Australian engineers have come up with a new technique that will dramatically reduce the size of quantum computer parts.

Researchers from leading institutions have come together to create a new way of implementing large-scale interferometers to miniaturise optical processing circuitry. 

Interferometers are used to split the beam of a laser for interferometry – where information is gathered about the state of quantum particles and waves.

It is an important part of quantum computing, which uses the behaviour of the smallest parts of the universe as a basis for processing data.

The team, in a paper published in Physical Review Letters, has shown that a small-scale physical interferometer can do the work of a much larger one by using a technique dubbed 'measurement-based linear optics'. 

“A clear advantage of our approach is that it harnesses existing compact methods for generating large-scale cluster states - a resource for quantum computing,” says lead author Dr Nicolas Menicucci. 

“Six beamsplitters and a few squeezed light sources give us the potential to access virtual optical networks of an immense size.”

Fully-functioning optical quantum computers will not be possible without the creation of interferometers that comprise hundreds or even thousands of optical elements.

Somewhat unsurprisingly, the team took inspiration from quantum physics to come up with a new way to approach the problem.

“Measurement-based linear optics circumvents many of the challenges facing the conventional optics approach by using large virtual interferometers instead of physical ones. By applying of a specific sequence of measurements to a continuous-variable cluster state, the measurements themselves program and implement the interferometer,” says first author Dr Andrews.

“We use a gigantic cluster state composed of modes of light correlated in time or frequency, which can be generated using just one or two optical parametric oscillators (which implement optical squeezing) and just a handful of beamsplitters.” 

The team's experimental collaborators have already demonstrated the technology, yielding cluster states composed of more than 1 million entangled modes.

“Measurement-based linear optics has the potential to reshape how we think about the interference of light,” says Dr Menicucci. 

“It ports the demonstrated scalability of continuous-variable cluster states to the broad range of linear-optics applications.”