This will serve as a very brief introduction to a complex and complicated phenomenon: a quantum computer.
A quantum computer is a super computer of sorts, based on quantum-physical laws. It utilizes quantum-mechanical insights into particles’ ability to be in more than one state simultaneously. Based on how these small particles behave, computers can execute more tasks at the same time and with much less energy, compared to a conventional computer.
Quantum computing is not yet marketable, but it is nonetheless under constant development. It is still unclear, what the full potential of quantum computing is, but these computers are estimated to end up becoming powerful enough to crack high-level encryption so quickly, that they will outperform cryptocurrency- and blockchain-technology, which bases its success on being hard to manipulate and decrypt.
In a conventional computer, a bit is a piece of information that can exist in two states - either as a 1 or as a 0. Qubits in a quantum computer can exist in both states at the same time, which enables them store even more information. This is based on the behavior of the smallest particles that - following the laws of quantum mechanics - can exist in different states simultaneously. They exist in what are called superpositions. In other words, a quantum computer can use superpositions to calculate with different numerical values at the same time. This increases the performance far beyond what a conventional computer is capable of.
The technological development in the wake of this phenomenon brings with it an enormous potential. At the same time, it creates big issues concerning internet security, including privacy, because it will become increasingly easy to breach encryption with this level of computer power.
If you are interested to learn more about science behind a quantum computer, read this.