Logical versus physical qubits
Classical computing resources deal with faulty physical means or errors generated by all kinds of sources. Error-correcting codes have been extensively studied (https://en.wikipedia.org/wiki/Error_correction_code) concerning those needs. Richard Hamming (1950) was the first to propose error-correcting codes in early 1950. Classical error correction codes use the concept of redundancy or information replication to spot inconsistencies in the outcome of a given channel or computation result. This way, the error can be detected and even corrected to recover the mitigated outcome.
Taking this to the quantum regime faces two main challenges. The no-cloning theorem (Lindblad 1999) states that there is no way we can copy a quantum state if this state is unknown. Knowing this state would mean measuring it, and this event will force the state to collapse and lose all its quantum information. These two challenges require inventive solutions to deal with errors...
