Nature Commun. 2, 378 (2011)

Although semiconductor-based quantum computers exploiting NMR have the potential to achieve all-optical operation, the internuclear coupling exhibited by semiconductors is too weak. Now, through cross-polarization experiments with GaAs under light illumination, Atsushi Goto and co-workers in Japan have shown that light can be used to control nuclear spin–spin coupling strength and even semiconductor on/off switching in GaAs. First, they measured the temporal magnetization behaviour of 71Ga and 75As at 10 K using an optical-pumping double-resonance NMR system. When illuminated by infrared light from a Ti:sapphire laser, the magnetization of GaAs sample rapidly increased and then oscillated on a millisecond timescale. When the intensity of the pumping light was increased from 100 mW to 166 mW, the contact time changed from 3.1 ms to 0.8 ms. Using a damping oscillation model that takes the indirect scalar coupling into account, the researchers showed that the coupling became strong and extended its spatial interaction length to farther nuclei as the pump intensity was increased. Their findings encourage the development of semiconductor-based NMR quantum computers and introduce a variety of options for arranging qubits.