Solution Manual for Modern Quantum Mechanics, 2nd Edition
Unlock the answers to every textbook problem with Solution Manual for Modern Quantum Mechanics, 2nd Edition, making studying more efficient and effective.
2Chapter One1.AC{D, B}=ACDB+ACBD,A{C, B}D=ACBD+ABCD,C{D, A}B=CDAB+CADB, and{C, A}DB=CADB+ACDB. Therefore−AC{D, B}+A{C, B}D−C{D, A}B+{C, A}DB=−ACDB+ABCD−CDAB+ACDB=ABCD−CDAB= [AB, CD]In preparing this solution manual, I have realized that problems 2 and 3 in are misplacedin this chapter. They belong in Chapter Three. The Pauli matrices are not even defined inChapter One, nor is the math used in previous solution manual.– Jim Napolitano2.(a)Tr(X) =a0Tr(1) +Tr(σ)a= 2a0sinceTr(σ) = 0. AlsoTr(σkX) =a0Tr(σk) +Tr(σkσ)a=12Tr(σkσ+σσk)a=δkTr(1)a= 2ak. So,a0=12Tr(X) andak=12Tr(σkX).(b) Just do the algebra to finda0= (X11+X22)/2,a1= (X12+X21)/2,a2=i(−X21+X12)/2, anda3= (X11−X22)/2.3.Since det(σ·a) =−a2z−(a2x+a2y) =−|a|2, the cognoscenti realize that this problemreally has to do with rotation operators. From this result, and (3.2.44), we writedetexp±iσ·ˆnφ2= cosφ2±isinφ2and multiplying out determinants makes it clear that det(σ·a) = det(σ·a). Similarly, use(3.2.44) to explicitly write out the matrixσ·aand equate the elements to those ofσ·a.With ˆnin thez-direction, it is clear that we have just performed a rotation (of the spinvector) through the angleφ.4.(a)Tr(XY)≡