Spin is a fundamental property of all elementary particles. Classically it can be viewed as a tiny magnetic moment, but a measurement of an electron spin along the direction of an external magnetic field can have only two outcomes1: parallel or anti-parallel to the field. This discreteness reflects the quantum mechanical nature of spin. Ensembles of many spins have found diverse applications ranging from magnetic resonance imaging2 to magneto-electronic devices3, while individual spins are considered as carriers for quantum information. Read-out of single spin states has been achieved using optical techniques4, and is within reach of magnetic resonance force microscopy5. However, electrical read-out of single spins6,7,8,9,10,11,12,13 has so far remained elusive. Here we demonstrate electrical single-shot measurement of the state of an individual electron spin in a semiconductor quantum dot14. We use spin-to-charge conversion of a single electron confined in the dot, and detect the single-electron charge using a quantum point contact; the spin measurement visibility is ∼65%. Furthermore, we observe very long single-spin energy relaxation times (up to ∼0.85 ms at a magnetic field of 8 T), which are encouraging for the use of electron spins as carriers of quantum information.
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We thank D. P. DiVincenzo, H. A. Engel, T. Fujisawa, V. Golovach, Y. Hirayama, D. Loss, T. Saku, R. Schouten and S. Tarucha for technical support and discussions. This work was supported by the DARPA-QUIST programme, the ONR, the EU-RTN network on spintronics and the Dutch Organisation for Fundamental Research on Matter (FOM).
The authors declare that they have no competing financial interests.
Scanning electron micrograph of the device, showing all the Ti-Au gates on top of a GaAs/Al0.27Ga0.73As heterostructure. (PDF 91 kb)
Tuning the quantum dot into the spin read-out configuration. (PDF 461 kb)
Setting the injection threshold. (PDF 33 kb)
Measurement of the spin-relaxation time as in Fig. 3c, but at different magnetic fields. (PDF 14 kb)
Legends to supplementary Figures1 - 4. (DOC 31 kb)
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Elzerman, J., Hanson, R., Willems van Beveren, L. et al. Single-shot read-out of an individual electron spin in a quantum dot. Nature 430, 431–435 (2004). https://doi.org/10.1038/nature02693
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