Quick: what numbers multiply together to 15? The seemingly simply calculation was solved by a test tube of tiny molecules using the most complex quantum computing methods to date.

Quantum computers can be much faster than classical computers, but the machines didn't become a practical goal until 1994, when a programmer at Bell Labs devised a step-by-step way for the mini-machines to factor large numbers.

Now scientists at IBM's Almaden Research Center and Stanford University have hand-tailored a molecule to form the basis of a quantum computer.

Conventional computers get bogged down by big numbers

Conventional computers have difficulty factoring large numbers. But the answers are simple to verify and are used by many cryptography methods to protect data.

Quantum computers take advantage of the properties of billions of atoms or nuclei. By working together, the quantum bits – called qubits – can simultaneously act as the computer's processors and memory.

Finding the factors of the number 15, namely 3 and 5, required a seven qubit computer made of five flourine and two carbon atoms.

The computer was programmed by radio frequency pulses and detected by nuclear magenetic resonance instruments like those commonly used in hospitals.

Quantum computers have huge potential and recent progress is encouraging. But commercial ones are still many years away and the first will likely be a co-processor for solving math problems or unstructured searches.

The study appears in Thursday's issue of the journal, Nature.