#QEC is a set of techniques used to protect the information stored in qubits from errors and decoherence caused by noise. Today’s quantum computers have high error rates – **around one error in every hundred operations**. Once we reduce this to one in a million, we will start unlocking applications that are intractable on today’s supercomputers. For quantum computers to be useful, error rates **must be as low as one in a trillion.**  Qubit and/or quantum algorithm improvements alone will not be enough to reliably run algorithms with millions or billions of operations. This is where #QEC comes in. ![[Pasted image 20241226200545.png]] > Using QEC, we can turn unreliable physical qubits into useful, logical qubits.  QEC codes **rely on encoding the information on multiple qubits,** as Figure 1 shows. This means that if one qubit throws an error, others can help. Moreover, we do not need to measure the qubit directly to find out exactly where the error occurred, which would collapse its quantum state.  Instead, **we measure the collective properties of groups of physical qubits** so that we do not learn the value of the logical qubit but receive information about whether an error has occurred.  **This is incredibly challenging**.