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Ultrafast optical control of entanglement between two quantum-dot spins

Nature Physics volume 7, pages 223–229 (2011)Cite this article

Abstract

The interaction between two quantum bits enables the creation of entanglement, the two-particle correlations that are at the heart of quantum information science. In semiconductor quantum dots, much work has focused on demonstrating control over single spin qubits using optical techniques. However, optical control of two spin qubits remains a major challenge for scaling to a fully fledged quantum-information platform. Here, we combine advances in vertically stacked quantum dots with ultrafast laser techniques to achieve optical control of the entangled state of two electron spins. Each electron is in a separate InAs quantum dot, and the spins interact through tunnelling, where the tunnelling rate determines how rapidly entangling operations can be carried out. We achieve two-qubit gates with an interaction rate of 30 GHz, more than an order of magnitude faster than demonstrated in any other system so far. These results demonstrate the viability and advantages of optically controlled quantum-dot spins for multi-qubit systems.

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Figure 1: Sample structure.
Figure 2: Energy levels of the 2e system.
Figure 3: Optical spin pumping of the two-electron state.
Figure 4: Coherent control of the 2e spin state using two 13 ps pulses with a variable time delay.
Figure 5: Two-qubit phase gate.

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Acknowledgements

This work was supported by NSA/ARO, ARO MURI, DARPA and ONR.

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Authors and Affiliations

  1. Naval Research Laboratory, Washington, DC 20375, USA

    Danny Kim, Samuel G. Carter, Alex Greilich, Allan S. Bracker & Daniel Gammon

Authors
  1. Danny Kim
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  2. Samuel G. Carter
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  3. Alex Greilich
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  4. Allan S. Bracker
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Contributions

All authors were involved in writing the manuscript. D.K. was involved in all aspects. S.G.C. was involved with conceiving and carrying out the experiments, and analysing and modelling the data. A.G. was involved with sample development and characterization. A.S.B. was involved with sample fabrication, development and characterization. D.G. was involved with conceiving the experiment, sample development and data analysis.

Corresponding author

Correspondence to Daniel Gammon.

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The authors declare no competing financial interests.

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Kim, D., Carter, S., Greilich, A. et al. Ultrafast optical control of entanglement between two quantum-dot spins. Nature Phys 7, 223–229 (2011). https://doi.org/10.1038/nphys1863

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