Quantum computers promise to solve problems far beyond the reach of classical machines, from simulating new materials to transforming AI.
But one key challenge stands in the way: speed.
To be reliable, quantum computers must perform calculations and error corrections before their fragile quantum bits, or qubits, lose coherence.
Now, MIT researchers have built a new superconducting circuit that could dramatically speed up this process.
At its core is a newly invented component, the “quarton coupler,” which enables a record-breaking level of interaction between light and matter, crucial for reading and controlling qubits.
This breakthrough could make operations up to 10 times faster, bringing fault-tolerant, real-world quantum computing a major step closer.
The research, led by PhD graduate Yufeng “Bright” Ye and senior author Kevin O’Brien.
New coupler unlocks stronger quantum interactions
The quarton coupler builds on years of foundational work at MIT’s Research Laboratory of Electronics. Initially developed by Ye as part of a photon detector project to improve quantum information processing, the coupler quickly became a central focus of the lab due to its versatility.
This device is a superconducting circuit designed to produce extremely strong nonlinear interactions between particles of light (photons) and matter (qubits).
Nonlinear coupling is key to most quantum operations—it allows systems to behave in complex, non-additive ways that drive computation.
“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,” Ye explains.
Researchers can amplify its nonlinear effects by feeding more current into the quarton coupler, setting the stage for faster and more reliable quantum processing.
Record-setting speed in reading qubit states
One of the biggest bottlenecks in quantum computing today is the process of readout—measuring the state of a qubit without collapsing its quantum information too early.
The stronger the interaction between a qubit and its readout resonator, the faster and more accurately this measurement can occur.
To test their design, the MIT team built a chip with two superconducting qubits connected by the quarton coupler.
One qubit served as an artificial atom, storing quantum information, while the other acted as a resonator. Microwave photons were used to transfer the information between them.
This setup enabled light-matter coupling approximately 10 times stronger than previously demonstrated, vastly accelerating the readout process.
“The interaction between these superconducting artificial atoms and the microwave light that routes the signal is basically how an entire superconducting quantum computer is built,” Ye says.
Getting closer to fault-tolerant quantum systems
Faster operations and readouts are critical because qubits have limited coherence time—the duration they retain their quantum state.
Stronger nonlinear coupling means more operations can be performed before qubits degrade, allowing for more rounds of error correction and better computation fidelity.
“The more runs of error correction you can get in, the lower the error will be in the results,” Ye says.
In addition to faster light-matter coupling, the researchers also demonstrated strong matter-matter interactions between qubits, another crucial building block for scalable quantum computation.
Both types of interaction are essential for running complex quantum algorithms on large machines.
The goal is to integrate the quarton coupler into a larger quantum architecture that includes additional circuit components, like filters, to create a high-speed, low-error readout system.
“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,” says O’Brien.
The research was published in Nature Communications.