Quantum Information Processing Applied To Quantum Many-body Physics

The research contents of quantum information and quantum computing are accomplishing the tasks of information processing by using the basic ideas of quan-tum mechanics.With the development of quantum information,many unique quantum mechanical resources have been produced,such as quantum entangle-ment and quantum coherence,which have become the most important basic re-sources in the fields of quantum computing and quantum cryptography.Therefore,the methods of measuring and quantifying these resources have also become an important subject,namely quantum information processing theory.The remark-able achievements have von Neumann entropy,concurrence,quantum coherence,Renyi entropy and quantum discordQuantum many-body system is an effective physical carrier to achieve quan-tum information and quantum computing.Therefore,applying quantum infor-mation processing technology to many-body problems provides a new perspective to study quantum many-body theory.Firstly,we introduce the work of detect-ing quantum phase transitions by quantum coherence.We introduce a coherence susceptibility method,based on the fact that it signals quantum fluctuations,for identifying quantum phase transitions induced by quantum fluctuations.This method requires no prior knowledge of order parameter,and there is no need for careful considerations concerning the choice of a bipartition of the system.It can identify different types of quantum phase transition points exactly.At finite temperatures,where quantum criticality is influenced by thermal fluctuations,our method can pinpoint the temperature frame of quantum criticality,which perfectly coincides with recent experimentsMany-body localization(MBL)is a new quantum phenomenon,which is de-termined by an interplay between the interaction of the itinerant electrons and the quenched disorder.Many-body localization leads to finite temperature metal-insulator phase transition.In contrast,Anderson localization,which only address-es noninteracting particles in the presence of disorder,causes the metal-insulator phase transition at zero temperature.We recommend the nature of quantum many-body localization comprehensively,as follows.What are the necessary conditions for Anderson localization and many-body localization?Localization violates the eigenstate thermalisation hypothesis(ETH),has the poisson level s-tatistics,and protects quantum order.In the localization phase,entanglement entropy of the exact eigenstates satisfies the area law rather than the volume law,and many-body localization has the logarithmic growth of entanglement in time.One of the goals of quantum information and quantum computing is to realize quantum information processing machines in reality,benefiting from the dramat-ic experimental progress of the last few years,which has made the preliminary results.In different systems,such as ultracold atoms in optical lattices,trapped ions and superconducting quantum circuits,the medium-scale quantum processors containing several tens of qubits with long coherence time and high precision in manipulation are realized.One of the most promising uses of quantum processors is the simulation of quantum many-body systems.We present an experiment fully emulating the MBL dynamics with a 10-qubit superconducting quantum proces-sor,which represents a spin-1/2 XY model featuring programmable disorder and long-range spin-spin interactions.We provide essential signatures of MBL,such as the imbalance due to the initial nonequilibrium,the violation of eigenstate ther-malization hypothesis,and,more importantly,the direct evidence of the long-time logarithmic growth of entanglement entropy.Our results lay solid foundations for precisely simulating the intriguing physics of quantum many-body systems on the platform of large-scale multiqubit superconducting quantum processorsAt present,quantum many-body localization is still an attention-worth prob-lem,either theory or experiment.Exploring the formation mechanism of the localization has great significance.In outlook,we introduce Stark many-body lo-calization caused by a strong electric field instead of disorder,and prove that the Stark many-body localization can protect the nearest-neighbors entanglement by concurrence.