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PUBLISHED ONLINE: 10 JANUARY 2010 | http://www.nature.com/doifinder/10.1038/nphoton.2009.261
Web End =DOI: 10.1038/NPHOTON.2009.261
A matterless double slit
Ben King, Antonino Di Piazza* and Christoph H. Keitel
Double slits provide incoming particles with a choice. Those that survive passage through the slits have chosen from two possible paths, which interfere to distribute them in a wave-like manner. Such waveparticle duality1 continues to be challenged25 and investigated in a broad range of disciplines with electrons6, neutrons7, helium atoms8, C60 fullerenes9, BoseEinstein condensates10 and biological molecules11. All variants have hitherto involved material constituents. We present a matterless double-slit scenario in which photons generated from virtual electron positron pair annihilation in head-on collisions of a probe laser eld with two ultra-intense laser beams form a double-slit interference pattern. Such electromagnetic elds are predicted to induce material-like behaviour in vacuum, supporting elastic scattering between photons12,13. Our double-slit scenario presents, on the one hand, a realizable method with which to observe photon photon scattering and, on the other hand, demonstrates the possibility of both controlling light with light and non-locally investigating features of the quantum vacuum structure.
According to both special relativity and Heisenbergs uncertainty principle, virtual electronpositron pairs spontaneously pop into and out of existence in vacuum, on a timescale too short to leave a trace. However, it is the polarization of these pairs under an applied electromagnetic eld that is predicted to provide a rich variety of nonlinear processes14. A fundamental scale for such vacuum polarization effects is set by the critical eld of quantum electrodynamics Ecr
4p
p m2c3=h
e 1:3 1016 V cm 1, for
electron mass m and absolute charge e (in our units the ne-structure constant is given by a e2/4phc 1/137), corresponding to a
laser intensity of Icr 2.3 1029 W cm22. An electric eld of this
order is strong enough to provide a virtual electronpositron pair with an energy equal to its rest energy 2mc2 in the eetingly short time h/mc2 1.3 10221 s in which the virtual pair lives, promot
ing it to reality before the individual particles eventually annihilate one another. Even at much lower intensities I such as provided by strong or ultra-intense (I . 1 1023 W cm22) laser elds, the
polarized vacuum is predicted to exhibit birefringence and dichroism12,...