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18-Qubit Entanglement with Six Photons' Three Degrees of Freedom
Xi-Lin Wang1, Yi-Han Luo1, He-Liang Huang1
1Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026, China; CAS Centre for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei, Anhui 230026, China; and CAS-Alibaba Quantum Computing Laboratory, Shanghai 201315, China.
Abstract:
Full control of multiple degrees of freedom of multiple particles represents a fundamental ability for quantum information processing. We experimentally demonstrate an 18-qubit Greenberger-Horne-Zeilinger entanglement by simultaneous exploiting three different degrees of freedom of six photons, including their paths, polarization, and orbital angular momentum. We develop high-stability interferometers for reversible quantum logic operations between the photons' different degrees of freedom with precision and efficiencies close to unity, enabling simultaneous readout of 2^{18}=262 144 outcome combinations of the 18-qubit state. A state fidelity of 0.708±0.016 is measured, confirming the genuine entanglement of all 18 qubits.