Ultrafast optical spin echo in a single quantum dot


Many proposed photonic quantum networks rely on matter qubits to serve as memory elements1,2. The spin of a single electron confined in a semiconductor quantum dot forms a promising matter qubit that may be interfaced with a photonic network3. Ultrafast optical spin control allows gate operations to be performed on the spin within a picosecond timescale4,5,6,7,8,9,10,11,12,13,14, orders of magnitude faster than microwave or electrical control15,16. One obstacle to storing quantum information in a single quantum dot spin is the apparent nanosecond-timescale dephasing due to slow variations in the background nuclear magnetic field15,16,17. Here we use an ultrafast, all-optical spin echo technique to increase the decoherence time of a single quantum dot electron spin from nanoseconds to several microseconds. The ratio of decoherence time to gate time exceeds 105, suggesting strong promise for future photonic quantum information processors18 and repeater networks1,2.

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Figure 1: Experimental set-up for optical single-spin manipulation and detection.
Figure 2: Experimental demonstration of spin echo and single-spin dephasing.
Figure 3: Measurement of T2 using spin echo.
Figure 4: Magnetic field dependence of T2.


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This work was supported by the National Institute of Information and Communications Technology (NICT Japan), the Ministry of Education, Culture, Sports, Science and Technology (MEXT Japan), the National Science Foundation (CCF0829694), the National Institute of Standards and Technology (60NANB9D9170), the Special Coordination Funds for Promoting Science and Technology and the State of Bavaria. We thank T. Steinl, A. Wolf and M. Emmerling for their assistance with sample fabrication. P.L.M. was supported by a David Cheriton Stanford Graduate Fellowship.

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C.S., M.K., and S.H. grew and fabricated the sample. D.P., K.D.G. and P.L.M. carried out the optical experiments. B.F. wrote the data acquisition software. T.D.L. provided theoretical analysis and guidance. Y.Y. and A.F. guided the work. D.P. wrote the manuscript with input from all authors.

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Correspondence to David Press.

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Press, D., De Greve, K., McMahon, P. et al. Ultrafast optical spin echo in a single quantum dot. Nature Photon 4, 367–370 (2010). https://doi.org/10.1038/nphoton.2010.83

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