14. Quantum Dynamics (continued)

MIT 8.05 Quantum Physics II, Fall 2013
Instructor: Barton Zwiebach

In this lecture, the professor talked about translation operator, definition and basic properties of coherent states, time evolution and uncertainties, coherent states in the energy basis, general coherent states and time evolution, etc.

License: Creative Commons BY-NC-SA

[leonardoalanis]

Like, I could cry of how beautiful this lecture was.

[woodandgears]

Cc fixes:
2:16 different versions
3:24 "the phase", not face
14:01 the bra would be
28:47 use them for other bound states
29:44 where does the term coherent arise, and why does it cohere when you translate it
30:44 energy eigenstates - you super-pose two energy eigenstates
37:01 "exposition" should be "X position"
52:44, then you have the annihilators
1:01:11 to be true for any type of commutator
1:20:00 bra alpha

[zphuo]

@12:00 Define f(t) ≡ e^(tA)Be^(−tA) and calculate the first few derivatives of f(t) evaluated at t = 0. Then use Taylor expansions. It is Hardamard Lemma. So e^ABe^(−A) = B+ [A, B] + (1/2!)[A, [A, B]] + (1/3!)[...

[shreyashbhattacharjee]

At around 53:00, the professor mentions "the anhillator killing the vacuum". I understand that he refers to the zero state, but why use the word "vacuum"? Can somebody explain why this terminology has been used? What does Vacuum mean in this context?

[ONS]

When that poisson distribution showed up that blowed my mind so hard that i literally bursted out 'oh fk'

[davidhand]

I'm having an idiot moment about T_x0 = exp(-ipx/h bar) as an operator. Can someone please tell me what T_x0 psi is? Where do I put the psi in exp(-ipx/h bar)?

[jasonyao]

8:57
Btw for anyone who somehow never learnt this “Baker House doorbell” thing
This is the formula:
exp(X)exp(Y)=exp(Z)
where Z = X+ Y + [X, Y]/2+[X, [X, Y]]/12-[Y, [X, Y]]/12+…

[passerby]

Did anyone figure out why it's a Poisson distribution?

[yyc]

1:13:38 I didn't quite understand why Prof. Zwiebach generalized the α to be the complex number. Why can't we just keep it real?

[DatTran]

first video in 8.04 spring 2013: about 1, 5 milion views
now: almost 15 thousands views.
Wow people are actually giving up maybe because it's too hard for what they can ever imagine