Smaller, smarter building blocks for future quantum technology

Scientists at EPFL have made a breakthrough in designing arrays of resonators, the basic components that power quantum technologies. This innovation could create smaller, more precise quantum devices.

Qubits, or quantum bits, are mostly known for their role in quantum computing, but they are also used in analog quantum simulation, which uses one well-controlled quantum system to simulate another more complex one. An analog quantum simulator can be more efficient than a digital computer simulation, in the same way that it is simpler to use a wind tunnel to simulate the laws of aerodynamics instead of solving many complicated equations to predict airflow.

Key to both digital quantum computing and analog quantum simulation is the ability to shape the environment with which the qubits are interacting. One tool for doing this effectively is a coupled cavity array (CCA), tiny structures made of multiple microwave cavities arranged in a repeating pattern where each cavity can interact with its neighbors. These systems can give scientists new ways to design and control quantum systems.

Similarly to electrons in crystals, which can block the flow of electricity at certain frequencies, giving rise to semiconductors and insulators, in CCAs, light, in the form of can only propagate at specific wavelengths. By carefully tailoring the geometry of these resonators, scientists can precisely select the wavelengths at which photons can go through, and those at which they can’t.

An EPFL team, led by Prof. Pasquale Scarlino, head of the Hybrid Quantum Circuits Laboratory, in collaboration with Dr. Marco Scigliuzzo from the Laboratory of Photonics and Quantum Measurements at EPFL, and Prof. Oded Zilberberg from the University of Konstanz, has developed an innovative design for a CCA using niobium nitride (NbN), a superconductor relying on an advanced material property called high kinetic inductance, in which Scarlino’s laboratory is a leading expert.

Leveraging high kinetic inductance, Scarlino and his team have demonstrated a new class of CCAs where each cavity is highly miniaturized and unwanted disorder in the resonant frequencies of all cavities is kept to a minimum. Both these features are critical for achieving the functionalities required in future quantum computing and quantum simulation.

The research, published in Nature Communications, demonstrated the ability to create a compact array of up to 100 high-quality cavities. They showed how these structures work and used them to mimic a material called a photonic topological insulator, which can guide light along its edges in a very controlled and unusual way.

“We are already building on this work by studying artificial atoms coupled to this architecture,” says Vincent Jouanny, the paper’s first author.

“Our approach shows that compactness and precision are not opposing goals but complementary tools for advancing quantum device technology,” says Scarlino. “This work demonstrates how thoughtful design can balance compactness, high impedance, and low disorder, resulting in a versatile platform for coupled cavity arrays that opens new opportunities for advanced quantum simulations and the exploration of quantum phenomena.”

By leveraging the unique properties of niobium nitride, EPFL researchers have opened new possibilities for exploring complex quantum systems and developing scalable platforms for future innovations. This breakthrough in coupled cavity array design represents a significant step toward more compact, efficient, and reliable quantum devices.