Counterintuitive causal structures in inter-chip photonic quantum computing

Area of Science:

• Quantum Information Science
• Causal Inference
• Photonic Quantum Computing

Background:

• Causal theory offers a framework for event relations, recently extended to quantum systems.
• Quantum entanglement introduces non-classical correlations with potential causal implications.

Purpose of the Study:

• To apply causal analysis to a remote-controlled quantum computing model.
• To uncover and experimentally verify bidirectional causal structures arising from quantum entanglement.

Main Methods:

• Utilized causal analysis on a remote-controlled quantum computing model.
• Experimentally implemented the model on two photonic chips connected by 15-meter fibers.
• Performed timing analysis to quantify causal lags.

Main Results:

• Discovered a bidirectional causal structure rooted in quantum entanglement.
• Demonstrated that quantum operations can causally influence their control parameters.
• Achieved an average fidelity of 90.43±2.42% over 100 single-qubit unitaries.
• Showed a theoretical control parameter lag of up to 129.14 ns behind the operation.

Conclusions:

• This study provides the first systematic causal modeling of quantum entanglement in quantum computing.
• Revealed non-classical causal features, including counterintuitive causal behavior where operations precede controls.
• Findings have implications for advancing both quantum computing and causal inference theory.