{wiki}

In <Ciro's ASCII art circuit diagram notation>, it is a loop with three <Josephson junctions>:
``
+----X-----+
|          |
|          |
|          |
+--X----X--+
``

\Image[https://upload.wikimedia.org/wikipedia/en/0/04/Flux_Qubit_-_Holloway.jpg]

\Video[https://www.youtube.com/watch?v=daQJMwvxC_U]
{title=Superconducting Qubit by NTT SCL (2015)}
{description=
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. https://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 $\ket{L}$ and $\ket{R}$ (named for Left and Right).

When half the <magnetic flux quantum> is applied as <microwaves>, this produces the ground state:
$$
\ket{0} = \ket{L} + \ket{R}
$$
where $L$ and $R$ cancel each other out. And the first excited state $\ket{1}$ is:
$$
\ket{0} = \ket{L} - \ket{R}
$$
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 $\ket{0} + \ket{1}$.
}


Flux qubit

{wiki=Flux_qubit}

A flux qubit is a type of quantum bit, or qubit, used in quantum computing. It is based on superconducting circuits and exploits the principles of quantum mechanics to perform computations. Specifically, the flux qubit utilizes the magnetic flux through a superconducting loop, which can be controlled by external magnetic fields.


 Flux qubit

ID: flux-qubit