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High-fidelity, compact readout of spins in silicon quantum dots

Ciriano Tejel, Virginia; (2022) High-fidelity, compact readout of spins in silicon quantum dots. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Silicon has become one of the leading platforms for quantum computation, having demonstrated qubits with long coherence times and high fidelity operations. Moreover, the similarities between silicon quantum dots and transistors give hope for mass production of qubits easily integrable with control electronics. However, to fully leverage their scalability potential, the footprint of the additional circuits for control and readout needs to be minimised. Here, we introduce a compact spin-readout method based on spin-dependent tunnelling combined with a dispersive charge sensor: the radio-frequency single-electron box (SEB). Opposite to traditional charge sensors, the SEB only requires a single lead, reducing its footprint. Using this sensing technique, we demonstrate spin readout of a single electron spin in a CMOS device manufactured at the 300mm wafer-scale using industrial processes, in which we measure long single spin relaxation times (up to 9 s). Next, we focus on achieving a high readout fidelity, since it is essential to perform error correction and ultimately sets the fidelity of qubit operations. The readout fidelity is partly set by the ability of the sensor to detect rapid events with high accuracy. We demonstrate that a low-loss high-impedance resonator highly coupled to the SEB, together with a Josephson Parameter Amplifier, are central for optimal performance. With these modifications, we obtain an integration time τm = 100 ns for a signal to noise ratio equal to 1, which facilitates single-shot spin readout, reaching a measurement fidelity FM = 99.54%, above the fault-tolerant threshold, in a readout time Δt = 250 μs. We identify that the readout time is limited by the choice of the spin-to-charge conversion mechanism. In the last part of the thesis, we work towards performing Pauli spin blockade spin readout, which does not have such time limitation.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: High-fidelity, compact readout of spins in silicon quantum dots
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification: UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
UCL > Provost and Vice Provost Offices > UCL BEAMS
URI: https://discovery.ucl.ac.uk/id/eprint/10154074
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