Mid-circuit measurements are one of the biggest practical hurdles in quantum error correction on encoded qubits. Researchers in Innsbruck and Aachen have now proposed and experimentally demonstrated that a universal fault-tolerant quantum algorithm can be executed without such measurements. Using a trapped-ion quantum processor, the team successfully ran Grover's quantum search algorithm on three logical qubits.
A key bottleneck in today's leading approaches to quantum error correction is the need to repeatedly pause and measure the quantum processor mid-computation, a process that is slow, technically demanding, and itself a significant source of errors.
Now, a joint team from the University of Innsbruck, RWTH Aachen University, Forschungszentrum Jülich and spin-off Alpine Quantum Technologies (AQT) has demonstrated fault-tolerant quantum computation without any such interruptions.
In a study published in Nature Communications, the team presents a complete toolbox of fault-tolerant quantum operations that eliminates so-called mid-circuit measurements and feed-forward control entirely. Rather than stopping the computation to read out error information and classically deciding on a correction, the new approach processes error information coherently. The paper is titled "Demonstration of measurement-free universal logical quantum computation."
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