Microwave interference between a spin ensemble and its mirror image

B.-Y. Wu; Y.-T. Cheng; K.-T. Lin; Fahad Aziz; C.-X. Run; K.-M. Hsieh; J.-C. Liu; K.-V. Rangdhol; Y.-Y. Yeung; Sen Yang; Qiming Shao; Xin Wang; Y.-Y. Zhao; A. F. Kockum; G.-D. Lin; Franco Nori; I.-C. Hoi

doi:10.1103/swf5-ynd5

Microwave interference between a spin ensemble and its mirror image

B.-Y. Wu (Co-first Author)
, Y.-T. Cheng (Co-first Author)
, K.-T. Lin (Co-first Author)
, Fahad Aziz
, C.-X. Run
, K.-M. Hsieh
, J.-C. Liu
, K.-V. Rangdhol
, Y.-Y. Yeung
, Sen Yang
, Qiming Shao
, Xin Wang
, Y.-Y. Zhao
, A. F. Kockum
, G.-D. Lin
, Franco Nori
, I.-C. Hoi^*

^*Corresponding author for this work

Department of Physics

Research output: Journal Publications and Reviews › RGC 21 - Publication in refereed journal › peer-review

Abstract

We investigate microwave interference between a spin ensemble and its mirror image in a one-dimensional (1D) waveguide. Away from the mirror, the resonance frequency of the Kittel mode (KM) inside a ferrimagnetic spin ensemble displays sinusoidal shifts (compared to a setup without the mirror) as a function of the distance to the mirror. Furthermore, the radiative decay of the KM into the waveguide shows a cosine-squared oscillation as the distance to the mirror is varied. These shifting frequencies and decay rates are a consequence of the KM’s interaction with its own image, mediated by the waveguide. The decay is enhanced twofold when the spin ensemble sits at the magnetic antinode of the corresponding eigenmode in the waveguide; conversely, we measure an extension of the KM lifetime by a factor of 8 when the spin ensemble is approximately at a node. We can finely tune the KM decay rate to achieve maximal absorption of input photons at a critical coupling point. Moreover, by pumping the spin ensemble to generate a pump-induced magnon mode in a two-tone experiment, we achieve a pump-induced phase shift of up to about 90° for a coherent microwave probe field.

©2026 American Physical Society

Original language	English
Article number	053720
Number of pages	15
Journal	Physical Review A
Volume	113
Issue number	5
Online published	26 May 2026
DOIs	https://doi.org/10.1103/swf5-ynd5
Publication status	Published - May 2026

Funding

We thank Bimu Yao for fruitful discussions. I.-C.H. acknowledges financial support from City University of Hong Kong through the start-up Project No. 9610569, from the Research Grants Council of Hong Kong (Grant No. 11312322) and from Guangdong Provincial Quantum Science Strategic Initiative (GDZX2203001, GDZX2303005, and GDZX2403001). F.N. is supported in part by the Japan Science and Technology Agency (JST) [via the CREST Quantum Frontiers program Grant No. JPMJCR24I2, the Quantum Leap Flagship Program (Q-LEAP), and the Moonshot R&D Grant No. JPMJMS2061]. A.F.K. acknowledges support from the Swedish Foundation for Strategic Research (Grants No. FFL21-0279 and No. FUS21-0063), the Horizon Europe programme HORIZON-CL4-2022-QUANTUM-01-SGA via the Project No. 101113946 OpenSuperQPlus100, and from the Knut and Alice Wallenberg Foundation through the Wallenberg Centre for Quantum Technology (WACQT). G.-D.L. acknowledges support from National Science and Technology Council Grants No. NSTC-113-2112-M-002-025 and No. NSTC-112-2112-M-002-001. J.-C.L. and Q.S. acknowledge the funding support from RGC-GRF (16303322).

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GRF: Correlated Decay and Coherent Exchange Interaction between Two Distant Superconducting Qubits
HOI, I. C. (Principal Investigator / Project Coordinator)
1/01/23 → …
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title = "Microwave interference between a spin ensemble and its mirror image",

