Lecture 17 - More on Initialization

Monday, 5/13/24 (week 7, lesson 1):

Take mid-quarter survey to let me know how the class is doing and your ideas for improvement both for this quarter and for future iterations. Anonymous and voluntary!
(Re-)Read lecture slides on Implementation of quantum computing, pp. 13-22
Read 7.3 (incl. all subsections) before your activity!

Last time we talked about using lasers to initialize our systems to a known state:

![[Physics CPE 345 Quantum Computing Lecture slides Week 6 Implementation of quantum computing 240513.pdf#page=13]]

Here if we look at:

![[Physics CPE 345 Quantum Computing Lecture slides Week 6 Implementation of quantum computing 240513.pdf#page=15]]

The Rabi Oscillations are how the two different lasers (pictured in red and blue) are turned on for different durations. Namely, if we leave the red on for longer, we get a closer superposition to $| 1 ⟩$ , and if it's blue more to $| 0 ⟩$ .

We can oscillate between the $| 1 ⟩$ and $| 0 ⟩$ states by going back and forth. We want to go anywhere on the bloch-sphere using these lasers. Specifically, the laser detuning; how far off we are; determines what phase around the z-axis we'll be in.

![[Physics CPE 345 Quantum Computing Lecture slides Week 6 Implementation of quantum computing 240513.pdf#page=16]]

See:

![[Physics CPE 345 Quantum Computing Lecture slides Week 6 Implementation of quantum computing 240513.pdf#page=17]]

The idea here is that:

Putting the $| c ⟩$ state into $| r ⟩$ creates a dipole between $| 1 ⟩$ and $| r ⟩$
This dipole adds extra potential energy if $| t ⟩$ wants to move to $| r ⟩$
When $| t ⟩$ moves, it moves to a way higher potential $B$ .
So if we have something in $| r ⟩$ then we take the dotted line, meaning $| t ⟩$ doesn't change. This is what we want.

Note that here we don't actually care about replicating $c P H A S E$ itself (see that we have too many negatives here), but we do want to see entaglement, which we absolutely fuckin goteem.