# What happens to physical qubits when they decohere during quantum error correction?

Say you have a scaled up system with 98% fidelity so 2% decoheres. These are physical qubits doing error correction on information encoded on logical qubits. 98% of these entangled qubits will be doing error correction but 2% will interact with the environment and decohere. Since this 2% carries a small part of the coded information from the quantum gate where they were doing error correction, what happens to those physical qubits when they decohere? Is it just dead code?

If these bits were somewhere else in the heirarchy, then they may be corrected by some of the further apparatus. In either case the noise they caused by going wrong will, most likely, be corrected in the next round, but of course at every stage a little bit of noise leaks through and slowly builds. One designs the whole protocol such that this "little bit" is small compared to $$QN$$ where $$Q$$ is the number of logical steps and $$N$$ the number of logical qubits in the algorithm being computed.