Suppose we are attenuating up to 0.2 mean photon number. So, every RF cycle will not contain a photon. So while providing a 1-bit delay, it is possible that the interference can happen between a vacuum state and a photon or a vacuum-vacuum state or photon-photon state.
If there are two neighboring photons, then we will get the exact phase difference after interference resulting in the correct bit assignment. What will happen if a vacuum-photon state arrives at the other end of DLI? Will they interfere or simply pass with a 50% chance of detection in both the detector? This will generate errors in the key string. How to rectify this error?
I want to do sifting but got stuck at this point.
DPS QKD is a quantum key distribution protocol that uses differential phase shifts between adjacent pulses to encode information. The interference at the DLI depends on the relative phase between the pulses. If there are two neighboring photons with the same phase, they will interfere constructively and produce a bright output. If they have opposite phases, they will interfere destructively and produce a dark output. If there is a vacuum state between two photons, there will be no interference and the output will be random.
To determine whether the interference is caused by two neighboring photons or a photon and a vacuum state, one can use a phase post-selection technique. This technique involves measuring the phase difference between consecutive non-empty pulses sent by Alice and comparing it with Bob's measurement outcomes. If the phase difference matches Bob's outcome, then the interference is likely due to two neighboring photons. If not, then the interference is likely due to a photon and a vacuum state or a vacuum-vacuum state. This technique can reduce the errors in the key string by discarding the bits that are likely caused by vacuum states.
To do sifting, you need to perform error correction and privacy amplification after phase post-selection. Error correction is a process of identifying and correcting errors in the key string using classical communication. Privacy amplification is a process of reducing Eve's information on the key string by applying a random hash function. These steps can ensure that Alice and Bob share a secure key after sifting.
- Badges
- Science topic
- Similar topics
- Biological Science
- Microbiology
- Virology
- Virus