December 8, 2022

Spin-to-charge conversion achieves 95% overall qubit readout fidelity

Spin-to-charge conversion achieves 95% overall qubit readout fidelity a) Energy levels used to achieve SCC. b) A schematic diagram of SCC readout. c) The excitation spectrum of the nitrogen-vacancy (NV) center used here at cryogenic temperature of 8?K. d) Spin-flip process induces the photoluminescence (PL) decay. Credit: ZHANG Qi et al.

A team at the University of Science and Technology of China put forward an innovative spin-to-charge conversion method to achieve high-fidelity readout of qubits, stepping closer towards fault-tolerant quantum computing.

Fault-tolerant Quantum Computing requires the accumulated logic gate error and the spin readout fidelity to exceed the fault-tolerant threshold.

The readout fidelity of traditional resonance fluorescence method is strictly limited by such property. Since the spin state is difficult to measure, researchers blazed a trail to replace it with an easy-to-readout and measurable property: the charge state.

They first compared the optical readout lifetime of the charge state and spin state, finding that the charge state is more stable than the spin state by five orders of magnitude. Experiment results showed that the average non-demolition charge readout fidelity reached 99.96%.

Then the team adopted near-infrared (NIR) light (1064 nm) to induce the ionization of the excited spin state, transforming the spin state 0 and 1 to the “electrically neutral” and “negatively charged” charge states respectively. This process converted the spin readout to the charge readout.

The results indicated that the error of traditional resonance fluorescence method reached 20.1%, while the error of this new method can be suppressed to 4.6%. (

The article has been published in Nature Communications.

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