5 Four myths about quantum computing
Koen Groenland · Amsterdam University Press eBooks · 2025
Four myths about quantum computingThis chapter relies on a bit of quantum physics jargon.See the chapter 'An introduction to the quantum world' for a quick introduction. Myth 1: Quantum computers find all solutions at onceThis myth is likely the most technical, and builds on a misinterpretation of the concept of superposition.A single qubit can be in two states at the same time (0 and 1), two qubits can represent four states (00, 01, 10, 11), and three qubits are potentially in eight unique configurations simultaneously.As we increase the number of qubits, this number of coexisting states scales exponentially!This means that a mere 1000 qubits can effectively 'store' 2 1000 unique values, all at the same time.That's an incomprehensibly large number, much more than there are atoms in the visible universe.Even the fastest computers in the world couldn't loop through all these states in a lifetime.Each of these states can be interpreted like a file on a computer, be it an Excel spreadsheet, a web page, a CAD drawing, or whatever kind of data we choose to work with.A smart computer scientist can also devise a way to make 1000 bits represent 'solutions' to a problem.For example, imagine that we want to find an optimal aeroplane wing that generates incredible lift while requiring as few materials as possible.Using quantum superposition, we might represent 2 1000 such wings simultaneously.We picked the example of aeroplane wings because simulating their aerodynamic properties requires a pretty hefty computation.Let's assume that we have written such a computer program that accurately simulates any wing.Let's call that program f .It will output 1 if the wing works well (according to whatever metric), and 0 otherwise.Surely, the program takes a very large number of computation steps, which we'll call T. The program will need some input, denoted by x , which is a 1000-bit description of all the relevant properties of a hypothetical aeroplane wing.In other words, the computer program computes f (x) = 1 if x is a fantastic wing, and f (x) = 0 if it's rubbish.Now, a quantum computer should be able to execute any classical function, right?We should be able to run f on a quantum computer, but now we have the unique feature that the 1000-qubit input can represent a humongous number of potential aeroplane wings at the same time.By doing a mere T computational steps, we can check the properties of 2 1000 solutions!