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Voltage Switching Technique for Detecting Nuclear Spin Polarization in a Quantum Dot

We have introduced a source–drain voltage switching technique for studying nuclear spins in a vertical double quantum dot. Switching the source–drain voltage between the spin-blockade state and the zero-bias Coulomb blockade state can tune the energy difference between the spin singlet and triplet, and effectively turn on/off the hyperfine interaction. Since the change in the nuclear spin state affects the source–drain current, nuclear spin properties can only be detected by transport measurement. Using this technique, we have succeeded in measuring the timescale of nuclear spin depolarization. Furthermore, combining this technique and an RF ac magnetic field, we successfully detected continuous-wave NMR signals of 75As, 69Ga, and 71Ga, which are contained in a quantum dot.