Quantum technologies – devices that operate according to quantum mechanical principles – promise to bring users some unprecedented innovations in any context. Ironically, those same principles often create complications that prevent these supposedly wonderful devices from actually taking off.
A new study, published November 14 in Physical Review Letters, further solidifies this problem by demonstrating another, somewhat unexpected obstacle – the act of measurement. For the experiment, physicists built a microscopic quantum clock and found that the energy required to read quantum clocks could be up to a billion times greater than the energy required to run the clock.
According to the study, the findings shed light on “an often ignored phenomenon in the literature” or the cost of observation in quantum mechanics. Also, the extra energy could provide an opportunity to create more informative, ultra-precise clocks – if physicists can find a way, that is.
“Quantum clocks operating on the smallest scales were expected to reduce the energy costs of timekeeping, but our new experiment reveals a surprising twist,” senior author Natalia Ares, a physicist at the University of Oxford in the UK, said in a release. “Instead, the quantum tick in quantum clocks is much more than the clockwork itself.”
some (very dense) background
time is one extremely Difficult concepts in quantum mechanics; Its effect is weak or almost irrelevant in the quantum field. Nevertheless, real-life instruments are subject to real-life events that change over time. For researchers, this means that future quantum devices – such as sensors or navigation systems – must have ultra-precise internal clocks to minimize problems.
And then there is the problem of measurement, the famous Schrödinger’s cat thought experiment being the best example of this phenomenon. Quantum systems can exist in a superposition of different states, but when an observer tries to measure that system, there is only one answer. So the cat may be dead or alive, but we won’t know until we open that box.
A typical clock automatically generates heat – and hence a measure of entropy, or order – as it ticks and records the passage of time. According to the researchers, the effect of heat is usually so small that it does not matter in most cases, which is why most quantum researchers ignore the effects of clock ticking for quantum devices.
measuring quantum tick
For their experiment, the team created a quantum clock running on two electrons moving between two different fields. Each jump was equivalent to a “tick” of a regular clock. They tracked changes in tiny electrical currents and radio waves – two different quantum signals – and translated these changes into classical data for timekeeping. Then, the researchers compared the energy cost of the entropy created by the bouncing electron “ticks” and the energy required to measure these ticks.
Surprisingly, they found that, according to the paper, the latter “not only dwarfs the former, but also opens up tremendous accuracy.” That is, efficiency aside, the extra measurement energy actually allowed the team to control the clock more precisely.
Looking ahead, understanding such dynamics could be useful for synchronizing timing-related operations inside advanced computers, Edward Laird, a physicist at Lancaster University in Britain who was not involved in the new work, told Physics magazine. The researchers said the findings raise more fundamental questions about whether the act of observation itself gives direction to time.
“By showing that it is the act of measuring – not merely ticking – that guides time forward, these new findings make a powerful connection between the physics of energy and the science of information,” Florian Mayer, co-lead author of the study and a postdoctoral student at the Technische Universität Wien in Austria, said in the statement.
As the researchers write in the paper, energy efficiency has been an ongoing issue in the design of quantum technologies. So it is interesting that, as it stands, the paper can be taken as an invitation to look away from the hardware and rethink some of the inherent paradoxes in theoretical quantum mechanics.