As classical computers become smaller and more efficient, we are approaching the limits of classical physics. At the atomic or subatomic levels, the extremely tiny particles such as electrons or photons literally move to a different drumbeat. We know that they follow the laws of quantum mechanics.
In recent decades, our ability to use quantum phenomena for computation has increased. And any computers which utilise these laws of the extremely small particles are known as quantum computers.
At the heart of the quantum computer’s processing power is its ability to use quantum physical properties to store and perform calculations. The basic units of memory in the quantum world are known as qubits or quantum bits, similar to the classical bits.
Qubits are different from the classical bits in their ability to store more information. While a classical bit stores information either as zero or one, a single qubit due to its quantum mechanical properties is able to store much more information. If compared to a classical bit, a qubit can store information as zero, one or a linear combination of the two quantum states. Put simply, it means the qubit can be both zero and one. This phenomenon is known as superposition.
For ‘n’ qubits, it is possible to represent 2ⁿ states. Apart from the ability to store more information, qubits when connected together are also able to make use of the phenomenon of quantum entanglement to process information much faster. This is done almost in a parallel fashion.
Due to the ability of qubits to store and therefore process more information than computers based on classical physics, quantum computers can potentially work on computations which classical computing cannot do in a reasonable amount of time.
Yet, quantum computers are very difficult to make. Partly because there is not enough knowledge of how to prevent the quantum state from collapsing or better known as quantum decoherence. Our current knowledge does not allow us to maintain the quantum states at normal temperatures. At least for all practical purposes.