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20-qubit Schrödinger cat states with superconducting quantum processor

Date:12-08-2019 Print

Scientists, mainly from Zhejiang University led by Professor Haohua Wang and Institute of Physics of Chinese Academy of Sciences led by Professors Heng Fan and Dongning Zheng, successfully created Schrödinger cat states of up to 20-qubits with a superconducting quantum processor. 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. Altogether, there are 20 qubits integrated into the superconducting quantum device, all have long coherence time and can be controlled and readout with high fidelity.

In experiment, the system of qubits initialized coherently evolves to multi-component atomic Schrödinger cat states, i.e., superpositions of atomic coherent states including GHZ state, at specific time intervals. The fidelity of the generated 18-qubit GHZ state is larger than the threshold to demonstrate the state is genuine multiqubit entanglement.

This study entitled “Generation of multi-component atomic Schrödinger cat states of up to 20 qubits” was published on Science 365, 574-577 (2019).

The study was supported by the National Science Foundation, the Ministry of Science and Technology of China, the Chinese Academy of Sciences.

Fig.1 Time evolution of the multiqubit state by numerical simulation and experiment. The Schrödinger cat states in different forms including the GHZ state are created at specific time intervals. (Figure from Science 365, 574-577 (2019))
Fig.2 Device with 20 superconducting qubits and states distribution on Bloch sphere. (Image by authors from Zhejiang University and Institute of Physics)

Institute of Physics
FAN Heng

Key word:
Superconducting qubit; Entanglement; Schrödinger cat states;

Multiqubit entanglement are resource for quantum computation and quantum information. Here, deterministic generation of 18-qubit genuinely entangled Greenberger-Horne-Zeilinger (GHZ) state and multi-component atomic Schrödinger cat states of up to 20 qubits is reported.