Qubit ZooDescription
The dual-rail photonic qubit encodes logical states in occupation of two optical modes:
This is the canonical encoding for linear-optical quantum computing and integrated photonic platforms.
Figure
Hamiltonian
Passive linear-optical operations are generated by quadratic mode couplings:
For a beam splitter between two modes:
which implements arbitrary SU(2) single-qubit operations in the dual-rail subspace when combined with phase shifters.
Why it matters
Dual-rail is robust to global phase noise, naturally compatible with telecom/optical networking, and is the default logical encoding in many photonic fault-tolerant architectures.
Key Metrics
| Metric | Value | Notes | Fidelity reference |
|---|---|---|---|
| Encoding overhead | 2 modes / qubit | One photon across two rails | — |
| 1Q gate fidelity | >99% | High-quality integrated optics | Knill et al. 2001 |
| 2Q interaction | Measurement-induced | Ancilla + feed-forward required | — |
| Dominant error | Loss | Photon loss is primary failure mode | — |