• Open Access

Robust Two-Qubit Gates for Donors in Silicon Controlled by Hyperfine Interactions

Rachpon Kalra, Arne Laucht, Charles D. Hill, and Andrea Morello
Phys. Rev. X 4, 021044 – Published 6 June 2014

Abstract

We present two strategies for performing two-qubit operations on the electron spins of an exchange-coupled pair of donors in silicon, using the ability to set the donor nuclear spins in arbitrary states. The effective magnetic detuning of the two electron qubits is provided by the hyperfine interaction when the two nuclei are prepared in opposite spin states. This can be exploited to switch SWAP operations on and off with modest tuning of the electron exchange interaction. Furthermore, the hyperfine detuning enables high-fidelity conditional rotation gates based on selective resonant excitation. The latter requires no dynamic tuning of the exchange interaction at all and offers a very attractive scheme to implement two-qubit logic gates under realistic experimental conditions.

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  • Received 11 December 2013

DOI:https://doi.org/10.1103/PhysRevX.4.021044

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Authors & Affiliations

Rachpon Kalra1, Arne Laucht1, Charles D. Hill2, and Andrea Morello1,*

  • 1Centre for Quantum Computation and Communication Technology, School of Electrical Engineering & Telecommunications, University of New South Wales, Sydney, New South Wales 2052, Australia
  • 2Centre for Quantum Computation and Communication Technology, School of Physics, University of Melbourne, Melbourne, Victoria 3010, Australia

  • *a.morello@unsw.edu.au

Popular Summary

Computers are getting faster and more powerful with time: According to Moore’s law, the number of transistors per chip is doubling approximately every 18 months. Current commercial computer chips pack over a billion transistors, each only 22 nanometers wide, corresponding to fewer than 100 silicon atoms. In this size regime, quantum mechanics starts to dictate the behavior of electronic devices. It may be possible to adapt the existing trillion-dollar semiconductor industry to pursue a revolutionary paradigm—quantum computing. We describe two realistic proposals to realize two-qubit quantum logic gates with the electron spin of phosphorus atoms in silicon, exploiting the presence of a controllable nuclear spin in each atom.

An excellent candidate for the building block of a quantum computer is the spin of a single atom’s electron or nucleus in silicon, which offers outstanding quantum-coherence lifetimes in a physical platform compatible with standard nanoelectronics fabrication. Recent breakthrough experiments have shown that ultrasmall silicon devices containing an individual phosphorus impurity atom can be used to store and elaborate one bit of quantum information. To continue along this exciting path, it is necessary to couple multiple phosphorus atoms in a controllable way and demonstrate quantum logic operations between pairs of qubits. The proposed quantum logic gate based on conditional resonant rotation necessitates a small, “always on” exchange interaction that does not require any tuning, drastically reducing the demands posed on fabrication as compared to prior proposals of donor-based gates. We show that high-fidelity operations can be performed while tolerating a rather wide range of distances between atoms: Although the qubits are single-atom objects, it will not be necessary to place them in the device with atomic precision.

Our work shows how to reliably pursue application of the outstanding coherence times and control fidelities of single-electron spin qubits in silicon to large-scale quantum-information processing.

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Vol. 4, Iss. 2 — April - June 2014

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