Finding a quantum connection

Quantum is big. There is increasing excitement about research into quantum devices and the world of possibilities they provide. However one question which has remained unanswered is how to effectively communicate quantum information between these different kinds of devices.

A paper published by researchers from TU Delft and the University of Vienna is one of the first steps to answering this question.

The paper is titled Non-classical correlations between single photons and phonons from a mechanical oscillator. A collaboration between a research group in TU Delft, headed by Simon Gröblacher, and one in the University of Vienna headed by Markus Aspelmeyer, it was published in Nature on January 18.

Gröblacher, head of the Groeblacher Lab in the TU Delft Faculty of Applied Sciences, explained how quantum communication can work in different ways. Communicating quantum information over long distance usually uses optics, communicating with photons while processing it locally is often done using atoms, ions, or superconducting qubits. The researchers created a device which can act as an intermediate between these two systems that cannot ordinarily communicate with each other; "We made a mechanical system which we coupled to light, and we used the light to get the mechanical system into a quantum state. This could be used as an interconnect between a superconducting qubit and optical qubit." The device works by reflecting a laser off the mechanical system, which turns photons (light particles) into phonons (quantum-mechanical vibrations), and then back again.

While this is just a first step in discovering how to disperse quantum information between different systems, hopes for the long term applications of this technology lie in developing a quantum internet. This internet would connect quantum computers, which will have far greater computing power than classical computers. However, Gröblacher adds that the first quantum computers aren't exactly going to be desktops, due to their complexity. Likely they would be housed in centres which could communicate with each other using a mechanical oscillator similar to that created at TU Delft.

In addition to its potential as a means to connect different quantum devices, this research could help further develop our understanding of how quantum physics works. According to Gröblacher it is one of the first experiments examining how massive mechanical systems act in relation to both quantum and classical physics. He added "I really think that these mechanical systems that we use have the potential to test the boundary between classical and quantum physics."