Sebastian Deffner, Assistant Professor of Physics, University of Maryland, Baltimore County, writing in The Conversation ass the question, is there a limit to the speed in which quantum computing could eventually go?
If an object in the quantum world travels from one location to another, researchers can’t measure exactly when it has left nor when it will arrive. The limits of physics impose a tiny delay on detecting it. So no matter how quickly the movement actually happens, it won’t be detected until slightly later. (The lengths of time here are incredibly tiny – quadrillionths of a second – but add up over trillions of computer calculations.)
That delay effectively slows down the potential speed of a quantum computation – it imposes what we call the “quantum speed limit.”
Over the last few years, research, to which my group has contributed significantly, has shown how this quantum speed limit is determined under different conditions, such as using different types of materials in different magnetic and electric fields. For each of these situations, the quantum speed limit is a little higher or a little lower.
To everyone’s big surprise, we even found that sometimes unexpected factors can help speed things up, at times, in counterintuitive ways.
To understand this situation, it might be useful to imagine a particle moving through water: The particle displaces water molecules as it moves. And after the particle has moved on, the water molecules quickly flow back where they were, leaving no trace behind of the particle’s passage.
Now imagine that same particle traveling through honey. Honey has a higher viscosity than water – it’s thicker and flows more slowly – so the honey particles will take longer to move back after the particle moves on. But in the quantum world, the returning flow of honey can build up pressure that propels the quantum particle forward. This extra acceleration can make a quantum particle’s speed limit different from what an observer might otherwise expect.