title: Enhancing the coherence of a spin qubit by operating it as a feedback loop that controls its nuclear spin bath.
abstract: In many realizations of electron spin qubits the dominant source of decoherence is the fluctuating nuclear spin bath of the host material. The slowness of this bath lends itself to a promising mitigation strategy where the nuclear spin bath is prepared in a narrowed state with suppressed fluctuations. Here, this approach is realized for a two-electron spin qubit in a GaAs double quantum dot and a nearly tenfold increase in the inhomogeneous dephasing time T₂* is demonstrated. Between subsequent measurements, the bath is prepared by using the qubit as a feedback loop that first measures its nuclear environment by coherent precession, and then polarizes it depending on the final state. This procedure results in a stable fixed point at a nonzero polarization gradient between the two dots, which enables fast universal qubit control.
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Bluhm
authors.forename: Sandra
authors.initials: S
authors.lastname: Foletti
authors.forename: Diana
authors.initials: D
authors.lastname: Mahalu
authors.forename: Vladimir
authors.initials: V
authors.lastname: Umansky
authors.forename: Amir
authors.initials: A
authors.lastname: Yacoby