Fundamental Technologies Of High-dimensional Quantum Secure Communication

Quantum information science is an interdiscipline that study information science depending on quantum mechanics.Although there are many subfields,quantum infor-mation consists of two major branches:quantum computing and quantum communi-cation.Quantum computing is commonly designed to solve a class of problems using quantum properties,e.g.,quantum superposition and entanglement.Quantum comput-ing is performed by quantum computer.Though the advantages are not general,quan-tum computer can solve some problems much more efficiently and faster than even a most powerful classical supercomputer.Quantum communication is the art of transfer-ring a quantum state from one place to another to realize information transfer.The basic motivation of quantum communication is encoding quantum information using quan-tum states.This quantum information can achieve tasks that can hardly be done,at least much less efficiently,by classical information.The best example is quantum key dis-tribution(QKD).Quantum communication includes many subfields,such as quantum communication complexity,quantum coin flipping,quantum commitment and quan-turn digital signature.We mainly study on quantum technologies of the most promising application in quantum communication-QKD-and the related quantum information processing in this thesis.QKD is the process using quantum communication to establish a secure key shar-ing system between participants,usually two parties and being called Alice and Bob.No third party can learn any information about the shared key.This is guaranteed by two basic properties of quantum mechanics:the Heisenberg's uncertainty principle and non-cloning theorem.If the third party,conventionally being called Eve,tries to learn information about the key,the quantum state being transmitted will be changed.Then Alice and Bob will notice that and fail the key distribution establishment.Once the dis-tribution established,the shared key can then be used for the one-time pad encryption,which cannot be broken in principle.QKD is thus secure in principle.QKD is the first commercial application of quantum information and has cultivated a relative mature market.However,there are still some problems waiting being solved,such as,how to improve the secure key distribution rate to meet the demands of practicality and how to guarantee the security of a practical QKD system with imperfect devices.One basic way to improve key distribution rate is increasing the communication rate of the system,such as increasing the preparation,modulation and measurement rates of quantum states.Another way is to increase the dimensionality of the quantum states being used in the system.The practical security of the system depends on the specific performance of devices.We should firstly study and understand the properties of the devices before fixing the loopholes.QKD usually consists of three parts:a.the randomly preparation of initial quantum states;b.modulation of quantum states to load and extract information;c.projection measurement of quantum states.This thesis focuses works on the fundamental technologies of high-dimensional QKD covering all these three parts and the details are shown below:1.The implementation of a quantum random number generation(QRNG)based on the avalanche photodiodes(APD).QKD requires random preparation of quantum states and random choosing of measurement basis.These processes consume random numbers.The secure premise of QKD is to guarantee the truly random numbers being used.QRNG,the randomness of which is guarantee by quantum effects of physical resources,is being considered the most suitable choice.By generalizing von Neumann encoding method to high-dimensional situation,the QRNG proposed is robust to envi-ronmental disturbance and requires no complex post-processing.The proposed QRNG is suitable for practical application scenarios.2.Study on the non-Markovian property of afterpulsing of InGaAs/InP sing-photon avalanche detector(SPAD).The non-Markovian property,which means that afterpuls-ing correlated to the avalanching history,of afterpulsing of SPADs has been studied both theoretically and experimentally for the first time.As afterpulsing is a dominant limitation to high-efficiency and high-speed SPAD,the non-Markovian model makes the afterpulsing mechanism clearer and is instructive to the manufacturing technology.It also offers a new perspective to address the practical security of QKD with imperfect devices.3.Study on non-destructive manipulation of orbital-angular-momentum(OAM)photon states.The degree of freedom of OAM is a promising resource for high-dimensional quantum information processing and quantum communication as the quantum number of OAM can be infinite in principle.However,there are still many difficulties that impede the application of OAM photon states.These difficulties include superposi-tion state preparation and measurement with high-efficiency and effective realization of quantum transformation in high dimension.In this thesis,a.a modified single-path Sagnac interferometer that manipulate OAM photon states with high fidelity has been implemented.The proposed interferometer improves the fidelity by 5%?10%than the normal one.It is easy to implement and stable for longtime free running.These merits make the interferometer suitable for quantum communication.b.A phase manipula-tion module(PMM)based on the modified Sagnac structure was realized to implement a high-dimensional controlled-phase gate,one important quantum transformation both in quantum information processing and quantum communication.The PMM preserves the phase in the spin-O AM hybrid superposition states and is also suitable for classical communication.c.A scalable scheme for high-dimensional OAM sorting has been pro-posed to categorize different OAM states simultaneously.The scalable sorter consists of some elemental high-dimensional quantum transformations and greatly reduces the resources required.