A team of engineers at the University of New South Wales has developed a new quantum computing design that has the potential to make quantum chips easier and cheaper to make. It allows for the quantum bits, or qubits, to be placed with a lot more freedom.
The new set-up has been described in the journal Nature Communication. A silicon chip is taken to absolute zero, placed in a very strong magnetic field, and covered in a silicon oxide insulator. Metallic electrodes are placed on top of the insulator and the electrodes control the real quantum machinery: phosphorus atoms.
According to the team, it’s possible to create a stable qubit by entangling the spin of a phosphorus atom with one of its electrons. The choice of phosphorus is not random. The same lab had already demonstrated how stable phosphorus atoms are in these entangled architectures.
The entanglement is very important. This quantum mechanical property tells us that we can’t consider the spin of the atom and of the electron as separate. If we were to measure one, we would immediately affect the value of the other (even if the electron, for example, was sent somehow billions of light-years away).
"We call it the 'flip-flop' qubit," lead author Dr Guilherme Tosi said in a statement. "To operate this qubit, you need to pull the electron a little bit away from the nucleus, using the electrodes at the top. By doing so, you also create an electric dipole."
The ability to move the electron away, maintaining the entanglement is crucial. Often qubits set-up can only remain stable if the atom and electron are at maximum 10-20 nanometers apart, which is about 50 atoms. The proposed set up could work to 1,000 nanometers.
“This means we can now place the single-atom qubits much further apart than previously thought possible," senior author Professor Andrea Morello explained. "So there is plenty of space to intersperse the key classical components such as interconnects, control electrodes and readout devices, while retaining the precise atom-like nature of the quantum bit."
The qubits in this set-up are also controlled by electric signals instead of magnetic ones, which makes it much easier to distribute on an electronic chip. This approach could be one the team will develop into a real device. The university has received funding to build a 10-qubit prototype silicon quantum integrated circuit by 2022.
