The researchers – from Cambridge, Southampton and Cardiff Universities and the Skolkovo Institute of Science and Technology in Russia – have used polaritons as a type of ‘beacon’ to show the way to the simplest solution to complex problems. The team believes its concept could form the basis of a new type of computer that can solve problems that are currently unsolvable.
The search for an optimal solution to such problems is said to be analogous to looking for the lowest point in a mountainous terrain. A hiker may go downhill and think they have reached the lowest point of the entire landscape, but there may be a deeper drop just behind the next mountain.
Cambridge Professor Natalia Berloff and her colleagues approached the problem by asking if, instead of moving along the mountainous terrain in search of the lowest point, the landscape could filled with a magical dust that only shines at the deepest level, becoming an easily detectible marker of the solution.
The ‘magic dust’ polaritons are created by shining a laser at stacked layers of selected atoms, such as gallium, arsenic, indium and aluminium. The electrons in these layers absorb and emit light of a specific colour. Polaritons are ten thousand times lighter than electrons and may achieve sufficient densities to form a Bose-Einstein condensate, where the quantum phases of polaritons synchronise and create a single macroscopic quantum object that can be detected through photoluminescence measurements.
The researchers then had to determine how to create a potential landscape that corresponds to the function to be minimised and to force polaritons to condense at its lowest point. They say they have shown that polaritons can be created at the vertices of an arbitrary graph: as polaritons condense, the quantum phases of polaritons arrange themselves in a configuration that correspond to the absolute minimum of the objective function.
Professor Pavlos Lagoudakis from the University of Southampton, added: “We are currently scaling up our device to hundreds of nodes, while testing its fundamental computational power. The ultimate goal is a microchip quantum simulator operating at ambient conditions.”
