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April 6th, 2010

What is a qbit?

Abstract:
By Roy Johnson

Quantum computing is based on different mathematics and different hardware from conventional, binary computing.

Quantum computers already exist, in one form or another, and they work with qbits, not the usual 1/0 bits. A qbit is, mathematically, a state vector in a two-level quantum system or a vector that applies to complex numbers. Putting it simply and practically, a qbit can have the value 1,0 or both. In quantum language the simultaneous 1/0 value is called a superposition.

It seems impossible to use something that doesn't have a rigidly fixed and measureable value. It conjures up scary memories of the Heisenberg Uncertainty Principle and the Schrodinger's Cat problem.

In fact, we do know the maths that enable us to work with qbits - it's basically a matter of probabilities. If you think of the traditional 1/0 values as a sphere, 1 being the north pole and 0 being the south pole, the possible states of a qbit - determined by probability amplitude - will fall on the surface of that sphere.

Quantum states also have the unique property of entanglement. This is a non-local property of quantum states (qbits, for example) whereby two sets will have higher correlation than is possible in classical mathematics. Simply and somewhat inaccurately expressed, this allows quantum machines to work quickly on problems that a conventional machine can solve - but only with impossible time scales.

Source:
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