Researchers have presented something called a Gaussian boson sampling system. It's essentially a quantum device designed to solve a single problem. It's based on devices called "beam splitters," so let's take a closer look at how these devices work.
If light hits a mirror that is 50 percent reflective – called a beamsplitter – then half the light will be transmitted and the other half will be reflected. If the intensity of the light is low that there is only one photon, it is reflected or transmitted with the same randomness as a coin toss. That’s the idea behind a beamsplitter, which can take an incoming stream of photons from a laser beam and split it into two beams traveling in different directions.
A 45-degree beam splitter can be thought of as a four-port device (see Figure). In this figure, you can see that if two identical photons are introduced into the same beam splitter from two different ports, the result is not completely random. Both will exit through the same port, although the port they exit through is random.
These two simple ideas, along with the idea of entanglement, lead to a specific type of universal quantum computer, called a linear optical quantum computer. Photons solve a problem by the way they propagate through the network, which is determined by where they exit.
The so-called “entanglement” comes in the form of the path that the photons follow. Until we can measure this path, we cannot know details , so we must take into account that all photons take all possible paths. Under these conditions, if two photons arrive at a beam splitter at the same time through different ports, then their paths will be connected (entangled). The creation of a large network of beam splitters creates extensive entanglement states.
The number of output states scales very quickly with the number of inputs and beam splitters. In the current demonstration, the researchers used 50 inputs and – the exact type of device is not described – a chip with the equivalent of 300 beam splitters. The total number of possible output states is about 1030, which is about 14 orders of magnitude larger than the next largest demonstration of “quantum computing”.
Photons are sent into the network (one at each input) and exit in a state chosen randomly from all possible states. In less than four minutes, the researchers had obtained results that they estimate would take about 2.4 billion years to compute on a fast classical computer .
