Researchers at Sweden’s Chalmers University of Technology have introduced a new theoretical design for quantum systems based on what they call “giant superatoms.” The concept offers new ways to protect, control, and share quantum information and could bring scientists closer to building large-scale quantum computers.
Quantum computers are expected to transform fields such as drug discovery and cryptography by solving problems that traditional machines cannot reach. However, progress is limited by a major challenge known as decoherence. This occurs when a quantum bit (qubit) loses information due to interactions with its surroundings. Even small amounts of electromagnetic noise can destroy the fragile quantum states needed for calculations.
“Quantum systems are very powerful, but they are also very fragile. The key to making them useful is learning how to control their interaction with the surrounding environment,” said Lei Du, a postdoctoral fellow in applied quantum technology at Chalmers University.
Lei Du is the lead author of a study outlining this new type of quantum system. The design is built around a giant superatom that combines several key features. These systems reduce decoherence, maintain stability, and are composed of multiple interconnected “atoms” that function as a single unit.
What is a giant superatom?
Giant superatoms bring together two previously separate concepts in quantum physics: giant atoms and superatoms. Each has been studied independently, but this is the first time they have been integrated into a single system. These structures behave like atoms, but they do not exist in nature. Instead, they are designed by scientists (see fact box below).
Giant atoms and their “quantum echoes”
The idea of giant atoms was first introduced by Chalmers researchers more than a decade ago and is now widely used in the field. Giant atoms are typically designed as qubits (the smallest units of quantum information). Unlike regular atoms, they connect to light or sound waves at multiple physically separated points. This allows you to interact with your environment in multiple places at once, and helps store quantum information.
“A wave from one connection point can travel through the environment and return to affect atoms at another point, much like hearing an echo of your own voice before you’ve finished speaking. This self-interaction can produce highly beneficial quantum effects. “It reduces decoherence and gives the system some form of memory of past interactions,” explains Anton-Frisk Kockum, associate professor of applied quantum physics at Chalmers University and co-author of the study.
Extend entanglement across distance
Giant atoms have improved our understanding of quantum behavior, but they have limitations when it comes to entanglement. Entanglement allows multiple qubits to share a single quantum state and act as one coordinated system. This is essential for powerful quantum computers.
To overcome this limitation, the research team combined the concepts of giant atoms and superatoms. A superatom consists of multiple natural atoms that share the same quantum state and collectively behave as one large atom.
This combination is expected to facilitate the creation of complex quantum states needed for quantum communications, networks, and sensitive measurement systems.
“Giant superatoms are thought of as multiple giant atoms working together as a single entity, exhibiting nonlocal interactions between light and matter. This allows quantum information from multiple qubits to be stored and controlled within a single unit without the need for increasingly complex surrounding circuitry,” explains Lei Du.
“Giant superatoms open the door to entirely new capabilities and give us a powerful new toolbox. They allow us to control quantum information and create entanglements in ways that were previously very difficult or even impossible,” says Janine Spletstosser, professor of applied quantum physics at Chalmers University and co-author of the study.
Towards scalable and practical quantum systems
This research opens new possibilities for building scalable and reliable quantum systems. The researchers plan to move from theory to building these systems in practice. Their design can also be integrated with other quantum technologies and serve as building blocks for connecting different types of quantum platforms.
“Currently, there is a strong interest in hybrid approaches in which different quantum systems work together, because each has its own strengths,” says Anton-Frisk Kockum. “Our research shows that smart design can reduce the need for increasingly complex hardware, and brings giant superatoms one step closer to becoming a practical quantum technology.”
Controlling quantum information flow
Learn more: How to secure, control, and distribute quantum information
This study shows that the way a giant superatom interacts with light depends on its internal quantum state. This discovery gives researchers greater control over how quantum information moves through the system. They describe two different ways to connect these structures to achieve beneficial results.
In one setting, several giant superatoms are tightly linked in a specific arrangement. This allows quantum states to be passed between each other without decoherence, meaning no information is lost.
In other settings, the atoms are spaced further apart but connected in a carefully calibrated way to keep the waves in sync. This makes it possible to direct quantum signals and disperse quantum entanglement over long distances.
Understanding giant atoms and superatoms
Superatoms and giant atoms do not occur naturally, but are man-made systems that behave like atoms.
A superatom is a quantum system consisting of multiple natural atoms that share a single quantum state and respond to light as a single entity.
On the other hand, giant atoms connect to light or sound waves at several separate points in space. They are called “giants” because they are larger than the wavelengths of light they interact with.
Giant atoms define energy levels and follow the rules of quantum mechanics, but they can reach sizes up to millimeters and are visible to the naked eye. You can interact with your surrounding environment in multiple locations simultaneously through electromagnetic waves or sound waves. One way to imagine this is as a single atom coupled into waves at several distant points. This unusual setup allows the atoms to be affected by the waves they produce.
