Aluminum-based low-loss interconnects for superconducting quantum processors

Quantum processors are computing techniques that course of data and carry out computations by exploiting quantum mechanical phenomena. These techniques may considerably outperform typical processors on sure duties, each when it comes to pace and computational capabilities.

While engineers have developed a number of promising quantum computing techniques over the previous decade or so, scaling these techniques and making certain that they are often deployed on a large-scale stays an ongoing problem. One proposed technique to extend the scalability of quantum processors entails the creation of modular techniques containing a number of smaller quantum modules, which may be individually calibrated after which organized into a much bigger structure. This, nevertheless, would require appropriate and efficient interconnects (i.e., units for connecting these smaller modules).

Researchers on the Southern University of Science and Technology, the International Quantum Academy and different institutes in China have not too long ago developed low-loss interconnects for linking the person modules in modular superconducting quantum processors. These interconnects, launched in Nature Electronics, are based mostly on pure aluminum cables and on-chip impendence transformers.

“Our recent paper was based on core ideas from my postdoc research at the University of Chicago, which was published in Nature two years in the past,” Youpeng Zhong, one of many researchers who carried out the examine, advised Tech Xplore. “In that study, I used a niobium-titanium (NbTi) superconducting coaxial cable to connect two quantum processors.”

In one in every of his earlier works, Zhong tried to attach two distinct quantum processors utilizing NbTi superconducting cables, that are generally used to engineer cryogenic/quantum techniques. To cut back the connection loss (i.e., the lack of vitality that inherently occurred whereas vitality traveled from one processor to the opposite by means of the cables), he tried to wire-bond the quantum chips on to the connecting NbTi cable.

“I found that this was quite difficult, so I came up with the idea of trying new cables made of different superconducting metals, such as aluminum, the same material as our quantum circuits,” Zhong defined. “Coaxial cables made with pure aluminum are not readily available on the shelf, because aluminum is more lossy and difficult to solder than copper, making it unsuitable for normal cabling applications. Moreover, its superconducting transition temperature is below the liquid Helium temperature. Other than quantum interconnection applications, it’s rare to find scenarios where a pure aluminum coaxial cable is needed.”

To create his new low-loss interconnects, Zhong customized ordered pure aluminum coaxial cables and built-in them with on-chip impedance transformers. The ensuing interconnects exhibited considerably much less loss (i.e., one order of magnitude decrease) than routinely used interconnects based mostly on NbTi cables, and had been additionally straightforward to wire-bond to quantum chips.

“Pure aluminum cables turned out to be the perfect choice for quantum interconnects,” Zhong mentioned. “Our interconnects include the custom developed aluminum coaxial cable, wire-bond connection between the cable and the quantum chip and a quarter-wavelength transmission line on the quantum chip, which serves as an impedance transformer. The impedance transformer within the crew’s interconnect converts the wire-bond connection level to a present node of a standing wave mode that’s used to switch quantum states. This considerably minimizes the resistive loss on the level of connection between completely different quantum processors.

“Our findings remind us of how much potential improvement we could attain if we think outside the box,” Zhong mentioned. “For example, the work of Charles Kao laid the foundation to optical fibers as we all know today: with record loss of 0.2 dB/km they have become the backbone of the modern global communication network—indispensable to short and long-haul communications. The transformative impact of this highly technical and almost neglected material science research was awarded a half of the 2009 Nobel Prize in Physics. Another example is the use of stainless steel for Elon Musk’s Starship Mars Rocket.”

The latest work by this crew of researchers highlights the massive potential of aluminum cables for creating efficient interconnects to hyperlink processing modules in modular quantum systems. The low-loss interconnect created by Zong and his colleagues may quickly be built-in in different modular techniques, contributing to ongoing efforts at creating extra scalable quantum processors.

“Among my future research plans, one is to explore quantum entangling gates across different quantum processors,” Zhong added. “Another is trying to scale up the size of quantum processors by connecting multiple modules together.”

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