Clicks guide quantum compilation
Local engineers say quantum computers could be constructed cheaply and reliably using a new technique.
A University of Melbourne-led team has developed a technique to embed single atoms in silicon wafers, one-by-one, mirroring methods used to build conventional devices.
Using this method, they can create large scale patterns of counted atoms that are controlled so their quantum states can be manipulated, coupled and read-out.
Professor David Jamieson says his team’s vision is to use this technique to build a very, very large-scale quantum device.
“We believe we ultimately could make large-scale machines based on single atom quantum bits by using our method and taking advantage of the manufacturing techniques that the semiconductor industry has perfected,” Professor Jamieson said.
The technique takes advantage of the precision of an atomic force microscope, which has a sharp cantilever that touches the surface of a chip with a positioning accuracy of just half a nanometre, about the same as the spacing between atoms in a silicon crystal.
The team drilled a tiny hole in this cantilever, so that when it was showered with phosphorus atoms one would occasionally drop through the hole and embed in the silicon substrate.
The key was knowing precisely when one atom – and no more than one – had become embedded in the substrate. Then the cantilever could move to the next precise position on the array.
The team discovered that the kinetic energy of the atom as it ploughs into the silicon crystal and dissipates its energy by friction can be exploited to make a tiny electronic “click”.
Professor Jamieson said the team could “hear” the electronic click as each atom dropped into one of the 10,000 sites in the prototype device.
“One atom colliding with a piece of silicon makes a very faint click, but we have invented very sensitive electronics used to detect the click, it's much amplified and gives a loud signal, a loud and reliable signal,” Professor Jamieson said.
“That allows us to be very confident of our method. We can say, ‘Oh, there was a click. An atom just arrived. Now we can move the cantilever to the next spot and wait for the next atom’,” Professor Jamieson said.
The technique allows the experts to create a qubit ‘chip’, which can then be used in lab experiments to test designs for large scale devices.
“This will allow us to engineer the quantum logic operations between large arrays of individual atoms, retaining highly accurate operations across the whole processor,” says Professor Andrea Morello from the University of New South Wales.
“Instead of implanting many atoms in random locations and selecting the ones that work best, they will now be placed in an orderly array, similar to the transistors in conventional semiconductors computer chips.”