. Veldhorst et al., Nature 526, 410 (2015)