# quantum entanglement at microwave frequencies

Entanglement of optical photons using non-linear crystals has been around for a long time. Macroscopic entanglement using diamonds recently reported in the literature and receiving considerable attention. Quantum mechanics in biology has been the subject of fascinating research. Has anyone demonstrated entanglement of low frequency (i.e., microwave) photons? I see no theoretical objection, has it ever been demonstrated? Ditto entanglement at xray?

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The first report on entangled microwaves seems to be http://arxiv.org/abs/1204.0732, but there is a mistake in the proof of the entanglement (find it). A clear proof of spatially separated entanglement is reported in http://arxiv.org/abs/1210.4413.

Have fun to find the error in the first paper, recently published in PRL :p

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You can certainly entangle microwave photons with other quantum objects: http://arxiv.org/abs/1209.0441

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Well but my question is can you entangle two photons at microwave frequencies? –  carl Oct 6 '12 at 2:47
It is very difficult to measure single microwave photons. Compare the per photon energy to that of a visible photon, and to the room temperature energy scale, $kT$. –  user2963 Oct 6 '12 at 3:23