To understand what a quantum computer is we must first understand how a binary computer works. Binary means two things and for computers these are 1s and 0s. A binary computer uses only 1s and 0s to do all of its computation and storage of data. A single unit of information is called a bit and it can be either a 1 or a 0, on or off respectively. Two bits of information can be 00, 01, 10, or 11 a total of 4 possible values. It is important to note that we only need two bits of binary to determine what value we have with a two bit number.

A quantum computer uses qubits to store its information. A qubit can be photon, electron, or atomic nucleus. The information of a qubit is stored by the spin of the qubit. The lowest energy that a qubit can have is a down spin, which is represented by a 0. When the spin is up, this is the highest energy that the qubit can have and is represented by a 1. So far qubits are the same as normal bits on a computer. However, until we observe the qubit it can be in both positions at once. The position of the bit between observations is a superposition of the two states, meaning we don’t know where the atom is, only the probability that it is in an up or a down state. The state of the qubit can therefore be more complex than a normal bit.

Two qubits in quantum entanglement can be used to describe 4 bits of classical information through superposition of the particles. That is, in order to describe the state of two qubits, we need 4 pieces of information of the superposition to know where they are. The superposition of particles is related to the uncertainty of how things at a quantum scale work. Once observed we will loose the superposition of the particles and they will be forced into one of the base states and are not longer in superposition. Because we cannot read these superpositions, the computer must output a meaningful base state at the end of the process.

However, the ability of the qubits to store and manipulate data is still exponential in size. That means that for every N qubits that we have we can have 2^n bits of classical information. Two qubits holds four bits of information. Three qubits holds eight bits of information. 300 bits can hold 75 letters. 300 qubits can hold more bits than there are particles in the universe, 2^300. This is only true when all 300 qubits are entangled with each other creating a vast and complex series of superpositions.