Coarse graining makes it hard to see micro-macro entanglement

Area of Science:

• Quantum Physics
• Quantum Information Science

Background:

• Observing quantum phenomena like superposition and entanglement in macroscopic systems is difficult.
• Requires systems protected from environmental decoherence and precise measurements.

Purpose of the Study:

• Investigate the impact of coarse-grained photon number measurements on detecting micro-macro entanglement.
• Compare entanglement generation using a unitary quantum cloner versus a measure-and-prepare cloner.

Main Methods:

• Studied micro-macro entanglement created by amplifying one photon from an entangled pair.
• Compared probability distributions from unitary and measure-and-prepare cloners under coarse-grained measurements.

Main Results:

• The distance between probability distributions for the two cloners approaches zero with moderate coarse graining.
• Increased system size exacerbates the difficulty in proving micro-macro entanglement.

Conclusions:

• Coarse-grained measurements significantly hinder the observation of micro-macro entanglement.
• Detecting quantum entanglement in macroscopic systems becomes progressively more challenging with increasing size and measurement imprecision.