Diva of Information

Mission 1: Enter the Quantum World. Part of the Quantum Courier Service, a free course from the Oxford University Quantum Information Society.

The classical bit is a sturdy, dependable, and agonizingly boring factory worker. It clocks in exactly as a 1 or a 0, stays that way all day, and punches out.

The Quantum Bit (Qubit) is entirely different. It is a high-strung diva that considers being a simple 1 or 0 to be beneath its dignity, preferring to exist in a dramatic mathematical gray area called Superposition. Some qubits are so temperamental they demand a dressing room chilled to nearly minus 273 degrees Celsius, colder than deep space, just to function; that is the superconducting kind. Others, like the single particles of light this course will actually use, will happily perform at room temperature.

Picture a single arrow, free to point anywhere on a globe. Straight up is Heads (0); straight down is Tails (1). A classical bit is bolted to one pole or the other. A qubit in superposition points out along the equator, and here is the crucial part: it is not secretly Heads or Tails, hiding its "real" value from you until you look. Pointing sideways is its complete, honest state. Only when you force it to answer one blunt question, "up or down?", does it snap to a single pole, with the odds set by how it was tilted. Balanced on the equator, it answers Heads or Tails on a perfect fifty-fifty, and not one instant sooner.