Fast high fidelity qubit readout of a transmon molecule using longitudinal coupling
ORAL
Abstract
The most common technique of qubit readout in cQED relies on the transverse dispersive coupling between a qubit and a microwave cavity. However, despite important progresses, implementing fast high fidelity 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 introduce a transmon molecule based on two transmons coupled by a large inductance, which is inserted inside a 3D-cavity. The full system presents one transmon –used as qubit– with a large direct cross-Kerr(longitudinal) coupling to a non-linear readout resonator, called polaron mode. This polaron mode results from the hybridization between the microwave cavity and the second mode of the transmon molecule circuit. The direct cross-Kerr coupling is a key point of our readout scheme since it protects the qubit from Purcell effect. We will present qubit readout performance with fidelity as high as 95.7% in 120ns and discuss the quantum non-demolition properties of this novel readout.
*R. Dassonneville thanks CFM recherche foundation. This work is supported by the French Agence Nationale de la Recherche (ANR-CE24-REQUIEM).
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Presenters
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Vladimir Milchakov
- Univ. Grenoble Alpes, CNRS, Grenoble INP, Institut Néel, 38000 Grenoble, France