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Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization

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One fundamental requirement for quantum computation is to carry out universal manipulations of quantum bits at rates much faster than the qubit’s rate of decoherence. Recently, fast gate operations have been demonstrated in logical spin qubits composed of two electron spins where the rapid exchange of the two electrons permits electrically controllable rotations around one axis of the qubit. However, universal control of the qubit requires arbitrary rotations around at least two axes. Here, we show that by subjecting each electron spin to a magnetic field of different magnitude, we achieve full quantum control of the two-electron logical spin qubit with nanosecond operation times. Using a single device, a magnetic-field gradient of several hundred millitesla is generated and sustained using dynamic nuclear polarization of the underlying Ga and As nuclei. Universal control of the two-electron qubit is then demonstrated using quantum state tomography. The presented technique provides the basis for single- and potentially multiple-qubit operations with gate times that approach the threshold required for quantum error correction.

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Figure 1: Pump and measurement schemes.
Figure 2: Build-up of a gradient with two different pumping cycles.
Figure 3: Comparison of the gradient and the average nuclear field.
Figure 4: State tomography and universal gate.

Change history

  • 27 October 2009

    In the version of this Article originally published online, in the final paragraph, the value of the coherence time should have been 100 μs, and the final author name in reference 28 should have been Cywinski, L., Witzel, W. M. & Das Sharma, S. These changes have been made in all versions of the Article.


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We thank C. Barthel, M. Gullans, B. I. Halperin, J. J. Krich, M. D. Lukin, C. M. Marcus, D. J. Reilly, M. Stopa and J. M. Taylor for discussions. We acknowledge financial support from ARO/IARPA, the Department of Defense and the National Science Foundation under award number 0653336. This work was carried out in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the National Science Foundation under NSF award no. ECS-0335765.

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Authors and Affiliations



S.F. fabricated the samples. H.B developed the measurement software. Electron-beam lithography and sample growth were carried out by D.M. and V.U., respectively. S.F., H.B. and A.Y. planned and carried out the experiment, analysed the data and co-wrote the paper.

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Correspondence to Amir Yacoby.

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Foletti, S., Bluhm, H., Mahalu, D. et al. Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization. Nature Phys 5, 903–908 (2009).

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