WKB method in quantum physics, Summaries of Quantum Physics

a quick summary of WKB method in quantum physics

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2025/2026

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Chap
9
WKB
V(x)
-
turning
points
ID
,
2D
or
3D
·
-
-
i
i
for
radial
parts
.
&
bound
state
energy
and
un
>
classical
region
Q
=
Prob(x)
tunneling
rates
where
is
higher
>
V
E
---------
(2)
=
A
etikx
k
=
vm(E
-
v)/t
V
of
vixs
not
constant
but
slowly
varying
4(x)
=
A(x)e[
P(x)
(x)
close
to
Ike
Similarly
,
if
>
E
4(x)
=
A
etkx
k
=
xm(V
-
E)/t
but
turning
points
require
special
treatment
.
-
pf3
pf4
pf5
pf8

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Chap 9

WKB

V(x) ↑

turning

points ID

, 2D^ or^ 3D

i

i

for

radial (^) parts.

&

bound state^ energy

and un >

classical region

Q =^ Prob(x)^

tunneling

rates

where is^ higher^

> V

E

↑(2)

= (^) A etikx (^) k= vm(E- (^) v)/t

V

of

vixs not^ constant^ but^ slowly varying

4(x)

= (^) A(x)e[

P(x)

↑ (x)^ close^ to^ Ike

Similarly

, if

> E

4(x)

= (^) A etkx^ k

= xm(V

  • E)/t

but

turning

points (^) require special

treatment.

9 ./ (^) E > V region ,^

classical

region

V()

= El

=

  • 4

P(x) = 25E-VA]

4(x)

= (^) A(x)eib(x)

[

=(A^

  • (^) JAP') ed

classical momentum

f

= [A"+ (^) ziq+^ [AP"

  • A(0) JeiP

=> A"+ 2iAp+^ iAP"

  • All

=

A

Re :^ A"-AIP-AE All

Im

=

2Ap

Ap"

= (^0) or (^) (AP)

= (^0)

=> A

= F p

C is^ a (^) const.

Assume

1 and

CP's

↑(x)

= []p(x)^

dx

absorb th into

S

Y(x)

=

p(x)

Sp()dx

~

14(F

9.^2

Tunneling

for

>V

p(x)

real

for

EXV

po (^) imaginary ,^

the (^) derivation (^) is the (^) same

4 (2)^

C

e

I-[ S/p(x) Ide

1

P(x)/

V(X)

considerA

E -

5 =^ -

--

  • > (^) F

O (^) A

4 (2)

= (^) A zikx

H(x)

= (^) Feikx

+Be-

[kx

k =^ v -^2 mE /h

transmission prob (^) =

in the^ tunneling region^

A

4 (2)^

SpIda^

I

  • S Idx

-e

IP()) +^

E

(p(x) /

If

the (^) harrier is^ high

and wide (^).^ 7)

C (^) musthe^ small^

She h

  • 200 =^ So (p()(dx

e. g.

2 Alpha (^) decay.

  • ze

↑ (^) conbomb

I -^ -- & potential

  • (^) ze

E

Vi ra Y

E

=

  • Vo -

E is^ the emitted &t energy

= -Es

de

= Eme (^) N-1 dr

let u=^1 nu

=

(- Ein )-

  • ]

for

VV

]

Z

=

= k^ , - - k2NY NE

k

, = (E)

N

= (^1).^ 980MeV

kz =

(

= 1.^ 485 fn

~ U

T =

2 the^ prob.

is e^ at

ar,

each (^) collision

: The^ mob

of

emission per

unit

-^18

time is^ e

28

Oh

--

lifeline

= (^) e

T

A

I

> E

in

region

2

(01px)(d =^

↑ (^2) da

(x)

=

  • (6) Ai() (^) + ↓Rise
  • > a

=

D

bo

in region

I

Spa (

with (^) plc =

A

↑()= 24(x) [Bei3(

  • (^) 2x)

+ Ce

  • 15 - 0x)

4p(x)

=

v

( 2x)xsm(

> (- 2x)

  • ]
A

F

=

v (

2x)

  • ·

=> (^) B =^ - jeiπ/D C^ =^ je^

i)

D

if

turning point^

not at^ x= 0 but at^ x=^22

Eg

9.^3

D 4 (0)^ = (^0) ·

. p()dx^

E = (^) n or (^) Jopdx =^ (n - = Nh eg , for half H-^ O. V(x) = Simwise xEO

p(x)

IMCE-Emwi)

MwN I x= E N ~

> ... Odd mode (x (^) p(x)dx= mw( dx =^ mux= E D 2w only

En =^ (2n - 1) &w^ =

(^1) , , (^) ... chw Eg

. (^4)

same

approaches for^ [

E

for- C by

or try ,

02 = 0 , +^ NA^

(note : (^) D =D' (^) or D^ =^ - ja (^) (d = (^) In-EI n =^1 , 2

Note:

Guoy Phase !!