Quantum clock revolution could change how we measure time

Timekeepers once trusted wobbling pendulums and vibrating quartz. Now, the world’s best quantum clocks probe energy gaps inside single atoms, counting oscillations with parts‑per‑quintillion precision.

Professor Marcus Huber of the Atomic Institute at TU Wien and his collaborators have upended a rule that many physicists treated as gospel: double the accuracy, double the energy bill.

Old clocks needed more energy

Every clock marries a periodic event to a counter. The event must reset, but the counter must not, so each tick irreversibly shuffles some entropy into the surroundings, whether as heat, light, or molecular jostling.

For classical devices the link looks linear. Push a pendulum harder or fire a brighter laser, and you do suppress statistical noise, but only in lockstep with the fuel burned.

This intuition was formalized in the thermodynamic uncertainty relation, a bound suggesting that precision cannot outpace dissipation.

Tracking time with two motions

Huber’s team realized the bound is not a wall but a loophole waiting for the right architecture. They built a virtual ring of quantum sites, let one excitation circulate freely, and added a single lossy junction that “clicks” whenever the particle completes a lap.

One motion is fast and coherent, spreading like a wave and costing no entropy. The other motion (crossing the junction) happens rarely and irreversibly, acting like the minute hand.

“Combining a swift, entropy‑free shuttle with a slow, entropy‑producing register gives an exponential gain in accuracy per unit cost,” explained Florian Meier, a PhD student at the Atominstitut at TU Wien.

Achieving precision with less energy

Simulations show the clock’s precision scales roughly as the chain length to the 4⁄3 power while the needed entropy grows only logarithmically. In other words, each extra bit of dissipation can buy orders of magnitude better timing.

“Superconducting circuits already give us all the ingredients to test this idea in hardware,” noted study co‑author Simone Gasparinetti.

Earlier optical lattice clocks achieve parts‑in‑10¹⁸ stability yet still waste far more energy than Huber’s design would need at the same precision.

Quantum clock and future tech

Low‑dissipation timing matters once devices shrink to the nanoscale or fly deep in space, where power budgets are tight.

Quantum networks, for example, must distribute photons on picosecond schedules; swapping today’s power‑hungry drivers for a passive ring clock could simplify that task.

Precision gravimetry and navigation also benefit, since every tick saved from thermal noise translates to clearer signals. If validated in the lab, the method might trim the roadmap for redefining the second, now slated for 2030.

Quantum clock design reduces waste

The researchers engineered their ring clock using coherent transport, a process where quantum particles glide across the chain without loss. Only when the particle completes a full cycle does it interact with the environment, generating entropy.

This design sharply contrasts with fully dissipative clocks that register every tick by interrupting the system. Because only one segment of the ring needs to be thermodynamically active, most of the clock runs “clean,” saving energy.

“We’re not claiming magic. It’s still irreversible when a tick occurs. But quantum effects let us delay and localize that cost,” said Huber. 

Stability of the quantum clock

To ensure real‑world feasibility, the team simulated noise, disorder in coupling strengths, and unwanted dissipation.

The experts found that the clock still holds up well: the performance drop is gradual, and the accuracy gain remains impressive if imperfections are kept modest.

The needed physical platform already exists. Superconducting coupled cavity arrays can host hundreds of sites with tunable couplings and minimal loss.

Tick events could be detected via microwave photon counters or continuous readout of artificial atoms, techniques already tested in circuit quantum electrodynamics.

Implications for quantum tech

Quantum clocks like the ring model don’t just sharpen timekeeping, they push the boundaries of what self-contained quantum devices can do.

As researchers strive for scalable quantum networks and portable quantum sensors, designs that minimize external control and internal dissipation become increasingly important.

The principle behind this clock could influence fields beyond metrology. Engineers designing quantum repeaters, synchronizers, or energy-efficient processors might borrow the same structure: localized thermodynamic cost, distributed coherent transport.

Rethinking thermodynamic limits

Does the result violate thermodynamics? No, the second law still demands that entropy increase somewhere; Huber’s trick merely spends it sparingly by letting quantum coherence shoulder most of the workload.

The work also hints that the familiar arrow of time, stitched from countless microscopic irreversibilities, is compatible with islands of near‑reversible quantum motion. That insight could ripple beyond metrology into quantum control and information theory.

The study is published in the journal Nature Physics.

Image Credit: Alexander Rommel

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