According to IBM, quantum computers "exploit complex and fascinating laws of nature that are always there, but usually remain hidden from view." They must be talking about superposition and entanglement, phenomena that are observable and repeatably findable by experimentation, but not within the day-to-day purview of humans without powerful scientific devices and instrumentation.

posted at 1530893670

Quantum computers rely on superposition: a state of a qubit that is both up spin and down spin, or both <1 0> and <0 1> simultaneously. When qubits are placed into superposition (via a quantum gate such as a Hadamard Gate), eventually the superposition will collapse and a specific value shall be indicated. It is still unclear to the author whether on not superposition can be measured without collapsing the superposition, but it seems likely that any perturbation of a superposition forces it to collapse into a decided (and not vague/ambiguous/multiplicity of) value.

posted at 1530893882

All quantum operations must be reversible due to the physics involved ("a limitation held in place by nature herself"). Operations on the simplest qubits <0 1> and <1 0> can be demonstrated by pivoting around the unit circle (because calculations are simply multiplications of the matrices).
The qubits zero and one (<1 0> and <0 1> respectively) are sometimes written shorthand as in this diagram.

posted at 1530894171

Reversible Operations can be seen on this quantum circuit. The transformation dances across the unit circle and can happen forwards or backwards. Notice how signs are preserved through transitioning into and out of superposition.

posted at 1530894242