Quantum state measurement is not only a fundamental component of quantum physics, but also plays an important role in the development of various practical quantum technologies, including quantum communication, quantum computing, as well as quantum metrology. However, the fidelity of readout exponentially decays with the number of qubits, which would hinder the large-scale expansion of quantum information processing. In particular, qubit measurement is generally the most error-prone operation on a quantum computer. Here, we present a quantum state readout method, named compression readout, to avoid huge errors caused by multi-qubit measurement, by compressing the quantum state into a single ancilla qubit and measuring this ancilla qubit. Compared with conventional measurements, our method is significantly more resilient against the readout noise from qubit growth, making it a promising candidate for high-fidelity quantum state readout in large-scale quantum computing.
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