Quantum Communications via Satellite with Photon Subtraction

Abstract

Non-Gaussian continuous-variable quantum states represent a pivotal resource in many quantum information protocols. Production of such states can occur through photonic subtraction processes either at the transmitter side prior to sending a state through the channel, or at the receiver side on receipt of a state that has traversed the channel. In the context of quantum protocols implemented over communication channels to and from Low-Earth-Orbit (LEO) satellites it is unclear what photonic subtraction set-up will provide for the best performance. In this work we show that for a popular version of continuousvariable Quantum Key Distribution (QKD) between terrestrial stations and LEO satellites, photon subtraction at the transmitter side is the preferred set-up. Such a result is opposite to that found for fiber-based implementations. Our results have implications for all future space-based missions that seek to take advantage of the opportunities offered by non-Gaussian quantum states.

Improving QKD for Entangled States with Low Squeezing via Non-Gaussian Operations

“…Nonetheless, the magnitude of the key rate of receiver-PS is lower than the one obtained by means of the TMSV state. This result was originally presented in [19]. For the squeezing value of 8dB we see that QS at both receiver-side and transmitterside are not effective, being unable to recover any non-zero key rates for any non-zero photon loss.…”

“…This specific form of attack is not optimal for non-Gaussian states[19], but the bound on key rate we derive remains true.…”

“…To compute the key rate we follow the procedure presented in [19]. Since we are considering that the states involved are non-Gaussian, the calculations of the key rates are more complex relative to those required to obtain key rates using Gaussian states.…”

“…Thus, we will make use of this result emphasizing that the key rates presented here represent only a lower bound of the real values. For a complete discussion of how to calculate the key rate when non-Gaussian states are involved we refer the reader to [19], [20].…”

“…In addition, the subsequent improvement in the key rates of QKD schemes via PS has been investigated, e.g. [19], [20]. Another non-Gaussian operation known as quantum scissors (QS) [21] has also surfaced as a prominent tool for entanglement distillation of CV states [22], [23].…”