However superconducting qubits have a limit on how precise their parameters can be set based on how well we can fabricate devices. This may require per-device characterisation.
Flux qubit by Ciro Santilli 37 Updated 2025-07-16
In Ciro's ASCII art circuit diagram notation, it is a loop with three Josephson junctions:
+----X-----+
|          |
|          |
|          |
+--X----X--+
https://upload.wikimedia.org/wikipedia/en/0/04/Flux_Qubit_-_Holloway.jpg
Video 1.
Superconducting Qubit by NTT SCL (2015)
Source.
Offers an interesting interpretation of superposition in that type of device (TODO precise name, seems to be a flux qubit): current going clockwise or current going counter clockwise at the same time. youtu.be/xjlGL4Mvq7A?t=1348 clarifies that this is just one of the types of qubits, and that it was developed by Hans Mooij et. al., with a proposal in 1999 and experiments in 2000. The other type is dual to this one, and the superposition of the other type is between N and N + 1 copper pairs stored in a box.
Their circuit is a loop with three Josephson junctions, in Ciro's ASCII art circuit diagram notation:
+----X-----+
|          |
|          |
|          |
+--X----X--+
They name the clockwise and counter clockwise states and (named for Left and Right).
When half the magnetic flux quantum is applied as microwaves, this produces the ground state:
where and cancel each other out. And the first excited state is:
Then he mentions that:
  • to go from 0 to 1, they apply the difference in energy
  • if the duration is reduced by half, it creates a superposition of .
Transmon by Ciro Santilli 37 Updated 2025-07-16
Used e.g. in the Sycamore processor.
The most basic type of transmon is in Ciro's ASCII art circuit diagram notation, an LC circuit e.g. as mentioned at youtu.be/cb_f9KpYipk?t=180 from Video "The transmon qubit by Leo Di Carlo (2018)":
+----------+
| Island 1 |
+----------+
   |   |
   X   C
   |   |
+----------+
| Island 2 |
+----------+
youtu.be/eZJjQGu85Ps?t=2443 from Video "Superconducting Qubits I Part 1 by Zlatko Minev (2020)" describes a (possibly simplified) physical model of it, as two superconducting metal islands linked up by a Josephson junction marked as X in the diagram as per-Ciro's ASCII art circuit diagram notation:
+-------+       +-------+
|       |       |       |
| Q_1() |---X---| Q_2() |
|       |       |       |
+-------+       +-------+
The circuit is then analogous to a LC circuit, with the islands being the capacitor. The Josephson junction functions as a non-linear inductor.
Others define it with a SQUID device instead: youtu.be/cb_f9KpYipk?t=328 from Video "The transmon qubit by Leo Di Carlo (2018)". He mentions that this allows tuning the inductive element without creating a new device.
Video 1.
The superconducting transmon qubit as a microwave resonator by Daniel Sank (2021)
Source.
Video 2.
Calibration of Transmon Superconducting Qubits by Stefan Titus (2021)
Source. Possibly this Keysight which would make sense.
EdX course. Meh! Just give me the YouTube list!!
But seriously, this is a valuable little list.
The course is basically exclusively about transmons.
Video 1.
The transmon qubit by Leo Di Carlo (2018)
Source. Via QuTech Academy.
Video 2.
Circuit QED by Leo Di Carlo (2018)
Source. Via QuTech Academy.
Video 3.
Measurements on transmon qubits by Niels Bultink (2018)
Source. Via QuTech Academy. I wish someone would show some actual equipment running! But this is of interest.
Video 4.
Single-qubit gate by Brian Taraskinki (2018)
Source. Good video! Basically you make a phase rotation by controlling the envelope of a pulse.
Video 5.
Two qubit gates by Adriaan Rol (2018)
Source.
Video 6.
Assembling a Quantum Processor by Leo Di Carlo (2018)
Source. Via QuTech Academy.
Alice&Bob by Ciro Santilli 37 Updated 2025-07-16
Funding rounds:
Video 1.
Cat Qubits and LDPC Codes, a New Step Towards Quantum Error Correction by Alice&Bob
. Source.
Video 2.
Behind The Tech : Cryostats by Alice&Bob
. Source. Showcasing their Bluefors dilution refrigerators. They are named after Asterix characters.
