  The extension of the spin coherence times is a crucial issue for quantum
information and quantum sensing. In solid state systems, suppressing noises
with various techniques have been demonstrated. On the other hand, an
electrical control for suppression is important toward individual controls of
on-chip quantum information devices. Here we show the electrical control for
extension of the spin coherence times of 40 nm-deep ion-implanted single
nitrogen vacancy center spins in diamond by suppressing magnetic noises. We
applied 120 V DC across two contacts spaced by 10 micrometers. The spin
coherence times, estimated from a free-induction-decay and a Hahn-echo decay,
were increased up to about 10 times (reaching 10 microseconds) and 1.4 times
(reaching 150 microseconds), respectively. From the quantitative analysis, the
dominant decoherence source depending on the applied static electric field was
elucidated. The electrical control for extension can deliver a sensitivity
enhancement to the DC sensing of temperature, pressure and electric (but not
magnetic) fields, opening a new technique in solid-state quantum information
devices.
