The more qubits you add to build larger and larger quantum states, the harder it is to protect the system from heat, noise, cosmic rays. In the presence of noise the quantum state becomes entangled with the environment and then it quickly collapses into its eigenstates which we call decoherence (it behaves classically again). 

To maintain the quantum state, you need many more qubits to handle and repair errors and decoherences. They distinguish physical and logical qubits in these cases. 

Physical qubits are used for error correction, where the logical qubits are the number of effective qubits you can reliably use for computation.

You may need a million qubits for 1000 logical qubits, but this tech could improve. To break bitcoin or simulate black holes, you need about 7000 logical qubits, which may be 7 to 10 million physical qubits, which is really hard . 

 quatmim computing also has an encryption that cannot be broken so we do a bip to change the code over when that is near 

 How is a qbit technically made?