Fast High-Fidelity Single-Shot Readout of Spins in Silicon Using a Single-Electron Box

Abstract

Three key metrics for readout systems in quantum processors are measurement speed, fidelity, and footprint. Fast high-fidelity readout enables midcircuit 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 readout fidelity of 99.2% in less than6μsfitted from a physical model. 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.

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Plain Language Summary

Quantum computers require a readout method capable of discerning the state of their computational units, i.e., qubits. An ideal method should be able to read the information fast—much faster than the time qubits lose their quantum state—and to do so with high fidelity, determining the correct state at least 99% of the time to be able to implement quantum-error-correction protocols. A readout sensor should also be compact, to facilitate the design of highly connected qubit arrangements for enhanced computational performance. Here, we show how to fulfill these requirements for silicon spin qubits, a leading candidate to build high-fidelity quantum processors.

We develop a compact dispersive charge sensor: a radio-frequency single-electron box (SEB). The sensor is composed of a quantum dot that periodically exchanges single electrons with a charge reservoir due to the oscillatory electric field of an electrical resonator coupled to it. The magnitude and phase of such an alternating current can be used as a sensitive probe of the electrostatic environment of the SEB, and in our case of the state of electron spin qubits in silicon quantum dots.

The sensor, despite requiring fewer electrodes than conventional detectors, achieves a state-of-the-art spin readout fidelity of 99.2% in less than6μs, a timescale much shorter than typical coherence times for electron spin qubits. Furthermore, we develop a detailed model highlighting the most important technological parameters of the SEB.

This work should guide quantum engineers to better design, fabricate, and operate SEBs for compact, fast, and high-fidelity readout of semiconductor spin-based quantum processors.