Spin qubits in semiconductor gate defined quantum dots offer a good platform to manipulate quantum information in a scalable architecture. In these circuits, single or coupled electron spins are used as qubits for quantum information encoding and manipulation. One major hindrance for the realization of practical devices was the presence of nuclear spins in the host material which generate a fluctuating magnetic field inducing a fast dephasing of the electron spin. A great effort has been made to successfully address this issue in the past years. On the one hand, one of the remaining challenge is now to properly demonstrate the scalability of this architecture. On the other hand, one can also use the fast and sensitive technology of spin qubits to probe the dynamics of this nuclear spin bath. In the first part of this seminar, I will introduce how electron spins are manipulated in multiple spin qubits devices. In a second part, I will describe a recently realized multi-qubit device in which we operate 3 qubits [1]. In the third part, I will discuss how we can use a spin qubit to access the short time dynamics of its surrounding nuclear spin bath [2]. Finally I will show that by using a dedicated Bayesian inference algorithm, the resolution of a single nuclear spin fluctuation can be achieved while the spin qubit interacts with about one million of them.

References
[1] T. Nakajima et al., arXiv:1604.02232 (2016)
[2] M.R. Delbecq et al., Phys. Rev. Lett. 116, 046802 (2016)

Dr. Matt Delbecq is a researcher in the Center for Emergent Matter Science in RIKEN, Japan. He did his PhD work in the Mesoscopic group at Laboratoire Pierre Aigrain in the ENS Paris, with Takis Kontos, where he made significant achievements on coupling quantum dot circuits to microwave cavities. He joined RIKEN in 2013 and his current focus is on the interplay between electronic and nuclear spins in quantum dots.