Reliable preparation, manipulation and measurement protocols are necessary to exploit a physical system as a quantum bit1. Spins in optically active quantum dots offer one potential realization2,3 and recent demonstrations have shown high-fidelity preparation4,5 and ultrafast coherent manipulation6,7,8. The final challenge—that is, single-shot measurement of the electron spin—has proved to be the most difficult of the three and so far only time-averaged optical measurements have been reported9,10,11,12. The main obstacle to optical spin readout in single quantum dots is that the same laser that probes the spin state also flips the spin being measured. Here, by using a gate-controlled quantum dot molecule13,14,15, we present the ability to measure the spin state of a single electron in real time via the intermittency of quantum dot resonance fluorescence12,16. The quantum dot molecule, unlike its single quantum dot counterpart, allows separate and independent optical transitions for state preparation, manipulation and measurement, avoiding the dilemma of relying on the same transition to address the spin state of an electron.
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This work was supported by grants and funds from the University of Cambridge, EPSRC Science and Innovation Awards, the QIPIRC and EPSRC grant number EP/ G000883/1. Y.Z. is supported by the A. v. Humboldt Foundation and LGFG. We thank A. Imamoglu, X. Marie, T. Amand, D. Gammon and D. Steel for discussions.
The authors declare no competing financial interests.
This file contains Supplementary Information comprising Calculation and differential transmission spectroscopy of quantum dot molecule states and optical transitions, Measurement of the optically induced spin-flip rate for the T+3/2 transition, and a Discussion of fidelity calculation. Supplementary Figures 1-3 with legends and additional references are also included. (PDF 1805 kb)
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Vamivakas, A., Lu, CY., Matthiesen, C. et al. Observation of spin-dependent quantum jumps via quantum dot resonance fluorescence. Nature 467, 297–300 (2010). https://doi.org/10.1038/nature09359
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