Fluxonium Qubit Achieves Microwave Slow Light and Storage in Single-Atom System

Researchers are increasingly exploring ways to manipulate microwave signals within superconducting circuits, and a team led by Ching-Yeh Chen, Shih-Wei Lin, and Ching-Ping Lee from National Tsing Hua University, alongside collaborators including I. -C. Hoi from City University of Hong Kong, now demonstrate a significant advance in this field. They successfully slow and store microwaves using a single superconducting circuit element known as a fluxonium qubit, operating within a microwave waveguide. This achievement bypasses the need for complex systems previously required to achieve similar effects, instead creating a streamlined platform based on a carefully designed three-level system within the qubit itself.

The team’s experiments reveal a substantial slowdown of light, with a delay of 217 nanoseconds, alongside the ability to store microwave photons, paving the way for novel components such as microwave delay lines and memory devices for future superconducting communication networks. Microwave Storage and Slow Light with Fluxonium Atoms This research demonstrates the ability to significantly slow and store microwave photons within a single superconducting fluxonium artificial atom, effectively creating a reconfigurable microwave delay line.

The team implemented a three-level system, allowing them to map microwave photons onto a long-lived dark state, substantially reducing their group velocity. Researchers achieved a maximum group delay of 180 nanoseconds, corresponding to a reduction in group velocity to 0. 01c, where c is the speed of light. This capability enables the storage of microwave signals for extended periods and provides precise control over their temporal characteristics. The demonstrated technique offers potential applications in quantum memories, advanced radar systems, and high-precision microwave metrology. Furthermore, the single-atom implementation simplifies system complexity and paves the way for scalable quantum microwave technologies. Optical phenomena such as electromagnetically induced transparency (EIT), slow light, and quantum memory rely on three-level systems, which have been realised in several quantum hardware platforms including atomic systems, superconducting artificial atoms, and meta-structures. This work presents an EIT experiment in the microwave frequency range, utilising a single Fluxonium qubit within a microwave waveguide. The three-level system consists of two transitions involving the qubit combined with a metastable state.

Fluxonium Qubit Cooling And Parameter Analysis This supplementary material provides detailed information supporting the main research paper, clarifying the experimental setup and detailing the fitting parameters used for analysis. It also presents a rigorous method, the Akaike Information Criterion (AIC), for distinguishing between different physical regimes, specifically electromagnetically induced transparency (EIT) and Autler-Townes splitting (ATS). The fluxonium qubit is cooled to approximately 20 millikelvin in a dilution refrigerator. Attenuators and a Cryoperm magnetic shield minimise unwanted noise and environmental disturbances. Signals are routed through triple isolators to prevent reflections, and a Vector Network Analyzer and Arbitrary Waveform Generator are used for spectroscopic and time-domain measurements. Data obtained through one-tone spectroscopy reveals key qubit parameters: the Josephson energy is 9. 041GHz, the charging energy is 0. 995GHz, and the inductive energy is 0. 807GHz. The system is modeled as a three-level system with specific energy levels and driving fields, defined by detunings that characterise the interactions between the fields and the qubit.

The Akaike Information Criterion (AIC) is used to compare the goodness of fit of models describing EIT and ATS to the experimental data. Analysis of the data reveals a transition point at a control field strength of 14. 55MHz, where the AIC weight shifts from the EIT model to the ATS model, indicating a transition from the EIT regime to the ATS regime as the control field strength increases.

Fluxonium Qubit Demonstrates Light Slowing and Storage This research demonstrates the successful implementation of a three-level system within a single superconducting fluxonium qubit integrated with a microwave waveguide. By carefully controlling the qubit’s parameters, the team observed key quantum optical phenomena, including electromagnetically induced transparency (EIT), a significant slowdown of light propagation, and the storage of microwave photons. These results confirm the potential of this system for manipulating quantum information within superconducting circuits. The experiments achieved a delay time of 217 nanoseconds in slowing light and demonstrated photon storage with a maximum efficiency of 12%. Importantly, this work establishes a platform for exploring quantum optics using a simplified architecture, constructing the three-level system without requiring additional components between the qubit and the waveguide resonator. Future work could address limitations by fine-tuning the qubit’s parameters, potentially improving the delay time to 604 nanoseconds, and paving the way for developing advanced components, such as phase shifters and quantum memories, for use in future superconducting quantum information processing systems. 👉 More information 🗞 Slowing and Storing Microwaves in a Single Superconducting Fluxonium Artificial Atom 🧠 ArXiv: https://arxiv.org/abs/2512.13272 Tags: