Wireless terahertz cryogenic interconnect minimizes heat-to-information transfer in quantum processors

Quantum computers, devices that process information leveraging quantum mechanical effects, could outperform classical computers in some complex optimization and computational tasks. However, before these systems can be adopted on a large-scale, some technical challenges will need to be overcome.

One of these challenges is the effective connection of qubits, which operate at cryogenic temperatures, with external controllers that operate at higher temperatures. Existing methods to connect these components rely on coaxial cables or optical interconnects, both of which are not ideal as they introduce excessive heat and noise.

Researchers at the Massachusetts Institute of Technology (MIT) recently set out to overcome the limitations of these approaches for connecting qubits and controllers, addressing common complaints about existing connecting cables. Their paper, published in Nature Electronics, introduces a new wireless terahertz (THz) cryogenic interconnect based on complementary metal-oxide semiconductor (CMOS) technology, which was found to minimize heat in quantum processors while effectively transferring quantum information.

“In a quantum computer, the total power budget at cryogenic temperatures is very limited,” Jinchen Wang, first author of the paper, told Phys.org. “The logic is that if the system inside becomes too hot, it cannot remain cool even if millions of watts are expended outside. However, each microwave cable connecting room-temperature electronics to the cryogenic system core introduces an unwanted passive heat flow of approximately 1 mW. A 50-qubit Google quantum computer has more than 500 microwave cables to deliver control signals and receive readout data, making it unscalable.”

To realize their full potential, quantum systems should integrate tens of thousands or even millions of qubits, which is highly impractical, if not entirely unfeasible, using existing microwave cables. Wang and his colleagues set out to overcome this challenge using a wireless link that delivers control signals and receives readout data, while introducing no passive heat load.

“Since the space inside a quantum computer is a vacuum, it serves as an ideal thermal insulator,” explained Wang. “Technically, any wireless data transceiver can work. However, antenna size is inversely proportional to frequency. To ensure the antenna is small enough to be placed in the cryogenic station, we need to increase the wireless frequency to 200–300 GHz. This presents a significant challenge because generating a THz signal locally in the cryogenic station is not feasible due to low DC-to-THz efficiency.”

To solve this problem, the researchers employed a technique known as backscatter communication. Essentially, instead of generating power-hungry THz sources inside a quantum processor’s cryogenic station, they placed them outside it at room temperature, where they do not impact power consumption.

“The THz beam is then sent as a carrier wave into the cryogenic station, where it is modulated with the readout data from the quantum system core and reflected back,” said Wang. “This enables transceiver communication without burning excessive power—resembling how a mirror reflects light. Additionally, we incorporate techniques such as cross-polarization—where the uplink and downlink share the same antenna but use different polarizations to save space—and a cold-FET THz detector, a passive THz detector with zero power consumption, to further optimize our design.”

The wireless terahertz cryogenic interconnect system designed by the researchers is still at its early stages of development. Nonetheless, in initial tests, it was found to outperform a commercial microwave cable with I/O drivers (pJ/bit), yielding an energy efficiency of 34 fJ/bit for the downlink and 200 fJ/bit for the uplink.

In the future, the approach proposed by Wang and his colleagues could contribute to the large-scale deployment of quantum computers, making them easier to upscale. Notably, the newly developed wireless interconnect is also affordable and can be manufactured using standard, commercially available CMOS technology.

“In our paper, we theoretically proved that a THz link is one of the most promising techniques for data transmission in this scenario,” added Wang. “We now plan to design a multi-channel THz data link with a THz phased array outside of the cryo-station to get rid of the bulky THz horn antenna we used in this project. It will further reduce the radiative heat load and increase the scalability. We anticipate that our efforts will contribute to a real quantum computing system in four to eight years.”

© 2025 Science X Network

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