Quantum Computational Advantage Based On Gaussian Boson Sampling

Quantum computing utilizes the unique properties of quantum mechanics to solve some important problems that cannot be solved by classical computing,thus attracting extensive theoretical and experimental research.Universal quantum computers that can factorize 2048-bit integers require thousands of qubits and billions of Toffoli gates.Therefore,quantum error correction codes are necessary for universal quantum computers.Quantum error correction codes have strict requirements on the quality of quantum devices and require long-term development.Based on existing devices without quantum error correction,it is possible to achieve quantum speedup compared to classical computers on certain tasks.If the quantum speedup is large enough,such that any classical computer cannot solve the task in a reasonable amount of time,it is called quantum computational advantage.In the field of quantum computing,quantum computational advantage is a long-anticipated milestone.In 2020,we completed the optical quantum computer prototype jiuzhang based on Gaussian Boson sampling,and for the first time realized the photonic quantum computational advantage.This is the second experiment achieving the quantum computational advantage.It also proves that the quantum computational advantage widely exists in different quantum computing systems.This paper introduces the theories and technologies required to realize the photonic quantum computational advantage,and finally realizes the quantum computational advantage.This paper includes the following works:1.Designing a near-perfect spontaneous parametric down-conversion source,which is frequency uncorrelated without any filters,and satisfy high collection efficiency,high brightness and high quality simultaneously.2.Developing stimulated parametric down-conversion technology to increase the brightness of spontaneous parametric down conversion by 4 times.The brightness can be further improved with multiple cascades.3.Experimental producing 12-photon GHZ entanglement states,which is the current record for the number of entangled photons.4.Three-,four-and five-photon scattershot Boson sampling experiments,whose sampling rate exceed all previous Boson sampling experiments based on spontaneous parametric down conversion.5.Developing the theory of Gaussian Boson sampling in the case of non-uniform channel loss,and performing a proof-of-principle Gaussian Boson sampling experiment.6.Quantum computational advantage experiment jiuzhang based on Gaussian Boson sampling,and its upgraded version jiuzhang 2.0.The jiuzhang and jiuzhang 2.0 achieve quantum advantagc ratio of 1014 and 1024,respectively.We also apply several analyses and characterizations of the sampling results to verify the correctness of the experiment.