= Flux qubit
{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.
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 $\ket{0} + \ket{1}$.
}