Download PHYS6520 Quantum Mechanics II Spring 2013 HW #5

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Transcript
PHYS6520
Quantum Mechanics II
Spring 2013
HW #5
Due to the grader at 5pm on Friday 5 Apr 2013
(1) Consider scattering in one dimension x from a potential V (x) localized near
√ x = 0. The
initial state is a plane wave coming from the left, that is φ(x) ≡ �x|i� = eikx / 2π
(a) Find the scattering Green’s function G(x, x� ), defined in one dimension analogously
with (6.2.3). You only need concern yourself with scattering from the past to the future.
(b) Take the special case of an attractive δ-function potential, namely
h̄2
V (x) = −γ
δ(x)
2m
with
γ>0
Use the Lippman-Schwinger Equation to find the outgoing wave function ψ(x) ≡ �x|ψ (+) �.
(c) Determine the transmission and reflection coefficients T (k) and R(k), defined as
ψ(x) = T (k)φ(x) for x > 0
and
e−ikx
ψ(x) = φ(x) + R(k) √
for x < 0
2π
Show that |T |2 + |R|2 = 1, as must be the case.
(d) Confirm that you get the same result by using grade-school quantum mechanics and
matching right and left going waves on the left with a right going wave on the right at x = 0.
You’ll need to integrate the Schrödinger equation across x = 0 to match the derivatives.
(e) We showed last semester that this potential has one, and only one, bound state. Show
that your results for T (k) and R(k) have bound state poles at the expected positions when
k is treated as a complex variable.
(2) Modern Quantum Mechanics, Problem 6.3
(3) Modern Quantum Mechanics, Problem 6.4. I recommend Chapter 10 of the NIST Digital
Library of Mathematical Functions at http://dlmf.nist.gov/ as a good online reference for the
properties of spherical Bessel functions.
(4) Modern Quantum Mechanics, Problem 6.12