# Letters from the February 2, 2008, issue of Science News

## Eye for an eagle

The photo illustrating "Hatch a Thief" (SN: 12/15/07, p. 372) does not show a golden eagle. The bill of a golden eagle is black on the outer half and pale blue at the base, and the feathers on the back of its head are bright tawny. It could be a white-tailed eagle, a very close relative of the bald eagle with a widespread range in northern Eurasia and a small population in southwestern Greenland.

*Alan RyffSt. Clair Shores, Mich.*

*The reader is correct. According to Keith Bildstein of the Hawk Mountain Sanctuary in Pennsylvania, the photo does appear to show a white-tailed eagle in adult or near-adult plumage. Unfortunately, information on locality is unavailable.*—Susan Milius

## Fast and faster

I was disappointed to see optical quantum computers described as "exponentially faster than ordinary computers" ("15 × 3 = 5: Photons do their first quantum math," SN: 12/8/07, p. 356). Despite frequent misuse in the lay press, "exponentially" does not mean "a whole bunch." It refers to a specific mathematical functional relationship, not merely a comparison of two numbers. The article doesn't describe any such function. Even to posit an exponential relationship, we'd need an independent variable, of which ordinary and photon computer speeds are functions, in order to compare them.

*Dick DunnHygiene, Colo.*

*The amount of time it takes an ordinary computer to find prime factors of a number grows exponentially with that number's number of digits. For a quantum computer, it grows only as a power of the number of digits. That makes quantum computers exponentially faster, quite literally.*—Davide Castelvecchi