Studies On Linear Optical Based Quantum Networks And Quantum Sensing

Quantum entanglement serves as a core resource for quantum network,enabling quantum secure communication,distributed quantum computing,and quantum sensing.In these applications,photonics are widely used benefiting from its superior characteristics,e.g.,high reconfigurability and robustness.In this thesis,we prepare and manipulate entangled photons via a linear optical system,and study various subjects of quantum network and quantum sensing.In the first chapter,we have an overview of the development of quantum network and review several essential techniques for building future quantum network.In the second chapter,we theoretically and experimentally study the key aspects of linear optical system,including phase matching,visibility and collection efficiency of spontaneous parametric down-conversion(SPDC)source,as well as the frequency correlations between ordinary and extraordinary photons.It has been shown that the burden of quantum memory for quantum repeater can be reduced by using all-photonic quantum repeater.In the third chapter,we introduce the passive choice measurement to weak the requirement of number of entangled photon.In addition,we experimentally study the all-photonic quantum repeater by using an 12photon interferometer.Compared with original repeaters,our results show 1.74 and 1.89 times improvement of entanglement-generation rate with a pump power of 500 mW and 700 mW,respectively.It has been shown that quantum error correction and entanglement distiallation can be used to eliminate the effect of inevitable environment noise.In the fourth chapter,we first experimentally prepare 9-qubit Shor code through an 10-photon interferometer,and demonstrate its main functions including error-detection and fault-tolerance.Then,we experimentally investigate a quantum resetting protocol of a target photon under uncontrolled dynamics.This work provide a new way to quantum error correction.Finally,by combining the determined and random entanglement distillation we develop and experimentally demonstrate a more effective entanglement distillation scheme,where the distillation probability is higher than the limit of determined entanglement distillation scheme.Imperfect measurement device leads to a false conclusion about witnessing presence of entanglement,and further breaks the security of the quantum communication.In the fifth chapter,we demonstrate measurement-device-independent entanglement witnesses for three-part GHZ state.Remarkable,we experimentally demonstrate measurement-device-independent entanglement witnesses for the entanglement structure of GHZ-like states.Optical quantum sensing is a promising technique used to enhance the sensitivity beyond the classical limit in the measurement physical quantity that is not directly observable.In the sixth chapter,we first study the distributed quantum phase estimation under different cases of entangled/seperated modes/photons,provide a faithful verification of the gain effect of quantum entanglement on measurement precision.Then,to improve the precision we develop and demonstrate the combined strategy by combining parallel entanglement and conherence.Finally,we develop and demonstrate a distributed full-period quantum phase estimation strategy by combining the adaptive Bayesian estimation and the maximum likelihood estimation method based on GHZ state.The upper bound of sensitivity is higher than all previous results,even the Holevo’s bound.