Physicists Discover Quantum Speed Limit | Wired Science | Wired.com.
In my life (before 1990) there was still hope that we might someday reach the stars. Writers told stories about what a future star-faring humanity might look like. I’m not sure what happened in 1990, or if it was a gradual change that started much sooner (the theory of special relativity was first presented in 1905), but ever since, the epic idealism of SciFi and space travel has been steadily ground down. Today, Urban Fantasy and Paranormal themed novels apparently dominate the market. That’s not horrible; I like Urban Fantasy and Paranormal themes, but I miss the golden era when people still believed we might one day reach the stars.
As in many other strongly interacting systems, these excitations take the form of quasiparticles that can travel through the lattice. Neighboring quasiparticles begin with their quantum states entangled, but propagate rapidly in opposite directions down the lattice. As in all entangled systems, the states of the quasiparticles remain correlated even as the separation between them grows. By measuring the distance between the excitations as a function of time, the real velocity of the quasiparticles’ propagation can be measured. As measured, it is more than twice the speed of sound in the system.
The specific lattice strengths used in the experiment make it difficult to do direct comparisons to theory, so the researchers were only able to use a first-principles numerical model (as opposed to a detailed theoretical calculation). To phrase it another way, the velocity they measured cannot currently be derived directly from fundamental quantum physics.
It’s difficult to generalize these results as well. Systems with other physical properties will have different maximum speeds, just as light moves at different speeds depending on the medium; the researchers found things changed even within a simple one-dimensional lattice whenever they varied the interaction strength between the atoms.
However, showing that excitations must have a consistent maximum speed is a groundbreaking result. As with relativity, this speed limit creates a type of “light cone” that separates regions where interactions can occur and where they are forbidden. This has profound implications for the study of quantum entanglement, and thus most forms of quantum computing.
Despite recent anomalies in tests suggesting faster than light neutrino, the overwhelming evidence is that the anomaly is the result of a measurement error. How I would love to believe otherwise, but I think it much likelier that we’ll discover worm-hole technology before we’ll find a way to accelerate mass above the speed of light.
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