Group Delay Controlled by the Decoherence of a Single Artificial Atom

Y.-T. Cheng; K.-M. Hsieh; B.-Y. Wu; Z. Q. Niu; F. Aziz; Y.-H. Huang; P. Y. Wen; K.-T. Lin; Y.-H. Lin; J. C. Chen; A. F. Kockum; G.-D. Lin; Z.-R. Lin; Y. Lu; I.-C. Hoi

doi:10.1103/fkzb-fxv4

Group Delay Controlled by the Decoherence of a Single Artificial Atom

Y.-T. Cheng ^1,*, K.-M. Hsieh ^1,*, B.-Y. Wu ^1,*, Z. Q. Niu ^2,3,*, F. Aziz ⁴, Y.-H. Huang⁴, P. Y. Wen⁵, K.-T. Lin ^6,7, Y.-H. Lin^4,8 et al.

J. C. Chen^4,8, A. F. Kockum ⁹, G.-D. Lin ^6,7,10, Z.-R. Lin ^2,†, Y. Lu^11,12,13,‡, and I.-C. Hoi ^1,§

¹Department of Physics, City University of Hong Kong, Kowloon, Hong Kong SAR 999077, China
²State Key Laboratory of Materials for Integrated Circuits, Shanghai Institute of Microsystem and Information Technology (SIMIT), Chinese Academy of Sciences, Shanghai 200050, China
³ShanghaiTech University, Shanghai 201210, China
⁴Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
⁵Department of Physics, National Chung Cheng University, Chiayi 621301, Taiwan
⁶Trapped-Ion Quantum Computing Laboratory, Hon Hai Research Institute, Taipei 11492, Taiwan
⁷CQSE, Department of Physics, National Taiwan University, Taipei 10617, Taiwan
⁸Center for Quantum Technology, National Tsing Hua University, Hsinchu 30013, Taiwan
⁹Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
¹⁰Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan
¹¹Guangzhou Institute of Technology, Xidian University, Xi’an, China
¹²Advanced Interdisciplinary Research Center, Xidian University, Xi’an, China
¹³Faculty of Integrated Circuit, Xidian University, Xi’an, China

^*These authors contributed equally to this work.
^†Contact author: zrlin@mail.sim.ac.cn
^‡Contact author: kdluyong@outlook.com
^§Contact author: iochoi@cityu.edu.hk

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Phys. Rev. Lett. 135, 073601 – Published 13 August, 2025

DOI: https://doi.org/10.1103/fkzb-fxv4

Abstract

The ability to slow down light at the single-photon level has applications in quantum information processing and other quantum technologies. We demonstrate two methods, both using just a single artificial atom, enabling dynamic control over microwave light velocities in waveguide quantum electrodynamics (QED). Our methods are based on two distinct mechanisms harnessing the balance between radiative decay and nonradiative decoherence rates of a superconducting artificial atom in front of a mirror. In the first method, we tune the radiative decay of the atom using interference effects due to the mirror; in the second method, we pump the atom to effectively control its nonradiative decoherence. When the half of the radiative decay rate exceeds the nonradiative decoherence rate, we observe positive group delay; conversely, dominance of the nonradiative decoherence results in negative group delay. Our results advance signal-processing capabilities in waveguide QED.

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