The MCQST Colloquium Series features interdisciplinary talks given by visiting international speakers. The monthly colloquial covers topics spanning all MCQST research units and will be broadcasted live, being made available to audiences worldwide. The main goal of the series is to create the framework for idea exchange, to strengthen links with QST leading groups worldwide, as well as to act as an integral part of the local educational environment.

On 4 February 2020 we are excited to welcome Lieven Vandersypen, Professor at the Delft University of Technology, Netherlands.

Talk title

Simulating quantum magnetism with quantum dot Arrays

Abstract

Gate-defined quantum dots have recently emerged as an attractive platform for analog quantum simulation. A quantum dot array naturally emulates the extended Fermi-Hubbard model. The energy scales cover the most relevant parts of the phase diagram, with individually tunable hopping energies well below the on-site interaction energies and at the same time far exceeding the thermal energy. In addition, site-specific potential offsets are individually tunable, further extending the range of physical phenomena that can be explored.

Finally, the accessible observables include particle number, spin, spin correlations, addition energies and transport, complementing those of cold atom experiments. As a first illustration, we show the transition from Coulomb blockade to collective Coulomb blockade, the finite-size analogue of the metal to Mott insulator transition [1]. In a second experiment, we present evidence of Nagaoka ferromagnetism in a 2x2 quantum dot plaquette [2]. This is a form of magnetism that has not been observed before, highlighting the potential of quantum dots to provide new insights in Fermi-Hubbard physics. I will close with an overview and outlook of our recent work on silicon spin qubits [3-5].

[1] T. Hensgens, T. Fujita, L. Janssen, Xiao Li, C.J. van Diepen, C. Reichl, W. Wegschneider, S. Das Sarma, L.M.K. Vandersypen, Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array
Nature 548, 70–73 (2017)

[2] J.P. Dehollain, U. Mukhopadhyay, V.P. Michal, Y. Wang, B. Wunsch, C. Reichl, W. Wegscheider, M.S. Rudner, E. Demler, and L.M.K. Vandersypen, Nagaoka ferromagnetism observed in a quantum dot plaquette, Nature, in print (see arXiv:1904.05680)

[3] T.F. Watson, S.G.J. Philips, E. Kawakami, D.R. Ward, P. Scarlino, M. Veldhorst, D.E. Savage, M.G. Lagally, M. Friesen, S.N. Coppersmith, M.A. Eriksson, and L.M.K. Vandersypen, A programmable two-qubit quantum processor in silicon, Nature 555, 633-637 (2018)

[4] N. Samkharadze, G. Zheng, N. Kalhor, D. Brousse, A. Sammak, U.C. Mendes, A. Blais, G. Scappucci, and L.M.K. Vandersypen, Strong spin-photon coupling in silicon, Science 359, 1123-1127 (2018)

[5] X. Xue, T.F. Watson, J. Helsen, D.R. Ward, D.E. Savage, M.G. Lagally, S.N. Coppersmith, M.A. Eriksson, S. Wehner, and L.M.K. Vandersypen, Benchmarking Gate Fidelities in a Si/SiGe Two-Qubit Device, Phys. Rev. X 9, 021011 (2019)

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