Certified Quantum Randomness, One Qubit at a Time
[Posted on 3 October 2025]
Researchers at the Raman Research Institute, with collaborators have shown that Certified Quantum Randomness can be achieved using simple time-based tests on a single qubit – a novel step beyond earlier complex multi-particle setups.
Randomness is essential for securing everything from bank accounts to encrypting private discussions, yet computers alone cannot generate actual randomness. They use a predictable set of rules, so in theory even these "random" numbers can be guessed. The quantum world, however, is fundamentally random at its heart, and if we can design experiments accordingly, we can harness the randomness to produce numbers that really are a reliable source.
In just three years, this line of research that’s being conducted at the Raman Research Institute, an autonomous institute supported by the Department of Science and Technology (DST), Government of India, moved from closing loopholes in fundamental tests of physics, to creating usable devices that certify Randomness, to implementing those ideas on quantum computers in the cloud.
“Our trilogy turns discovery into device, advancing one idea across three frontiers—rigorous foundational validation, practical certification of randomness, and deployment—culminating in certified randomness running on quantum computers in the cloud,” said Professor Urbasi Sinha, head, Quantum Information and Computing (QuIC) lab at the RRI.
As a landmark experiment[1], the researchers at RRI in 2022 conducted an experiment to ascertain whether the world is classically predictable, or governed by the tenets of quantum mechanics. They managed to prove classical realism wrong by using particles of light in an interferometer and their correlations in time. This work was different from all other proven theories or concepts in that all possible contradictions to the result were methodically obliterated. Every possible loophole that could cast doubt was systematically closed, and the result was confirmed strongly.
With the results of the previous research, with work published in 2024[2], the researchers shifted from exploring the principles of the work to finding real-world applications. . They used their loop-hole free photonic architecture to develop a quantum random number generator. This new device was capable of randomness generation certified by quantum mechanics. It produced random bits nearly a million units strong, the digital equivalent of a million coin flips, and the randomness certified by quantum temporal correlations. This demonstrated that the fundamental physics behind this work was now ready for technological advancements in communication and encryption systems.
The most recent advance in this body of work now comes in 2025, when the team with collaborators from the Indian Institute of Science (and the University of Calgary), showed that certified Quantum Randomness does not need elaborate optical tables or specialized labs at all. It could be realized on a general-purpose quantum computer available through the cloud. This shift was a major leap, because earlier demonstrations had depended on intricate, proof–of-concept optical arrangements and precise eliminations of hidden influences. Although rigorous, such an approach was practical only within highly specialized physics laboratories.
Certified randomness has been achieved earlier using entangled particles which are separated in space. However, a loop-hole free implementation is currently not feasible on available quantum computers. The innovation was to shift from spatial separation to temporal. Rather than carefully separating particles over long distances, the scientists took one qubit – the simplest unit of a quantum computer, and devised a series of basic stepwise temporal measurements on it. By observing the qubit at different times, it was possible to quantum-certify the outcomes and measure the degree of genuine unpredictability.
This was not just a conceptual success, but a technological one. For the first time, randomness certified by the laws of physics – via temporal (Leggett-Garg) correlations – was generated on a commercially available, cloud-accessible quantum computer: IBM’s superconducting-qubit platform.
“The simplicity of this approach is precisely what makes it powerful: using only a single noisy qubit, without error correction and with low-depth circuits, one can still achieve the strict standards required to prove genuine unpredictability. This showed that even today’s noisy and small-scale quantum processors can deliver a resource as fundamental as Certified Randomness” said Pingal Pratyush Nath, PhD student at the Indian Institute of Science.
The novelty lies in bringing an idea once confined to custom-built optics labs into a platform that anyone with internet access can, in principle, use. In addition, it helps broaden the scope of what quantum computers are capable of, extending from solving specialised problems, to now offering a genuine resource for secure communications. Certified randomness is integral for cryptography, especially for the plausibly secure systems where digital keys must remain unconditionally unguessable, and this research makes it plausible for such protocols to be executed on a quantum device easily. Simultaneously, the technique serves as a means to quantitatively assess the precision of individual qubits, providing a convenient yet effective validation of quantum hardware.
By proving that certified randomness can thrive both in delicate optical setups and in the chips of commercial quantum processors, the researchers have provided not only a powerful tool for secure technology, but also a striking benchmark of quantum reality itself.
References:
Pingal, N., Sinha, A. and Sinha, U., 2025.
Certified random number generation using quantum computers.
Frontiers in Quantum Science and Technology, 4
https://doi.org/10.48550/arXiv.2502.02973
Previous Works:
[1] Joarder, K., Saha, D., Home, D. & Sinha, U., 2022. W
Loophole-free interferometric test of macrorealism using heralded single photons.
PRX Quantum, 3(1), p.010307.
https://doi.org/10.1103/PRXQuantum.3.010307
[2] Nath, P.P., Saha, D., Home, D. & Sinha, U., 2024.
Single-system-based generation of certified randomness using Leggett-Garg inequality.
Physical Review Letters, 133(2), p.020802.
https://doi.org/10.1103/PhysRevLett.133.020802
Watch the SimplyPhy here: https://youtu.be/KLgn-PYGGQA
For further inquiries, contact at outreach@rrimail.rri.res.in
Article by Ajith Shanbhag
Illustrations by Arunima V
Video by Rahul Iyer