- Encoded quantum information
- Error checks + classical decoding
- Recover the logical state
background
Store information across a code
Physical qubits are the hardware systems. A logical qubit encodes information across multiple physical qubits using an error-correcting code. Checks extract information about errors without simply measuring the encoded answer. Arbitrary unknown quantum states cannot just be copied for a majority vote.
Sources: IBM Quantum Learning
background
More resources can help under conditions
Error correction needs sufficiently reliable operations, appropriate checks and decoding. Larger codes can suppress logical errors in the right regime; additional hardware is not automatically an improvement. An experiment preserving a logical memory is different from running a useful fault-tolerant application.
Sources: IBM Quantum Learning · Google Quantum AI and collaborators, research manuscript
Check your understanding
Are 100 physical qubits the same as 100 logical qubits?
Reveal the answer
No. Logical encoding consumes physical qubits and other resources. The relationship depends on the code, error rates and target task.
Sources and review scope
Source-linked. Editorial review: .