= Transmon
{title2=2007}
{wiki}
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 https://youtu.be/cb_f9KpYipk?t=180[] from <video The transmon qubit by Leo Di Carlo (2018)>:
``
+----------+
| Island 1 |
+----------+
| |
X C
| |
+----------+
| Island 2 |
+----------+
``
https://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: https://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[https://www.youtube.com/watch?v=dKTNBN99xLw]
{title=The superconducting <transmon> qubit as a microwave resonator by <Daniel Sank> (2021)}
\Video[https://www.youtube.com/watch?v=5ggYJJjlw8o]
{title=Calibration of Transmon Superconducting Qubits by Stefan Titus (2021)}
{description=Possibly this <Keysight> which would make sense.}