“Virtual” Interferometers Could Minimize Size of Optical Processing Circuitry

A novel technique dubbed “measurement-based linear optics” could enable miniaturization of the optical processing circuitry required for quantum computers by using virtual interferometers instead of large-scale physical ones.

According to researcher Rafael Alexander, conventional interferometers that comprise hundreds or even thousands of optical elements are essential to implementing fully functional optical quantum computers.

Measurement-based linear optics implements a huge multimode interferometer consisting of beamsplitters (green) and phase delays (blue). The size of the virtual interferometer can be many hundreds or thousands of optical elements, despite the small size of the physical experiment. Courtesy of R. Alexander et al./APS.

“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 a specific sequence of measurements to a continuous-variable cluster state, the measurements themselves program and implement the interferometer,” said Alexander.

The virtual, measurement-based interferometers are programmed in real time through the choice of homodyne measurement angles. The effects of finite squeezing are captured as uniform amplitude damping.

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

Alexander said that the team, composed of researchers from RMIT University, the University of Sydney and the University of Technology Sydney, used “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 compared its technique to existing physical interferometers and considered use of its technique for Boson sampling. The technique demonstrated efficiency in time and squeezing, showing the capacity to yield cluster states composed of more than one million entangled modes.

To overcome noise distortion — a common problem faced by virtual approaches — the team converted the noise to simple photon loss, which made the noise distortion easier to manage.

According to Alexander, the team drew inspiration for its novel approach to virtual interferometry from quantum teleportation.

“Measurement-based linear optics has the potential to reshape how we think about the interference of light,” said Menicucci. “It ports the demonstrated scalability of continuous variable cluster states to the broad range of linear-optics applications.”

The research was published in Physical Review Letters (doi: 10.1103/PhysRevLett.118.110503).