Sonicator by Ciro Santilli 37 Updated 2025-07-16
These can be used to break cells apart from tissue, and also break up larger DNA or RNA molecules into smaller ones, suitable for sequencing.
Google Quantum AI by Ciro Santilli 37 Updated 2025-07-16
Google's quantum hardware/software effort.
The "AI" part is just prerequisite buzzword of the AI boom era for any project and completely bullshit.
According to job postings such as: archive.ph/wip/Fdgsv their center is in Goleta, California, near Santa Barbara. Though Google tends to promote it more as Santa Barbara, see e.g. Daniel's t-shirt at Video "Building a quantum computer with superconducting qubits by Daniel Sank (2019)".
Video 1.
Control of transmon qubits using a cryogenic CMOS integrated circuit (QuantumCasts) by Google (2020)
Source. Fantastic video, good photos of the Google Quantum AI setup!
Daniel Sank by Ciro Santilli 37 Updated 2025-07-16
Started at Google Quantum AI in 2014.
Has his LaTeX notes at: github.com/DanielSank/theory. One day he will convert to OurBigBook.com. Interesting to see that he is able to continue his notes despite being at Google.
Sycamore processor by Ciro Santilli 37 Updated 2025-07-16
This is a good read: quantumai.google/hardware/datasheet/weber.pdf May 14, 2021. Their topology is so weird, not just a rectangle, one wonders why! You get different error rates in different qubits, it's mad.
Figure 1.
Google Sycamore Weber quantum computer connectivity graph
. Weber is a specific processor of the Sycamore family. From this we see it clearly that qubits are connected to at most 4 other qubits, and that the full topology is not just a simple rectangle.
IBM Quantum Computing by Ciro Santilli 37 Updated 2025-07-16
The term "IBM Q" has been used in some promotional material as of 2020, e.g.: www.ibm.com/mysupport/s/topic/0TO50000000227pGAA/ibm-q-quantum-computing?language=en_US though the fuller form "IBM Quantum Computing" is somewhat more widely used.
Ilana Wisby by Ciro Santilli 37 Updated 2025-07-16
Founding CEO of Oxford Quantum Circuits.
As mentioned at www.investmentmonitor.ai/tech/innovation/in-conversation-with-oxford-quantum-circuits-ilana-wisby she is not the original tech person:
she was finally headhunted by Oxford Science and Innovation to become the founding CEO of OQC. The company was spun out of Oxford University's physics department in 2017, at which point Wisby was handed "a laptop and a patent".
Did they mean Oxford Sciences Enterprises? There's nothing called "Oxford Science and Innovation" on Google. Yes, it is just a typo oxfordscienceenterprises.com/news/meet-the-founder-ilana-wisby-ceo-of-oxford-quantum-circuits/ says it clearly:
I was headhunted by Oxford Sciences Enterprises to be the founding CEO of OQC.
Rigetti Computing by Ciro Santilli 37 Updated 2025-07-16
Video 1.
Forest: an Operating System for Quantum Computing by Guen Prawiroatmodjo (2017)
Source. The title of the talk is innapropriate, this is a very basic overview of the entire Rigetti Computing stack. Still some fine mentions. Her name is so long, TODO origin? She later moved to Microsoft Quantum: www.linkedin.com/in/gueneverep/.

Pinned article: Introduction to the OurBigBook Project

Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
We have two killer features:
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    Articles of different users are sorted by upvote within each article page. This feature is a bit like:
    • a Wikipedia where each user can have their own version of each article
    • a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
    This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
    Figure 1.
    Screenshot of the "Derivative" topic page
    . View it live at: ourbigbook.com/go/topic/derivative
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    Figure 2.
    You can publish local OurBigBook lightweight markup files to either https://OurBigBook.com or as a static website
    .
    Figure 3.
    Visual Studio Code extension installation
    .
    Figure 4.
    Visual Studio Code extension tree navigation
    .
    Figure 5.
    Web editor
    . You can also edit articles on the Web editor without installing anything locally.
    Video 3.
    Edit locally and publish demo
    . Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.
    Video 4.
    OurBigBook Visual Studio Code extension editing and navigation demo
    . Source.
  3. https://raw.githubusercontent.com/ourbigbook/ourbigbook-media/master/feature/x/hilbert-space-arrow.png
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    Figure 6.
    Dynamic article tree with infinitely deep table of contents
    .
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