An efficient quantum key distribution scheme based on optical quantum state fusion and fission

A new quantum key distribution (QKD) scheme, based on quantum state fusion and fission, is proposed. By using quantum state fusion and a spatial-temporal mode conversion circuit, two polarization modes of two photons can be converted into one temporal-polarization mode of one photon. Also, by using quantum state fission and a temporal-spatial mode conversion circuit one temporal-polarization mode of one photon can be converted into two polarization modes of two photons with the help of an ancilla photon. When the state fusion and fission processes are applied in QKD system, the sender can transmit two polarization qubits at one time and the receiver detects two single photons separately after state fission. Thus, the total count rate of photons is improved. More importantly, the quantum bit error rate decreases. The numerical analysis results show that by using this scheme the key generation rate is improved efficiently and communication distance can be increased by 6~30Km depending on different polarization misalignment errors.