Chalmers University Researchers Resolve Quantum Scaling Bottleneck Through Efficient Cable Multiplexing

Chalmers researchers solve quantum heat issues by allowing qubits to share cables, enabling the scale-up to thousands of qubits with minimal speed loss.

By: AXL Media

Published: Apr 15, 2026, 6:17 AM EDT

Source: Information for this report was sourced from Chalmers University of Technology

Overcoming the Thermal Barrier to Quantum Scaling

The advancement of large scale quantum computing has long been hindered by the physical and thermal limitations of control hardware. Superconducting quantum processors must operate at temperatures near absolute zero, specifically -273.15°C, to maintain qubit coherence. Currently, the industry standard requires a dedicated cable for each individual qubit to transmit control signals from external electronics to the cooled environment. According to Ingrid Strandberg, a staff scientist at Chalmers, these cables emit heat and occupy significant space within the cryostat, creating a ceiling for how many qubits a single system can support before the internal temperature rises and halts computation.

Strategic Implementation of Time-Domain Multiplexing

To address this congestion, researchers investigated an approach known as time-domain multiplexing, which allows several qubits to share a single cable by sending control signals in rapid, sequential succession. This method utilizes microwave switches placed adjacent to the quantum processor to route signals to their intended targets. While there were initial concerns that forcing qubits to "wait" for their turn would significantly delay processing, the study’s lead author, Marvin Richter, explained that common quantum algorithms can actually be executed without major increases in runtime. In some specific operations, such as gates connecting two qubits, the sharing of cables results in no additional time cost at all.

A Logarithmic Breakthrough in Computation Time

The research team conducted extensive computer simulations on processors ranging in size from 121 to 1,000 qubits to measure the impact of multiplexing. A pivotal finding of the study is that computation time increases logarithmically rather than linearly as more qubits share a single cable. Simone Gasparinetti, an Associate Professor of Quantum Technology, noted that this slower-than-expected increase provides a viable path for scaling systems to the thousands of qubits required for practical applications. This mathematical discovery provides the necessary motivation for the industry to focus on developing low-dissipation microwave switches to make cable sharing a standard feature.