Higher Josephson harmonics in a tunable double-junction transmon qubit
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arXiv
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| Main Authors: | , , , , , , , , , , , , , |
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| Format: | Preprint |
| Published: |
2025
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| _version_ | 1866914193550082048 |
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| author | Shagalov, Ksenia Feldstein-Bofill, David Jakobsen, Leo Uhre Sun, Zhenhai Wied, Casper Paulsen, Amalie T. J. Severin, Johann Bock Marciniak, Malthe A. Potts, Clinton A. Kringhøj, Anders Hastrup, Jacob Flensberg, Karsten Krøjer, Svend Kjaergaard, Morten |
| author_facet | Shagalov, Ksenia Feldstein-Bofill, David Jakobsen, Leo Uhre Sun, Zhenhai Wied, Casper Paulsen, Amalie T. J. Severin, Johann Bock Marciniak, Malthe A. Potts, Clinton A. Kringhøj, Anders Hastrup, Jacob Flensberg, Karsten Krøjer, Svend Kjaergaard, Morten |
| contents | Tunable Josephson harmonics open new avenues for qubit design. We demonstrate a superconducting circuit element consisting of a tunnel junction in series with a SQUID loop, yielding a Josephson potential whose harmonic content is strongly tunable by magnetic flux. Through spectroscopy of the first four qubit transitions, together with an effective single-mode model renormalized by the internal mode, we resolve a second harmonic with an amplitude up to $\sim10\%$ of the fundamental. We identify a flux sweet spot where the dispersive shift vanishes, achieved by balancing the dispersive couplings to the internal and qubit modes. This highly tunable element provides a route toward protected qubits and customizable nonlinear microwave devices. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_08470 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Higher Josephson harmonics in a tunable double-junction transmon qubit Shagalov, Ksenia Feldstein-Bofill, David Jakobsen, Leo Uhre Sun, Zhenhai Wied, Casper Paulsen, Amalie T. J. Severin, Johann Bock Marciniak, Malthe A. Potts, Clinton A. Kringhøj, Anders Hastrup, Jacob Flensberg, Karsten Krøjer, Svend Kjaergaard, Morten Quantum Physics Mesoscale and Nanoscale Physics Tunable Josephson harmonics open new avenues for qubit design. We demonstrate a superconducting circuit element consisting of a tunnel junction in series with a SQUID loop, yielding a Josephson potential whose harmonic content is strongly tunable by magnetic flux. Through spectroscopy of the first four qubit transitions, together with an effective single-mode model renormalized by the internal mode, we resolve a second harmonic with an amplitude up to $\sim10\%$ of the fundamental. We identify a flux sweet spot where the dispersive shift vanishes, achieved by balancing the dispersive couplings to the internal and qubit modes. This highly tunable element provides a route toward protected qubits and customizable nonlinear microwave devices. |
| title | Higher Josephson harmonics in a tunable double-junction transmon qubit |
| topic | Quantum Physics Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2512.08470 |