Persistent Narrowing of Nuclear-Spin Fluctuations in InAs Quantum Dots Using Laser Excitation

We demonstrate the suppression of nuclear-spin fluctuations in an InAs quantum dot and measure the timescales of the spin narrowing effect. By initializing for tens of milliseconds with two continuous wave diode lasers, fluctuations of the nuclear spins are suppressed via the hole-assisted dynamic nuclear polarization feedback mechanism. The fluctuation narrowed state persists in the dark (absent light illumination) for well over 1 s even in the presence of a varying electron charge and spin polarization. Enhancement of the electron spin coherence time (T2*) is directly measured using coherent dark state spectroscopy. By separating the calming of the nuclear spins in time from the spin qubit operations, this method is much simpler than the spin echo coherence recovery or dynamic decoupling schemes. Published in Physical Review Letters, v108 n18 article ID 187401, 1 May 2012. Prepared in cooperation with the H. M. Randall Laboratory of Physics, The University of Michigan, Ann Arbor and the Department of Physics, The University of California San Diego, La Jolla. Sponsored in part by AFOSR and DARPA.