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Vladimir MILCHAKOV presents

Optimized transmon molecule for high fidelity quantum

non demolition readout using cross-Kerr coupling

Monday 28th march 2022 at 2.00 pm

Amphi of the Building A of CNRS

The presentation will be given in English.



The most common technique of superconducting qubit readout in cQED relies on the transverse dispersive coupling between a qubit and a microwave cavity. However, despite important progress, implementing fast high fidelity and quantum non-demolition (QND) readout remains a major challenge. Indeed, inferring the qubit state is limited by the trade-off between speed and accuracy due to Purcell effect and unwanted transitions induced by readout photons in the cavity. To overcome this, we propose and experimentally demonstrate a new readout scheme based on a transmon molecule inserted inside a 3D-cavity. The full system presents a transmon qubit mode coupled to a readout mode through an original non-pertubative cross-Kerr coupling. This cross-Kerr coupling is a key point of our readout scheme since it protects the qubit from Purcell effect. A first generation of V-shape qubits had presented promising results however its 3us relaxation time limited fidelity and QND-ness of the readout. In order to improve the qubit and readout performance, I have optimized during my PhD different parameters such as the circuit geometry, the electric circuit parameters, the nanofabrication process leading to relaxation time of about 20us. I will present the readout performance based on the cross-Kerr coupling of this second generation of transmon circuit with readout fidelity higher than 99% and quantum non-demolition estimation near 99%.