Key Points
- Researchers have discovered that measuring a quantum clock is its biggest source of energy consumption.
- The energy cost of “reading” the clock can be up to a billion times greater than the energy needed to run it.
- This finding challenges the long-held assumption that the energy cost of measurement in quantum physics is negligible.
- The study suggests that the act of measurement itself is what makes time irreversible at the quantum level.
In a surprising discovery, researchers have found that the very act of measuring a quantum clock is its biggest source of energy loss. A new study, led by the University of Oxford and published in Physical Review Letters, shows that the energy cost of “reading” a quantum clock is far greater than the cost of actually running it. This finding could have big implications for the design of future quantum technologies.
Clocks, from old-fashioned pendulums to modern atomic clocks, need irreversible processes to mark the flow of time. But at the tiny quantum scale, these processes are very weak, making timekeeping a huge challenge. For future quantum devices, such as sensors and navigation systems, energy-efficient internal clocks are essential. Until now, however, the energy cost of these quantum clocks was a mystery.
To figure this out, the researchers built a microscopic clock using single electrons hopping between two tiny regions. Each “hop” was like a “tick” of the clock. They then used two different methods to detect these ticks. In both cases, the sensors had to convert the tiny quantum signals (the electron hops) into classical data that could be recorded.
The researchers calculated the energy dissipated by both the clock and the measurement equipment. They were stunned by the results: the energy needed to read the quantum clock—to turn its tiny signals into something we can record—was up to a billion times greater than the energy used by the clock’s own mechanism.
This discovery turns a common assumption in quantum physics on its head—that the energy cost of measurement is so small it can be ignored. It also suggests that the act of observing makes time irreversible, giving it a forward direction.
This finding also changes the focus for future research. Instead of trying to build better quantum systems to make more efficient clocks, the study suggests that scientists should focus on finding smarter, more energy-efficient ways to measure the ticks.
“Quantum clocks running at the smallest scales were expected to lower the energy cost of timekeeping, but our new experiment reveals a surprising twist,” said lead author Professor Natalia Ares.
However, the researchers believe this imbalance could be a feature rather than a bug. The extra energy used in measurement can yield more detailed information about the clock’s behavior, potentially leading to new ways to create highly precise clocks more efficiently.
