In this, the last chapter in the ‘How Small Is It’ video book, we’ll cover quantum superposition and quantum entanglement. We’ll also finish the work on the double slit experiment we covered in our first chapter on ‘The Microscopic’. We’ll be using electron spin and polarized light in most of our examples. Beginning with light, we’ll cover exactly how polarization works. Then we’ll use it to illustrate how we know which slit light went through in the double slit experiment. This illustration will highlight the nature of quantum linear superposition. As part of this we’ll take a look at Schrodinger’s Cat. With superposition in hand, we’ll cover how these superposition states can become entangled across multiple particles. We’ll start with some classical behavior associated with water waves and spinning coins. Then, using electron spin, we’ll illustrate entanglement. We’ll follow that with Einstein’s problem with ‘spooky action at a distance’. We’ll cover several experiments both thought (from John Bell) and real as quantum physics progressed in its ability to manage the quantum world. We’ll see what a ‘ghost image’ is and how it was used to show Einstein was wrong. As part of this segment, we’ll cover the ‘Quantum Eraser’ experiment.
We’ll end with a look at Quantum Computers. Here we cover how electrons are controlled in such a way that they can be put into and taken out of a superposition state at will. And in addition, they can be managed into and out of entangled states. This ability enables quantum computing.}
Music: @00:00 Bach - Flute Concerto in B Flat, Adagio; conducted by Eckart Haupt; from the album Meditation: Classical Relaxation, 2010 @13:21 Puccini - La Bohéme Act II- Musette Waltz; Sofia Philharmonic Orchestra; from the album 100 Must-Have Italian Opera Highlights, 2014 @26:50 Svendsen - Romance in G; Miklos Szenthelyi; from the album Meditation: Classical Relaxation, 2010
We understand light as an electromagnetic wave.
The direction of the electric field is called the wave's linear polarity.
Here we see the polarity at different angles from a fixed reference.
It is also possible for the polarity to be rotating clockwise or counterclockwise around the line of motion.
These properties hold for the basic unit of light, the photon.
When light passes through a polarized lens,
the amount of light that makes it through depends entirely on the angle between the incoming light's polarization
and the polarization direction of the lens.
To see this, here are a couple of experiments you can do at home if you have three pairs of polarized glasses.
Photons leaving the background table have a wide variety of polarizations.
We start with a lens that only allows light polarization in the vertical direction to pass through.
All the other light is blocked.
We'll call this lens A.
If we bring a second lens, lens C, and orient it the same as the first,
all the light that passes through A passes through C.
But as we rotate lens C, we see that the amount of light passing through is going down.
By the time we reach 90 degrees, C is blocking all the light that passes through A.
Now if we bring in a third lens, lens B, and place it in between the first two and angle it at 45 degrees,
we see that light that could not make it through C before is now coming through.
In other words, lens B, designed to reduce the amount of light that reaches C,
actually enables more light to get through C.
To see what is happening here, we need to go down to the photon level.
Classically, we calculated the percentage of light that goes through a lens.
But a photon will go through or not go through.
It cannot be divided.
In quantum mechanics, it's the angle between the orientation of the photon's quantum state
and the orientation of the lens's polarization that provides the probability for passing through the lens.
In addition, the interaction between the lens and the photon
will change the orientation of the photon's state
to equal the orientation of the lens it passed through.
With this understanding, we can examine how light made it through lens C once we added lens B.
Here we have a number of photons with random polarizations
trying to pass through the vertically polarized lens A.
Some make it, some don't.
All the photons that pass through A have now been changed to have the quantum state vertical
to match the lens.
With this polarization, the probability of passing through lens C,
which is rotated 90 degrees from the vertical, is zero.
No light gets through C.
Now we introduce lens B, which is rotated 45 degrees from vertical.
We see that some of the vertically polarized photons coming through lens A
will pass through lens B.
In addition, the interaction between the photons and lens B
change the photon's quantum state to oriented at 45 degrees to match the lens.
This enables some of the photons that pass through lens B
to now pass through lens C.
The key takeaway here is that objects like lenses, crystals, electric fields, etc.
can and do modify the quantum states of the particles that encounter them.
