Before I start talking about what quantum computers might be capable of you must know what is quantum computing and how it works?
Quantum computing as defined by google is “It is the use of quantum phenomena such as superposition and entanglement to perform computation. Computers that perform quantum computations are known as quantum computers.”
Though if you are a normal human you probably didn’t understand what this statement really means. So I will simplify it for you. You don’t need to know what the quantum phenomena are and how they play a role in making quantum computers but what you should know about is quantum entanglement to understand quantum computing.
In layman's terms quantum entanglement is a force (kind of) with which if two objects are bound together, they will always stay in the exact same state no matter the distance between them.
Now let’s get to know what superposition is? Let’s take a bit as an example, a bit can have a maximum of 2 states which are 1 or 0, these are used to represent information in normal computers. Whereas a Qubit or quantum bit is used in storing information in quantum computers.
These quantum bits can be in different proportions of states at a time, what this means is that they can have some value of 1 and some value of 0 which can be manipulated using quantum gates just like the logic gates in our everyday computers.
AND one more thing…
We need quantum computers! Why? Because our present technology is reaching very close to the size of an atom which can hamper the basic laws of physics on which our modern day computers work. When we reach the point where we have to make components the size of a few atoms the laws of quantum mechanics won’t let us use our laws of physics because of phenomena like quantum tunnelling. So why not use these laws of quantum mechanics to our advantage and make quantum computers which can be much faster than traditional computers.
But then why don’t we see quantum computers everywhere? This is because we are limited by the technology of our time and the right technology to mass produce quantum computers and run them just doesn't exist.
Though some companies have successfully made computers that use quantum computing but they are still far from perfection. Some of the famous companies are : microsoft, intel, IBM, etc.