Janusz Jacak

Recent experimental implementations of publicly verifiable quantum random number generators (PV-QRNGs) based on quantum entanglement reflect growing interest in this emerging paradigm of QRNG technology, originally proposed in our earlier work. These implementations employ specific representatives of entangled multi-qubit state families defined by us, which enable public verification of randomness without revealing the generated strings. PV-QRNGs address the limitations of local computational testing and offer enhanced scalability and reliability. This approach is especially relevant in the context of quantum and post-quantum cryptography, where the certification of high-quality randomness is essential. We present the theoretical foundations of PV-QRNGs and explore their potential to advance secure, scalable, and transparently verifiable quantum randomness generation.

Validation of the randomness of a quantum random number generator (QRNG) can be performed via robust statistical testing, which generally reduces to the problem of finding long range patterns in the generated random bit sequence. This problem is computationally exhaustive and poses one of important challenges for industrial implementation of self-testing integrated QRNG devices. Furthermore, classical statistical testing cannot in principle confirm the quantum non-determinism (from which the QRNG device can deviate due to its implementation imperfections). Instead, classical testing can confirm that up to certain parameters threshold, deterministic patterns were not detected. The device independent QRNG schemes are based on quantum entanglement, which is a non-classical resource that can be verified in terms of quantum measurements non-classical correlations statistically violating Bell type (e.g. CHSH) inequalities for classical limits on such correlations. This reults in a fundamental (independent from a technical implementation) confirmation that the process used to generate randomness based on entangled quantum states is indeed non-deterministic. In this paper we describe a series of recent experimental developments focused on generating quantum entanglement based randomness in a quntum optics device-independent approach, with validation of the randomness through experimentally verified violation of the CHSH inequality [1]. The experimental setup for entanglement based QRNG involves generation of entanglement in photon polarizations in the SPDC type II process with a single-photon detectors (SPAD) for quantum measurements of entangled photons. Statistical processing of the measurements outcomes shows violation of the classical limits on the correlations, violating the CHSH inequality and hence proving that the QRNG generated randomness is based on a quantum, non-deterministic process. The further direction for this research is towards miniaturization of the robust quantum optics setups to be more adequate for integrated entanglement QRNG devices. This work is part of the NCBR research and development project (contract no. POIR.01.01.01-00-0173/15) aimed at advancing QRNG setups with technical achievements reported in the SeQre.net platform [2]. 1. J.F. Clauser, M.A. Horne, A. Shimony, R.A. Holt, Proposed experiment to test local hidden-variable theories, Phys. Rev. Lett., 23 (15): 880–4, doi: https://doi.org/10.1103%2FPhysRevLett.23.880, (1969) 2. SeQre.net, Quantum Cryptography R&D Platform managed by the Department of Quantum Technology at WUST and CompSecur / SeQre, https://seqre.net/qrng

We present a simple idealistic quantum entanglement based protocol for quantum random number generation allowing a trusted third party to publicly perform arbitrarily complex tests of randomness without any violation of the secrecy of the generated bit sequences. The protocol diminishes also an average time of the randomness testing (thus enabling arbitrary shortening of this time with increasing number of entangled qubits).

We summarize research results preceding currently ongoing deployment of the QKD experimental systems in a real network environment of optical fiber metropolitan backbone network in the city of Wroclaw, Poland. Research on QKD deployment in practical telecommunication network environments resulted in evaluation of boundary conditions for QKD feasibility versus quantum channel and transmission parameters and a successful resolution of channel quality problem by proper alignment of experimental QKD setups (both the non-entanglement based QKD setup and the entanglement based QKD setup). This research allowed for the current deployment of the QKD metropolitan network in Wroclaw.