1Why Qubits Are FragileA qubit is powerful because it can hold phase and possibility, but those same features make it easy for heat, stray fields, and measurement to erase.Advanced 2Error-Correcting Codes & SurfacesHow redundancy, checks, and geometry turn unreliable bits and qubits into dependable information.Advanced 3Logical vs Physical QubitsA physical qubit is a fragile device; a logical qubit is a protected idea built from many such devices.Advanced 4Thresholds & OverheadEvery system has a point where an action becomes worth doing, and a cost you pay before useful work begins.Advanced 5The Road to Fault ToleranceFault tolerance is the discipline of keeping a system useful when parts of it break, by designing for failure before it arrives.Advanced