Single-electron refrigerator
There's no room for milk and eggs but this new single-electron refrigerator might get as cold as 10 mK.
The yellowish structure is the normal metal island to be cooled. To the left, the T-shaped structure is the gate, which is capacitively coupled to the metal island. The gate completes the circuit for the application of the RF signal. On the right are the four superconducting leads, which connect to the metal island via tunnel junctions. Two of these leads are used as temperature probes and two are for cooling. One lead would be enough for cooling but multi-terminal configuration gives more flexibility.
(Courtesy Jukka Pekola).