Quantum computers require precise time measurement for manipulating quantum states, but new research has revealed a fundamental limitation: clocks cannot achieve perfect resolution and precision simultaneously due to their finite energy and entropy generation. This imposes inherent constraints on quantum computing’s capabilities. As quantum technology advances, overcoming these time measurement challenges will become critical, possibly leading to new discoveries in quantum mechanics.
Quantum computing is becoming more accessible for performing calculations. However, research indicates that there are inherent limitations, particularly related to the quality of the clock utilized.
There are different ideas about how quantum computers could be built. But they all have one thing in common: you use a quantum physical system – for example, individual atoms – and change their state by exposing them to very specific forces for a specific time. However, this means that in order to be able to rely on the Vienna University of Technology in the team of Marcus Huber and first author of the first paper. “In order to achieve the desired state in the end, the rotation must be applied for a very specific period of time. Otherwise, you turn the state either too short or too far.”
Entropy: Time makes everything more and more messy
Marcus Huber and his team investigated in general which laws must always apply to every conceivable clock. “Time measurement always has to do with entropy,” explains Marcus Huber. In every closed physical system, entropy increases and it becomes more and more disordered. It is precisely this development that determines the direction of time: the future is where the entropy is higher, the past is where the entropy was even lower.
As can be shown, every measurement of time is inevitably associated with an increase in entropy: a clock, for example, needs a battery, the energy of which is ultimately converted into frictional heat and audible ticking via the clock’s mechanics – a process in which a fairly ordered state occurs the battery is converted into a rather disordered state of heat radiation and sound.
On this basis, the research team was able to create a mathematical model that basically every conceivable clock must obey. “For a given increase in entropy, there is a tradeoff between time resolution and precision,” says Florian Meier, the first author of the second paper. “That means: Either the clock works quickly or it works precisely – both are not possible at the same time.”
Limits for quantum computers
This realization now brings with it a natural limit for quantum computers: the resolution and precision that can be achieved with clocks limit the speed and reliability that can be achieved with quantum computers. “It’s not a problem at the moment,” says Marcus Huber. “Currently, the DOI: 10.1103/PhysRevLett.131.160204