A photonic chip including not less than 128 tunable components appears to be a true “Swiss army knife” with a wide range of applications.
While performing studies on the measurement of light wavelengths with the help of this photonic chip, Caterina Taballione from the University of Twente accidentally chanced upon yet another application: when single photons are sent through the system in the place of continuous light, the optical components can also carry out quantum operations. The same chip functions as a photonic quantum processor.
It is now possible to manipulate light on a chip on a highly advanced level, specifically using combinations of materials. Silicon nitride can now be used to develop optical waveguides with very low losses, or indium phosphide can be used to develop very narrow laser light sources. The chip presented by Caterina Taballione in her thesis includes many components that can combine or split the light to and from separate channels, such as in a rail yard.
In addition, it has ring-shaped resonators that can act as a filter. The power of the chip is in the fact that it is possible to control the components from the outside, rendering it flexible and programmable. Moreover, all this is possible not just in a classical approach but even in quantum photonics, as is one of the unpredicted outcomes. This already paved the way for a new company known as QuiX.
Temperature is used to control the components. The chip has several so-called Mach-Zehnder interferometers with the ability to split light from one to two light-conducting channels, or waveguides. Prior to rejoining of both channels, it is possible to control one of them by applying a temperature variation.
The outcome is that the signals from both channels do not have the same phase anymore. It is also possible to temperature-control the ring-shaped components. Using this approach, Taballione could present a highly precise way of measuring wavelengths of light. In order to achieve this, she combined the temperature control to an artificial neural network.
The system is highly reconfigurable—one of the advantages for using it in the forthcoming 5G mobile standard in which it is essential to very precisely direct wireless signals from a base station to a user. Calculation of the ideal combination of antennas for performing this, what is called “beam forming,” is essentially a task that the new chip can carry out in a fast and energy-efficient manner.
All of these are robust applications demonstrating the potential of the photonic chip. However, what would happen if separately detectable single photons are introduced at the inputs in the place of a continuous light source?
In that scenario, the components support typical quantum effects such as entanglement, coalescence, and superposition. The photons observed at the outputs are the result of quantum processing by means of temperature control of the components.
While a single-photon light source and detector essentially function at low temperatures, the quantum processor itself runs at room temperature. Therefore, quantum computing using photons has an edge over the use of “qubits” only operating at a temperature of a few Kelvin.
This accidentally discovered application makes the chip a robust platform for quantum experiments, specifically if the number of inputs and outputs is enlarged further, and thus the number of components. Moreover, incorporating a single-photon light source and detector would make the system more robust.
The UT researchers involved, thus, founded a new company known as QuiX, to enable the chip to be widely available for other researchers and R&D departments.
Caterina Taballione did her PhD research in the Laser Physics and Nonlinear Optics group of Prof. Klaus Boller, which is part of UT’s MESA+ Institute. This study was made possible by the MEMPHIS II programme (merging electronics and micro and nano photonics in integrated systems) of the Dutch Research Council NWO.