Quantum computers will be built like LEGO

Quantum computers can perform calculations based on the principles of quantum mechanics, and are expected to outperform classical computers in certain types of optimization and processing tasks.

Although physicists and engineers have demonstrated various quantum computing systems over the past decades, reliably scaling these systems so that they can solve practical problems while correcting errors that arise during computation has so far been a challenge.

Việc liên kết các qubit bên trong máy tính lượng tử vẫn là một vấn đề. — Linking qubits inside quantum computers remains a problem.

Building a quantum computer as a single, unified device has proven extremely difficult. These machines rely on manipulating millions of qubits, the basic units of quantum information, but assembling such a large number into one system is a major challenge.

Just as small LEGO blocks fit together to form larger, more complex designs, researchers can build smaller, higher-quality modules and then connect them together to form a complete quantum system.

Researchers at the University of Illinois at Urbana-Champaign recently introduced a new modular quantum architecture that enables fault-tolerant, scalable, and reconfigurable scaling of superconducting quantum processors. Fault-tolerant scaling is essential to maintaining quantum effects and the conditions necessary to perform long-term quantum computations.

The interconnection cable protocol links qubit blocks together like LEGO bricks.

The system they propose, presented in a paper published in the journal Nature Electronics , consists of several modules (i.e. superconducting qubit devices) that can operate independently and are connected to other modules through interconnects and form a larger quantum network.

To put it simply, with these connections, each qubit in the system will only need to be "plug and play" like we add peripheral devices to a regular computer. This type of interconnect cable also has the effect of reducing the system's calculation error to less than 1%.

“The starting point for this research was the current understanding in the field of superconducting quantum computing that we would need to split the processor into multiple independent devices – an approach we call ‘modular quantum computing’,” describes Wolfgang Pfaff, co-author of the study.

In recent years, this has become a popular belief, and even companies like IBM are pursuing it. This research could realize an engineering-friendly connection to the modular approach.

Essentially, Pfaff and his colleagues are devising a strategy to connect quantum devices while minimizing signal degradation or power loss as quantum information is transmitted between them. Furthermore, they want to be able to easily connect, disconnect, and reconfigure the devices.

“In simple terms, our method involves using a high-quality superconducting coaxial cable called a bus resonator,” Pfaff explains.

They connect a capacitive qubit to a cable via a custom connector, placing the cable very close (sub-mm precision) to the qubit and then multiple qubits if they are connected to the same cable.

The researchers' new approach to creating modular quantum networks has significant advantages over previous approaches to scaling quantum systems.

In initial tests, they found that this method allowed them to securely connect superconductor-based quantum devices and disconnect them later without damaging them, without causing significant signal loss in the quantum gates.

“With our approach, I think we have the opportunity to build reconfigurable quantum systems from scratch, with the option to, for example, ‘plug’ more processor modules into the network of quantum devices over time,” Pfaff added.

"We are currently working on a design to see if we can increase the number of connected elements, making our network larger. We are also looking at how to better compensate for losses in the system and make the architecture compatible with quantum error correction."