Research On Characteristics Of Single Molecule Quantum Coherence Dynamics

It has been 30 years for the development of the single-molecule spectroscopy,which is still booming due to its unique advantages at the nanometer scale.The Nobel Prize in Chemistry in 2014 and 2016 respectively awarded to single molecules related works,which are super-resolution imaging and molecular motors,bring new opportunities to this field.The combinations of the single-molecule spectroscopy with many other disciplines have also injected new life into the single-molecule research.In physics,a single molecule can be used as a single photon source for quantum secure communication.Preparation and manipulation of the coherent states of a single molecule make it a potential candidate for single qubits in quantum computers.Researches on quantum sensors and optoelectronic devices based on single molecules also have made important breakthroughs.Furthermore,single molecules also involve the catalytic process of chemical reactions,the synthesis of nanomaterials,etc.,especially in biology.Super-resolution imaging and molecular motors based on the single-molecule spectroscopy provide an indispensable research basis for understanding life behaviors and developing biotechnology.Especially in recent years,the rise of quantum biology has led to increasing attention to the study of the single-molecule quantum coherence and its ultrafast dynamics.This thesis mainly focuses on the measurement and application of singlemolecule quantum coherent dynamics.Firstly,we discuss the research background of the single-molecule dynamics and highlight the research progress of single-molecule quantum coherent dynamics,including observation and manipulation of single-molecule quantum coherent dynamics.Then,we briefly introduce the applications of quantum coherent effect in biology and materials science in recent years.Additionally,this thesis introduces the basic principles of measurement for single-molecule dynamics,involving the quantum coherent modulation imaging microscopy based on single-molecule fluorescence detection.This microscopy is a new imaging technology that combines single-molecule ultrafast dynamics with ultrafast optics.Finally,the main content of the thesis will be elaborated,including the invention of single-molecule quantum coherent modulation microscopic imaging,the use of this mthod to measure the single-molecule coherent characteristics and its applications in energy transfer and bio-imaging.(A)By analyzing the quantum coherent modulation intensity of single molecules,we obtain their quantum coherent information.Then we quantitatively describe the single-molecule quantum coherent information through defining quantum coherent visibility,and realize the visualization and real-time observation of single-molecule quantum coherent information.By using this technique to study quantum coherent imaging of organisms,the physiological processes of cells are revealed,which are not available with conventional fluorescence intensity imaging.(B)We invente quantum coherent modulation-enhanced single-molecule imaging microscopy(QCME-SMIM)technique.By modulating the probability of single-molecule excited states through QCMESMIM,we achieve two orders of magnitude improvement in single-molecule imaging contrast.(C)Based on this method,we studied the energy transfer between single molecules and two-dimensional materials,breaking through the limitations of traditional fluorescence measurements and determing the extremely weak signal of energy transfer.The main innovations in the work of this thesis:1.Proposing a new approach for measuring the quantum coherent dynamics of single-molecule.Single-molecule fluorescence detection has excellent signal-to-noise ratio due to its free-background signal.However,the fluorescence produced by spontaneous radiation always loses single-molecule coherent information.By combining ultrafast optics and single-molecule spectroscopy,we have not only demonstrated the preparation and detection of the single-molecule quantum coherent state,but also determine the manipulation of the single-molecule quantum coherent state by modulating the phase difference between the pulse pairs.By reflecting the single-molecule quantum coherent information in the excited state population probability,we can extract the single-molecule quantum coherent dynamics information by fluorescence.2.Achieving real-time observation and visualization of single-molecule quantum coherent information.Single-molecule quantum coherent information is generally obtained by fitting a single-molecule fluorescence signal with the delay of an ultrafast pulse pair,which requires long time and is difficult to achieve real-time observation of coherent information.We reduced the acquisition time of single-molecule quantum coherent information from dozens of seconds to sub-second and obtained single-molecule quantum coherent imaging by defining coherent visibility based on single-molecule quantum coherent modulation method.Finally,we realized real-time observation and visualization of single-molecule quantum coherent information.3.Developing a new method for improving the contrast of microscopic imaging based on single-molecule quantum coherent modulation.Singlemolecule fluorescence imaging in biological systems is often interfered by background light such as auto-fluorescence from biological tissues,which always hinders the interested structures.In the experiment,we control the single-molecule quantum state by modulating the relative phase of ultrafast laser pulse pairs,based on the unique single quantum characteristic of singlemolecule.By modulating and demodulating the time series of the singlemolecule fluorescence,the influence originating from background and interference light is effectively suppressed;The contrast of microscopic imaging based on single-molecule quantum coherent modulation has achieved an enhencement of 515 times.4.Appling single-molecule quantum coherence to biological imaging.We studied the energy transfer between single-molecule and two-dimensional materials based on single-molecule quantum coherence,which overcomes the interference of two-dimensional material self-fluorescence on weak energy transfer signals.The variation of energy transfer efficiency with distance is observed.It provides an effective technical means for energy transfer of organic-inorganic hybrid materials.Additionally,we studied quantum coherent imaging of biological cells such as chlorella and Escherichia coli,based on the single-molecule quantum coherent modulation.In the experiment,we observed changes of quantum coherent time with cell activity,revealing the cellular activity process hidden in the traditional fluorescence imaging.These studies based on the single-molecule quantum coherence have laid an important foundation for the development of physiological processes,such as gene expression,signal transmission and cancer diagnosis.