The Experimental Research On The Preparation, Application And Evolution Of Entangled-photon States

Quantum entanglement,a kind of counterintuitive nonlocal correlation,is fundamental in quantum physics both for its essential role in understanding the nonlocality of quantum mechanics and its practical application in quantum information processing. At the same time,entanglement will become degraded due to the unavoidable interaction with the environment.Moreover,the evolution of entanglement may possess some distinct properties.It has been shown that entanglement between two particles evolved in independent reservoirs may disappear completely at a finite time in spite of the asymptotical coherence decay of single particle.This thesis mainly concerns the preparation,application and evolution of entangled states.We also make discussions on some fundamental problems of quantum mechanics with the technology of quantum information.The main results of the dissertation are as follow:1.We prepare a four-photon polarization-entangled state with high visibility directly from a single down-conversion source and finish a four-party quantum communication complexity scenario by using the obtained entangled state.Due to the interference-free experimental setup and the complete compensation of the walk-off effect in the birefringent crystals,the visibility of the prepared four photons state can reach as high as(95.53±0.45)%.The success probability for us to get the correct result in the four-party communication complexity scenario is(81.54±1.38)%, which greatly surpass the classical limit of 50%.This four-photon state can also be used to fulfill decoherence-free quantum information processing and other advanced quantum communication schemes.2.We experimentally realize the 1→2 optimal universal quantum cloning and the ancilla-free 1→3 optimal phase-covariant quantum cloning.In our experiment,these two kinds of cloning can be exchanged readily and the two Hong-Ou-Mandel-type interference setups may also be used to implement other quantum information processing.3.We experimentally demonstrate that measurement can recover the quantum coherence of a single photon polarization state evolved in a dephasing environment.The experimental result that measurement can induced quantum coherence recovery gives us a deep understanding of quantum measurement.This method can be extended to other two-level quantum systems.The measurement setup is also useful to demonstrate entanglement recovery and the violation of the Leggett-Garg inequality.4.We experimentally realize the violation of Leggett-Garg-type inequalities which are also used to distinguish the quantum evolution process and classical evolution process.We also experimentally compare the conditions of violation of two kinds of Leggett-Garg-type inequalities.The experimental maximal violation of Leggett-Garg-type inequalities excludes the classical reality description of quantum systems and support the quantum description in a different way.When these Leggett-Garg-type inequalities are applied to quantum systems evolved in noise environment,they can be used as the criterion to distinguish the quantum evolution process and classical evolution process.By changing input states,we compare two Leggett-Garg-type inequalities and find the tighter one. The method we used can be extend to other lager quantum systems and is important in the realization of macroscopic quantum coherence.5.We experimentally investigate the collapse and revival of entanglement in a non-Markovian environment.We even observe the revival of entanglement after it suffers from sudden death when the input state is the partially entangled state. With the application of a spin-echo like technology,we can readily control the time when the revival from sudden death occurs.Finally,we experimentally characterize the entanglement dynamics in different quantum channels by using maximally entangled states and verify the factorization law of entanglement dynamics.Different from irreversible evolution in a Markovian environment,entanglement dynamics in a non-Markovian noise with memory effect appears to be more fundamental. The observed entanglement collapse and revival(even revival from sudden death) gives us a deep understand of entanglement.The revival phenomenon has potential application in quantum information processing since it extends the usage time of entanglement. What is more,by using the spin-echo technology,we can readily control the time when the entanglement revival occurs,which will play an important role on the construction of the quantum network.The factorization law greatly simplify the description of the entanglement dynamics and will lead to the discovery of more robust entanglement-based quantum information processing protocols.