# Question / Statement A quantum computer computes all possible solutions to a problem at the same time. Or it´s more bombastic cousin : A quantum computer uses the power of the multi-verse to find solutions. # Answer / Explanation The core idea of all [[Quantum Algorithm|quantum algorithms]] is to **use intrinsically quantum** effects like [[Superposition|superposition]] and [[Entanglement|entanglement]]. By using these non-classical features of quantum mechanics, scientists hope to both speed-up previously existing computations and find new unique computations of the quantum realm. Two examples of speed-ups would be the [[Shor Algorithm|Shor algorithm]] or the [[Grover Algorithm|Grover algorithm]]. The mistake of the statement lies within a common **confusion between the concept of [[Superposition|superposition]] and** one which is more common to us, which is the **parallelization of tasks**, a.k.a doing things simultaneously. Quantum algorithms are **not as simple as parallelization** of a classical algorithm, if so a bigger classical supercomputer would be able to do everything a quantum computer does! To understand the difference, what is parallelization anyway? ![[parallelization.excalidraw.light.svg]] In a serial or, "one-thing-after-another" approach, after each completed step of an algorithm we perform the **next step on the output** of the previous one. If different parts of the result are to be treated as independent by the incoming steps, then we can use different processing units (depicted as workers above) to **evaluate multiple instances at the same time**. Importantly, all the data (all the bricks) will be stored in memory simultaneously, and therefore we can access each of the red squares at any point. The idea of a quantum algorithm is to use [[Superposition|superpositions]] and [[Entanglement|entanglement]]. Staying with the example used in [[Interference|interference]], designing a quantum algorithm is like figuring out the pattern of stones you have to throw into a lake to get a certain interference pattern. ![[interference_lake.excalidraw.light.svg]] Coming back to the data blocks of our earlier example. We store the information as a superposition: ![[superposition_quantum_computing.excalidraw.light.svg]] The [[Quantum Algorithm|quantum algorithm]] performs operations on the [[Quantum State|quantum state]]. The result (second row) is still in a [[Superposition|superposition]]. The main difference between the classical parallelization case and the [[Quantum Computer|quantum computer]], is that the [[Measurement|measurement]] will only reveal a single state of the superposition. We do *not* have access to all the data at the same time. While we might compute on multiple states at the same time, we can never read it out at the same time! The second part of the statement is a bit more difficult. The statement about the multi-verse concerns rather the [[Interpretations of Quantum Mechanics|interpretation of quantum mechanics]] than the actual formalism. Today, we do not know of a way to formulate a statement which can discern between, e.g. [[Q-Bism]] and the [[Multi-World Interpretation|multi-world interpretation]]. Thus, the statement about the multi-verse is adherent to a certain interpretation of quantum mechanics, which is usually considered more of a philosophical question than one in physics. >[!read]- Further Reading >- [[Quantum Computer]] >- [[Quantum Algorithm]] >- [[Superposition]] >[!ref]- References