A nanophotonic platform for the tin-vacancy centre

Abstract

Quantum networking will enable quantum devices to exchange information. As of today, the technology is still at an early research stage, and entanglement has only been demonstrated at low rates and between a few nodes. Among the concerted efforts to establish new scalable architectures, colour centres in wide-bandgap semiconductors are particularly attractive, as they could leverage well-established semiconductor manufacturing processes on the route towards commercial technologies. In this thesis, we study the tin-vacancy centre in diamond, a colour centre best described as a forward-facing platform. Its inversion-symmetric structure brings about a system with a reduced coupling to phonons and electric noise. It promises outstanding optical properties, even within nanostructures, and thus integration into photonic integrated circuits. This thesis demonstrates a series of building blocks for quantum networking with the tin-vacancy centre. Firstly, we integrate tin-vacancy centres into diamond waveguides and study their optical coherence. We show that they are spectrally stable in this environment, and that we can control the optical transition and collect its resonant photons. These capabilities enable the study of two-photon interference effects, a key element of many quantum networking protocols. Secondly, we implant spin-active tin isotopes, and study the resulting two-qubit system. We show a signature optical splitting, consistent across all emitters, that is an order of magnitude larger than the homogeneous linewidth. This enables direct optical initialisation and readout of the nuclear spin and showcases its potential as a long-lived optically-accessible deterministic quantum memory. Finally, we integrate the diamond waveguide with a tapered optical fibre, which results in an efficient optical interface with new capabilities. We show single-shot readout of the nuclear spin, collect many-photon states, and directly measure the high quantum efficiency. The device is interfaced solely via the input-output fibre, with no confocal excitation, and thus forms the basis of a scalable quantum node. In combination with other achievements, such as high-fidelity quantum control, these results establish that the tin-vacancy centre meets all the requirements for a functional quantum node. Quantum networking experiments such as spin-photon or remote entanglement are now within reach.