viaTHE SOUNDS OF SCIENCE with Bernie Hobbs
It sounds like a pinball machine heard through a couple of tin cans and a bit of string, but that is actually the pinging noise of individual ions (charged phosphorous atoms) being fired into a silicon chip.
And it's the first step in an Australian quest to build a quantum computer based on silicon chips.
The physics equation that describes what you're hearing is simpler than most — "one ping = one atom" says Professor David Jamieson, who headed up the research.
Quantum computers will only work if we can precisely control and measure the "on-off" state of atoms — the direction of their spin. And doing that means we need to precisely place individual atoms in a matrix so nano-circuits can be built around them.
Jamieson and his team manage that by using a mini particle accelerator to fire phosphorous ions (P+) through a stencil with nano-scale holes in it. The individual ions that get through the stencil are placed in precise spots on the silicon chip, proving that the scale of single ion placement necessary for quantum chips can be done.
It all sounds very CERN, but it's a controlled, scaled down version of the normal process that changes "a dumb block of silicon into the very smart silicon chips in our phones and PCs", says Jamieson.
To record the sound, Jamieson, Dr Changyi Yang, and their collaborators in the Australian Research Council Centre of Excellence for Quantum Computation and Communication Technology used tiny electrodes to detect the impact of each ion as it hit the silicon surface, then used some serious signal processing and amping to generate the pings.
(If a 2005 paper titled 'Controlled shallow single-ion implantation in silicon using an active substrate for sub-20-keV ions' sounds like your kind of reading, you can get the full story.)
Ten years on, colleagues have managed to control the spin of the individual phosphorous ions as easily as if they were dialling a knob, by changing the voltage above them.