Experimental Realization of a Protected Superconducting Circuit Derived from the 0–π Qubit

作     者：András Gyenis Pranav S. Mundada Agustin Di Paolo Thomas M. Hazard Xinyuan You David I. Schuster Jens Koch Alexandre Blais Andrew A. Houck 

作者机构：Department of Electrical Engineering Princeton University Princeton New Jersey 08544 USA Institut quantique & Département de Physique Université de Sherbrooke Sherbrooke Quebec J1K 2R1 Canada Graduate Program in Applied Physics Northwestern University Evanston Illinois 60208 USA The James Franck Institute and Department of Physics University of Chicago Chicago Illinois 60637 USA Department of Physics and Astronomy Northwestern University Evanston Illinois 60208 USA Canadian Institute for Advanced Research Toronto Ontario M5G 1M1 Canada 

出 版 物：《PRX Quantum》 (PRX. Quantum.)

年 卷 期：2021年第2卷第1期

页      面：010339-010339页

核心收录：

基　　金：National Science Foundation, NSF, (1420541) National Science Foundation, NSF 

主　　题：Quantum computation Quantum information with solid state qubits 

摘      要：Encoding a qubit in logical quantum states with wave functions characterized by disjoint support and robust energies can offer simultaneous protection against relaxation and pure dephasing. One of the most promising candidates for such a fully protected superconducting qubit is the 0–π circuit [Brooks et al., Phys. Rev. A 87, 052306 (2013)]. Here we realize the proposed circuit topology in an experimentally obtainable parameter regime, where the ground-state degeneracy is lifted but the qubit is still largely noise protected. More precisely, the logical states of this qubit feature disjoint support and are exponentially protected against relaxation and exponentially (first order) protected against dephasing due to charge (flux) noise. We name the resultant device the “soft 0–π qubit. Multitone spectroscopy measurements reveal the energy-level structure of the system, which can be precisely described by a simple two-mode Hamiltonian. Using a Raman-type protocol, we exploit a higher-lying charge-insensitive energy level of the device to realize coherent population transfer and logical operations. The measured relaxation (T1=1.6 ms) and dephasing (TR=9μs, T2E=25μs) times demonstrate that the soft 0–π circuit not only broadens the family of superconducting qubits but also constitutes an important step toward quantum computing with intrinsically protected superconducting qubits.