  Scalar atomic magnetometers have many attractive features but their
sensitivity has been relatively poor. We describe a Rb scalar gradiometer using
two multi-pass optical cells. We use a pump-probe measurement scheme to
suppress spin-exchange relaxation and two probe pulses to find the spin
precession zero crossing times with a resolution of 1 psec. We realize magnetic
field sensitivity of 0.54 fT/Hz$^{1/2}$, which improves by an order of
magnitude the best scalar magnetometer sensitivity and surpasses the quantum
limit set by spin-exchange collisions for a scalar magnetometer with the same
measurement volume operating in a continuous regime.
