Random numbers have many applications, ranging from gambling to cryptography, where the security and unpredictability of the generated numbers are vital. Zahidy et al. developed a new type of quantum random number generator that can provide the required security and unpredictability based on the intrinsic randomness of quantum mechanics.

The researchers observed that unwanted mode excitation in a multi-mode fiber, which leads to the detrimental effect of crosstalk, is in fact a random phenomenon with multiple possible outcomes. Crosstalk is the unwanted transfer of signals between communication channels. Initially, the researchers were trying to reduce the crosstalk in order to improve the quantum channel.

Characterizing crosstalk is crucial in communication to maximize the capacity of the channel. In quantum communication, crosstalk may present a side-channel that leaks information. Consequently, having complete knowledge of this behavior is necessary.

“Eventually, however, we used crosstalk to our advantage to create a source of randomness and assembled our experiment to demonstrate that,” said first author Mujtaba Zahidy.

By sending a photon of light in a definite orbital angular momentum (OAM) through their special optical fiber, the researchers randomly generated other OAMs. Random numbers were generated by looking at the output and detecting the OAM mode.

“We believe the innovation of this work is to exploit one of the drawbacks of the quantum channel for an on-demand application, that is randomness generation based on quantum phenomena,” said author Davide Bacco.

“Our proposed idea can be improved to a more secure source of randomness, namely, a semi-device-independent protocol,” said Zahidy.

This class of protocols offers higher security due to less assumptions about the experimental components.

Source: “Quantum randomness generation via orbital angular momentum modes crosstalk in a ring-core fiber,” by Mujtaba Zahidy, Hamid Tebyanian, Daniele Cozzolino, Yaoxin Liu, Yunhong Ding, Toshio Morioka, Leif Katsuo Oxenløwe, and Davide Bacco, AVS Quantum Science (2022). The article can be accessed at https://doi.org/10.1116/5.0074253.

This paper is part of the Quantum Networks: Past, Present and Future Collection, learn more here.