Is quantum physics the future

Quantum system looks to the future

Science fiction on a quantum scale: In the movie “Dr. Strange “the hero can overlook millions of possible future variants in advance. A new quantum system can now also do this - albeit initially only for 16 future lines at the same time. It uses the state and arrival time of photons to predict the position of a coin in a box that has been shaken several times. The highlight: Such quantum-based predictions could make simulations and artificial intelligence significantly more powerful.

The superposition is one of the great peculiarities of the quantum world - and thus also of quantum computers. Because as long as a quantum bit is not measured, it is neither zero nor one, but both at the same time. The probabilities of both states overlap - similar to how Schrödinger's cat in the famous allegory can crouch dead and alive in the box at the same time. A quantum computer can thus represent and calculate many possible solutions to a task at the same time.

Superimposed future lines

Farzad Ghafari from Griffith University in Brisbane and his colleagues have now gone one step further. Because they have constructed a quantum simulator that anticipates the possible future lines of a system by superimposing them. Which of these paths a process follows depends on events or actions in the present - similar to a route that changes with every new turn.

The highlight: In quantum physics, the result of this turning can be mapped as a wave function with a certain probability. As soon as I decide on a branch, the wave functions of all path variants of the other branch collapse. A quantum computer can use this principle to superimpose possible future lines. “This superposition allows us to compare the statistical futures of classical processes using quantum interference,” the researchers say.

How does the coin fall?

Specifically, the scientists used their quantum simulator to predict the outcome of a classic coin tossing experiment. A coin is placed in a closed box and the box is then briefly shaken once at each step. Each shake may cause the coin to tip over on its other side - or it may not. If you shake the box four times, there are theoretically 16 possibilities for the sequence of heads or tails.

The quantum simulator maps the state of the coin via the polarization and the path of photons, which are passed through a system of mirrors and filters. “The principle goes back to an idea by the physicist Richard Feynman,” explains co-author Jayne Thompson from the National University of Singapore. “He realized that a particle moving from point A to point B doesn't necessarily follow a single path. Instead, it runs through all possible routes between the two points simultaneously. "

Photon state as a future prediction

The researchers have now expanded this principle by calculating statistical future variants using this superposition of the photon paths. “Instead of measuring the classic result after each step, our quantum computer retains the photon and thus creates an overlay,” the researchers explain. This allows him to map the 16 possibilities of the coin experiment in a kind of 16-dimensional quantum state space.

And indeed: the quantum simulator managed to correctly map the various possibilities of coin tossing. In contrast to a normal simulation, however, it did not work through the future variants one after the other, but rather simultaneously. “This technology therefore requires much less working memory to simulate such stochastic processes,” say Ghafari and his colleagues.

Helpful for artificial intelligences

This form of “future prediction” using quantum superposition could therefore make many predictions faster and easier. “For example, many current AI algorithms learn by looking at how small changes in their behavior can lead to different future results,” explains Ghafari. The AI ​​then chooses the action that will cause the desired outcome.

“Our technology could enable such systems to determine the effects of their actions much more efficiently,” emphasize the researchers. “Because the quantum superposition sees all possible futures for every action.” Her quantum simulator can still only capture 16 such future lines at the same time, but the underlying algorithm is in principle limitlessly scalable, as Ghafari and his team explain. (Nature Communications, 2019; doi: 10.1038 / s41467-019-08951-2)

Source: Griffith University

April 24, 2019

- Nadja Podbregar