We propose a quantum key distribution (QKD) system operating at cryogenic temperature to build secure microwave wireless link between quantum computers. One of the state-of-the-art methods of building high quality quantum computers is based on superconducting technology. Limited by the microwave components working at cryogenic temperature, the frequencies of superconducting quantum computing are generally from f=4GHz to f=10GHz. So building quantum secure link at this frequency range at cryogenic temperature is important for the accomplishment of private quantum communication.

Continuous Variable (CV) QKD is one way to build secure link depending on quantum mechanics. We consider a one-way light-of-sight (LOS) point to point microwave communication link between two users: Alice and Bob. The process of this scheme is as follow: Alice starts from a single thermal state and prepares coherent states from a two-dimensional Gaussian distribution. Then she sends her states to Bob through an insecure diffraction-only channel with transmissivity T. Bob uses a homodyne detection to measure the income states and get the outcome. To examine the security of this link, we assume the attacker Eve hiding in the channel and operating collective attack to steal information. To minimize risk of leakage, Alice and Bob carry out privacy amplification in the post-processing and use reverse reconciliation (RR) to prepare their secret key.

In conclusion, this work focuses on the secure wireless distance between different superconducting quantum computers’ communication systems by using microwave CVQKD. The results may benefit the communication systems between both quantum computers and inter-satellite.

Reference:
[1] Zhang, M., Foshat, P., Poorgholam Khanjari, S., Imran, M. , Weides, M. and Delfanazari, K. Microwave Quantum Key Distribution with Cryogenic Microwave Components for Superconducting Quantum Computing. 2022 International Symposium on Quantum Computing: Circuits Systems Automation and Applications (QC-CSAA), Knoxville, TN, USA, 18-19 July 2022

Keywords: Quantum Key Distribution (QKD), Microwave, Quantum Communication, Cryogenic Components