by Ciro Santilli (@cirosantilli, 32)
Video 1. How To Build A Quantum Computer by Lukas's Lab (2023) Source.
Super quick overview of the main types of quantum computer physical implementations, so doesn't any much to a quick Google.
He sais he's going to make a series about it, so then something useful might actually come out. The first one was: Video "How to Turn Superconductors Into A Quantum Computer by Lukas's Lab (2023)", but it is still too basic.
The author's full name is Lukas Baker, www.linkedin.com/in/lukasbaker1331/, found with Google reverse image search, even though the LinkedIn image is very slightly different from the YouTube one.
As of 2023 he was a PhD student at NYU.
5 Companies Working With Diamond NV Quantum Computing Technology.
Video 1. Architecture All Access: Quantum Computing by James Clarke (2021) Source.
Based on the Josephson effect. Yet another application of that phenomenal phenomena!
It is fun to see that the representation of information in the QC basically uses an LC circuit, which is a very classical resonator circuit.
As mentioned at en.wikipedia.org/wiki/Superconducting_quantum_computing#Qubit_archetypes there are actually a few different types of superconducting qubits:
  • flux
  • charge
  • phase
and hybridizations of those such as:
Input:
  • microwave radiation to excite circuit, or do nothing and wait for it to fall to 0 spontaneously
  • interaction: TODO
  • readout: TODO
Video 1. Quantum Computing with Superconducting Qubits by Alexandre Blais (2012) Source.
Video 2. Quantum Transport, Lecture 16: Superconducting qubits by Sergey Frolov (2013) Source. youtu.be/Kz6mhh1A_mU?t=1171 describes several possible realizations: charge, flux, charge/flux and phase.
Video 3. Building a quantum computer with superconducting qubits by Daniel Sank (2019) Source. Daniel wears a "Google SB" t-shirt, which either means shabi in Chinese, or Santa Barbara. Google Quantum AI is based in Santa Barbara, with links to UCSB.
Video 4. A Brief History of Superconducting Quantum Computing by Steven Girvin (2021) Source.
Video 5. Superconducting Qubits I Part 1 by Zlatko Minev (2020) Source.
The Q&A in the middle of talking is a bit annoying.
Video 6. Superconducting Qubits I Part 2 by Zlatko Minev (2020) Source.
Video 7. How to Turn Superconductors Into A Quantum Computer by Lukas's Lab (2023) Source. This video is just the introduction, too basic. But if he goes through with the followups he promisses, then something might actually come out of it.
Non-linearity is needed otherwise the input energy would just make the state go to higher and higher energy levels, e.g. from 1 to 2. But we only want to use levels 0 and 1.
The way this is modelled in by starting from a pure LC circuit, which is an harmonic oscillator, see also quantum LC circuit, and then replacing the linear inductor with a SQUID device, e.g. mentioned at: youtu.be/eZJjQGu85Ps?t=1655 Video "Superconducting Qubits I Part 1 by Zlatko Minev (2020)".
This is unlike atomic systems like trapped ion quantum computers, where each atom is necessarily exactly the same as the other.
Superconducting qubits are regarded as promising because superconductivity is a macroscopic quantum phenomena of Bose Einstein condensation, and so as a macroscopic phenomena, it is easier to control and observe.
This is mentioned e.g. in this relatively early: physicsworld.com/a/superconducting-quantum-bits/. While most quantum phenomena is observed at the atomic scale, superconducting qubits are micrometer scale, which is huge!
Physicists are comfortable with the use of quantum mechanics to describe atomic and subatomic particles. However, in recent years we have discovered that micron-sized objects that have been produced using standard semiconductor-fabrication techniques – objects that are small on everyday scales but large compared with atoms – can also behave as quantum particles.
Atom-based qubits like trapped ion quantum computers have parameters fixed by the laws of physics.
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.
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.
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:
(1)
where and cancel each other out. And the first excited state is:
(2)
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 .
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.
Funding rounds:
  • March 2022: 27M Euros
About their qubit:
Google's quantum hardware/software effort.
The AI is just prerequisite buzzword of the era for any project.
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!
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.
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.
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.
They also internally named an division as "IBM Q": sg.news.yahoo.com/ibm-thinks-ready-turn-quantum-050100574.html
Open source superconducting quantum computer hardware design!
Video 1. OpenSuperQ intro by Quantum Flagship (2021) Source.
Their main innovation seems to be their 3D design which they call "Coaxmon".
Video 1. The Coaxmon by Oxford Quantum Circuits (2022) Source.
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.
oxfordquantumcircuits.com/story mentions that the core patent was by Dr. Peter Leek: www.linkedin.com/in/peter-leek-00954b62/
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/.
Video 1. Topological Quantum Computer by Professor John Preskill. Source.
Video 2. Topological Quantum Computation by Jason Alicea (2021) Source.
Video 3. Anyons by Yuly Billig (2022) Source.
TODO understand.
Video 1. Trapping Ions for Quantum Computing by Diana Craik (2019) Source.
A basic introduction, but very concrete, with only a bit of math it might be amazing:
Sounds complicated, several technologies need to work together for that to work! Videos of ions moving are from www.physics.ox.ac.uk/research/group/ion-trap-quantum-computing.
