[[Quantum Information|Quantum information]] is notoriously difficult to store. Quantum computers have to walk a difficult line between perfect isolation of quantum information to avoid [[Decoherence|decoherence]] in the [[Qubit|qubits]] while ensuring easy access to manipulate the quantum information during the computation. The most direct way to work with [[Qubit|qubits]] are [[Physical Qubit|physical qubits]]: one can perform operations directly on the [[Platform - Cold Atoms|cold atoms]], [[Platform - Ions|ions]], etc that encode the quantum information. However, these [[Physical Qubit|physical qubits]] decohere quite quickly and only few quantum operations can be performed. These devices are called [[Near-Term Quantum Device|near-term quantum devices]]. In contrast, *fault-tolerant quantum computers* use [[Quantum Error Correction|quantum error correction]] algorithms to bundle many [[Physical Qubit|physical qubits]] into fewer [[Logical Qubit|logic qubits]]. These are less affected by [[Decoherence|decoherence]] and store quantum information for longer time. As of early 2025, first error corrected qubits have been demonstrated in hardware. However, a *fault-tolerant quantum computer* is still under development. The crucial difference is that the correction of quantum information is not equivalent to performing fault-tolerant operations en masse on many qubits. Building fault-tolerant computers in the long run is essential since algorithms such as the [[Grover Algorithm|Grover algorithm]] or the [[Shor Algorithm|Shor algorithm]] have been developed for fault-tolerant quantum computers. >[!read]- Further Reading > - [[Logical Qubit]] >[!ref]- References >- R. Acharya et al., Quantum error correction below the surface code threshold, Nature 1 (2024). >- Q. Xu, J. P. Bonilla Ataides, C. A. Pattison, N. Raveendran, D. Bluvstein, J. Wurtz, B. Vasić, M. D. Lukin, L. Jiang, and H. Zhou, Constant-overhead fault-tolerant quantum computation with reconfigurable atom arrays, Nat. Phys. **20**, 1084 (2024).