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Single-Photon Atomic Cooling - Raizen Lab - The University of ...

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Following the same logic leads to a similar equation for the second expectation<br />

value<br />

one finds<br />

〈 F · I〉 = F 2 + I2 − J2 . (2.27)<br />

2<br />

If these terms are collected and evaluated in the coupled basis |I,J,F,Fz〉<br />

F(F + 1) − I(I + 1) + J(J + 1)<br />

gF = gJ<br />

+gI<br />

2F(F + 1)<br />

F(F + 1) + I(I + 1) − J(J + 1)<br />

.<br />

2F(F + 1)<br />

(2.28)<br />

This still leaves the problem <strong>of</strong> determining gJ and gI. <strong>The</strong> latter<br />

accounts for the complex structure <strong>of</strong> the nucleus and so its value is found<br />

experimentally. <strong>The</strong> value <strong>of</strong> gJ, however, can be found in a manner very<br />

similar to that used to find gF, the difference being that one must consider<br />

the coupling between S and L and take the projection <strong>of</strong> these vectors along<br />

J. <strong>The</strong> result is<br />

gJ = gL<br />

J(J + 1) − S(S + 1) + L(L + 1)<br />

+gS<br />

2J(J + 1)<br />

J(J + 1) + S(S + 1) − L(L + 1)<br />

,<br />

2J(J + 1)<br />

(2.29)<br />

where gS and gL are the electron spin and electron orbital “g-factors.”<br />

<strong>The</strong> value <strong>of</strong> each <strong>of</strong> the “g-factors” considered above are listed in Ta-<br />

ble 2.3. <strong>The</strong> value <strong>of</strong> gS is known extraordinarily well and its measurement [52]<br />

has served as an important test <strong>of</strong> QED theory [53]. <strong>The</strong> value <strong>of</strong> gL quoted<br />

is derived from<br />

gL ≈ 1 − me<br />

37<br />

mnuc<br />

(2.30)

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