![]() Typically, measurements of the coherent electron-spin precession involve averaging over many experimental runs, and thus over many Overhauser field configurations. Under typical experimental conditions, this so-called ‘Overhauser field’ has a random magnitude and direction. Through the hyperfine interaction, an electron spin in a GaAs quantum dot is subjected to an effective magnetic field produced by the nuclear spins. Understanding the dynamics of this system is also of great fundamental interest 11, 12. To further advance spin-based quantum computing, it is vital to mitigate decoherence due to the interaction of the electron spin with the spins of nuclei of the host material. The promise of quantum-dot spin qubits as a solid-state approach to quantum computing is demonstrated by the successful realization of initialization, control and single-shot readout of electron-spin qubits in GaAs quantum dots using optical 6, magnetic 7 and fully electrical 8, 9, 10 techniques. Using a multiple-pulse Carr–Purcell–Meiboom–Gillecho sequence, the decoherence time can be extended to more than 200 μs, an improvement by two orders of magnitude compared with previous measurements 1, 2, 5. This behaviour was recently predicted 3, 4, and can, as we show, be quantitatively accounted for by a semiclassical model for the dynamics of electron and nuclear spins. At lower fields, the echo first collapses, but then revives at times determined by the relative Larmor precession of different nuclear species. At fields above a few hundred millitesla, the coherence time measured using a single-pulse spin echo is 30 μs. Here, we show that coherence in such devices can survive much longer, and provide a detailed understanding of the measured nuclear-spin-induced decoherence. For electrons in gate-defined GaAs quantum dots, spin-echo measurements have revealed coherence times of about 1 μs at magnetic fields below 100 mT (refs 1, 2). ![]() In many types of electron-spin qubits, the primary source of information loss is decoherence due to the interaction with nuclear spins of the host lattice. Qubits, the quantum mechanical bits required for quantum computing, must retain their quantum states for times long enough to allow the information contained in them to be processed.
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