Quantum computing is one of the first great technologies of the 21st century, but the details are still shrouded in mystery. I can explain conventional digital computing down to the electron in a MOSFET, and with this newsletter, I have made it my mission to do the same for quantum computing.

Welcome to the Quantum Edge newsletter. Here you will read about the physics, chemistry, and all sciences that create the foundation for quantum computing. Join me in my quest to translate the mysteries of the quantum world to the language of the dinner table and the coffee shop.

In today’s newsletter: Transmons: Qubits Going from Research to Implementation, and how to talk and listen to qubits

Last week I wrote about trapping a single electron and using electrons as qubits. I caveated the choice with: “I mostly think and write in terms of electrons as qubits because they are (or were when I started writing this) the most common particle used as a qubit.“ I missed the boat a bit on that one. Single electron qubits are one of the options and trapped electrons are showing promise in R&D settings. They are not, however, the most commonly used type of qubit.

A better justification for focusing on electrons would be: “I mostly think and write in terms of electrons as qubits because they are a) one of the particles that can be used as a qubit, b) familiar to me because of my electronics background, and c) can be exploited and used as a qubit on an individual scale.” I’ll go with that.

The eventual “most common type of particle used as a qubit” is not settled yet. However, IBM and Google both use devices called transmons as their qubits. Transmons are easier to create and much easier to create in sets on a chip than are trapped electrons. Transmons are often fabricated in a semiconductor together with the microwave network for communications. They do have problems with scaling up the number of qubits on a chip and they aren’t the most stable of qubits, but they work and are currently more stable than a lot of other options, so they deserve a little explanation.

“Transmon” is a shortened version of “transmission line shunted plasma oscillation qubit.“ Goodness. It requires supercooling to get the qubit element down to superconducting temperatures. They operate at just a few tenths to hundredths of a degree K above absolute zero. Contrary to my statement in the prior issue about trapped electron qubits, transmons are the most prevalent type of qubits in large superconducting quantum processors.

Transmons come in the form of a very small circuit (this is going to be another mouthful. Sorry) that combines a non-linear inductor and a capacitor to create a small charge field. They use an architecture called a Josephson Junction, which is constructed of two superconducting materials separated by a very thin insulator with a capacitor in parallel.

The result is a small charge field that can be manipulated with microwaves in the 3–6 GHz range. Each qubit requires a waveguide to direct the microwave energy at it. The charge field operates under the same quantum properties as a single electron qubit.

A lot of things can be used to form a qubit. The important message is that “qubit” is more a way a thing acts than it is a thing. When used as a qubit, a transmon is effectively equal to a trapped particle qubit. Today, transmons are easier to build and manipulate at scale, but that may not be the last word in qubits. Something else might come along and work better as a qubit than any of the current structures, or something in use today could be improved enough to win the race. It’s kind of like VHS vs. Beta, but we don’t know which is which yet. (Are you old enough to remember what “VHS” and “Beta” are?)

Qubits are set up by directing microwave pulses at them. The pulses are set to a frequency that is tuned to the shape of the qubit. Different pulse shapes do different things. Some pulse shapes set up the qubit to hold data. Other pulses set it up to be used as a quantum logic gate. Some pulses set up entanglement or kick off quantum operations.

A qubit state is recovered and read with a microwave resonator that changes frequency depending on the qubit state. The shifted frequency is measured and then sent out of the quantum processor to conventional electronics as a 0 or a 1.

Photon qubits do something similar except the pulses are in the light part of the electromagnetic spectrum rather than the microwave spectrum. The operation is nearly identical other than that. Pulses of a specific shape at the right frequency hit the qubit to configure it. Resonators detect energy from the qubit and shift the frequency depending on the state of the qubit and then translate the energy pulses to 0s and 1s based on the frequency.

We’ve asked and answered this question before. However, as we dig deeper, it is worth asking again. More information in our heads means we can take a more complex look at the answer.

A qubit is the smallest piece of a quantum computer that can be used to hold the smallest piece of quantum information. There are a number of ways to create qubits, but as a qubit, every type does the same thing. A qubit holds information in the form of a multi-dimensional vector. When properly manipulated, the 3D vector space collapses into either a 0 or a 1.

A qubit can be a single subatomic particle, but it can also be anything in the quantum world that exhibits the key quantum properties of superposition and entanglement. This includes electrons, photons, some types of individual atoms, some types of grouped atoms, and some fields. As long as it exhibits the correct quantum properties, it can be used as a qubit.

The same principle exists in the conventional digital computing world. The most common type of constructs used as a bit in digital computers is the Mosfet/capacitor circuit and the Mosfet switch. Mechanical relays can also be used, as can old vacuum tubes. Some older computers used resistors and diodes to hold and switch bits. A lot of different things can be used to make and switch a bit - as long as the thing complies with “Benson’s law of useable-for-computing (see newsletter issue 9, or book chapter 10), it can be used as a bit.

To be a quantum computer qubit, the thing must comply with the same law. Qubits just come with a fifth parameter: “5) operate on the principles of quantum mechanics.”

Stay tuned for more of the quantum adventure next week.

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I’ve wrapped the first ten issues of The Quantum Edge newsletter into book form. The collection, called “The Quantum Computing Anthology, Volume 1”, is now available in Kindle and paperback on Amazon. The book collects newsletter issues 1 through 10 and has some additional material and edits for continuity and clarity. I will add another volume to the series every ten newsletter issues, so look for Volume 2 (newsletter issues 11 - 20) in early 2026.

You can order the Kindle or paperback editions on Amazon today: The Quantum Computing Anthology, Volume 1

Check your email box Thursday - probably. (Okay, some of these weekly issues have come out on Friday, or not at all. But, in a quantum world, how can you tell?)

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Positive Edge is the consulting arm of Duane Benson, Tech journalist, Futurist, Entrepreneur. Positive Edge is your conduit to decades of leading-edge technology development, management and communications expertise.