Superconducting Quantum Processors

Superconducting Quantum Processors
Superconducting Quantum Processors - Five quantum modules interconnected by newly developed, low-loss quantum interconnects. Credits: Yan Qiu

Computing systems, known as quantum processors, use quantum mechanics to process data and perform calculations. For some tasks, these systems can outperform traditional CPUs noticeably in terms of both speed and computing power.

Over the past decade, engineers have created a number of promising quantum computing systems, but scaling these systems and ensuring that they can be used at scale is still a challenge. Making modular systems with a large number of small quantum modules that can be individually calibrated and then combined into a larger architecture is one way to increase the scalability of quantum processors. However, this requires suitable and efficient interconnections (ie devices that connect these small modules together).

Low-loss interconnects have recently been created by scientists at the Southern University of Science and Technology, the International Quantum Academy, and other institutions in China to interconnect various modules in modular superconducting quantum processors. Originally published in Nature Electronics, these interconnects are built on impedance transformers and pure aluminum wires.

Youpeng Zhong, one of the researchers who led the study, told Tech Xplore: “Our current publication builds on the core principles of my postdoctoral research that I did at the University of Chicago and was published in Nature two years ago. In that research, I connected two quantum processors using a niobium-titanium (NbTi) superconducting coaxial cable.”

In one of his previous research, Zhong attempted to connect two different quantum computers using NbTi superconducting cables, which are often used to design cryogenic/quantum systems. He tried to wire the quantum chips to the connected NbTi cable in order to reduce the connection loss.

When this turned out to be extremely challenging, Zhong said, “I thought of trying new cables made of other superconducting metals such as aluminum, which is the same material as our quantum circuits. “Pure aluminum coaxial cables are not easily accessible off the shelf as they are less lossy and harder to solder than copper, making them unsuitable for standard wiring applications. Moreover, the superconducting transition temperature is lower than the liquid helium temperature.

Except for applications involving quantum connectivity, applications that require pure aluminum coaxial cable are rare.

Zhong specifically purchased pure aluminum coaxial cables for its innovative low-loss interconnects and integrated in-chip impedance transformers into them. The resulting interconnects were easier to connect to quantum chips and had much lower losses (by an order of magnitude) than conventional interconnects built using NbTi cables.

According to Zhong, pure aluminum cables proved to be the ideal option for quantum interconnections. Our interconnects consist of a wire-bond connection between the cable and the quantum chip, a quarter wavelength transmission line acting as an impedance transformer on the quantum chip, and a custom-built aluminum coaxial cable. The cable-junction is converted by the impedance transformer in the team's interconnect to a current node of a standing wave mode, which is used to transfer quantum states. As a result, the resistance loss at the junction between several quantum processors is greatly reduced.

“Our findings remind us how much potential improvement we can have if we think outside the box,” Zhong said. “For example, the work of Charles Kao laid the foundation for optical fibers as we all know today: with a record loss of 0,2 dB/km, they have become the backbone of the modern global communications network – indispensable for short and long distance communication. The transformative impact of this highly technical and nearly neglected materials science research has earned it half the 2009 Nobel Prize in Physics. Another example is the use of stainless steel for Elon Musk's Starship Mars Rocket.”

The latest research from this group of scientists demonstrates the enormous potential of aluminum cables for creating efficient interconnects to interconnect processing modules in modular quantum computers. In the near future, other modular systems could use the low-loss interconnect developed by Zong and colleagues, advancing ongoing attempts to design more scalable quantum processors.

Zhong continued, “One of my future research priorities is to investigate quantum entanglement gates between various quantum computers. “Another is trying to put together a large number of modules to increase the size of quantum processors.”


Günceleme: 11/03/2023 13:01

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