A major flaw of this presentation is not explaining the readout process.
Video 2. How To Trap Particles in a Particle Accelerator by the Royal Institution (2016) Source. Demonstrates trapping pollen particles in an alternating field.
Video 3. Ion trapping and quantum gates by Wolfgang Ketterle (2013) Source.
Video 4. Introduction to quantum optics by Peter Zoller (2018) Source. THE Zoller from Cirac–Zoller CNOT gate talks about his gate.
Trapped ion people acknowledge that they can't put a million qubits in on chip (TODO why) so they are already thinking of ways to entangle separate chips. Thinking is maybe the key word here. One of the propoesd approaches inolves optical links. Universal Quantum for example explicitly rejects that idea in favor of electric field link modularity.
Video 1. Quantum Simulation and Computation with Trapped Ions by Christopher Monroe (2021) Source.
Video 2. Quantum Computing with Trapped Ions by Christopher Monroe (2018) Source. Co-founder of IonQ. Cool dude. Starts with basic background we already know now. Mentions that there is some relationship between atomic clocks and trapped ion quantum computers, which is interesting. Then he goes into turbo mode, and you get lost unless you're an expert! Video 1. "Quantum Simulation and Computation with Trapped Ions by Christopher Monroe (2021)" is perhaps a better watch.
Video 1. Quantum Computing with Networked Ion traps by NQIT (2018) Source. The video is a bit useless. But it does show the networked approach proposal a little bit. Universal Quantum's homepage particularly rejects that.
This job announcement from 2022 gives a good idea about their tech stack: web.archive.org/web/20220920114810/https://oxfordionics.bamboohr.com/jobs/view.php?id=32&source=aWQ9MTA%3D. Notably, they use ARTIQ.
Merger between Cambridge Quantum Computing, which does quantum software, and Honeywell Quantum Solutions, which does the hardware.
In 2015, they got a 50 million investment from Grupo Arcano, led by Alberto Chang-Rajii, who is a really shady character who fled from justice for 2 years:Merged into Quantinuum later on in 2021.
TODO vs all the others?
As of 2021, their location is a small business park in Haywards Heath, about 15 minutes north of Brighton[ref]
Funding rounds:
Co-founders:
Homepage says only needs cooling to 70 K. So it doesn't work with liquid nitrogen which is 77 K?
Homepage points to foundational paper: www.science.org/doi/10.1126/sciadv.1601540
Video 1. Universal Quantum emerges out of stealth by University of Sussex (2020) Source. Explains that a more "traditional" trapped ion quantum computer would user "pairs of lasers", which would require a lot of lasers. Their approach is to try and do it by applying voltages to a microchip instead.
Video 2. Quantum Computing webinar with Sebastian Weidt by Green Lemon Company (2020) Source. The sound quality is to bad to stop and listen to, but it presumaby shows the coding office in the background.
Video 3. Fireside Chat with with Sebastian Weidt by Startup Grind Brighton (2022) Source. Very basic target audience:
These people are cool.
They use optical tweezers to place individual atoms floating in midair, and then do stuff to entangle their nuclear spins.
Uses photons!
The key experiment/phenomena that sets the basis for photonic quantum computing is the two photon interference experiment.
The physical representation of the information encoding is very easy to understand:
  • input: we choose to put or not photons into certain wires or no
  • interaction: two wires pass very nearby at some point, and photons travelling on either of them can jump to the other one and interact with the other photons
  • output: the probabilities that photos photons will go out through one wire or another
Video 1. Jeremy O'Brien: "Quantum Technologies" by GoogleTechTalks (2014) Source. This is a good introduction to a photonic quantum computer. Highly recommended.
Good talk by CEO before starting the company which gives insight on what they are very likely doing: Video "Jeremy O'Brien: "Quantum Technologies" by GoogleTechTalks (2014)"
PsiQuantum appears to be particularly secretive, even more than other startups in the field.
They want to reuse classical semiconductor fabrication technologies, notably they have close ties to GlobalFoundries.
So he went to the US and raised N times more from the American military-industrial complex.
Once upon a time, the British Government decided to invest some 80 million into quantum computing.
Jeremy O'Brien told his peers that he had the best tech, and that he should get it all.
Some well connected peers from well known universities did not agree however, and also bid for the money, and won.
Jeremy was defeated. And pissed.
So he moved to Palo Alto and raised a total of $665 million instead as of 2021. The end.
Makes for a reasonable the old man lost his horse.
www.ft.com/content/afc27836-9383-11e9-aea1-2b1d33ac3271 British quantum computing experts leave for Silicon Valley talks a little bit about them leaving, but nothing too juicy. They were called PsiQ previously apparently.
The departure of some of the UK’s leading experts in a potentially revolutionary new field of technology will raise fresh concerns over the country’s ability to develop industrial champions in the sector.
More interestingly, the article mentions that this was party advised by early investor Hermann Hauser, who is known to be preoccupied about UK's ability to create companies. Of course, European Tower of Babel.
www.youtube.com/watch?v=v7iAqcFCTQQ shows their base technology:

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