QRC Seminar Series - Prof. Alex Retzker

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Prof. Alex Retzker

Prof. Alex Retzker

Hebrew University of Jerusalem, Israel

5th December 2022, 5:00pm - 6:00pm (GST)



Erasure qubits: Overcoming the T1 limit in superconducting circuits


The amplitude damping time, T1, has long stood as the major factor limiting quantum fidelity in superconducting circuits, prompting concerted efforts in the material science and design of qubits aimed at increasing T1. In contrast, the dephasing time, Tφ, can usually be extended above T1 (via, e.g., dynamical decoupling), to the point where it does not limit fidelity. In this talk I will present a scheme for overcoming the conventional T1 limit on fidelity by designing qubits in a way that amplitude damping errors can be detected and converted into erasure errors. Compared to standard qubit implementations our scheme improves the performance of fault-tolerant protocols, as numerically demonstrated by the circuit-noise simulations of the surface code. I will describe two simple qubit implementations with superconducting circuits and discuss procedures for detecting amplitude damping errors, performing entangling gates, and extending Tφ. Our results suggest that engineering efforts should focus on improving Tφ and the quality of quantum coherent control, as they effectively become the limiting factor on the performance of fault-tolerant protocols.


Alex Retzker did his PhD in the group of Benni Reznik at the Tel Aviv University (Israel) and his postdoc with Martin Plenio at Imperial College. Currently he is a Prof. of Physics at the Hebrew University of Jerusalem, leader of a theory group in the field of quantum technologies, and also part of the Amazon Web Service Center for Quantum Computing at Pasadena (CA, USA). In addition, he is a co-founder of a quantum technology startup: NVision Imaging concentrating on quantum sensing applications for medicine.