Prof Ferdinand Kuemmeth's gives seminar on quantum dot arrays

ORGANISERS: Pavlo Zubko and Alice Pyne

SPEAKER: Prof Ferdinand Kuemmeth | Copenhagen University

TIME&VENUE: 30th January 2019 | 1pm | LG17 Lecture Room, Bentham House, 4-8 Endsleigh Gardens

TITLE: Spin exchange in quantum dot arrays

ABSTRACT: Modern computers process information classically, using the charge of large ensembles of electrons. Quantum effects remain a detail rather than a resource. Quantum computers based on individual spins in the solid-state environment will require a detailed understanding and appropriate use of coherent spin interactions, with the Heisenberg exchange interaction likely playing a central role. Using an array of quantum dots in a GaAs heterostructure, defined and controlled by top gates, we explore the properties of a multielectron dot for inducing coherent spin exchange processes between neighboring and non-nearest-neighbor one-electron dots.

Our measurements indicate that a multielectron quantum dot with 50-100 electrons serves as an excellent mediator, preserving speed and coherence of the resulting spin-spin coupling while providing functionalities that may be of practical importance. These include speed (mediated two-qubit rates up to several gigahertz), distance (of order of a micrometer), voltage control, possibility of sweet spot operation (reducing susceptibility to charge noise), and reversal of the interaction sign [1] (useful for dynamical decoupling from noise). By detuning two one-electron dots with respect to the multielectron dot, we map out different configurations useful for long-distance spin exchange, including indirect, direct, and on-site exchange mediated by the multielectron dot [2]. Our results show a pathway to implementing fast, non-nearest neighbor two-qubit gates in semiconducting spin qubits. I will show our recent efforts into extending the mediated spin coupling into two dimensions.

[1] F. K. Malinowski, F. Martins, et al, Phys. Rev. X 8, 011045 (2018)

[2] F. K. Malinowski, F. Martins, et al, arXiv:1808.09736