• MIT engineers have demonstrated the strongest nonlinear light-matter coupling in a quantum system using a novel superconducting circuit architecture, the 'quarton coupler.'
• The new coupler enables interactions approximately 10 times stronger than previous demonstrations, potentially leading to a 10-fold increase in quantum processing speed.
• This breakthrough could accelerate the realization of fault-tolerant quantum computers and unlock new applications in materials science and machine learning.

Researchers at MIT have achieved a significant milestone in quantum computing by demonstrating a novel superconducting circuit architecture that enables record-breaking nonlinear light-matter coupling. This advancement, achieved through a device called a 'quarton coupler,' strengthens the interaction between light (photons) and matter (artificial atoms or qubits), crucial components of quantum computers. The stronger coupling promises faster readout and processing speeds, addressing a key bottleneck in the development of practical and reliable quantum computers. This could pave the way for fault-tolerant quantum computers capable of performing complex simulations and computations currently beyond the reach of classical computers.

• What: MIT researchers demonstrated record-breaking nonlinear light-matter coupling using a novel superconducting circuit architecture (quarton coupler) which allows for faster and more reliable quantum information processing and readout.
• Who: Yufeng “Bright” Ye (lead author), Kevin O’Brien (senior author), Jeremy B. Kline, Alec Yen, Gregory Cunningham, Max Tan, Alicia Zang, Michael Gingras, Bethany M. Niedzielski, Hannah Stickler, Kyle Serniak, and Mollie E. Schwartz, all from MIT and/or MIT Lincoln Laboratory.
• When: The research was published in Nature Communications on April 30, 2025. The work builds upon years of theoretical research starting in 2019.
• Where: The research was conducted at the Research Laboratory of Electronics (RLE) at MIT and MIT Lincoln Laboratory, in Cambridge, MA, USA.

The MIT researchers' achievement represents a significant step forward in the development of practical quantum computers. The demonstrated 'quarton coupler' overcomes limitations of previous designs by enabling stronger nonlinear light-matter coupling. This is crucial for faster readout and quantum operations. The ability to linearize transmons into nearly-linear resonator modes is another key advantage, potentially leading to more efficient quantum information processing. While further work is needed to integrate this architecture into a full-fledged quantum computer, the fundamental physics demonstrated in this study provides a solid foundation for future advancements. The observed correlated photon hopping process highlights the complexities that arise in this near-ultrastrong nonlinear coupling regime. The potential impact is substantial, as it could accelerate the development of fault-tolerant quantum computers capable of solving complex problems in materials science, machine learning, and other fields.

This would really eliminate one of the bottlenecks in quantum computing. Usually, you have to measure the results of your computations in between rounds of error correction. This could accelerate how quickly we can reach the fault-tolerant quantum computing stage and be able to get real-world applications and value out of our quantum computers.

Most of the useful interactions in quantum computing come from nonlinear coupling of light and matter. If you can get a more versatile range of different types of coupling, and increase the coupling strength, then you can essentially increase the processing speed of the quantum computer.

This work is not the end of the story. This is the fundamental physics demonstration, but there is work going on in the group now to realize really fast readout.

The development of the quarton coupler, enabling near-ultrastrong nonlinear light-matter coupling, represents a significant acceleration in the pursuit of fault-tolerant quantum computers by potentially increasing quantum processor speeds by a factor of ten. This advancement facilitates faster and more accurate quantum data measurements and enhances interactions between photons and artificial atoms, key components of quantum systems. The enhanced speed and efficiency arise from the coupler's ability to achieve stronger nonlinear coupling, essential for running quantum algorithms and performing more operations, including error correction, within the limited coherence time of qubits. While integrating the coupler into larger quantum systems and improving qubit coherence remain challenges, the fundamental physics demonstrated provides a robust foundation for future research and development, paving the way for applications such as simulating new materials and accelerating machine learning models. This breakthrough has the potential to unlock a wide range of applications for quantum computing across various fields, provided that the technology can be adapted into complex quantum processors with built-in readout circuits.