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Passive decoy-state quantum key distribution with orbital angular momentum and pulse position modulation

Combing the orbital angular momentum and pulse position modulation, we propose a novel passive decoy-state quantum key distribution scheme with the single-intensity two-mode source. Besides, we give the lower bound of single-photon counting rate and the upper bound of single-photon error rate. Moreover, the system performance is numerically studied. The simulations demonstrate that the performance of scheme with orbital angular momentum coding is improved in terms of error rate, key generation rate and secure transmission distance. Meanwhile, by using the pulse position modulation technology, the performance is further enhanced. And the longer the frame length, the better the system performance. Therefore, our scheme does not need to modulate the light intensity, and exploits the combination of orbital angular momentum and pulse position modulation to eliminate the basis-dependent flaw and improve the key generation rate. It has certain reference value to the realization of the system.