Re: Generation of Entangled Photons

Joe Rongen

<diogenes500@gmail.com> wrote in message
news:1138561007.728914.257460@g44g2000cwa.googlegroups.com...
> Hi,
>
> I'm wondering what the most efficient method to date is for
> generating pairs of entangled photons (efficiency being percentage of
> pairs created per number of photons input). As far as I can tell
> non-linear crystals yields around 10^-9 pairs/input photon, and I find
> numbers for production in fibers from 10^-9 to 10^-8 or even 10^-7 (A
> theoretical finding I believe, OPTICS EXPRESS, Vol. 12, No. 14 , 3086
> ). Anyone know what the correct numbers are? Better processes than
> non-linear crystals or fibers? The (realistic) upper limit for
> crystal/fiber generation or any other method? Also, if you know it, a
> citation would be wonderful.


Not sure if it's "better" but this "Presstime Bulletin" appeared
in "Photonics Spectra" January 2006, page 18:
"Entanglement demonstrated between remote ensembles."

"A team of researchers in C.I.T. in Pasadena and at Bell Labs in N.J.
has reported the entanglement of ensembles of cesium atoms separated
by 2.8 m and the storage of the entanglement for up to 1 usec. The
investigators note that the separation distance is limited by fiber optic
attenuation to approximately 2 km. [......]
In the experimental setup, a 150-ns "write" pulse of 852-nm radiation,
detuned by 10 MHz below an atomic transition in cesium and sufficiently
weak to minimize unwanted excitations, was divided in a beamsplitter
before exciting two ensembles of 100,000 cooled atoms each.
This generated forward-scattering anti-Stokes fields that were filtered
and combined to interfere in a second beamsplitter, entangling the
ensembles.
The output of the second beamsplitter was directed to a pair of single-
photon detectors, with. a signal at either one - but not the other -
indicating
entanglement. After a delay, the scientist exposed the ensembles to a
130-ns "read" pulse of 894-nm radiation, mapping the state of the atoms
to the propagating optical field. Subsequent statistical analysis of photo-
detection events and measurements of off-diagonal coherence verified
entanglement."