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.

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Issue 6.0, Mar 27, 2025

In today’s newsletter: Continuing the discussion on electron charge with some illustrations

I started the discussion on subatomic particle charge, back in Issue number 4. Today, I’m going to expand on the concept a bit. I ran across an animation from Wikipedia that does a pretty good job of showing the early experiment that proved electrons have a charge and started us on our way to quantum mechanics.

In the late 1890s*, glass tubes with electrodes were not an uncommon tool of the electrical experimenter. J. J. Thompson, credited with discovering and naming the electron, demonstrated that electrons in such a glass tube could be deflected by magnets or by an electric current.

Thompson evacuated most of the gas (air) out of the tube. He then applied current at electrode A. The grey vertical bars at B are two grounded aluminum plates with slits that were used to focus the beam. The Beam projected as a spot on the end of the bulb in area E. When Thompson connected a battery to the electrodes at D and C, the spot at E moved in the direction of the positive battery electrode. Thompson saw the same effect when placing a magnet cluse to the tube.

Other scientists had tried similar experiments prior to Thompson, but failed to show the same results. Thompson, however, was convinced (and proven right) that the experiment would work if more of the gas was evacuated out of the tube. With a strong enough of a vacuum, he was able demonstrate the effect and prove the existence of electrons.

The fact that either an electric field or a magnet could have the same effect led to the idea that electricity and magnetism are somehow connected. Today, we refer to the force as electromagnetism out of deference to that connection. Electromagnetism is one of the four fundamental forces of nature: gravity, electromagnetism, weak nuclear force, and strong nuclear force. We will at some point touch on all four, but not today.

Electron Beam Deflection in the Real World.

You are undoubtably reading this on some form of flat LCD (liquid crystal display) or LED (light emitting diode) display screen. However, up until the early part of this century, most television and computer screens were no more flat than the Earth is. The display screens were called cathode ray tubes (CRTs) and were based on or inspired by the experiments of Thompson. CRTs have the same basic components as Thompson’s 1890s vacuum tube:

• (A) A cathode generating an electron beam

• (B) A beam focuser

• (C/D) Electromagnets to move the beam around

• (E) A screen to see the beam

• All enclosed in a glass tube with the air removed

Back in the days before LCD and LED flat screens, TVs and computer monitors utilized this electron deflection property to make pictures on a TV “picture tube.” The electromagnet deflecting coils C/D move the electron beam across the screen in a zigzag pattern (Figure 2, F). The electron beam (shown in bright green in area F, called raster lines) moves across the screen based on the polarity of the electromagnet at C/D. After a pass across the screen, the cathode turns off, stopping the beam, and the magnetic deflectors change polarity so that the beam moves back to the right again (illustrated with the grey return lines).

The beam varies in intensity to create an image out of the combined set of raster lines. The viewing side of the tube is flattened for better picture representation and is painted with a florescent material. The florescent material glows briefly where the beam hits it. This whole process scans across the screen top to bottom about 60 times a second (50 times in many parts of the world). The florescent material glows just long enough to maintain the image between scans.

The first and last cathode ray tubes ever made have the same basic structure, as shown in Figure 3.

Is it a Magnet or a Particle?

This magnetic deflection process makes electrons seem a bit like super small magnets. They are not magnets, but magnetism and electricity are two parts of the same force. Magnets and electricity don’t just interact in a vacuum. They also affect each other in wires. If you spin a magnet inside of a coil of wire, electrons in the wire will move as an electric current. This process is at the heart of electric generators used to power our world. Conversely, if you run a current through a coil of wire surrounding a magnet, the magnet will spin and can be utilized as an electric motor.

Overlapping behaviors between magnets and electrons is where the idea of electron “spin” comes from. Electrons, in some ways, act like little spinning magnets. Over the last century physicists have determined that electrons don’t really spin. They just act like they do. They “spin” in one of two directions and always “spin” at a constant value. If electron spin were a physical motion, like a spinning top or ball, electrons would have spins of different speeds and some would be stopped, but electrons don’t slow down or stop. A spinning basketball will slow and eventually stop. An electron will not. I wish we had a different word for it, but we don’t so, “spin” it is.

Fun fact: Opposite magnetic poles are called North and South. Opposite battery terminals are called negative and positive. Opposite electron spins are called up and down. Fun fact number two: spin up and spin down for an electron still result in a negative charge for the particle. Weird, huh. More on that in a later issue.

I started my discussion of spin in Issue number 5. I will get back to it next week. In the mean time, reflect on the fact that, while CRTs were big, heavy and fragile, Thompson’s 1890’s experiments got us watching late night infomercials way sooner than if we had waited until the 21st century for LCDs to be cheap enough.

In Summary…

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