“This is a crucial advance,” says Ramón Aguado, a CSIC researcher at the Madrid Institute of Materials Science (ICMM) and co author of the study. He explains that the team has successfully retrieved information stored in Majorana qubits by applying a technique known as quantum capacitance. According to Aguado, this method functions as “a global probe sensitive to the overall state of the system,” enabling scientists to access information that was previously difficult to observe.
To clarify the importance of the result, Aguado describes topological qubits as “like safe boxes for quantum information.” Instead of keeping data in one fixed location, these qubits spread information across two linked quantum states called Majorana zero modes. Because the data is distributed in this way, it gains natural protection.
This structure makes topological qubits especially attractive for quantum computing. “They are inherently robust against local noise that produces decoherence, since to corrupt the information, a failure would have to affect the system globally,” Aguado explains. However, that same protective feature has posed a major challenge for researchers. As he notes, “this same virtue had become their experimental Achilles’ heel: how do you “read” or “detect” a property that doesn’t reside at any specific point?”
Building the Kitaev Minimal Chain
To overcome this obstacle, the team engineered a modular nanostructure assembled from small components, similar to building with Lego blocks. This device, called a Kitaev minimal chain, consists of two semiconductor quantum dots connected through a superconductor.
Aguado explains that this approach allows researchers to construct the system from the ground up. “Instead of acting blindly on a combination of materials, as in previous experiments, we create it bottom up and are able to generate Majorana modes in a controlled manner, which is in fact the main idea of our QuKit project.” This careful design gives scientists direct control over the formation of Majorana modes.
Real Time Measurement of Majorana Parity
After assembling the minimal Kitaev chain, the team applied the Quantum Capacitance probe. For the first time, they were able to determine in real time and with a single measurement whether the combined quantum state formed by the two Majorana modes was even or odd. In practical terms, this reveals whether the qubit is in a filled or empty state, which defines how it stores information.
“The experiment elegantly confirms the protection principle: while local charge measurements are blind to this information, the global probe reveals it clearly,” says Gorm Steffensen, a researcher at ICMM CSIC who also participated in the study.
The researchers also detected “random parity jumps,” another significant outcome of the experiment. By analyzing these events, they measured “parity coherence exceeding one millisecond,” a duration considered highly promising for future operations involving topological qubits based on Majorana modes.
Collaboration Between Delft and ICMM CSIC
The study brings together an innovative experimental platform developed mainly at Delft University of Technology and theoretical work carried out at ICMM CSIC. The authors emphasize that the theoretical contribution was “crucial for understanding this highly sophisticated experiment,” highlighting the combined effort behind this advance in quantum computing.