Sums and differences of product operators 211x2x+ 2lly2y=11 12+1112 zero-quantum cohere 2I1 2y (not observable) 211xI2x-211v2v=1112+I1I2 louble-quantum conerence 2I1xl2y+2I12x=I112-I1 (not observable) The single-element operators I* and I- correspond to a transition from the mz=-/2 to the mz =+12 state and back, resp., hence"raising" and"lowering operator". Products of three and more operators ble Only the operators Ix and ly represent observable magnetization. However, other terms like antiphase magnetization 2 I1x I2z can evolve into observable terms during the acquisition period Pictorial representations of product operators (cf. the paper in Progr:. NMR Spectrosc. by Sorensen et al.) coherences L,1 polarisation 2I28 Sums and differences of product operators 2 I1xI2x + 2 I1yI2y = I1 + I2 - + I1 - I2 + zero-quantum coherence 2 I1yI2x - 2 I1xI2y = I1 + I2 - - I1 - I2 + (not observable) 2 I1xI2x - 2 I1yI2y = I1 + I2 + + I1 - I2 - double-quantum coherence 2 I1xI2y + 2 I1yI2x = I1 + I2 + - I1 - I2 - (not observable) The single-element operators I+ and I- correspond to a transition from the mz = - 1 /2 to the mz = + 1 /2 state and back, resp., hence "raising" and "lowering operator". Products of three and more operators are also possible. Only the operators Ix and Iy represent observable magnetization. However, other terms like antiphase magnetization 2 I1x I2z can evolve into observable terms during the acquisition period. Pictorial representations of product operators (cf. the paper in Progr. NMR Spectrosc. by Sørensen et al.) aa aa aa aa aa aa aa aa ab ab ab ab ab ab ab ab ba ba ba ba ba ba ba ba bb bb bb bb bb bb bb bb Ix I1 z I2 z 2I I I +I 1 z 2 z 1 z 2 z Iy I I 1 x 2 z I I 1 y 2 z x x x x y y y y z z z z coherences polarisations