Experimental Research On Quantum Measurement And Quantum Coherence Based On Photonic Systems

The quantum information technology developed by the combination of quantum physics and information technology has led the new direction of the scientific and technological revolution.Quantum technology,such as quantum communication,quantum computation,quantum cryptography,quantum precise measurement and so on,has incomparable advantages compared with classical technology and attracts great attention of scientists.Quantum measurement is necessary for the realization of these quantum technologies and quantum tasks.It is also the key to connect the classical world with the quantum world.Designing measurements to get the desired information and designing optimal measurements to get more information are what we are devoted to.By measuring the current system to retrodict the past information of the system is widely used in quantum communication and quantum cryptography.So it is important to study the effect of different measurements in the extraction of past information.An important principle of quantum mechanics related to quantum measurement is the uncertainty principle.It states that two incompatible observables cannot be accurately measured simultaneously,and there is an inherent limitation in measurement accuracy.It is of great significance to study the inherent limitation of measurement accuracy for the measurement process.Quantum measurements play an important role in quantum system.Quantum coherence is also the most distinguished feature of quantum system,characterizing the superposition properties of quantum states.As a fundamental property of quantum systems and an important resource,it is important to develop tools for efficient estimation and quantification of coherence,and various coherence quantifiers have been proposed.About coherence estimation,one possibility for coherence estimation is to perform quantum state tomography.However,estimation of coherence measures in general does not require the complete information about the state of the system,so this method has redundant information.There are various approaches for detecting and estimating coherence of unknown quantum states.Nevertheless,these methods typically contain optimization procedures and require feedback.Thus,efficient estimation of coherence in today' s experiments remains a challenge.In addition,being a fundamental property of quantum systems,coherence is of great significance in the study of the wave-particle duality.Coherence is the core and basis of the interference phenomenon.If quantified coherence is used to characterize the wave property,which would provide a new perspective regarding the wave-particle duality.This thesis focuses on the above issues,and conduct the following research:1.We experimentally retrodict the trajectories of single photons in double interferometers by measuring the final state of the photon.When a photon passes through double interferometers,a sequence of measurements is made on a photon to determine which path the photon followed,so a series measurement results of retrodiction can be regarded as a photon trajectory.We use different measurements to obtain information about the partial trajectory and the entire trajectory of the photon.Furthermore,we also observe the effect of different measurements in the extraction of trajectory information.2.Uncertainty principle is an important principle of quantum mechanics related to quantum measurement,and it introduces intrinsic limitations on the measurement precision of noncommuting observables.We experimentally investigate majorization uncertainty relations(MURs)for two measurements and multiple measurements in the high-dimensional systems,and study the intrinsic distinction between direct-product MURs and direct-sum MURs.Our experimental results reveal that by taking different nonnegative Schur-concave functions as uncertainty measure,these two types of MURs have their own particular advantages.3.We put forward a general method to directly measure quantum coherence of an unknown quantum state using two-copy collective measurement scheme.We simulate the performance of this method for qubits and qutrits,and compare the precision of collective measurement scheme with other methods for coherence estimation,finding our scheme leads to a higher precision in a large parameter range.Furthermore we also report an experimental demonstration of collective measurement scheme for qubit states.4.Being a fundamental property of quantum systems,coherence plays an important role for the study of the wave-particle duality.Here,we experimentally demonstrate the wave-particle duality based on two kinds of coherence measures for the first time.The wave property is quantified by the coherence in the l1-norm measure and the relative entropy measure.The particle property is quantified by the path information.This work not only could deepen people's understanding of quantum coherence but also provides a new perspective regarding the wave particle duality.