Random Quantum Clocks to Probe the Foundations of Time

By Atif SuhailReviewed by Louis CastelOct 24 2025

In 2025, a team of physicists led by Mark Mitchison at King’s College London reported a striking new development in our understanding of time: the creation of clocks built not from oscillations or resonance, but from pure quantum randomness. Their results, published in Physical Review X (2025), demonstrate how intrinsically unpredictable events at the quantum level can be harnessed to measure the passage of time.¹

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The team designed an experiment that used entangled particles, such as electrons and photons, arranged in pairs. The correlations between their outcomes, governed by the probabilistic rules of quantum mechanics, were converted into “ticks” of a novel clock. The research was conducted in laboratory settings at King’s College London, with the explicit goal of probing whether time can emerge from quantum events themselves, and whether clocks of this type could reveal the quantumness of reality in ways conventional timekeepers cannot.¹

As lead researcher Mark Mitchison noted, this effort aimed to identify the minimum ingredients needed to build a clock. Their answer was startling: randomness itself, when properly modeled and interpreted, is sufficient. By using a new mathematical framework, the researchers showed that causally linked random events, known as a Markovian process, can be transformed into a functioning clock. This shift not only challenges how we build timekeeping devices but also reaches deep into some of the hardest questions in modern physics, including the nature of time in quantum gravity and cosmology.¹

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Understanding Time

Understanding time has long been a central puzzle in theoretical physics. In classical physics, time is treated as an external, continuous parameter, a background against which motion unfolds. Isaac Newton saw time as absolute and universal, the same for all observers, while Einstein’s relativity reframed it as relative and dynamical, intertwined with space.²

Quantum mechanics complicates this further. In standard formulations, time is treated as a parameter rather than an observable, a tool used to describe change but not itself part of the quantum state. This asymmetry creates deep tension with relativity, where space and time are placed on equal footing. The clash is most evident in the search for a quantum theory of gravity, which must reconcile these divergent treatments of time.²

This is often described as the “problem of time” in quantum gravity. Does time exist fundamentally, or does it emerge from more primitive relationships? Approaches such as the Page–Wootters mechanism suggest that time emerges from correlations between subsystems, while other theories explore whether sequences of quantum events define time for an observer.²

Against this backdrop, the King’s College work offers a concrete, testable step. By building clocks from randomness, the researchers have turned a philosophical question into a laboratory reality.

What Are Quantum Clocks Made from Randomness?

In the quantum world, randomness is fundamental. The outcome of a measurement on a quantum system, such as whether a spin points up or down or whether a photon passes through a filter, cannot be predicted with certainty but only with probability. Quantum superposition and entanglement further intensify this unpredictability, producing correlations that have no classical analog.³

The King’s team used this unpredictability as a timekeeping resource. Instead of the regular oscillations of atomic clocks, their clocks “ticked” whenever a quantum event occurred. Each measurement outcome, expressed as a binary result (0 or 1), was treated as a tick. The passage of time was then defined by the probability distribution of these outcomes, as the system evolved internally without any external reference.^{1, 3}

This represents a significant departure from atomic clocks, which track time by counting the highly regular oscillations of atoms like cesium. In those systems, time is measured through predictable, repeating cycles. Randomness clocks, on the other hand, derive time from the inherently unpredictable evolution of a quantum system. Rather than being imposed externally, time in this case emerges from the system’s internal dynamics.³

Entropy production, state transitions, and correlations between entangled subsystems formed the heartbeat of the clock, providing a rhythm not from periodicity but from probability.

What Does This Means for Quantum Physics?

The King’s College quantum clocks exhibited remarkable precision relative to the theoretical limits established for classical random event clocks. Classical Markovian processes, such as random jumps in stock markets or biological fluctuations, are bound by strict accuracy limits. Quantum clocks, by contrast, are not restricted by these bounds, which explains why they can outperform classical counterparts.¹

The researchers demonstrated that such clocks could reliably measure intervals and even exhibit forms of synchronization when multiple systems were compared. Crucially, deviations from expected classical patterns signaled the presence of underlying quantum effects. This makes these clocks not only tools for timekeeping but also diagnostic probes of quantumness in physical systems.¹

The implications are profound:

• They suggest that time may be emergent, arising from internal quantum events rather than an external, universal flow.
• They provide a new experimental lens to test where classical descriptions of time fail and where quantum descriptions must take over.
• They open new theoretical pathways for understanding the role of time in quantum gravity and cosmology, where the universe itself may lack an external clock.

Methodology

The experiment relied on a quantum architecture built from entangled particles such as photons and electrons, prepared in correlated pairs. The setup was carefully engineered to ensure that interactions between these particles produced discrete, stochastic events measurable as data points.¹

Each measurement outcome, expressed as a 0 or 1, was interpreted as a “tick” of the clock. The probability distributions of these binary results were used to define the passage of time. To validate the design, researchers tracked entropy production, state transitions, and correlation statistics across the entangled subsystems.^{1, 4}

This approach drew inspiration from earlier theoretical models of reset quantum clocks and the Page–Wootters framework, but extended them by using randomness itself as the operational driver rather than a passive element of noise. In this way, the experiment transformed a fundamental feature of quantum mechanics into the engine of a working timekeeper.⁵

Applications and Implications for the Quantum Industry

Although still at an early stage, quantum randomness clocks could have wide-ranging applications across the emerging quantum industry. In quantum computing, they could serve as internal time references for synchronizing qubit operations, reducing reliance on classical systems and enhancing scalability and reliability. Within quantum networks and secure communication, clocks built from quantum randomness may provide natural resistance to eavesdropping while enabling precise alignment of entangled nodes.⁶

Commercial interest is likely to grow as these systems mature, with the King’s College framework offering a pathway toward timekeeping devices that outperform classical standards. Randomness clocks may also integrate seamlessly with quantum sensors used in applications such as gravitational wave detection or subterranean mapping, where time accuracy is critical.^{1, 7}

Beyond practical uses, these devices offer profound scientific opportunities, creating new platforms for testing time symmetry, exploring the arrow of time, and investigating whether spacetime itself exhibits a quantum structure. By studying the behaviour of such clocks in extreme conditions, researchers may uncover experimental evidence that bridges quantum mechanics and gravity.⁶

Want to learn more about time invariance? Read on here

References and Further Studies

1. Prech, K.; Landi, G. T.; Meier, F.; Nurgalieva, N.; Potts, P. P.; Silva, R.; Mitchison, M. T., Optimal Time Estimation and the Clock Uncertainty Relation for Stochastic Processes. Physical Review X 2025, 15, 031068.
2. Dias, E. O., Quantum Formalism for Events and How Time Can Emerge from Its Foundations. Physical Review A 2021, 103, 012219.
3. Woods, M. P.; Silva, R.; Pütz, G.; Stupar, S.; Renner, R., Quantum Clocks Are More Accurate Than Classical Ones. PRX Quantum 2022, 3, 010319.
4. Woods, M. P., Autonomous Ticking Clocks from Axiomatic Principles. Quantum 2021, 5, 381.
5. Woods, M. P.; Silva, R.; Oppenheim, J. In Autonomous Quantum Machines and Finite-Sized Clocks, Annales Henri Poincaré, Springer: 2019; pp 125-218.
6. Mannalath, V.; Mishra, S.; Pathak, A., A Comprehensive Review of Quantum Random Number Generators: Concepts, Classification and the Origin of Randomness. arXiv preprint arXiv:2203.00261 2022.
7. Van Vu, T.; Saito, K., Thermodynamics of Precision in Markovian Open Quantum Dynamics. Physical review letters 2022, 128, 140602.

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