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