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Do all pure entangled states violate Bell's inequalities for correlation functions?
Marek Zukowski1, Caslav Brukner, Wiesław Laskowski
1Instytut Fizyki Teoretycznej i Astrofizyki, Uniwersytet Gdański, PL-80-952 Gdańsk, Poland.
Physical Review Letters
|June 13, 2002
Summary
Pure entangled states with more than two qubits can avoid violating Bell inequalities. This challenges the universality of Gisin's theorem for multipartite quantum systems and suggests alternative methods for refuting local realism.
Area of Science:
- Quantum Information Theory
- Quantum Entanglement
- Bell Inequalities
Background:
- Gisin's theorem states all pure entangled two-qubit states violate Bell inequalities.
- Bell inequalities are crucial for testing local realism against quantum mechanics.
Purpose of the Study:
- To investigate whether pure entangled states with N>2 qubits can avoid violating Bell inequalities.
- To explore the limitations of Bell inequalities in refuting local realism for multipartite systems.
Main Methods:
- Analysis of N-particle correlation functions for specific pure entangled states.
- Examination of Bell inequalities involving two dichotomic observables per station.
Main Results:
- Existence of pure entangled N>2 qubit states that do not violate any Bell inequality.
- Demonstration that Mermin-Ardehali-Belinskii-Klyshko inequalities are not always optimal for refuting local realism.
Conclusions:
- Gisin's theorem does not universally apply to all multipartite entangled states.
- Bell inequality violations are not a necessary condition for entanglement in N>2 qubit systems.
- Alternative approaches may be needed to verify quantum correlations in complex systems.