Time: it is perpetually limited and we never have enough of it. Some claim it is an illusion, while others claim it flies like an arrow.
This arrow of time is a significant problem in physics. Why does time flow in a specific direction? And can this course be reversed?
A new study provides an essential debate point on the topic. In an experiment with enormous consequences for our knowledge of quantum computing, an international team of researchers has developed a time-reversal program for a quantum computer.
Their approach also revealed an essential fact: the time-reversal process is so intricate that its spontaneous occurrence in nature is exceedingly unlikely, if not impossible.
In many instances, the laws of physics do not prevent us from traveling forward and backward in time. It is conceivable to do a time-reversal operation in some quantum systems. The team has constructed a thought experiment based on a plausible scenario.
Schrodinger’s Equation governs the evolution of a quantum system and provides us the likelihood of a particle being in a given location.
The Heisenberg Uncertainty Principle is another key property of quantum physics, which states that we cannot know the exact position and momentum of a particle since everything in the universe behaves as both a particle and a wave simultaneously.
The researchers hoped to see whether a single particle might spontaneously switch direction for a fraction of a second. They use the analogy of a cue shattering a triangle of billiard balls, sending the balls in all directions — a good representation of the second law of thermodynamics, which states that an isolated system will always progress from order to chaos — and then having the balls return to order.
The researchers set out to determine whether or not this is possible, both in nature and in the laboratory. Their thought experiment began with a confined electron, whose location within a tiny region of space was rather certain.
The principles of quantum mechanics make precise knowledge of this problematic. The objective is to have the highest chance that the electron is located within a particular location. As time passes, this likelihood “spreads out,” making it more likely that the particle is in a larger location. The researchers then propose a time-reversal procedure to return the electron to its original location. The thought experiment was followed with real-world mathematics.
Due to random oscillations, the researchers evaluated the probability of this occurring to a real-world electron. If we were to observe 10 billion “freshly localized” electrons every second for the duration of the universe’s existence (13.7 billion years), we would observe this phenomenon only once.
And it would only set the quantum state back one 10-billionth of a second, or roughly the time between a traffic light turning green and the car behind you blaring their horn.
Although time reversal is unusual in nature, it is achievable in the laboratory. The team decided to simulate the confined electron concept on a quantum computer and develop a time-reversal operation to return it to its initial state.
It was evident that as the size of the simulation increased, its complexity (and accuracy) decreased. In 85 percent of situations, researchers were able to reverse time using a two quantum-bit (qubit) configuration replicating a confined electron. In a three-qubit configuration, only fifty percent of the cases were successful and there were more errors.
Although time reversal programs in quantum computers are unlikely to result in a time machine (Deloreans are better suited for that), they may have crucial implications in the future for making quantum computers more precise.
Reference(s): Scientific Reports