Tuning the coherent electron-nuclear interaction in a semiconductor quantum dot
An electron hosted in a quantum dot (QD) provides a natural realization of the central spin system, as it interacts with the ∼ 10^5 nuclear spins that compose the quantum dot. Ideally, this system can be used to implement a multi-qubit register formed by collective excitations of the nuclei surrounding the electron, or to probe fundamental many-body physics through engineering of collective states. However, a tuneable interaction between the electron and the nuclear ensemble is required to fully benefit from this system. This work describes the realization of an in situ tuneable coherent exchange interaction between the electron and the nuclear ensemble in a GaAs QD via a non-collinear interaction mediated by an anisotropy of the electron g-factor. The first part of this work develops the infrastructure needed to explore the physics of the electron and nuclear spins in the latter part of the work. This begins with a review of the physics relevant to control of the electron spin hosted in a QD, and the formalism of the interactions between the electron and nuclei. This is followed by protocols to process GaAs heterostructructures into diode devices, allowing a single electron to be deterministically loaded into the QD, as well as the construction of a confocal microscope and associated microwave and laser systems to perform all-optical control of the electron spin in the GaAs QD. Following this, extrinsic strain is explored as a method to introduce a tuneable coherent electro-nuclear interaction in a GaAs QD. Two different strain devices are described, and the applied strain is characterized. The drawbacks of the strain-induced interaction are briefly discussed. The final part of the work describes the coherent electron-nuclear interaction mediated by an electron g-factor anisotropy. This begins with the implementation and optimization of nuclear cooling algorithms, pioneered in InGaAs QDs, in the GaAs QD system, which enables control over the mean-field polarization of the nuclear ensemble, as well as the resolution of collective excitations of the nuclear ensemble via electron spin resonance experiments. The mechanism behind the electro-nuclear interaction is described and the interaction is fully characterized via electron spin resonance spectroscopy and dynamical decoupling pulse sequences. Further, by selecting the mean-field nuclear polarization, the strength of the electro-nuclear interaction can be controllably varied. This in turn enables the activation rate of collective nuclear excitations – and thus the interaction between the central spin and its register – to be tuned fully in situ, solely via pulse sequences. This work demonstrates the realization of a tuneable solid-state central spin system, a promising step ahead for the realization of quantum computing protocols and the exploration of many-body physics in the solid-state.
Central spin system, GaAs, Non-collinear interaction, Nuclear spins, Physics, Quantum, Quantum dot, Spin
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