According to quantum mechanics, chiral states cannot be non-degenerate eingenstates of a parity-conserving Hamiltonian. This is in contradiction to the existence of chiral molecules—a fact known as as the Hund paradox1. The origin of molecular and biological chirality is conjectured to be related to parity-breaking interactions2,3 or environmental decoherence4, but a quantum superposition of two chiral molecular states with distinctive optical activities has never been observed5. To make progress in addressing these questions, it would be helpful to construct an artificial quantum system that breaks the parity symmetry and that can be prepared in a superposition of two chiral states. Here we report the synthesis of the parity-breaking antisymmetric spin exchange interaction in all-to-all connected superconducting circuits, which allows us to show various chiral spin dynamics in up to five-spin clusters. We also demonstrate the entanglement of up to five qubits in Greenberger–Horne–Zeilinger states based on a three-spin chiral logic gate. Our results are a step towards quantum simulation of magnetism with antisymmetric spin exhange interaction and quantum computation with chiral spin states.
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The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.
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The authors thank W. Liu, Q. Guo and K. Huang for technical support. This research was supported by the National Key Research and Development Program of China (grants nos. 2018YFA0307200, 2017YFA0304202 and 2016YFA0300601), the National Natural Science Foundations of China (grants nos. 11434008, 11574380, 11725419 and 11874322) and the Fundamental Research Funds for the Central Universities of China (grant no. 2016XZZX002-01). D.W.W. was also supported by the key research programme of the Chinese Academy of Sciences (grant no. XDPB08-3). M.O.S. was supported by the Air Force Office of Scientific Research (award no. FA9550-18-1-0141), the Office of Naval Research (award no. N00014-16-1-3054) and the Robert A. Welch Foundation (grant no. A-1261). Devices were made at the Nanofabrication Facilities at the Institute of Physics in Beijing, the University of Science and Technology of China in Hefei and the National Center for Nanoscience and Technology in Beijing.
The authors declare no competing interests.
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Wang, D., Song, C., Feng, W. et al. Synthesis of antisymmetric spin exchange interaction and chiral spin clusters in superconducting circuits. Nat. Phys. 15, 382–386 (2019) doi:10.1038/s41567-018-0400-9
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