Hybrid Josephson junctions and electrothermal effects in graphene devices
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School of Science |
Doctoral thesis (article-based)
| Defence date: 2026-01-23
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Language
en
Pages
102 + app. 88
Series
Aalto University publication series Doctoral Theses, 20/2026
Abstract
In this thesis, I explore hybrid graphene-based Josephson junction (SGS) devices integrated with superconducting microwave cavities. The field of quantum computing has advanced rapidly in recent times, with realisations of various hardware platforms such as ion-traps, ultracold atoms, spin qubits, topological systems, and Josephson junction-based superconducting qubits, each aiming to reach the fault-tolerant quantum computing regime. Alongside these developments, two-dimensional materials such as graphene exhibit unique mechanical and electronic properties, such as atomically thin, high carrier mobility, and gate-tunable proximity-induced supercurrent, which makes SGS junctions an attractive architecture for long-lived, magnetic-field-resilient quantum circuits. Critical current fluctuations are a key dominant factor for decoherence in a Josephson junction. In the first experiment, I investigate low-frequency 1/f noise in the critical current of a hexagonal boron nitride encapsulated edge-contacted SGS junction. Fluctuations in the inductance of the SGS junction were tracked using microwave reflection measurements, and then the critical current noise was extracted from these measured fluctuations. We find significant fluctuations in the critical current, on the order of per unit band of 1 Hz. The critical current noise grows away from the charge neutrality point, which we attribute to the variation of the proximity-induced gap in the SGS junction. In a second set of experiments, I study various electrothermal effects that emerged in graphene devices. A superconductor–insulator–normal-metal–insulator–superconductor (SINIS) junction is formed from a monolayer graphene flake and coupled to a superconducting cavity. The device exhibits thermal self-oscillations arising from a highly nonlinear temperature-dependent resistance. We show that the modelling of these thermal oscillations provides a method to evaluate electronphonon coupling in graphene. In addition, these oscillations can be harnessed for the parametric amplification of microwave signals. In another device, we demonstrate the generation of a thermoelectric current in a graphene-based Cooper pair splitter, which is formed from two graphene quantum dots connected to an aluminium superconductor. Finally, I investigate microwave quantum optomechanics utilizing the Josephson capacitance of a Cooper pair box and find several orders of magnitude enhancement in both the optomechanical and the cross-Kerr couplings. Mediated by the Josephson capacitance, this three-partite system reaches the single photon ultrastrong coupling regime, enabling the generation of non-classical states of light and mechanical motion, as well as providing a platform for a single phonon counter. Together, these results demonstrate the potential of graphene–superconductor hybrids as a versatile building block for future quantum circuits, combining the design flexibility of superconducting platforms with the exceptional properties of two-dimensional materials.Description
Supervising professor
Hakonen, Pertti, Dr., Aalto University, Department of Applied Physics, FinlandOther note
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Error in the ISBN for the electronic version.
Parts
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[Publication 1]: M. Haque, M. Will, M. Tomi, P. Pandey, M. Kumar, F. Schmidt, K. Watanabe, T. Taniguchi, R. Danneau, G. Steele, and P. Hakonen. Critical current fluctuations in graphene Josephson junctions. Scientific Reports, 11, 19900 (2021).
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202111019881DOI: 10.1038/s41598-021-99398-3 View at publisher
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[Publication 2]: J. Manninen, M. Haque, D. Vitali, and P. Hakonen. Enhancement of the optomechanical coupling and Kerr nonlinearity using the Josephson Capacitance of Cooper-pair box. Physical Review B, 105, 144508 (2022).
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202205243381DOI: 10.1103/PhysRevB.105.144508 View at publisher
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[Publication 3]: Z. B. Tan, A. Laitinen, N. S. Kirsanov, A. Galda, V. M. Vinokur, M. Haque, A. Savin, D. S. Golubev, G. B. Lesovik, and P. Hakonen. Thermoelectric current in a graphene Cooper pair splitter. Nature Communications, 12, 138 (2021).
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202101251466DOI: 10.1038/s41467-020-20476-7 View at publisher
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[Publication 4]: M. Haque, M. Will, A Zyuzin, D. S. Golubev, and P. Hakonen. Thermal self-oscillations in monolayer graphene coupled to a superconducting microwave cavity. New J. Phys., 24, 103008 (2022).
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202211096388DOI: 10.1088/1367-2630/ac932c View at publisher
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[Publication 5]: M. Will, M. Haque, Y. Chaudhry, D. S. Golubev, and P. Hakonen. Low-noise microwave parametric amplifier based on self-heated nonlinear impedance with subnanosecond thermal response. Phys. Rev. Applied, 23, 014037 (2025).
Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202504303414DOI: 10.1103/PhysRevApplied.23.014037 View at publisher