A New Way To Read the “Unreadable” Qubit Could Transform Quantum Technology

By Spanish National Research Council (CSIC) February 19, 2026

Collected at: https://scitechdaily.com/a-new-way-to-read-the-unreadable-qubit-could-transform-quantum-technology/

Researchers have demonstrated a new way to read Majorana qubits, highly stable but notoriously difficult-to-measure quantum bits, using a global quantum capacitance probe.

Quantum computers are often described as machines that could solve certain problems far beyond the reach of today’s fastest supercomputers.

But getting from headline potential to a working device has been painfully difficult, and one of the toughest roadblocks involves a mysterious type of quantum building block called a Majorana qubit. These qubits are especially appealing because they are designed to protect fragile quantum information from many of the disturbances that normally cause errors.

In a new Nature study, an international research team that includes the Spanish National Research Council (CSIC) reports a key step forward: they were able to read out the information stored in a Majorana based system. The effort was supported by almost five million euros from the European Innovation Council’s Pathfinder program.

“This is a crucial advance,” explains Ramón Aguado, a CSIC researcher at the Madrid Institute of Materials Science (ICMM) and one of the study’s authors. “Our work is pioneering because we demonstrate that we can access the information stored in Majorana qubits using a new technique called quantum capacitance,” continues the scientist, who explains that this technique “acts as a global probe sensitive to the overall state of the system.”

Why Majorana Qubits Are So Challenging

To better understand this achievement, Aguado explains that topological qubits are “like safe boxes for quantum information,” only that, instead of storing data in a specific location, “they distribute it non-locally across a pair of special states, known as Majorana zero modes.”

That unusual structure is what makes them 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.” In other words, small disturbances are unlikely to disrupt the stored information.

Yet this strength has also created a major experimental challenge. As Aguado 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?.” If the information is spread out rather than localized, measuring it becomes far more complicated.

To tackle this problem, the researchers engineered a modular nanostructure assembled from small components, similar to building with Lego. This device, known as the Kitaev minimal chain, is designed to host Majorana modes under controlled conditions. “The experimental team is able to create a chain with two semiconductor quantum dots coupled through a superconductor,” describes Aguado, who indicates that, in this way, “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.”

Reading the Qubit’s State

After constructing the minimal Kitaev chain, the team applied the Quantum Capacitance probe to examine the system. For the first time, they were able to determine in real time and with a single measurement whether the shared quantum state formed by the two Majorana modes had even or odd parity. This distinction corresponds to whether the qubit is full or empty, which defines its fundamental state.

“The experiment elegantly confirms the protection principle: while local charge measurements are blind to this information, the global probe reveals it clearly,” says researcher Gorm Steffensen, also part of the team at the ICMM-CSIC.

The researchers also reported another “highly relevant” finding: the detection of “random parity jumps.” This observation made it possible to measure “parity coherence exceeding one millisecond, a very promising value for future operations of a topological qubit based on Majorana modes.” Such coherence times are considered encouraging for future quantum computing applications.

The project brings together an advanced experimental platform developed primarily at Delft University of Technology and theoretical work carried out by ICMM-CSIC. According to the authors, this theoretical input was “crucial for understanding this highly sophisticated experiment,” highlighting the importance of close collaboration between theory and experiment in pushing quantum technology forward.

Reference: “Single-shot parity readout of a minimal Kitaev chain” by Nick van Loo, Francesco Zatelli, Gorm O. Steffensen, Bart Roovers, Guanzhong Wang, Thomas Van Caekenberghe, Alberto Bordin, David van Driel, Yining Zhang, Wietze D. Huisman, Ghada Badawy, Erik P. A. M. Bakkers, Grzegorz P. Mazur, Ramón Aguado and Leo P. Kouwenhoven, 11 February 2026, Nature.
DOI: 10.1038/s41586-025-09927-7