When considering the combined state of two spin-1/2
particles, they can have a total spin of either one (if the spins are aligned) or zero (if the spins are anti-aligned). The latter of these possibilities is known as the singlet configuration. The precise
quantum state is
1/sqrt(2) (|+-> - |-+>)
using the
ket notation, where the first element of the ket represents the z-component of the spin of the first particle, and the second element the z-component of the second particle.
Compare
triplet