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Quantum walks on a programmable two-dimensional 62-qubit superconducting processor

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Science  28 May 2021:
Vol. 372, Issue 6545, pp. 948-952
DOI: 10.1126/science.abg7812

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Simulating quantum walkers

Quantum walks are the quantum mechanical analogs of classical random walks, describing the propagation of a quantum walker across a lattice, and find application in developing algorithms for simulating quantum many-body systems. Gong et al. used an 8-by-8 two-dimensional (2D) superconducting qubit square lattice containing 62 functional qubits to show how multiple (two) walkers traverse a 2D qubit array, interfering as they go. The authors were also able to program the paths that the walkers follow, demonstrating a Mach-Zehnder interferometer in which a single or multiple quantum walkers coherently traverse two paths before interfering and exiting at a single port. The results illustrate the potential for superconducting-based quantum processors in simulating large-scale quantum systems.

Science, abg7812, this issue p. 948

Abstract

Quantum walks are the quantum mechanical analog of classical random walks and an extremely powerful tool in quantum simulations, quantum search algorithms, and even for universal quantum computing. In our work, we have designed and fabricated an 8-by-8 two-dimensional square superconducting qubit array composed of 62 functional qubits. We used this device to demonstrate high-fidelity single- and two-particle quantum walks. Furthermore, with the high programmability of the quantum processor, we implemented a Mach-Zehnder interferometer where the quantum walker coherently traverses in two paths before interfering and exiting. By tuning the disorders on the evolution paths, we observed interference fringes with single and double walkers. Our work is a milestone in the field, bringing future larger-scale quantum applications closer to realization for noisy intermediate-scale quantum processors.

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