We report the preparation and verification of a genuine 12-qubit entanglement in a superconducting processor. The processor that we designed and fabricated has qubits lying on a 1D chain with relaxation times ranging from 29.6 to 54.6 µs. The fidelity of the 12-qubit entanglement was measured to be above 0.5544±0.0025, exceeding the genuine multipartite entanglement threshold by 21 statistical standard deviations. Our entangling circuit to generate linear cluster states is depth-invariant in the number of qubits and uses single-and double-qubit gates instead of collective interactions. Our results are a substantial step towards large-scale random circuit sampling and scalable measurement-based quantum computing.

Quantum walks are the quantum analogs of classical random walks, which allow for the simulation of large-scale quantum many-body systems and the realization of universal quantum computation without time-dependent control. We experimentally demonstrate quantum walks of one and two strongly correlated microwave photons in a one-dimensional array of 12 superconducting qubits with short-range interactions. First, in one-photon quantum walks, we observed the propagation of the density and correlation of the quasiparticle excitation of the superconducting qubit and quantum entanglement between qubit pairs. Second, when implementing two-photon quantum walks by exciting two superconducting qubits, we observed the fermionization of strongly interacting photons from the measured time-dependent long-range anticorrelations, representing the antibunching of photons with attractive interactions. The demonstration of quantum walks on a quantum processor, using superconducting qubits as artificial atoms and tomographic readout, paves the way to quantum simulation of many-body phenomena and universal quantum computation.

Amorphous SnO thin films were prepared on quartz and 190 nm SiO2/Si(001) substrates by electron beam evaporation. X-ray diffraction results reveal that amorphous SnO transforms into polycrystalline α-SnO (tetragonal litharge structure) after rapid thermal annealing in Ar ambient at 350–400°C and starts decomposing into o-SnO2 (orthorhombic structure) with the expulsion of Sn atoms at 450–500°C . The optical properties were characterized via spectroscopic ellipsometry. The polycrystalline SnO thin films have a higher refractive index n and a narrower bandgap Enormalg than the amorphous ones, which is due to the polarizability enhancement in the crystallization process. Moreover, the relationship between n and Enormalg of the amorphous and polycrystalline SnO thin films can be explained by the “Moss rule” law, and a decreasing trend in n was verified with the transformation from SnO to SnO2 . Bottom-gate-type thin film transistors (TFTs) employing polycrystalline SnO channels on the SiO2/Si(001) substrates exhibit p-type field-effect transistor characteristics. The optimum field-effect mobilities μsat and μlin are 0.46 and 0.87cm2normalV−1normals−1 , respectively, which are the same order of magnitude as those reported for epitaxial SnO TFTs.

Superconducting quantum circuits are a promising candidate for building scalable quantum computers. Here, we use a four-qubit superconducting quantum processor to solve a two-dimensional system of linear equations based on a quantum algorithm proposed by Harrow, Hassidim, and Lloyd [Phys. Rev. Lett. 103, 150502 (2009)PRLTAO0031-900710.1103/PhysRevLett.103.150502], which promises an exponential speedup over classical algorithms under certain circumstances. We benchmark the solver with quantum inputs and outputs, and characterize it by nontrace-preserving quantum process tomography, which yields a process fidelity of 0.837±0.006. Our results highlight the potential of superconducting quantum circuits for applications in solving large-scale linear systems, a ubiquitous task in science and engineering.