QMGreensite_merged

The operators have physical interpretations; for example,

E¼I^ S^ þI^ S^ þI^ S^ þI^ S^ ½ 2 : 219 Š

denotes equal populations of all energy levels, and

Iz¼^12 I^ S^ þI^ S^ 
I^ S^ 
I^ S^



½ 2 : 220 Š

denotes equal polarization across the two single-quantum transitions of
theIspin.

IaSa

IbSa

I

a IbSb

IbS–

IaS+

IaS–

b IbS+

I–Sa

I+Sa

I–Sb

I+Sb

c

I–S+

e

I–S– I+S+

d

I+S–

aSb

FIGURE 2.4 Single-transition-basis operators for IS spin system.
(a) Populations, (b) S-spin and (c) I-spin single-quantum coherences,
(d) double-quantum coherences, and (e) zero-quantum coherences.

2.7 PRODUCTOPERATORFORMALISM 83