Spin triplet-singlet relaxation in silicon quantum dots sensed via high-fidelity dispersive charge sensing*

Silicon quantum dot devices can be industrially fabricated, allowing to scale-up spin-based quantum computers using large-scale integration processes. To assess the viability of this approach, benchmarking the spin dynamic figures of merit becomes of primary importance. Here, we present a parametric characterisation of the spin triplet-singlet relaxation time in a linear array of three industry-fabricated silicon quantum dots contained in a fully-depleted silicon nanowire multi-gate transistor. We use one of the dots as a radio-frequency single-electron box (SEB) for single-shot readout of the spin state of a double quantum dot via Pauli-spin blockade. We probe the SEB dispersively via a high-impedance LC resonator to enhance sensitivity which allows us to achieve average readout fidelities above 99% in less than 1 ms. We study the magnetic field and temperature on the triplet-singlet relaxation time along the (3,1)-(4,0) transition and find a dependence compatible with relaxation mediated by a combination of direct phonon plus Raman relaxation. Finally, we find relaxation times up to 250 ms, on par with state-of-the-art results in academic devices.