Public defence in Engineering Physics, M.Sc. Mohammad Tasnimul Haque

Title of the thesis: Hybrid Josephson junctions and electrothermal effects in graphene devices

Thesis defender: Mohammad Tasnimul Haque
Opponent: Assistant Professor Ville Maisi, Lund University, Sweden
Custos: Professor Pertti Hakonen, Aalto University School of Science

This thesis investigates graphene-based superconductor–graphene–superconductor (SGS) Josephson junctions integrated with superconducting microwave cavities for quantum technologies. Graphene’s high electron mobility, atomic thickness, and gate-tunable proximity-induced superconductivity make SGS junctions promising for long-lived and magnetic-field-resilient quantum circuits.

We first study low-frequency 1/𝑓 critical current noise in encapsulated SGS junctions using microwave reflection measurements, finding significant fluctuations that increase away from the charge neutrality point. Next, we explore electrothermal effects in graphene devices, including thermal self-oscillations in a graphene SINIS junction, which enable the extraction of electron–phonon coupling and parametric microwave amplification. We also demonstrate thermoelectric current generation in a graphene-based Cooper pair splitter.

Finally, we study theoretically microwave quantum optomechanics mediated by Josephson capacitance and achieve ultrastrong single-photon coupling, enabling non-classical states and single-phonon detection. Overall, this work highlights graphene–superconductor hybrids as versatile building blocks for future quantum circuits. 

Keywords: Graphene, Josephson junctions, Superconducting circuits, 1/f noise, Microwave optomechanics, Quantum computing 

Contact information: 
mohammad.haque@aalto.fi 
Linkedin: https://www.linkedin.com/in/mohammad-tasnimul-haque-249184115/ 

Research Group: https://www.aalto.fi/en/department-of-applied-physics/quantum-circuits-and-correlations-nano 

Thesis available for public display 7 days prior to the defence at Aalto University's public display page.