The future confronts us with a vast number of possibilities. These possibilities grow exponentially when going further into the future. For instance, if we have two possibilities to choose from each minute, in less than half an hour, there are 14 million possible futures. In less than a day, the number exceeds the number of atoms in the universe.

Farzad Ghafari, Geoff Pryde, Griffith University, Brisbane, Australia, Mile Gu, Nanyang Technological University, Singapore, and colleagues have constructed a prototype quantum device that can simulate these possible futures in a quantum superposition. This is similar to Schrödinger’s famous cat, which exists in a superposition of its alive and dead states. The team developed a photonic quantum information processor, in which the potential future outcomes of a decision process are represented by the locations of photons. The device is built using an experimental laser setup, which generates the required photons.

The state of the quantum device is a superposition of multiple potential futures, weighted by their probability of occurrence. The team used the machine to measure how much our bias towards a specific choice in the present impacts the future. By interfering the superpositions with each other, the researchers can compare the futures without looking at each possible future individually.

Many current artificial intelligence (AI) algorithms learn by seeing how small changes in their behavior can lead to different outcomes. According to the researchers, their technique could enable quantum enhanced AIs to learn the effect of their actions much more efficiently. Currently, the prototype simulates at most 16 futures simultaneously. However, the underlying quantum algorithm can in principle scale without bound.

• Interfering trajectories in experimental quantum-enhanced stochastic simulation,
  Farzad Ghafari, Nora Tischler, Carlo Di Franco, Jayne Thompson, Mile Gu, Geoff J. Pryde,
  Nat. Commun. 2019.
  https://doi.org/10.1038/s41467-019-08951-2