Introduction

Basic hardware noise sources and the role of fault tolerance.

Noise	Unwanted interactions that scramble qubit states, caused by environment, control imperfections, and crosstalk.
Decoherence	The process by which quantum information leaks into the surrounding environment over time, destroying superposition.
Gate Errors	Imperfect operations that cause incorrect transformations, arising from calibration drift, pulse shape errors, and leakage.
Measurement Errors	Readout mistakes that misreport a qubit’s state, stemming from insufficient dispersive shift, thermal photons, or amplifier noise. Fault tolerance combines quantum error correction, redundancy, and error detection techniques to maintain reliable computation even in the presence of hardware imperfections.