Sandoko Kosen

Popular Summary Quantum computers have the potential to address complex problems beyond the capacity of current supercomputers. The main challenge is to scale hardware to handle such tasks. A popular method involves an array of tiny superconducting devices on a low-loss chip, controlled by on-chip transmission lines. As the number of devices increases, crosstalk, which is an unintended control of components within the processor, can have harmful effect on the quantum computation.

Abstract High-fidelity and rapid readout of a qubit state is key to quantum computing and communication, and it is a prerequisite for quantum error correction. We present a readout scheme for superconducting qubits that combines two microwave techniques: applying a shelving technique to the qubit that reduces the contribution of decay error during readout, and a two-tone excitation of the readout resonator to distinguish among qubit populations in higher energy levels.

The realisation of superconducting quantum processors with arrays of increasing numbers of qubits faces several interesting engineering and physics challenges [1–3]. From the hardware perspective, scaled-up circuit designs and fabrication processes must not degrade the device performance, which otherwise would adversely affect the fidelity of quantum algorithms.