Quantum timekeeping is supposed to be the ultimate in efficiency, with tiny devices that tick using the rules of quantum mechanics instead of swinging pendulums or vibrating quartz. Yet new work on a prototype quantum clock shows that the real energy hog is not the clockwork itself but the act of reading it out. The surprising result is that extracting the time from a quantum device can cost far more energy than keeping it running in the first place.
That finding forces a rethink of what it means to build “ideal” clocks in the quantum era. If the measurement step dominates the energy budget, then the limits of precision timing will be set as much by information theory as by hardware engineering, and the design of future quantum sensors, networks, and computers will have to account for the hidden price of simply looking at the time.
Why a quantum clock is not just a smaller wristwatch
At first glance, a quantum clock sounds like a miniature version of the atomic clocks that already define international time standards, but the new devices work in a more stripped down and abstract way. Instead of relying on large ensembles of atoms and bulky microwave cavities, the prototype described in recent work uses a tiny “double quantum dot” system, where an electron hops between two potential wells and its quantum state evolves in a way that can be used to mark the passage of time. In this picture, the clock is less a physical dial and more a carefully prepared quantum system whose internal dynamics encode a ticking pattern.
That abstraction matters because it lets researchers probe the fundamental thermodynamic cost of timekeeping, not just the engineering overhead of lasers, vacuum chambers, and control electronics. By focusing on a minimal quantum system and the electronics that read it out, the team could separate the energy needed to keep the clock’s internal dynamics going from the energy dissipated when a detector interacts with the system and converts its state into a classical “time stamp.” A graphic illustrating this split between the clockwork and the readout highlights how different quantum clocks are from familiar mechanical or quartz devices, where the dial and the hands feel like part of the same machine.
The billion-fold gap between ticking and telling the time
The central result of the new research is stark: in the studied setup, the energy dissipated when reading the quantum clock can exceed the energy needed to run the clock itself by an enormous factor. The investigators found that the entropy generated in the measurement process, which is a direct measure of energy irreversibly lost as heat, can be up to a billion times larger than the entropy associated with the internal clock dynamics. In other words, the thermodynamic cost of turning quantum ticks into a usable time signal dwarfs the cost of the ticking itself.
That conclusion did not come from a back-of-the-envelope estimate but from a detailed calculation of entropy production in both parts of the system. The team explicitly evaluated how much energy is dissipated by the double quantum dot as it evolves and how much is dissipated by the detector that monitors it and records the outcome. Earlier this month, a report on this work explained that the researchers calculated the entropy generated by the clock and the readout electronics separately, and found that the measurement stage dominates by orders of magnitude, a result that is captured in their analysis of the entropy generated in each component.
From abstract theory to a concrete “Hidden Energy Cost”
For years, theorists have suspected that there must be a thermodynamic price for precise timekeeping, especially when quantum effects are involved, but the new work turns that suspicion into a quantified “Hidden Energy Cost.” The researchers behind the study framed their result as a direct link between information and energy: the more accurately you want to know the time, the more information you must extract from the quantum system, and the more entropy you inevitably create in the process. That link is not just philosophical, it shows up as a measurable heat load in the readout circuitry.
Coverage of the study on a Hidden Energy Cost in what the authors call Quantum Timekeeping emphasized that the surprise was not only the existence of this cost but its scale. The work describes how the act of reading the clock makes the process effectively irreversible, which is where the entropy spike comes from. Once the quantum state is projected into a definite outcome and stored in a classical memory, there is no way to undo the measurement without expending even more energy, so the information gain about the time is inseparable from a thermodynamic loss.
Why measurement is so expensive in the quantum world
To understand why reading a quantum clock is so costly, it helps to recall that quantum measurement is not a passive glance but an active interaction. In the double quantum dot clock, the detector must couple strongly enough to the electron to distinguish different states that correspond to different times, and that coupling inevitably disturbs the system and dumps energy into the environment. The more sharply the detector resolves the state, the more it suppresses quantum superpositions and the more entropy it produces, which is why higher timing precision comes with a higher energy bill.
