Abstract
High-fidelity qubit readout is critical in order to obtain the thresholds needed to implement quantum error-correction protocols and achieve fault-tolerant quantum computing. Large-scale silicon qubit devices will have densely packed arrays of quantum dots with multiple charge sensors that are, on average, farther away from the quantum dots, entailing a reduction in readout fidelities. Here, we present a readout technique that enhances the readout fidelity in a linear SiMOS four-dot array by amplifying correlations between a pair of single-electron transistors, known as a twin SET. By recording and subsequently correlating the twin SET traces as we modulate the dot detuning across a charge transition, we demonstrate a reduction in the charge readout infidelity by over one order of magnitude compared to traditional readout methods. We also study the spin-to-charge conversion errors introduced by the modulation technique and conclude that faster modulation frequencies avoid relaxation-induced errors without introducing significant spin-flip errors, favoring the use of the technique at short integration times. This method not only allows for faster and higher-fidelity qubit measurements but it also enhances the signal corresponding to charge transitions that take place farther away from the sensors, enabling a way to circumvent the reduction in readout fidelities in large arrays of qubits.
- Received 25 July 2023
- Accepted 6 November 2023
DOI:https://doi.org/10.1103/PRXQuantum.5.010301
Published 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 Society
Physics Subject Headings (PhySH)
Popular Summary
Quantum computing has the potential to solve certain problems that are intractable by any known classical algorithms, spanning from cryptography and logistics to fluid dynamics and pharmaceutical design. In order for quantum computers to be useful, millions of qubits need to be operated and measured, which requires a large number of sensors for readout, adding complexity to the circuit design. Additionally, the quality of the measurement of the quantum state, known as readout fidelity, needs to be high while maintaining short measurement times.
In this work, we focus on improving the readout fidelity of a quantum processor made from silicon quantum dots by finding correlations between the signals of a pair of charge sensors known as single-electron transistors (SETs). Our experiments show that by applying a pulse that modulates the readout signal of the SETs and correlating the independent signals, we can reduce the readout errors by more than 1 order of magnitude, resulting in faster measurements and allowing farther qubits to be measured with equitable fidelity. Moreover, this process does not introduce significant qubit errors, making it a suitable approach for high-fidelity qubit readout.
In the future, new ways to correlate the signals from a larger number of sensors and better modulation pulses can be studied to further improve the readout quality. Likewise, this technique may be employed with other types of fast sensors, making it versatile to implement. The technique we present not only allows for better and faster readout but can also reduce the total number of sensors needed in a large-scale quantum computer, facilitating the design and relaxing fabrication constraints.
