Abstract
Quantum computation relies on accurate measurements of qubits not only for reading the output of the calculation, but also to perform error correction. Most proposed scalable silicon architectures utilize Pauli blockade of triplet states for spin-to-charge conversion. In recent experiments there have been instances when instead of conventional triplet blockade readout, Pauli blockade is sustained only between parallel spin configurations, with |T0⟩ relaxing quickly to the singlet state and leaving |T+⟩ and |T−⟩ states blockaded—which we call parity readout. Both types of blockade can be used for readout in quantum computing, but it is crucial to maximize the fidelity and understand in which regime the system operates. We devise and perform an experiment in which the crossover between parity and singlet-triplet readout can be identified by investigating the underlying physics of the |T0⟩ relaxation rate. This rate is tunable over 4 orders of magnitude by controlling the Zeeman energy difference between the dots induced by spin-orbit coupling, which in turn depends on the direction of the applied magnetic field. We suggest a theoretical model incorporating charge noise and relaxation effects that explains quantitatively our results. Investigating the model both analytically and numerically, we identify strategies to obtain on demand either singlet-triplet or parity readout consistently across large arrays of dots. We also discuss how parity readout can be used to perform full two-qubit state tomography and its impact on quantum error-detection schemes in large-scale silicon quantum computers.Received 22 April 2020Revised 2 June 2020Accepted 3 December 2020DOI:https://doi.org/10.1103/PRXQuantum.2.010303Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasQuantum computationQuantum tomographyPhysical SystemsQuantum dotsSemiconductorsQuantum InformationCondensed Matter & Materials Physics
Highlights
The recent demonstration of large-scale quantum computation [1] has opened the door to the exploration of nearterm applications of noisy, intermediate-scale devices
The parity-readout scheme may seem to be unable to provide the same level of information as the individual measurements of each spin qubit. This concern is already present with traditional singlet-triplet blockade readout—the outcome of the readout is a single bit of information, while the input is two qubits
Measurements on single qubits based on tunneling to a large reservoir [41], may be impractical for a dense two-dimensional array of qubits in a large-scale quantum computer
Summary
The recent demonstration of large-scale quantum computation [1] has opened the door to the exploration of nearterm applications of noisy, intermediate-scale devices. We can tune the T0 blockade lifting rate by 4 orders of magnitude by controlling Zeeman energy difference, which is tuned in our system by varying the angle of the external magnetic field relative to the crystal lattice, since the Zeeman energy difference is dominated by spin-orbit interaction [24] Incorporating this observation, we use perturbation theory to model the blockade time in the system both analytically [25] and computationally. We find that both models fit qualitatively the experimental data, but the fitted charge-dephasing time is more reasonable than the fitted relaxation time, suggesting a different type of underlying mechanism in silicon than in GaAs [23] These results are an important tool to be able to understand how to tune the readout from parity to singlet-triplet and vice versa. We discuss how to perform full two-qubit state tomography as well as error detection [4,5,18], utilizing parity readout
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