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Physics team entangles photons that never coexisted in time

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Posted May 29, 2013
Time line diagram. (I) Birth of photons 1 and 2, (II) detection of photon 1, (III) birth of photons 3 and 4, (IV) Bell projection of photons 2 and 3, (V) detection of photon 4. Credit: Phys. Rev. Lett. 110, 210403 (2013) DOI: 10.1103/PhysRevLett.110.210403

Time line diagram. (I) Birth of photons 1 and 2, (II) detection of photon 1, (III) birth of photons 3 and 4, (IV) Bell projection of photons 2 and 3, (V) detection of photon 4. Credit: Phys. Rev. Lett. 110, 210403 (2013) DOI: 10.1103/PhysRevLett.110.210403

Researchers at the Hebrew University of Jerusalem have succeeded in causing entanglement swapping between photons that never coexisted in time. In their paper published in the journal Physical Review Letters, the team explains how their experiment proves true an entanglement phenomenon first described by researchers last year at the University of Erlangen-Nuremberg.

 

The idea seems not just counterintuitive, but impossible—that photons could be entangled that never existed at the same time—but that’s just what the team in Germany, led by Joachim von Zanthier, suggested. In this new effort, the team in Israel, led by Hagai Eisenberg, has proven it’s possible by actually doing it.

Entanglement is, of course, where the quantum states of two particles are linked—what happens to one happens to the other regardless of the distance between them. This new work shows that they can be linked via time as well.

To prove it, the researchers first used a laser to cause entanglement between a pair of photons, P1, P2. They then measured the polarization of P1, which was immediately followed by the entangling of another pair of photons, P3, P4. This was followed by measuring P2 and P3 simultaneously and causing them to become entangled with one another—a process known as projective measurement. Then, P4 was measured. Measuring P1 caused its demise of course—before P4 was born—but the measurement of P4 showed that it had become entangled with P1 nevertheless, if only for a very short period of time.

Read more at: Phys.org

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