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Physics

Improved Readout of Spin Qubits

Ryan Wilkinson

Published Feb 23, 2023• 0 citations
Publisher

Abstract

Improved Readout of Spin QubitsTwo teams demonstrate an innovative way to measure the states of spin-based qubits-a key task in quantum computing. By Ryan WilkinsonQ uantum computers require a method for determining the states of their computational units, or qubits.Ideally, qubit readout should be fast, accurate, and performed using hardware that facilitates high qubit connectivity.This hardware should also be easy to integrate into the computing architecture.Now two independent teams show how these criteria can be met in the case of a promising type of quantum computer that uses electron spins in silicon as its qubits [1, 2].The groups' demonstrations could bring large-scale versions of these machines closer to reality.Giovanni Oakes at Quantum Motion Technologies, UK, and his colleagues developed a compact sensor for qubit readout.This detector has a small footprint, needing fewer electrodes than conventional sensors.It also offers high readout fidelity and speed, discerning the correct state of a qubit with 99.2% fidelity in a measurement time of under 6 µs.Crucially, this timescale is much shorter than the typical time it takes for a silicon spin-based qubit to lose its state through decoherence, Credit: G. A.

DOI
10.1103/physics.16.s27

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Improved Readout of Spin QubitsTwo teams demonstrate an innovative way to measure the states of spin-based qubits-a key task in quantum computing. By Ryan WilkinsonQ uantum computers require a method for determining the states of their computational units, or qubits.Ideally, qubit readout should be fast, accurate, and performed using hardware that facilitates high qubit connectivity.This hardware should also be easy to integrate into the computing architecture.Now two independent teams show how these criteria can be met in the case of a promising type of quantum computer that uses electron spins in silicon as its qubits [1, 2].The groups' demonstrations could bring large-scale versions of these machines closer to reality.Giovanni Oakes at Quantum Motion Technologies, UK, and his colleagues developed a compact sensor for qubit readout.This detector has a small footprint, needing fewer electrodes than conventional sensors.It also offers high readout fidelity and speed, discerning the correct state of a qubit with 99.2% fidelity in a measurement time of under 6 µs.Crucially, this timescale is much shorter than the typical time it takes for a silicon spin-based qubit to lose its state through decoherence, Credit: G. A.
Qubit Readout Mystery SolvedTheoretical work provides a long-awaited explanation for why measurements of qubits in superconducting quantum computers are less accurate than expected.By Ryan Wilkinson Q uantum computers that use superconducting quantum bits (qubits) offer high efficiency and scalability.But their operation is limited by the fact that the readout of their qubits is more error prone than predicted by theory.This poor performance has been unexplained for two decades, despite many attempts to understand it.Now Marie Frédérique Dumas and her colleagues at the University of Sherbrooke, Canada, have developed a theoretical framework that solves this mystery [1].The researchers hope that their framework will enable superconducting quantum computers to perform calculations more accurately and without needing as many error-correction measures.
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As quantum processors grow in complexity, the focus is shifting towards the scaling of the entire quantum computing system, including the quantum hardware but as well the classical support electronics. Silicon-based quantum computing offers the enticing possibility that the quantum processor, the quantum-classical interface, and the classical layer can all, in principle, be manufactured using complementary metal-oxide semiconductor (CMOS) technology, creating an opportunity to move from distributed quantum-classical systems to integrated quantum computing solutions. Here, we review the state-of-the-art in spin-based quantum computing in silicon and present different approaches to help scale the technology using CMOS technology. We discuss the use of industry-manufactured silicon devices as the basic qubit element and present radio-frequency reflectometry techniques for fast high-fidelity spin readout. Finally, we show how quantum-classical co-integration can enable large-scale control and readout via frequency- and time-domain multiplexing.
Recent advances in quantum error correction codes for fault-tolerant quantum computing and physical realizations of high-fidelity qubits in multiple platforms give promise for the construction of a quantum computer based on millions of interacting qubits. However, the classical-quantum interface remains a nascent field of exploration. Here, we propose an architecture for a silicon-based quantum computer processor based on complementary metal-oxide-semiconductor (CMOS) technology. We show how a transistor-based control circuit together with charge-storage electrodes can be used to operate a dense and scalable two-dimensional qubit system. The qubits are defined by the spin state of a single electron confined in quantum dots, coupled via exchange interactions, controlled using a microwave cavity, and measured via gate-based dispersive readout. We implement a spin qubit surface code, showing the prospects for universal quantum computation. We discuss the challenges and focus areas that need to be addressed, providing a path for large-scale quantum computing.
Three key metrics for readout systems in quantum processors are measurement speed, fidelity and footprint. Fast high-fidelity readout enables mid-circuit measurements, a necessary feature for many dynamic algorithms and quantum error correction, while a small footprint facilitates the design of scalable, highly-connected architectures with the associated increase in computing performance. Here, we present two complementary demonstrations of fast high-fidelity single-shot readout of spins in silicon quantum dots using a compact, dispersive charge sensor: a radio-frequency single-electron box. The sensor, despite requiring fewer electrodes than conventional detectors, performs at the state-of-the-art achieving spin read-out fidelity of 99.2% in less than 6 μμμs. We demonstrate that low-loss high-impedance resonators, highly coupled to the sensing dot, in conjunction with Josephson parametric amplification are instrumental in achieving optimal performance. We quantify the benefit of Pauli spin blockade over spin-dependent tunneling to a reservoir, as the spin-to-charge conversion mechanism in these readout schemes. Our results place dispersive charge sensing at the forefront of readout methodologies for scalable semiconductor spin-based quantum processors.
Abstract Recent advances in quantum error correction codes for fault-tolerant quantum computing and physical realizations of high-fidelity qubits in multiple platforms give promise for the construction of a quantum computer based on millions of interacting qubits. However, the classical-quantum interface remains a nascent field of exploration. Here, we propose an architecture for a silicon-based quantum computer processor based on complementary metal-oxide-semiconductor (CMOS) technology. We show how a transistor-based control circuit together with charge-storage electrodes can be used to operate a dense and scalable two-dimensional qubit system. The qubits are defined by the spin state of a single electron confined in quantum dots, coupled via exchange interactions, controlled using a microwave cavity, and measured via gate-based dispersive readout. We implement a spin qubit surface code, showing the prospects for universal quantum computation. We discuss the challenges and focus areas that need to be addressed, providing a path for large-scale quantum computing.