

Device with 20 superconducting qubits and states distribution on Bloch sphere. (Image by authors from Zhejiang University and Institute of Physics) Device with 20 superconducting qubits and states distribution on Bloch sphere. (Image by authors from Zhejiang University and Institute of Physics) In addition, they showed that the generated 18-qubit Greenberger-Horne-Zeilinger (GHZ) state is genuine entangled. So far, it is the largest GHZ state ever created in solid state quantum computation platforms. The achievement of those results is a big step toward building a quantum computer.



The superconducting qubit based on Josephson junction is one of the most promising schemes to build a quantum computer, because of its long coherence time, high fidelity control and precise readout.



In particular, scalability is one of the main advantages for the superconducting quantum processor, which can integrate a great number of qubits. To coherently control all qubits in a superconducting quantum processor, it is necessary to show that each qubit can be controlled precisely, and any pair of qubits can be entangled. It may be more challenging to show that all qubits can be entangled to generate a GHZ state and Schrödinger cat states.



The generation of multiqubit entanglement is a benchmark for demonstrating the performance of quantum devices and the control. To achieve those aims, the scientists from China peculiarly designed an all-to-all device with all qubits connected with others.