Abstract

Spin qubits in silicon are excellent candidates for scalable quantum information processing (QIP) [1] due to their long coherence times and the enormous investment in silicon MOS technology. I will discuss qubits based upon single phosphorus (P) dopant atoms in Si [2]. Projective readout of such qubits had proved challenging until single-shot measurement of a single donor electron spin was demonstrated [3] using a silicon single electron transistor (Si-SET) and the process of spin-to-charge conversion. The measurement gave readout fidelities > 90% and spin lifetimes T1 > 6 seconds [3], opening the path to demonstration of electron and nuclear spin qubits in silicon. Integration of an on-chip microwave transmission line enables single-electron spin resonance (ESR) of the P donor electron. We use this to demonstrate Rabi oscillations of the electron spin qubit, while a Hahn echo sequence reveals electron spin coherence times T2 > 0.2 ms [4]. We also achieve single-shot readout of the 31P nuclear spin (with fidelity > 99.8%) by monitoring the two hyperfine-split ESR lines of the P donor system. By applying (local) NMR pulses we can demonstrate coherent control of the nuclear spin qubit, giving a coherence time T2 > 60 ms [5]. Finally, I will discuss very recent experiments on single-atom qubits in isotopically enriched 28Si devices, in which the near elimination of the background 29Si nuclear spin bath allows for significantly longer spin coherence times, of order 1 second.

[1] D.D. Awschalom et al., Quantum Spintronics, Science 339, 1174 (2013). [2] B.E. Kane, A silicon-based nuclear spin quantum computer, Nature 393, 133 (1998). [3] A. Morello et al., Single-shot readout of an electron spin in silicon, Nature 467, 687 (2010). [4] J.J. Pla et al., A single-atom electron spin qubit in silicon, Nature 489, 541 (2012). [5] J.J. Pla et al., High-fidelity readout and control of a nuclear spin qubit in Si, Nature 496, 334 (2013).