Qubits that never interact could exhibit past-future entanglement

The physicists, Carlos Sabín, Borja Peropadre, Marco del Rey, and Eduardo Martín-Martínez at the Institute of Fundamental Physics at the Spanish National Research Council (CSIC) in Madrid (Sabín is now at the University of Nottingham in the UK, and Martin-Martinez is now at the University of Waterloo in Ontario, Canada), have published a paper on this new kind of entanglement in a recent issue of Physical Review Letters .

“We show that it is possible in a real experiment to entangle two systems that neither interact with each other nor interact with a common resource at the same time, and without the need of measurements,” Sabín told . “The trick is to use the correlations between different times – between past and future – contained in the vacuum of a quantum field.”

In quantum theory, the quantum field is the system that contains all particles that are too small to be described classically. Although no particles exist in the vacuum region of a quantum field, physicists have known since the 1970s that this vacuum contains quantum correlations, or entanglement.

(a) A diagram of different spacetime regions and (b) a diagram of entanglement show that significant entanglement is generated at both sides of the lines that discriminate between regions. Image credit: Sabín, et al. ©2012 American Physical Society…
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