A Glass Sphere 100 Nanometers Wide Becomes Quantum-Entangled With Light at Room Temperature
University of Florence physicists, writing in Science, entangled a levitated nanoparticle's motion with a light field without cooling the lab to near absolute zero.
A team led by Francesco Marin at the University of Florence has entangled the motion of a tiny levitating glass sphere with light without chilling the experiment to ultralow temperatures. The work is published in Science and is reported by Phys.org.
Entanglement is the quantum link in which two objects' properties become so intertwined that neither can be fully described without the other. Physicists are exploring how light could connect objects this way, in hopes of building secure communication networks that span vast distances and new tests of the fundamental laws of physics. The link is fragile, though. Small disturbances from the environment break it, and it gets harder to protect as objects get larger.
Earlier experiments produced brief bursts of entanglement between photons and vibrating macroscopic particles, but only at temperatures close to absolute zero. Researchers have more recently recognized that tiny glass spheres levitated by light could offer an alternative, because they float almost completely isolated from their surroundings.
Marin's team tested the idea with a glass sphere just 100 nanometers across. They held it in a tightly focused laser beam known as an optical tweezer, placed between two facing mirrors inside a near-vacuum chamber. The trouble was that the light needed to create entanglement also tended to set off unwanted oscillations that eventually knocked the sphere out of its trap.
To get around this, the researchers combined two lasers of slightly different colors. The first cooled and steadied the sphere's back-and-forth motion, while the second was free to entangle that motion with the light. As the sphere oscillated, information about its movement was imprinted on the light leaving the mirrors. By measuring that light over many hours, the team reconstructed the full pattern of connections between the sphere's motion and the light.
Even with the lab at room temperature, the measured correlations crossed a mathematical threshold that confirms the two were genuinely entangled. The entanglement also persisted in the light traveling away from the mirrors, which matters for any network that would need to carry the link over a distance.
Marin's group now wants to strengthen the entanglement with refined techniques and to control it actively instead of just observing it. Eventually, the authors say, several levitated spheres could be entangled through a shared field of light. That would offer new ways to test quantum mechanics at ever larger scales, and perhaps even how it interacts with gravity. It could also lead to quantum networks in which information passes between moving objects that store it and the light that carries it. The paper is Q. Deplano et al., "Stationary entanglement of a levitated oscillator with an optical field," Science (2026).
