Our paper explores the different types of qubits that can be realized with two twisted d-wave junctions in a SQuID loop, by varying the twist angle of the junction and the external magnetic flux. You can view the arXiv pre-print here.
This theoretical project was led by Alessandro Coppo and Valentina Brosco from ISC-CNR in Rome, in collaboration with Luca Chirolli from QRC-Abu Dhabi and Nicola Poccia from IFW-Dresden. This project can be seen as a direct extension of our “flowermon” qubit work recently published in PRL. In the current work, we show that by a simple extension of the flowermon junction into two junctions in SQuID loop, a wide range of qubits can be implemented. At low flux values, the circuit is quite similar to the single junction flowermon, keeping its protection from decoherence while allowing for frequency tuning by flux. At higher values of magnetic flux, the circuit enters a more conventional flux-biased protected regime (similar to engineered circuits such as the ‘rhombus’ etc.), where it is protected from charge noise but not fluctuations in the magnetic flux. The critical flux point where the circuit enters the flux-biased regime shows a unique “supersymmetry”, with a double degeneracy that extends to the higher excitations of the system.
This device is thus a useful platform to explore the physics of protected circuits as well as general problems in quantum physics.
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