  Measurement devices could benefit from entangled correlations to yield a
measurement sensitivity approaching the physical Heisenberg limit. Building
upon previous magnetometric work using pseudo-entangled spin states in
solution-state NMR, we present two conceptual advancements to better prepare
and interpret the pseudo-entanglement resource as well as the use of a 13-spin
cat state to measure the local magnetic field with a sensitivity beyond the
standard quantum limit.
