Comments on: A Step Toward Quantum Communications with Space

By: How to Get Six Pack Fast

How to Get Six Pack Fast — Wed, 15 Apr 2009 15:02:11 +0000

I noticed that this is not the first time you write about this topic. Why have you chosen it again?

By: JN

JN — Sat, 19 Apr 2008 10:09:23 +0000

Hi Frend
http://www.hypothesis-of-universe.com/en/index.php?nav=home

By: Ignoramus

Ignoramus — Sat, 22 Mar 2008 13:13:51 +0000

"Now, for the first time, Italian scientists have carried out a successful mock single-photon exchange"
Another successful piece of sensationalist writing by O'Neil.
It is interesting stuff but why not write like Michael Wood-Vasey above, and save your breath?

By: Michael Wood-Vasey

Michael Wood-Vasey — Tue, 18 Mar 2008 13:14:14 +0000

Unfortunately, much of the press coverage of this has implied that one photon was launched from Earth, reflected by the satellite, and then detected again on Earth. This is very much not what was done.

The Villoresi experiment is interesting, but is _not_ single-photon exchange from the ground to a satellite back to the ground. It's actually detection of single photons on the ground from an initial launch of 10^15 — 10^16 photons. The satellite itself then reflects 10^5 photons toward the ground-based detector of which the ground system only detects ~1. From the article:

"For each laser shot, about 1.2 10^5 photons leave the satellite in the whole solid angle subtended by the downlink field-of-view,"

"The return rate observed for Ajisai corresponds to a total attenuation along the light path of -157 dB"

This type of setup has been successfully used for decades for laser-ranging of the precise distance to the moon. The APOLLO project (http://physics.ucsd.edu/~tmurphy/apollo/) is one of the current most successful projects doing this sort of work.