Entanglement and quantum information
Can noise be turned into a helper in quantum teleportation?
Open access · cc by · source: Europe PMC
By first entangling photons' polarisation with their frequency in a tailored way, the researchers made later noise undo the scrambling, so teleported quantum states came out with high fidelity instead of being ruined.
Study at a glance
- Design
- Other — Three-photon linear-optics teleportation experiment with dephasing noise from birefringent crystals, run with and without spatial-light-modulator phase functions that create hybrid entanglement.
- N
- No sample size; several input polarisation states were teleported under three noise configurations, with and without hybrid entanglement, using photon coincidence counts.
- Population
- Polarisation qubits of photons from spontaneous parametric down-conversion
- Outcome
- Fidelity of the teleported polarisation state relative to the input state
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Key findings
Without the modulators, dephasing noise pulled teleportation fidelities down sharply even though the auxiliary photons were entangled. With hybrid entanglement, fidelities in all noise configurations were well above the classical limit of two thirds and roughly equal to the noise-free reference. This worked even though the auxiliary polarisation state looked classical before the Bell measurement and did not violate a Bell inequality, and it did not require correlated photon frequencies.
Methodology
The team built a photonic teleportation setup in which one photon's polarisation state is sent to a distant party using a pair of auxiliary photons. Noise was added by passing photons through birefringent crystals, which couple polarisation to frequency and erase coherence. Before the noise, spatial light modulators imprinted frequency-dependent phases that create hybrid entanglement between polarisation and frequency, chosen so that the later noise cancels them. They teleported several different polarisation states with noise on one side, the other, or both, and compared runs with and without the modulators.
Limitations
The noise here was artificial and fully controlled, and the method assumes the experimenters know how long the dephasing lasts and can set the initial system-environment correlations; real channels with unknown or fluctuating noise were not tested. Only pure dephasing was studied, not other noise types like photon loss. Count rates were very low because the gratings and modulators discard photons, so each measurement needed long accumulation, and exact fidelity values are only shown in figures.
How this study connects
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