The researchers behind the study connect this behavior to broader principles of quantum thermodynamics and information theory, where measurement and feedback are known to carry energetic penalties. In their analysis, the detector and its memory elements act as a kind of Maxwell’s demon that acquires information about the system, but the demon pays for that knowledge through heat dissipation when it resets its memory and when it forces the system into definite states. A detailed discussion of this point in the context of Scientists Uncover a Hidden Energy Cost in Quantum Timekeeping notes that the entropy associated with the readout can exceed that of the clockwork itself, which is exactly what the billion-fold gap reflects.
Inside the tiny clock that revealed the problem
The experimental and theoretical work centers on a very specific device, a tiny quantum clock built from a double quantum dot that can be integrated on a semiconductor chip. In this architecture, an electron tunnels between two closely spaced potential wells, and the probability of finding it in one dot or the other oscillates in time. By calibrating those oscillations, the system can serve as a clock, with the relative occupation of the dots encoding the elapsed time since the clock was started. The elegance of this design is that it uses a minimal number of quantum degrees of freedom to implement a timing function.
What makes this setup so revealing is that it is small and clean enough for the team to track every significant source of entropy. A report on this device, published on Nov 16, 2025, explains that the team calculated the entropy, described as the amount of energy dissipated, generated both by the clock itself and by the measurement apparatus. That calculation showed that the clock’s internal dynamics are relatively frugal, while the detector that reads out the electron’s position is responsible for the vast majority of the energy loss, which is why the device became a showcase for the hidden cost of measurement.
Rethinking “efficient” timekeeping in quantum technologies
These findings land at a moment when quantum technologies are moving from lab curiosities into practical tools, from quantum computers and simulators to precision sensors and communication networks. In all of those platforms, timing is critical, whether it is synchronizing qubits in a processor, coordinating entangled photons in a network, or stabilizing the phase of a quantum sensor. The new work suggests that designers cannot treat timing as a free side channel, because every high precision time stamp extracted from a quantum system carries an energy price that may rival or exceed the cost of running the system itself.
That shift in perspective has concrete implications for how engineers might build future devices. Instead of focusing solely on lowering the power consumption of the core quantum hardware, they may need to optimize the entire measurement and control stack, from cryogenic amplifiers to classical logic that processes time tags. The researchers behind the double quantum dot clock argue that the hidden energy cost should be treated as a feature, not a flaw, because it encodes fundamental limits that can guide better designs. Their analysis, summarized in the discussion of a feature, not a flaw, points toward architectures that gather information more efficiently, for example by batching measurements, using weaker continuous monitoring, or exploiting correlations so that fewer destructive reads are needed.
What comes next for quantum clocks and their energy budgets
The immediate next step for this line of research is to test whether the billion-fold imbalance between running and reading the clock holds across other quantum architectures. Atomic clocks based on trapped ions or neutral atoms, superconducting qubit systems, and optomechanical resonators all rely on measurement chains that convert fragile quantum states into classical timing signals. If similar entropy accounting shows that their readouts also dominate the energy budget, then the hidden cost identified in the double quantum dot device will look less like a curiosity and more like a universal constraint on quantum timekeeping.
At the same time, the work opens a path toward more energy aware quantum engineering. By treating every measurement as a thermodynamic event with a calculable cost, researchers can start to compare different readout strategies not just on speed and fidelity but on energy efficiency. That could influence choices as varied as the design of single photon detectors in quantum communication links and the architecture of timing distribution in large scale quantum computers. The studies reported on Nov 13, 2025, under the themes of Reading a quantum clock and Scientists Uncover a Hidden Energy Cost in Quantum Timekeeping, show that even a tiny clock can expose big gaps in our intuition about where energy really goes in advanced technology, and they hint that the next breakthroughs in quantum performance may come as much from smarter measurement as from better qubits.
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