14 DAY TRIAL // Physicists at the Massachusetts Institute of Technology and Harvard University have succeeded in creating a system where photons can be used to control the quantum states of other photons. The advancement eliminates one of the major obstacles on the road to developing quantum computers.
Until now, the most widely-used approach to creating such a device has been through ions trapped in electric fields. However, this method has its disadvantages, and would be far surpassed by a quantum device that utilizes photons.
Getting the elementary light particles to interact has proven to be extremely difficult, since they have the nasty habit of passing right through each other. The research team created an approach that allows one photon to influence another via the use of a proxy atom.
In a paper published in the September 2 issue of the top journal Science, the team explains that they use cesium atoms as intermediaries. A single photon is sufficient to alter the state of such an atom, while the latter can in turn change the quantum state of a different photon.
For all intents and purposes, this means that one photon changes the other's state, since the cesium atom itself is inconsequential to the calculations a quantum bit (qubit) needs to conduct. With this innovation, it may be possible to open up the way for creating a quantum Internet.
Due to the fact that a qubit can take on the values of “1,” “0” and “1 and 0” at the same time, a simple string of 16 qubits could represent as many as 64,000 different numbers at the same time. When put to use in a computer, this ability would increase computational speeds several times over.
In order to create qubits, experts need to have photons that are in a state of superposition, which means that they exist in multiple configurations at the same time. By suspending cesium atoms between two tiny mirrors in a vacuum cavity, the experts set up the mechanism to do just that.
“The only way to make two photons interact with one another is to use atoms as a mediator. The [first] photon changes the state of the atom, and therefore it modifies the atom’s interaction with the other photon,” explains the MIT Lester Wolfe professor of physics, Vladan Vuletic.
In this scenario, the cavity chamber itself would act like a quantum switch, which is a fundamental building block for quantum computer. What it does is put photons in a state where they might be delayed by bouncing off the mirrors repeatedly, or they might not be.
“This is one of those really off-scale, super experiments that happens every now and then in science. When one does a theory paper, it looks right and so forth, but on the other hand, nobody quite buys it until somebody does an experiment. And this is a magnificent experiment,” Stephen Harris comments.
The expert, a quantum-optics pioneer himself, is a professor of applied physics and electrical engineering at the Stanford University, but was not involved in the new study.