Entanglement is an extremely strong correlation that can exist between quantum systems. These correlations are so strong that two or more entangled particles have to be described with reference to each other, even though the individual objects may be spatially separated.
It has been shown that even if two uncorrelated quantum systems that don’t know anything about each other can still become entangled in a quantum vacuum without being limited by the speed of light.
Quantum theory states that the quantum vacuum isn’t really empty. Quantum fluctuations of the electro-magnetic field vacuum are entangled. These fluctuations can interact locally with two space-like separated atoms and entangle them even if the two atoms never communicated with one another, or even if they never exchanged any information at all. This phenomenon is known as entanglement harvesting.
Researchers explored the crucial role of relative space-time positioning between the two detectors in an operational two-party entanglement-harvesting protocol. Specifically they show that the protocol is robust if imprecision in spatial positioning and clock synchronization are much smaller than the spatial separation between the detectors and its light-crossing time thereof. This in principle guarantees robustness if the imprecision is comparable to a few times the size of the detectors, which suggests entanglement harvesting could be explored for tabletop experiments. On the other hand, keeping the effects of this imprecision under control would be demanding on astronomical scales.
This is possible because the electro-magnetic vacuum contains entanglement between spacelike separated regions. The two atoms can interact locally with the field and harvest the entanglement of the vacuum state of the field.
Research Assistant Professor Eduardo Martin-Martinez and the director of the Institute for Quantum Science and Technology Barry C. Sanders showed that the entanglement-harvesting protocol is robust and suggest it could be explored for tabletop experiments. The results, Precise space-time positioning for entanglement harvesting, were published in the New Journal of Physics.
Potential applications for this protocol include quantum source generation, metrology and communication, in addition to fundamental insights into the structure of spacetime.