Silicon Quantum Computing (SQC), a spinout from the University of New South Wales (UNSW) in Australia, has been working for many years to develop quantum processors using quantum dot technology and manufactured using precise STM (Scanning Tunneling Microscope) lithography. This is in contrast with other companies working on quantum dot qubits such as Intel, Diraq, or Quantum Motion that are using the more traditional optical lithography using deep ultraviolet (DUV) light prevalent in today’s high volume semiconductor fabrication facilities. The advantage of SQC’s approach is that it allows placing atoms on the chip with sub-nanometer precision and makes it easier to change the chip configurations. The disadvantage is that the process would not be easily transferable to a high volume semiconductor fab nor could it ever achieve the low chip cost characteristics or huge quantity production that we see with high volume semiconductors. However, the company has indicated that their technical strategy is to focus on precision and quality rather than quantity and they have constructed their own fabrication facility at UNSW Sydney to build their chips.

The company has announced their first analog quantum processor chip that has been specifically designed to accurately model the quantum states of a small, organic polyacetylene molecule. The device consists of placing 10 quantum dots made out of phosphorus atoms that are controlled by 6 electrodes (G1 to G6). The electrodes can precisely control the position of the quantum dots to mimic the bonds and energy levels of the carbon atoms in the polyacetylene molecule. This device can then act as an analog model to the molecule itself. And by injecting it with current and measuring the results they can predict how the actual molecule would behave. This approach is conceptually analogous to how an aeronautical engineer might create a scale model of a new airplane and test it in a wind tunnel to predict how the full size airplane would behave in actual flight.

A scanning tunneling microscope image of a 10-quantum dot quantum analogue simulator – mimicking a polyacetylene molecule. Credit: Silicon Quantum Computing

The advantage of SQC’s approach is that it may be a lot easier to scale up and they are indeed already working on modelling larger, more complex molecules which may be commercially relevant. Although this analog quantum simulation approach cannot cover the wide gamut of applications that are theoretically possible with gate based machines, quantum simulation of chemical reactions is a very important application that can be used in areas such as drug discovery and material design. For more about SQC’s announcement, you can read their press release announcing this development here an FAQ document with additional details here, and a technical research paper here.

June 22, 2022