Why is a quantum computer faster?

Published: December 12, 2024

A classical computer uses bits - 0 and 1, and performs all operations sequentially, even if it's a supercomputer with many processors and cores. A quantum computer uses qubits and performs operations in parallel.

A qubit is a quantum thing that exists in a state of superposition - it is simultaneously zero and one. After measurement, it takes on one of the values - 0 or 1. Thus, one qubit can represent two states at once - 0 and 1, 2 qubits - 4 states, and so on in accordance with exponential growth (this is when a value grows faster the larger it becomes).

To find out the number of possible states, you need to raise 2 to the power of the number of qubits. For example, for 100 qubits this number will be 1.26×10³⁰, for 300 qubits 2.03×10⁹⁰, and this is already more than the estimated number of atoms in the Universe, which is estimated at 10⁸⁰. The quantum computer from Atom Computing has 1180 qubits, which is currently a record.

And all the power lies in the fact that a quantum computer operates with all these states simultaneously. In general terms, this comes down to changing the shape of the wave function that describes the state of all qubits.

For example, if we have a database of a billion rows and we need to find the right one, a classical computer will run through the entire database sequentially, while a quantum computer will operate with all billion rows simultaneously.

There are tasks where, due to exponential complexity, an ordinary computer quickly exhausts its capabilities, and the solution drags on for billions of years. A quantum computer, thanks to true parallel processing, will solve such a task in minutes.

And it's worth emphasizing that a quantum computer is not suitable as a complete replacement for an ordinary one, which will handle many tasks better. It can be used for specific tasks like modeling molecular shapes and chemical reactions. But even if it's only used for this, we can expect a breakthrough in medicine - for example, new drugs will be developed in hours rather than years and decades.