I can explain digital logic down to the electron in a MOSFET, but I can't come close to the same with quantum computing. This newsletter is a journal of my quest to learn the fundamentals of quantum computing and explain them on a human level.

Welcome to the Quantum Edge newsletter. Join me in my year-long journey into the weirdness that is quantum computing.

Issue 4.0, Feb 27, 2025

Last week, I wrote about the mass of a subatomic particle. Mass, charge, and spin, as you may remember are the three main properties of subatomic particles. The values are listed in the top left of each box in the table in Figure 1, below. I ended the newsletter promising to define charge this week and spin next week.

Indirect Observation of Charge

Much of experimental Physics is about observing the affects of one thing on another rather than direct examination. Everything is too small to see so, like the Beachketball experiment in issue 2, physicists have to bounce particles off or each other to get scatter patterns or crash them into each other at high speed to break particles into pieces and record the smash patterns.

Experimental observations more than 100 years ago led to the discovery of the electron and the decision to say that an electron has a negative charge. In the late 1800s, scientists experimented cathode ray tubes. Their cathode ray tube was a sealed glass tube with most of the air removed. It had a wire going through each end of the tube, exposed at both the outside and the inside. so that electricity could be connected. Connecting the ends of the tube up to a battery would cause a glow. In 1897, J. J. Thompson surmised that the glow in the tube was caused by little particles, which he first called corpuscles, but later named them electrons.

In further experiments he observed that a magnet next to the tube caused the glow inside the tube to bend. As luck would have it, magnets had already been discovered, and someone had designated one side of the magnet as positive and the other as negative. The glowing in the tube bent toward the positive end of the magnet and away from the negative end. Thompson decided that since opposites attract, the stuff must be negatively charged.

What is a Charge

We all know about charging batteries and getting a charge out of a funny comedian, but the kind of charge that exists with subatomic particles is different. Batteries have “electric charge”, and subatomic particles have a property that is called “atomic charge.” The two are related but are not the same thing.

Electric charge refers to a bunch of electrons that have the potential to flow through a circuit and do some electrical work. That electrical work can be lighting up a room, calculating in a computer, or shocking you as you grab the doorknob.

Atomic charge is about particles attracting or repelling each other.

Atomic Charge

The effect that I mentioned earlier is that opposite charges are attracted to each other. Pluses and minuses are opposites, and they pull each other together somewhat like North and South poles of magnets. This effect is pretty easy to prove in a physics lab and the world has 100 or more years of proof that opposite particles attract.

An electron has a charge of -1. It is called negative because of the earlier experiment with a magnet and cathode ray tube. Electrons have a negative charge both on an electricity level and at the individual subatomic level. And, remember, an electron is an elementary particle. There is nothing smaller inside.

Protons in the atomic nucleus have a charge of +1. Protons, though, are composite particles made up of quarks. What about the charges of the quarks inside the proton? Quarks are elemental particles and they each do have a charge.

If you remember from last week’s beachketball analogy, a proton has three quarks inside: two up quarks and one down quark. An up quark has a charge of +2/3 while a down quark has a charge of -1/3. Add the charges of the three quarks (+2/3, +2/3, and -1/3) and you get a total combined charge of +1. Gluons don’t have a charge.*

Neutrons, the other particle that form atomic nuclei with protons, have a charge of zero, hence the name: a neutral tron, or neutron. The are made up of two down quarks and one up quark (-1/3, -1/3 and +2/3) for a total of zero thirds of a charge, or just zero.

If Plus and Minus Attract, Why Don’t They Stick?

If positive charged protons and negative charged electrons attract each other, why don’t they just cling to each other? Good question. After all, magnets, which we like to use as an analogy, will slam together and hold tight, but electrons don’t slam into and stick to protons under normal circumstances.

This is actually one of the original questions in quantum physics. 100 years ago, when Ernst Rutherford discovered the proton, this was the big question. The electron and proton clearly attract each other, but they don’t stick together. What gives?

100 years on and there is still only a vague answer.

The Answer in Another Thought Experiment

Last week, I described elemental particles as a point that can never be zoomed in on. I also talked about the particle’s sphere of influence which makes it act a bit bigger than it really is. In Figure 3, above, an electron is represented as a golf ball surrounded by a red sphere of influence.

That little “point”, the electron, I described is moving very fast. So fast, in fact, that depending on how you look at it, it may seem like a point, a wave, a very wiggly line or a small cloud.

Here’s a way of thinking about it: If you grab ahold of one end of a string and shake it around very fast, it starts to look more like a jumbled mess than a string. Or, if you put a set of wired earbuds into your pocket or a bag, they invariable come out as a tangled mess. that jumbled or tangled mess can be thought of as the sphere of influence.

The size and make up of that sphere of influence interacts with the sphere of influence of the atomic nucleus and keeps electrons mostly in their place. Again, with the caution that this is not what is really happening with electrons, but it is a decent way of imagining what is going on. That mess of string or earbud wire is essentially what keeps the electrons and protons from sticking together.

Quantum Particle Spin

Quantum computers perform their calculations based on the spin of quantum particles. Like the other labels in the quantum world, spin isn’t really about something spinning like a top. Spin is a property that quantum particles have, and the magic is that they can be in more than one spin state at the same time. Tune in next week as I jump into the quantum concept of spin.

In Summary…

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