Macro-Scale Quantum Entanglement

[Recusant]

For some values of "macro."

By passing light through a cloud of cesium (aka caesium) atoms onto a membrane of silicon nitride, physicists entangled the cloud and the membrane. This is the first time that entanglement has been induced in such large objects.

"Quantum entanglement realized between distant large objects" | University of Copenhagen

Entanglement is the basis for quantum communication and quantum sensing. It can be understood as a quantum link between two objects which makes them behave as a single quantum object.

Now, researchers from the Niels Bohr Institute, University of Copenhagen, have succeeded in making entanglement between two distinctly different and distant objects. One is a mechanical oscillator, a vibrating dielectric membrane, and the other is a cloud of atoms, each acting as a tiny magnet – what physicists call spin. These very different entities have now become possible to entangle by connecting them with photons, particles of light. Atoms can be useful in processing quantum information and the membrane – or mechanical quantum systems in general – can be useful for storage of quantum information.

Professor Eugene Polzik, who led the effort, states that: "With this new technique, we are on route to pushing the boundaries of the possibilities of entanglement. The bigger the objects, the further apart they are, the more disparate they are, the more interesting entanglement becomes from both fundamental and applied perspectives. With the new result, entanglement between very different objects has become possible".

[Continues . . .]

The paper is behind a paywall.

Abstract:

Entanglement is an essential property of multipartite quantum systems, characterized by the inseparability of quantum states of objects regardless of their spatial separation. Generation of entanglement between increasingly macroscopic and disparate systems is an ongoing effort in quantum science, as it enables hybrid quantum networks, quantum-enhanced sensing and probing of the fundamental limits of quantum theory. The disparity of hybrid systems and the vulnerability of quantum correlations have thus far hampered the generation of macroscopic hybrid entanglement. Here, we generate an entangled state between the motion of a macroscopic mechanical oscillator and a collective atomic spin oscillator, as witnessed by an Einstein–Podolsky–Rosen variance below the separability limit, 0.83 ± 0.02 < 1. The mechanical oscillator is a millimetre-size dielectric membrane and the spin oscillator is an ensemble of 109 atoms in a magnetic field. Light propagating through the two spatially separated systems generates entanglement because the collective spin plays the role of an effective negative-mass reference frame and provides—under ideal circumstances—a back-action-free subspace; in the experiment, quantum back-action is suppressed by 4.6 dB.

[Tank]

Fascinating!