Special CPM Seminar

Single-atom spin qubits in silicon

Andrea Morello

Centre for Quantum Computation & Communication Technology
University of New South Wales

A phosphorus donor in silicon is, almost literally, the equivalent of a hydrogen atom in vacuum. It possesses electron and nuclear spins 1/2 which act as natural qubits [1], and the host material can be isotopically purified to be almost perfectly free of other spin species, ensuring extraordinary coherence times (~180 s) [2].

I will present the current state-of-the-art in silicon quantum information technologies, a progress that started with the single-shot readout of the spin state of an electron bound to a single P atom [3]. This method was subsequently integrated with a broadband, on-chip microwave transmission line [4] to deliver coherent electromagnetic pulses and perform arbitrary rotations of the electron spin, thereby demonstrating the first single-atom spin qubit in silicon [5].

The ³¹P nuclear spin can also be read out electrically - in single-shot and with fidelity > 99.8% - from a measurement of electron spin resonance, and coherently manipulated with radiofrequency pulses [6]. This yields a nuclear spin qubit in solid state with operation and readout fidelities comparable with those of ion trap systems

Finally, I will discuss current efforts to couple multiple donor qubits through the exchange interaction and perform entangling quantum logic gates. The ability to control the state of the ³¹P nuclear spin greatly simplifies the implementation of CNOT and SWAP gates, and allows for high-fidelity two-qubit operations without the requirement of atomic-precision in the donor locations

[1] B. Kane, Nature 393, 133 (1998)
[2] M. Steger et al., Science 336, 1280 (2012)
[3] A. Morello et al., Nature 467, 687 (2010)
[4] J. Dehollain et al., Nanotechnology 24, 015202 (2013)
[5] J. Pla et al., Nature 489, 541 (2012)
[6] J. Pla et al., Nature 496, 334 (2013)