Generation And Transmission Of Time-bin Qubits

Quantum information science is a newly emerging science which develops rapidly due to the intersection and fusion of quantum physics and information science.Because it can provide absolutely secure communication in principle and huge parallel computing capability,it has become a key research direction in the field of science and technology.Quantum network is an important research field in the quantum information,which consists of quantum channel and quantum node.Quantum channels are used to transmit quantum information.Quantum nodes deal with the extraction,storage and purification of information.Trapped ions,atoms and quantum dots can be used as nodes of quantum networks.In the construction of quantum nodes based on atoms,the alkali metal rubidium atom can be used as a quantum node because the spin wave excited by the atom has good coherence and long enough time coherence.Therefore,a series of experiments have been carried out in the rubidium atomic band,such as the generation and storage of nonclassical light fields with continuous variables and separated variables.Spontaneous Raman scattering is a basic method to construct the entanglement between light and atoms.In this way,the correlated Stokes photons and spin wave excitations can be generated.The spin waves are usually stored in the atomic array,and the scattered Stokes photons are used to transmit the quantum states.Therefore,the entangled states of atomic spin waves and Stokes photons generated by spontaneous Raman process which are particularly suitable for quantum information carriers in quantum network.Several degrees of freedom can be used to encode the photonic component of the light-matter entangled state: polarization,orbital angular momentum,spatial,or time-bin encoding.The polarization entanglement states between photon and collective excited state are generated in probability.Orbital angular momentum coding is more suitable for high dimensional entanglement research.Spatial qubit encoding can expand the capacity of quantum memory.However,for long distance transmission,encoding in the form of photonic time-bin qubits is favorable,since this approach is robust against decoherence in optical fibers.In this paper,we measure the coherence preservation of the early and late pulses of a single photon time-bin qubit over a long distance of 2.3km.The results show that the coherence retention is more than 80%.The non-equilibrium Mach-Zehnder interferometer is an important measuring device for time-bin qubit transmission.We build an all-fiber non-equilibrium Mach-Zehnder interferometer and study the contrast of the interferometer under active frequency stabilization and Passive frequency stabilization phase locking.This paper will be elaborated from the following parts:(1)The first chapter reviews the research background of quantum repeater and the most promising DLCZ(Duan,Lukin,Cirac,and Zoller)scheme.The principle of non-equilibrium Mach-Zehnder interferometer for measuring time-bin qubit,the development of single photon detector and the working principle of single photon detector used in experiment are introduced.(2)We investigate the generation and transmission of time-bin qubits at795 nm,which is corresponding to the D1 transition line of rubidium atom.The optical light is encoded on the time-bin qubit and transmitted in the optical fiber for a long distance.The phase relationship between the early and late time pulses early is observed with an unbalanced M-Z interferometer to determine the coherent contrast.(3)An all-fiber non-equilibrium M-Z interferometer at 795 nm and1560nm has been constructed.The interferometer in an thermal insulation material,so the influence of external environment on the phase of the interferometer is reduced.Under this case,the phase stability of passive frequency stabilization of the interferometer is studied.In addition,the phase of the interferometer is locked to 0 phase and 90 phase by active frequency stabilization,and the interference contrast of the interferometer in these two cases is compared.(4)The last part of the thesis is summary and prospect.On the basis of this work,we will use difference frequency generation to convert the light from 795 nm to communication band,and carry out the experimental study of time-bin qubit frequency conversion.Then,the time-bin qubits in the atomic band and the communication band are measured by non-equilibrium M-Z interferometer,which provides a research basis for the long-distance quantum entanglement distribution.