Two stations holding an entangled photon pair sit apart
PHYSICS · Multi-part · Fermi University Physics · Quantum Information & Technology · Quantum states, measurement and entanglement · Quantum states, measurement and entanglement
Quantum Information and Technology, Ch Nonlocality: EPR, Bell inequalities and the CHSH game
Problem
Two stations holding an entangled photon pair sit 400m apart. At each station, the setting is chosen and the measurement completed within 0.9μs of the choice. The pair is prepared close to maximally entangled and the standard CHSH inequality is used; each station detects and uses 75% of the pairs sent to it.
((a)) Compute the light-travel time between the stations, and say whether the locality loophole is closed.
((b)) Compare the detection efficiency with the threshold quoted in this section for a maximally entangled state and the standard CHSH inequality, and say whether the detection loophole is closed.
((c)) Say what change, keeping the same 75% efficiency, could close the detection loophole, and give the threshold it would then need to beat.
((d)) State which assumption no amount of redesign, of timing or of detection, can close outright.