Practical Amplification For A Single Photon Qudit Encoded In Three Degrees Of Freedom

Quantum communication refers to the transmission of information using the basic principles of quantum mechanics.Quantum communication can sense eavesdropping,which is the biggest advantage of quantum communication compared with classical communication.Quantum communication includes quantum teleportation,quantum key distribution,quantum secret sharing,quantum secure direct communication,and other important branches.Quantum communication is highly valued by the country and belongs to the major strategic needs of the country.In the field of quantum communication,photons have become an important information carrier because of their operability and high-speed transmission characteristics.Simultaneous coding of multiple degrees of freedom(DOFs)in a single photon can effectively improve its channel capacity.Multi DOFs super coded photons have been widely used in quantum teleportation,quantum key distribution,and quantum secure direct communication to improve communication efficiency.In practical applications,long-distance quantum communication needs to distribute a single photon or entangled state in the quantum channel.However,in the actual photon transmission process,channel noise may lead to photon transmission loss,which greatly limits the communication distance,reduces the communication efficiency,and even threatens the security of communication.Noiseless linear amplification of quantum states is an important method to resist the loss of photon transmission and be widely used to improve the fidelity of target photon states.In the first work of this paper,we propose a practical noiseless linear amplification(NLA)protocol for protecting the single-photon qudit encoded in polarization and double-longitudinal momentum DOFs.This NLA adopts the imperfect entangled state generated from a practical spontaneous parametric down-conversion(SPDC)source as the auxiliary state and can be realized under current experimental conditions.After performing the NLA protocol,the fidelity of the target state can be increased and the encoded information in all DOFs can be well preserved.The second work of this paper realizes the numerical simulation of important parameters in the three DOFs quantum state amplification scheme,which directly shows the amplification effect of the scheme.In the third work of this paper,a noiseless linear amplification scheme of polarization and frequency two DOFs encoded coherent states using photon catalytic technology is proposed.In this scheme,the beam splitter is used to split the coherent states into N paths,and the photon catalytic operation is run on each path.The signal state and auxiliary state in multiple spatial modes are operated through the photon catalytic amplifier at the same time.Finally,a new coherent state is extracted according to the response of the detector in each amplifier to realize the amplification of the coherent state.This scheme can effectively improve the average photon number of coherent states and perfectly retain the information encoded by each photon in polarization and frequency DOFs.The devices used in this paper are linear optical elements,which can be prepared under the current experimental conditions,and have a strong practicability.The three works of this paper have wide applications in the field of quantum communication in the future.