Fabio Lingua

Research

We work at the interface of superconducting circuits and continuous-variable (CV) quantum information, using Josephson parametric amplifiers (JPAs) and kinetic inductance parametric amplifiers (LKIPAs), operated at millikelvin temperatures to generate and control large-scale entangled states of microwave light. By pumping a JPA with carefully engineered combinations of coherent tones, we synthesize a "microwave frequency comb" (dozens to hundreds of squeezed, entangled modes) and engineer the entanglement structure between them into specific graph topologies.

At the core of this work is the squeezing of microwave light: cluster states are a particular flavor of multimode squeezing, where quantum correlations are distributed across many modes according to a chosen graph rather than concentrated pairwise. Our recent work demonstrated square-ladder CV cluster states across up to 94 modes [1,2], and most recently two-dimensional honeycomb and square-lattice cluster states spanning 191 modes [3], among the largest continuous-variable entangled states realized to date at microwave frequencies. These cluster states are a core resource for measurement-based quantum computation, offering a route toward scalable CV quantum information processing that does not rely on sequential gate operations.

Alongside the experimental platform, we develop the theoretical and computational framework needed to understand, design and control it. We are interested in methods for solving the "inverse parametric problem", to calculate the pump waveform required to realize a particular structure of correlations [4], and techniques for dynamic routing, and design of scattering between modes [5] (e.g. non-reciprocity). This framework let us treat the frequency comb as a programmable quantum network, opening possibilities for on-demand generation and reconfiguration of multimode entangled states useful for quantum computation, simulation and sensing.

Our group combines digital RF signal synthesis and digital demodulation techniques, the design, fabrication, and testing of non-linear superconducting circuits, and measurements in different cryogenic environments. We collaborate closely with the broader quantum and applied physics community at KTH's Department of Applied Physics.

We have an active collaboration with Prof. Vaishali Adya's group, who work on optical squeezing. The goal of this collaboration is to translate our microwave squeezing recipes and RF-based control techniques to the optical regime, bridging the two platforms and exploring how multimode squeezing and cluster-state generation methods developed for microwaves can inform and extend optical CV quantum information experiments.

Teaching and thesis projects

We regularly offer thesis projects and research credit courses within our group. If you are interested in working with us, please reach out.

References

[1] F. Lingua, J. C. Rivera Hernández, M. Cortinovis, D. B. Haviland, "Continuous-variable square-ladder cluster states in a microwave frequency comb," Phys. Rev. Lett. 134, 183602 (2025). DOI: 10.1103/PhysRevLett.134.183602

[2] J. C. Rivera Hernández, F. Lingua, S. W. Jolin, D. B. Haviland, "Control of multi-modal scattering in a microwave frequency comb," APL Quantum 1, 036101 (2024). DOI: 10.1063/5.0203426

[3] F. Lingua, M. Cortinovis, J. C. Rivera Hernández, D. B. Haviland, "Continuous-variable two-dimensional cluster states in the microwave domain," arXiv:2604.07107 (2026). arXiv:2604.07107

[4] M. Cortinovis, F. Lingua, D. B. Haviland, "Solving the inverse parametric problem," Phys. Rev. Applied 26, 014007 (2026). DOI: 10.1103/1bdh-lcxq

[5] C. L. Bock, J. C. Rivera Hernández, F. Lingua, D. B. Haviland, "Non-reciprocal scattering in a microwave frequency comb," Phys. Rev. Applied 24, 014027 (2025). DOI: 10.1103/kz53-dryz