= Quantum error correction
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Technique that uses multiple non-<ideal> qubits (physical qubits) to simulate/produce one perfect qubit (logical).
One is philosophically reminded of classical <error correction codes>, where we also have multiple input bits per actual information bit.
TODO understand in detail. This appears to be a fundamental technique since all physical systems we can manufacture are imperfect.
Part of the fundamental interest of this technique is due to the <quantum threshold theorem>.
For example, when https://www.bloomberg.com/news/articles/2020-04-06/quantum-computing-startup-raises-215-million-for-faster-device[PsiQuantum raised 215M in 2020], they announced that they intended to reach 1 million physical qubits, which would achieve between 100 and 300 logical qubits.
<video Jeremy O'Brien: "Quantum Technologies" by GoogleTechTalks (2014)> https://youtu.be/7wCBkAQYBZA?t=2778 describes an error correction approach for a <photonic quantum computer>.
Bibliography:
* https://errorcorrectionzoo.org/domain/quantum_domain