Project MASSS – Marie-Sklodowska Curie Action by Leandro Tosi
Absorption Spectroscopy using cQED-setup
In order to perform the spectriscopy of Andreev States in the InAs nanowire we need:
- To fabricate the weak link and to control the number of channels
- To be able to impose a phase difference in the weak-link
- To send microwave photons to promote transitions
- To read-out the state of the weak-link
As described in previous section, we taylor our weak-link in the Al full-shell nanowires by etching the Al in part of the wire and then we deposite a metallic electrode close enough to be able to gate the wire.
In addition to a DC voltage, we send microwave photons through the gate which works as an anntena (modulating the electronic density at GHz frequencies) promoting transitions between Andreev States.
We place the weak-link in a superconducting loop where we can apply a very small magnetic field (like an SQUID) to impose the phase difference link to the magnetic flux we thread.
In order to read the state of the system we use a circuit QED set-up. the idea is the following. The inductance of the superconducting loop hosting the weak-link depends on the inductance of Andreev states which is calculated taking into account the occupation of these states. If the occupation of the states changes, as it the case one a photon of a well defined energy is absorved, the inductance changes. To read this inductance's change we couple the superconducting loop to a microwave resonator. Thanks to this mutual coupling, a change in the Andreev inductance induces a shift in the resonator's frequency.
What we measure is essentially this shift of the resonator's frequency as we send an excitation through the gate.
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