Let me show how different classical computers (CC) are from quantum computers (QC) by comparing them. If a CC adds 2 bits a QC add 2 qubits. A bit has 2 possible states and always holds either of those 2. A qubit theoretically holds an infinite number of states (tests have been done with limited number states,) but all at the same time. This is called superposition. Upon measurement you get an ‘approximation’. Sometimes referred to as ‘collapse of the wave function’. An average of a lot of measurements gets ‘the state’. You can see this is calculating with matrices, or like parallel computing. But the difference is that the internal state is not necessarily the external state.

From the difference and from characteristics of quantum mechanics we can deduce a number of interesting properties of a ‘quantum computer’

• it is about calculating (or managing/combining/mixing/…) of complexity
• this complexity is never certain (the internal state is unknown, the external state (measured) is uncertain)
• you can’t clone complexity
• the calculation is reversible
• entanglement can integrate in detail

Now the question is what would we use it for. We might use a quantum computer to control a complex process or system. We don’t necessarily need/want to know the internal state. Uncertainty is not a problem as long as it is within safety (human) constraints. You don’t have to clone, because the system itself is not clonable. And reversibility gives you enormous control over a process like this.

What sort of complex, man made processes do we have today

• nuclear power plants
• particle colliders
• economies/societies
• markets
• subsidy systems
• …

And with these systems we are encountering the limit of the power of the classical computer. We can grow these systems by increasing computing power by innovations like grid computing and parallelism. But we can’t manage anything a factor more complex than these.

What system would we want to manage if we could handle this type of complex systems? I think we would be very interested in a global energy grid, for example. Perhaps we could revive central planning societies?! If we understand climate I suspect it would be in this category. All these systems are so immense they only need a controller. A controller to make it simplify for a human operator. A controller that interfaces to a complex system based on entanglement. We don’t need a quantum computer, we need a quantum controller, an interface between us and a system we want to ‘deal with’.