- #1
The Head
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- 2
Homework Statement
Using (x,p) = i (where x and p are operators and the parentheses around these operators signal a commutator), show that:
a)(x^2,p)=2ix AND (x,p^2)=2ip
b) (x,p^n)= ixp^(n-1), using your previous result
c)evaluate (e^ix,p)
Homework Equations
For operators, in general:
(ab,c)=a(b,c)+(a,c)b
(a,bc)=(a,b)c + b(a,c)
The Attempt at a Solution
I have no trouble showing (a):
(x^2,p)=x(x,p)+(x,p)x=x(i) + i(x)=2ix
Same general strategy for (x,p^2)
In (b), I get lost when trying to apply the result I have already found. My attempt:
(x,p^n)=(x,p*p^(n-1)=(x,p)p^(n-1)+p(x,p^(n-1))=ip^(n-1) + p(x,p^(n-1))
I don't know where to go from here. I have tried pulling out more factors of p from the second term, but that gets me no where (at least from what I can see). I have also just played around a lot with the commutator, even starting from the end:
ixp^(n-1)=(x,p)p^(n-1)= xp^n - pxp^(n-1), but again, after this, whichever path I take doesn't seem to be fruitful.
Thanks!