Dr Andrea Morello reported on the progress of a team led by University of New South Wales engineers and physicists which has developed a “single electron reader”, one of the key building blocks needed to make a quantum computer using silicon.
Quantum computers promise exponential increases in processing speed over today’s computers through their use of the “spin” or magnetic orientation of individual electrons to represent data in their calculations.
“Our device detects the spin state of a single electron in a single phosphorus atom implanted in a block of silicon. The spin state of the electron controls the flow of electrons in a nearby circuit,” said Dr Morello, the lead author of the paper entitled Single-shot readout of an electron spin in silicon, which was published recently in the journal Nature.
Single-shot readout of an electron spin in silicon
Andrea Morello1, J. J. Pla 1, F. A. Zwanenburg 1, K. W. Chan 1, K. Y. Tan 1, H. Huebl 1, M. Möttönen 1,3,4, C. D. Nugroho 1, C. Yang 2, J. A. van Donkelaar 2, A. D. C. Alves 2, D. N. Jamieson 2, C. C. Escott 1, L. C. L. Hollenberg 2, R. G. Clark 1, & A. S. Dzurak 1
1. Centre for Quantum Computer Technology, School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney NSW 2052, Australia
2. Centre for Quantum Computer Technology, School of Physics, University of Melbourne, Melbourne VIC 3010, Australia
3. Department of Applied Physics/COMP, Aalto University, P.O. Box 15100, 00076 Aalto, Finland
4. Low Temperature Laboratory, Aalto University, P.O. Box 13500, 00076 Aalto, Finland
We present the first demonstration of single-shot readout of an individual electron spin in a silicon nanostructure, with readout fidelity better than 90% and spin lifetime up to 6 s.
The electron spin of a donor in silicon is an excellent candidate for a solid-state qubit. It is known to have very long coherence and relaxation times in bulk , and several architectures have been proposed to integrate donor spin qubits with classical silicon microelectronics . However, controlling and manipulating single spins in silicon has proved challenging, and has hindered the measurement of single spins so far.
Here we show the first experimental proof of single-shot readout of an electron spin in silicon. This breakthrough has been obtained with a device consisting of implanted phosphorus donors, tunnel-coupled to a silicon Single-Electron Transistor (Si-SET), where the SET island is used as a reservoir for spin-to-charge conversion .
When an electron tunnels from the donor to the SET island, the SET current switches from zero to the maximum value. In the presence of a large external magnetic field that induces a Zeeman energy splitting of the donor spin states, the electron tunneling process becomes spin-dependent, and the spin of the electron can be inferred, in single-shot, from a fast measurement of the SET current.
Because of the exceptionally large charge transfer signal, we are able to measure the spin state of the electron on a < 10 microseconds scale, with readout fidelity better than 90%.
The spin lifetime (T1) is obtained by measuring the occurrence of excited spin states as a function of wait time between initialization and readout. We find a magnetic-field dependence T1-1 ∝ B5 consistent with that of phosphorus donors in silicon , and quantitatively close to the spin lifetimes measured by conventional spin resonance in bulk Si:P crystals.
We measured a record value of T1 ≈ 6 s at B = 1.5 T, the longest ever observed for single spins in solid state by electrical means.
Our experiment demonstrates for the first time the ability to perform a projective, single-shot measurement of an electron spin in silicon. The long spin lifetime and high readout fidelity confirm the suitability of spins in silicon as carriers of quantum information.
 A.M. Tyryshkin, S.A. Lyon, A.V. Astashkin, and A.M. Raitsimring, Phys. Rev. B 68, 193207 (2003).
 L.C.L. Hollenberg, A.D. Greentree, A.G. Fowler, and C.J. Wellard, Phys. Rev. B. 74, 045311 (2006).
 A. Morello et al., Phys. Rev. B 80, 081307(R) (2009).
 A. Morello et al., arXiv:1003.2679 (2010).
Andrea Morello, email@example.com