Skip to content
PaperFren

Entanglement and quantum information

Can looping around an exceptional point switch entangled states?

Tang Z, Chen T, Tang X, et al. · Light, science & applications · 2024

Open access · cc by · source: Europe PMC

Steering a lossy photonic system around an exceptional point converts one entangled Bell state into another, with the result set by the loop's direction and robust to small errors.

Save to libraryView originalAsk PaperFrenStudy view

Study at a glance

Design
Other — Non-Hermitian quantum walk theory with a two-photon polarisation experiment reconstructed by quantum state tomography
N
No sample N; the experiment used an 8-step quantum walk with four Bell-state inputs, two encircling directions, and ten random disorder realisations
Population
Polarisation-entangled photon pairs from type-I down-conversion in a BBO crystal
Outcome
Fidelity of output states to target Bell states and theory-experiment similarity

Structured fields used in claim comparison tables when every cited study has a complete layer.

Key findings

In theory, a clockwise loop sent two Bell states to the same output and a counterclockwise loop sent them to the partner state, with fidelities up to 98.3%. In the 8-step experiment all output fidelities to ideal Bell states were at least 84%, and theory-experiment similarity exceeded 92%. A loop that did not enclose the exceptional point lost the chiral behaviour, and random angle disorder barely changed the fidelities, which stayed above 0.8.

Methodology

The authors designed a non-Hermitian quantum walk with gain-loss operators whose eigenstates closely match the four Bell states and share a four-fold exceptional point. They varied two parameters in a loop around the point, clockwise or counterclockwise, first in theory with 100 steps and then experimentally with polarisation-entangled photon pairs using wave plates and partially polarising beam splitters. Output states were reconstructed by two-photon tomography, and robustness was tested by adding random wave-plate angle errors.

Limitations

The experiment only used 8 steps because photon loss makes long walks hard, so it approximates rather than fully meets the adiabatic condition, and fidelities are lower than in theory. Gain and loss are simulated by relative loss in passive optics, so the system is not a truly amplifying one, and the lost photons are a source of error. Robustness was tested only against small angle disorder, not against other realistic noise such as decoherence in a larger network. Whether this scales to more qubits is not shown.

How this study connects

Role on claims

Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.

  • SupportsQuantum entanglementconcept

    Special states and paths can control how entanglement evolves.

    Entanglement dynamics can be engineered: scar states on a superconducting qubit ladder showed slow entanglement growth and revivals lasting about a microsecond versus 50 ns decay for generic states, and loops around an exceptional point in a photonic walk switched Bell states with fidelities of at least 84%.

    Evidence for the claim as stated.

Related papers in this topic

Same topic cluster — not a recommendation engine.