Across the globe, physicists in academia and industry alike are competing to be the first to build a scalable universal quantum computer. Amongst the multitudes of quantum computing architectures, solid-state quantum processors based on spins in silicon are emerging as a strong contender. Silicon is an ideal material to host spin qubits: it supports long coherence times [1], has excellent prospects for scaling, and is ubiquitous in the semiconductor industry. While semiconductor spin qubits were proposed over two decades ago [2], it is only within the past few years that we have learned how to reliably fabricate and control multi-qubit devices in silicon.

In this seminar, I will describe our state-of-the-art four-qubit Si/SiGe quantum processor [3] and explain how we have overcome major barriers to realizing large-scale quantum computing in silicon. First, I will discuss charge control and spin-state readout in the device. Then, I will describe the use of an on-chip micromagnet to mediate electrically driven spin resonance [4-5]. Using this technique, we achieved site-selective qubit control with fidelities exceeding 99.9%. I will give an overview of our three primitive two-qubit gates—the decoupled-CZ gate [4], the resonant CNOT gate [5], and the resonant SWAP gate [6]—and discuss the limitations to control fidelities. Finally, I will show how these advances enable the development of large-scale quantum processors capable of complex quantum information processing.

References:
[1] Tyryshkin et al., Nature Mat. 11, 143 (2011)
[2] Loss and Divincenzo, Phys. Rev. A 57, 120 (1998)
[3] Sigillito et al., Phys. Rev. Applied 11, 061006 (2019)
[4] Watson et al., Nature 555, 633 (2018)
[5] Zajac, Sigillito, et al., Science 359, 439 (2018)
[6] Sigillito et al., npj Quantum Information 5, 110 (2019)