Fraxonium: Fractional fluxon states for qudit encoding
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arXiv
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| Format: | Preprint |
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2026
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| _version_ | 1866913128619442176 |
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| author | Chirolli, Luca Brosco, Valentina Vool, Uri Catelani, Gianluigi Amico, Luigi |
| author_facet | Chirolli, Luca Brosco, Valentina Vool, Uri Catelani, Gianluigi Amico, Luigi |
| contents | We propose a superconducting circuit hosting $d$ low-lying states, well separated from the rest of the spectrum, that naturally realizes a qudit system protected from leakage errors. The system represents a generalization of the fluxonium and the low-energy states are constituted by fractional fluxon states, that we call {\it fraxons}, localized in the minima of a suitably designed Josephson potential. The latter is tailored through a Fourier engineering approach, that employs multi-harmonic Josephson building block elements composed by a Josephson junction and an inductance connected in series. We present the spectrum of a $d=4$ and a $d=5$ qudit system and study in detail the qutrit case. We analyze the dipole matrix elements for coupling to radiation and propose a non-Abelian, stimulated Raman adiabatic passage (STIRAP) protocol for single-qutrit gates, that is particularly suited for the present system. The proposed platform opens novel perspectives in circuit engineering and quantum computing beyond the qubit paradigm. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_14586 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Fraxonium: Fractional fluxon states for qudit encoding Chirolli, Luca Brosco, Valentina Vool, Uri Catelani, Gianluigi Amico, Luigi Quantum Physics Mesoscale and Nanoscale Physics We propose a superconducting circuit hosting $d$ low-lying states, well separated from the rest of the spectrum, that naturally realizes a qudit system protected from leakage errors. The system represents a generalization of the fluxonium and the low-energy states are constituted by fractional fluxon states, that we call {\it fraxons}, localized in the minima of a suitably designed Josephson potential. The latter is tailored through a Fourier engineering approach, that employs multi-harmonic Josephson building block elements composed by a Josephson junction and an inductance connected in series. We present the spectrum of a $d=4$ and a $d=5$ qudit system and study in detail the qutrit case. We analyze the dipole matrix elements for coupling to radiation and propose a non-Abelian, stimulated Raman adiabatic passage (STIRAP) protocol for single-qutrit gates, that is particularly suited for the present system. The proposed platform opens novel perspectives in circuit engineering and quantum computing beyond the qubit paradigm. |
| title | Fraxonium: Fractional fluxon states for qudit encoding |
| topic | Quantum Physics Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2605.14586 |