abstract = "We investigate microwave interference between a spin ensemble and its mirror image in a one-dimensional (1D) waveguide. Away from the mirror, the resonance frequency of the Kittel mode (KM) inside a ferrimagnetic spin ensemble displays sinusoidal shifts (compared to a setup without the mirror) as a function of the distance to the mirror. Furthermore, the radiative decay of the KM into the waveguide shows a cosine-squared oscillation as the distance to the mirror is varied. These shifting frequencies and decay rates are a consequence of the KM{\textquoteright}s interaction with its own image, mediated by the waveguide. The decay is enhanced twofold when the spin ensemble sits at the magnetic antinode of the corresponding eigenmode in the waveguide; conversely, we measure an extension of the KM lifetime by a factor of 8 when the spin ensemble is approximately at a node. We can finely tune the KM decay rate to achieve maximal absorption of input photons at a critical coupling point. Moreover, by pumping the spin ensemble to generate a pump-induced magnon mode in a two-tone experiment, we achieve a pump-induced phase shift of up to about 90° for a coherent microwave probe field. {\textcopyright}2026 American Physical Society",

author = "B.-Y. Wu and Y.-T. Cheng and K.-T. Lin and Fahad Aziz and C.-X. Run and K.-M. Hsieh and J.-C. Liu and K.-V. Rangdhol and Y.-Y. Yeung and Sen Yang and Qiming Shao and Xin Wang and Y.-Y. Zhao and Kockum, \{A. F.\} and G.-D. Lin and Franco Nori and I.-C. Hoi",

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doi = "10.1103/swf5-ynd5",

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T1 - Microwave interference between a spin ensemble and its mirror image

AU - Wu, B.-Y.

AU - Cheng, Y.-T.

AU - Lin, K.-T.

AU - Aziz, Fahad

AU - Run, C.-X.

AU - Hsieh, K.-M.

AU - Liu, J.-C.

AU - Rangdhol, K.-V.

AU - Yeung, Y.-Y.

AU - Yang, Sen

AU - Shao, Qiming

AU - Wang, Xin

AU - Zhao, Y.-Y.

AU - Kockum, A. F.

AU - Lin, G.-D.

AU - Nori, Franco

AU - Hoi, I.-C.

PY - 2026/5

Y1 - 2026/5

N2 - We investigate microwave interference between a spin ensemble and its mirror image in a one-dimensional (1D) waveguide. Away from the mirror, the resonance frequency of the Kittel mode (KM) inside a ferrimagnetic spin ensemble displays sinusoidal shifts (compared to a setup without the mirror) as a function of the distance to the mirror. Furthermore, the radiative decay of the KM into the waveguide shows a cosine-squared oscillation as the distance to the mirror is varied. These shifting frequencies and decay rates are a consequence of the KM’s interaction with its own image, mediated by the waveguide. The decay is enhanced twofold when the spin ensemble sits at the magnetic antinode of the corresponding eigenmode in the waveguide; conversely, we measure an extension of the KM lifetime by a factor of 8 when the spin ensemble is approximately at a node. We can finely tune the KM decay rate to achieve maximal absorption of input photons at a critical coupling point. Moreover, by pumping the spin ensemble to generate a pump-induced magnon mode in a two-tone experiment, we achieve a pump-induced phase shift of up to about 90° for a coherent microwave probe field. ©2026 American Physical Society

AB - We investigate microwave interference between a spin ensemble and its mirror image in a one-dimensional (1D) waveguide. Away from the mirror, the resonance frequency of the Kittel mode (KM) inside a ferrimagnetic spin ensemble displays sinusoidal shifts (compared to a setup without the mirror) as a function of the distance to the mirror. Furthermore, the radiative decay of the KM into the waveguide shows a cosine-squared oscillation as the distance to the mirror is varied. These shifting frequencies and decay rates are a consequence of the KM’s interaction with its own image, mediated by the waveguide. The decay is enhanced twofold when the spin ensemble sits at the magnetic antinode of the corresponding eigenmode in the waveguide; conversely, we measure an extension of the KM lifetime by a factor of 8 when the spin ensemble is approximately at a node. We can finely tune the KM decay rate to achieve maximal absorption of input photons at a critical coupling point. Moreover, by pumping the spin ensemble to generate a pump-induced magnon mode in a two-tone experiment, we achieve a pump-induced phase shift of up to about 90° for a coherent microwave probe field. ©2026 American Physical Society

U2 - 10.1103/swf5-ynd5

DO - 10.1103/swf5-ynd5

M3 - RGC 21 - Publication in refereed journal

SN - 2469-9926

VL - 113

JO - Physical Review A

JF - Physical Review A

IS - 5

M1 - 053720

ER -

Microwave interference between a spin ensemble and its mirror image

Abstract

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GRF: Correlated Decay and Coherent Exchange Interaction between Two Distant Superconducting Qubits

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