{wiki}

= Superconducting quantum computer
{synonym}

Based on the <Josephson effect>. Yet another application of that phenomenal phenomena!

Philosophically, <superconducting qubits are good because superconductivity is macroscopic>.

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 https://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:
* <transmon>

Input:
* <microwave> radiation to excite circuit, or do nothing and wait for it to fall to 0 spontaneously
* interaction: TODO
* readout: TODO

\Video[http://youtube.com/watch?v=t5nxusm_Umk]
{title=Quantum Computing with Superconducting Qubits by Alexandre Blais (2012)}
{description=
* https://youtu.be/t5nxusm_Umk?t=176 <quantum computing is hard because we want long coherence but fast control>
* https://youtu.be/t5nxusm_Umk?t=784 <superconducting quantum computer need non-linear components>
}

\Video[http://youtube.com/watch?v=Kz6mhh1A_mU]
{title=Quantum Transport, Lecture 16: Superconducting qubits by Sergey Frolov (2013)}
{description=https://youtu.be/Kz6mhh1A_mU?t=1171 describes several possible realizations: charge, flux, charge/flux and phase.}

\Video[https://www.youtube.com/watch?v=uPw9nkJAwDY]
{title=Building a quantum computer with superconducting qubits by <Daniel Sank> (2019)}
{description=
Daniel wears a "Google SB" t-shirt, which either means <shabi> in <Chinese (language)>, or <Santa Barbara>. <Google Quantum AI> is based in <Santa Barbara>, with links to <UCSB>.
* https://youtu.be/uPw9nkJAwDY?t=293 <superconducting qubits are good because superconductivity is macroscopic>. Explains how in non superconducting metal, each electron moves separatelly, and can hit atoms and leak vibration/photos, which lead to observation and quantum error
* https://youtu.be/uPw9nkJAwDY?t=429 made of <aluminium>
* https://youtu.be/uPw9nkJAwDY?t=432 shows the <circuit diagram>, and notes that the thing is basically a <LC circuit>
  ``
  +-----+
  |     |
  |   +-+-+
  |   |   |
  C   X   X
  |   |   |
  |   +-+-+
  |     |
  +-----+
  ``
  using the newly created just now <Ciro's ASCII art circuit diagram notation>. Note that the block on the right is a <SQUID device>.
* https://youtu.be/uPw9nkJAwDY?t=471 mentions that the frequency between states 0 and 1 is chosen to be 6 GHz:
  * higher frequencies would be harder/more expensive to generate
  * lower frequencies would mean less energy according to the <Planck relation>. And less energy means that thermal energy would matter more, and introduce more noise.

    6 GHz is about $6^9 \times h = 6 \times 10^9 \times 6.62 \times 10^{-34} \approx 4\e{-24} J$

    From the definition of the <Boltzmann constant>, the temperature which has that average energe of particles is of the order of:
    $$
    T = E/k_b = 4\e{-24}/1.38\e{-23} \approx 0.3K
    $$
  This explains why we need to go to much lower temperatures than simply the <superconducting temperature of aluminum>!
}

\Video[https://www.youtube.com/watch?v=xjlGL4Mvq7A]
{title=A Brief History of Superconducting Quantum Computing by Steven Girvin (2021)}
{description=
* https://youtu.be/xjlGL4Mvq7A?t=138 <superconducting quantum computer need non-linear components> (too brief if you don't know what he means in advance)
* https://youtu.be/xjlGL4Mvq7A?t=169 <quantum computing is hard because we want long coherence but fast control>
}

\Video[https://www.youtube.com/watch?v=eZJjQGu85Ps]
{title=Superconducting Qubits I Part 1 by Zlatko Minev (2020)}
{description=
The Q&A in the middle of talking is a bit annoying.

* https://youtu.be/eZJjQGu85Ps?t=2443 the first actually useful part, shows a <transmon> diagram with some useful formulas on it
}

\Video[https://www.youtube.com/watch?v=SDiiFOham6Y]
{title=Superconducting Qubits I Part 2 by Zlatko Minev (2020)}

\Video[https://www.youtube.com/watch?v=xsdleM-f0i8]
{title=How to Turn Superconductors Into A Quantum Computer by Lukas's Lab (2023)}
{description=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.}


Discussion on "Superconducting quantum computing" by Ciro Santilli 32