Entangled GHZ probes
Collective phase accumulation can amplify a small signal.
$$\lvert\mathrm{GHZ}\rangle=(\lvert0\rangle^{\otimes N}+\lvert1\rangle^{\otimes N})/\sqrt2$$
Physical intuition
Collective phase accumulation can amplify a small signal.
Deep dive: physical mechanism
A shared superposition acquires a relative phase N times faster than one qubit for the same interrogation.
What is measured experimentally?
Parity oscillations can show enhanced phase frequency.
Assumptions, noise and limitations
Uncorrelated dephasing can erase the scaling advantage rapidly.
Research and simulation exercise
Compare GHZ and product probes at fixed total experimental time.
Connect the ideas
Explore the chapter overview, learning path, and references.