Instead of using silicon to recognize an ‘on-off’ (1 bit) state to store data, it uses parts of an atom to store multiple states (on, off and a superposition of both). This results in the number of calculations possible at any one time is significantly greater than today's possibilities making it 'faster' than current computers significantly.
To indicate the improvement in speed, there is an exponential link between the size of a printed circuit and its enhancement. Today’s smallest Intel chips on the market are around 15nm. An atom is 0.1nm with its quantum components being tiny fractions of that.
Today, quantum computing is not a practical reality. There are inherent problems with quantum computers, particularly around the stability of data storage in the quantum realm although companies such as Google are working on error-correction systems on these.But, some think it's just a matter of time.
BlockChain technology relies on a type of mathematics called RSA Cryptography.
In this, a Secret Key is created to 'sign' transactions and a Public Key is created to prove that a transaction was 'signed' by the Secret Key. This way if Bob has £10 and wants to pay Alice, he can create a transaction that moves money from his account into Alice's by 'signing' it. No one can dispute that Bob did this and somebody can tell he did do it by checking the transaction signature against his Public Key.
Therefore, it is critical that secret keys remain secret.
Should a criminal want to access your details or take money from you without your permission, they would need your Secret Key. They wouldn't need access to your private residence or place of work, they would just need to guess it - no risk involved! The BlockChain is stored on everybody's computer, so the criminal wouldn't even need to be connected to the Internet - they could just do it at home