Magazine article Science News

15 = 3 X 5: Photons Do Their First Quantum Math

Magazine article Science News

15 = 3 X 5: Photons Do Their First Quantum Math

Article excerpt

Two teams of physicists have independently confirmed that 15 equals 3 times 5--an arduous task considering that they've done it by manipulating the quantum states of photons. The results are a step toward optical quantum computers, which could do some calculations exponentially faster than ordinary computers can and crack the encryption codes that protect data traveling over the Internet.

Multiplying two whole numbers is easy, but the inverse operation generally isn't: Identifying when a number is the product of other whole numbers becomes exponentially more complex as the numbers get bigger, quickly overwhelming even the fastest supercomputers.

This is good for privacy. When Web-based programs request sensitive data over the Internet, they ask the sender's Web browser to encrypt the data using a number, called the public key, that is the product of two prime numbers. Decrypting the data requires identifying those two prime numbers, which only the legitimate recipient knows. Anyone wishing to steal the data would have to break the public key into its prime factors.

In 1994, mathematician Peter Shor, now at the Massachusetts Institute of Technology (MIT), theoretically demonstrated that a computer based on the principles of quantum mechanics could quickly fred the prime factors of public keys.

A quantum computer would represent information as quantum states of some physical system, such as the magnetic alignments of atoms or the polarization directions of photons. Shor's algorithm exploits the ability of such systems to exist simultaneously in multiple states. The quantum computer could in essence try dividing a number by all possible factors at the same time. Only states corresponding to the true factors--those that give zero as remainder--would have any probability of actually being measured.

In 2001, researchers ran a simplified version of Shor's algorithm using magnetic orientations of the atomic nuclei in fluorocarbon molecules (SN: 1/12/02, p. …

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