The Heart of the Weirdness of Quantum Computing and Quantum Physics
Quantum computers utilize the unique properties of quantum physics that manifest at the smallest levels of reality (one of the largest objects that exhibits quantum properties is made up of 60 carbon atoms). Objects that have quantum properties are smaller than anything we can really experience as human beings. Because the everyday reality we grew up with does not mirror what happens at the smallest levels, we find descriptions of the quantum-level of physical reality “spooky”.
However, here are the two ideas in quantum physics (QP) behind most of the largest reality disconnects:
QP can model groups of subatomic particles as a single object called a state vector.
The axioms of QP also separate out the idea of a particle’s state from its measurement.
In classical mechanics (pre-1900s), if the energy of an electron is defined as +1, then when you measure its energy it will be +1. So the electron has an energy of +1, its measurement must therefore be +1. In QP, the state vector of a particle represents all that can be known about it, and it is usually some form of probability distribution (a “fuzzy” description of the likely properties of the particle, not its precise properties). So the particle does not have an energy value until it is measured. State and measurement are different concepts — in a sense the state is “bigger” than the measurement. In fact it can be shown that a quantum state — unlike a measurement — cannot in general be represented by a classical description (e.g. a normal computer memory) no matter how many trillions of gigabytes can be stored.
It is this property of quantum physics, more than any other, that enables most of the weirdness that we hear about in the quantum world: entanglement, teleportation, superposition, etc. Superposition comes from the fact that a state can represent multiple measurements at the same time. Entanglement comes from the fact that two particles can be spread across a vast space, but still be part of the same state (until they’re measured). If you’re a non-physicist scratching your head at this, don’t worry. Physicists themselves can’t agree what this all means in relation to our understanding of humanly perceived reality. But the good news is — QP works GREAT as a scientific theory. Otherwise we wouldn’t have smartphones, the internet, or nuclear power, to name but three.