Semiconductor quantum dots are excellent artificial atoms that naturally appear when growing InAs on GaAs. The lattice mismatch between the two materials leads to the spontaneous formation of InAs islands with lens shape, that are typically 10-20 nm wide and 3-5 nm high. 

These nanostructures are excellent artificial atoms to make efficient quantum devices. To that end, they can be inserted in optical microcavities, which is of course a great challenge since the quantum position is random and their energy difficult to control. A solution is to fabricate many devices, test thousands of them to find one where the quantum dot is well coupled to the cavity. Such technique has been widely used in many groups to obtain proof of principle demonstrations.

Our group invented a technology, called in-situ lithography, that enables the fabrication of many devices in a fully controlled way, operating either in the weak or strong coupling regime. The lithography is performed at 10K; we measure optically the quantum dot position and draw a cavity around it. Recently, the technology was improved to control electrically the devices and suppress sources of charge noise.

To know more on the in-situ lithography technique check our posts here (“A deterministic technique to insert a single quantum dot in a cavity“) and here (“Electrically tunable bright single photon source“).