We are excited to announce that our paper on long-distance qubit-qubit coupling has appeared in Nature Physics: Photon-mediated long-range coupling of two Andreev pair qubits by L. Y. Cheung, R. Haller, A. Kononov, C. Ciaccia, J. H. Ungerer, T. Kanne, J. Nygård, P. Winkel, T. Reisinger, I. M. Pop, A. Baumgartner & C. Schönenberger https://www.nature.com/articles/s41567-024-02630-w.

In this work two Andreev qubits realized with the unique InAs nanowires supplied by J. Nygard from the Niels-Bohr Institute are coupled over a μ/2 transmission line (TL) resonator. This TL is built from two λ/4 TLs in series coupled capacitively together. This gives rise to two fundamental modes in the resonator, a symmeric and an asymmetric one. We demonstrate strong coupling of each qubit to both resonator modes when tuned into resonance. The cool feature of this design is that one can strongly couple the two qubits without having to worry about qubit decay to the readout port, since we couple the qubits by the mode that is fully decoupled from the readout port. However, one can also tune the qubits to the other mode to readout the qubits one by one.  

Andreev qubit coupler: The bottom horizontal line in image (a) is the long microwave resonator that couples two Andreev qubits, one located on the left side (b), and the other on the right side (c). The port in the middle part of image (a) is the readout port. The tininess of the actual qubit can be imagined by looking at an individual nanowire shown in (d). The nanowire is coated with a superconductor (cyan) and the actual Andreev bound state that forms the qubit states is located in the central white section indicated by the red arrow. A similar nanowire is located at the respective spot also on the left quantum device.
Long distance qubit coupler