- 초청연사 -

조명래 (National Physical Laboratory, UK) 16:00~18:00 

Title An electron interferometer in quantum hall graphene and superconducting quantum information processing at NPL

Abstract

The concept of van der Waals heterostructure enables us to harness exotic properties of 2D materials in their cleanest limit. Thanks to such progress, recently several studies have demonstrated electron quantum optics devices with graphene by exploiting the wave nature of electrons in the quantum Hall regime.^{[1, 2, 3, 4]} Previously this had been only possible with high-mobility GaAs 2D electron gas. Here, we present the realization of a graphene Mach-Zehnder interferometer with fully tunable beam splitters.^[2] Coherent splitting and mixing of the copropagating but opposite-valley (with the same spin) channels of the PN interface are independently achieved by tuning the filling factors below, above, and around the flake of graphene in the quantum Hall regime. Measuring the modulation of the electrical current through the PN junction reveals a quantum interference pattern. This experiment provides an additional material platform in the field of electron quantum optics.

Next, we present a brief introduction of NPL’s Superconducting Quantum Information Processing (SQIP) group and our ongoing projects. Among the various quantum platforms, superconducting quantum circuits stand out with their scalability which stems from the accumulated experience of microelectronic circuits. Our projects include but are not limited to 1) detection of decoherence sources in quantum circuits 2) fabrication process optimization for quantum circuits 3) novel instrumentations at the mK regime, potentially leading to new, highly advanced capabilities in both nanotechnology and quantum computing.

[1] Di S. Wei, Toeno Van der Sar, Javier D. Sanchez-Yamagishi, et al. Mach-Zehnder interferometry using spin- and valley-polarized quantum Hall edge states in graphene. Science Advances 3, e170060 (2017)

[2] M. Jo, P. Brasseur, A. Assouline, et al. Quantum Hall Valley Splitters and a Tunable Mach-Zehnder Interferometer in Graphene. Physical Review Letters 126, 146803 (2021)

[3] Déprez, C., Veyrat, L., Vignaud, H. et al. A tunable Fabry–Pérot quantum Hall interferometer in graphene. Nature Nanotechnology 16, 555–562 (2021)

[4] Ronen, Y., Werkmeister, T., Haie Najafabadi, D. et al. Aharonov–Bohm effect in graphene-based Fabry–Pérot quantum Hall interferometers. Nature Nanotechnology 16, 563–569 (2021)