A team from the University of Geneva (UNIGE) has demonstrated that it is possible to perform joint measurements on particles that are separated, a significant advancement for the fields of quantum communication and computing. The study was published in the journal Physical Review X.
The study defies classical intuition and relies on the principle of quantum entanglement, a phenomenon that links particles across distances as if they were connected by an invisible thread.
This breakthrough holds exciting potential for quantum communication and computing, where information becomes accessible only upon measurement. The UNIGE team has also created a classification system, or "catalog," that categorizes different types of measurements and the number of entangled particles required for each.
Quantum physics, by departing from the rules of classical physics, has enabled researchers to describe the behavior of atoms and subatomic particles. This field of science, which investigates the most fundamental components of nature, relies heavily on the ability to measure both the individual and collective properties of these entities.
However, such measurements are notoriously difficult: the instruments used are themselves governed by quantum mechanics, and their interaction with the particles can alter the very properties they are intended to observe.
These findings could have implications not only for communication technologies but also for the development of quantum computers.
The field of quantum measurements is still poorly understood because it has received little attention so far. Until now, research has mainly focused on the states of quantum systems themselves, which feature properties — like entanglement or superposition — that are more directly applicable to areas such as quantum cryptography or quantum computing.
Alejandro Pozas Kerstjens, Senior Research and Teaching Assistant, Department of Applied Physics, Physics Section, Faculty of Science, UNIGE
Particles Linked by an Invisible Thread
These measurements are critical for the advancement of future technologies like quantum communication, which depends on encoding information into particles, such as photons (light particles). To retrieve this information, the particles must first be measured. A key question is whether it is feasible to conduct a joint measurement on two or more distinct particles, each holding a piece of the information, without physically bringing them into contact.
A team from the Physics Department at the University of Geneva (UNIGE), including Jef Pauwels, Alejandro Pozas Kerstjens, Flavio Del Santo, and Nicolas Gisin, has shown that certain basic yet fundamental measurements can be performed on separate particle systems, provided that the measurement instruments share entangled particles.
Entanglement, a fundamental principle of quantum physics, connects two or more particles in such a way that the state of one instantaneously dictates the state of the other. Measuring one entangled particle immediately reveals the corresponding property in its partner, no matter how far apart they are.
However, there’s a twist: depending on their complexity, some measurements require more — or fewer — entangled particles to be performed properly.
Alejandro Pozas Kerstjens, Senior Research and Teaching Assistant, Department of Applied Physics, Physics Section, Faculty of Science, UNIGE
The research team has created a classification system, essentially a catalog, that outlines various types of measurements and the necessary entanglement resources to perform them.
Promising Applications
These findings mark progress towards a more systematic understanding of measurements within quantum systems. They hold potential applications not only in quantum communication but also in the field of quantum computing.
For example, in classical computer simulations, computations are distributed across multiple machines, and the results are then combined. A comparable strategy is being explored for quantum computers, but in this case, accessing the results involves conducting measurements across several machines.
“Thanks to our joint remote measurement protocols, it would be possible to eliminate the need for centralization: each quantum computer would measure its own part, and the overall result could be reconstructed without any physical transfer of data. This is a promising direction that we plan to explore further,” concluded the researcher.
Journal Reference:
Pauwels, J., et al. (2025) Classification of Joint Quantum Measurements Based on Entanglement Cost of Localization. Physical Review X. doi/10.1103/PhysRevX.15.021013