Towards an experimental demonstration of some novel qubit behavior

TL;DR

This paper explores a novel quantum behavior in photon angle measurements, revealing parity-dependent effects and proposing modifications to interferometers to observe these phenomena, with implications for quantum phase inference.

Contribution

It introduces a new quantum angle measurement effect dependent on photon number parity and suggests modifications to interferometers to observe this behavior.

Findings

Odd photon number states never align with the y-axis in angle measurement.

Even photon number states can align with the y-axis in angle measurement.

Quantum phase inference algorithms can surpass the Heisenberg limit.

Abstract

We show that the quantum angle measurement for x-polarized photon number states results in an angle which will never correspond to the y-axis for an odd number of photons; yet for an even number of photons it always can. The analogy of this surprising effect for other particles or ions (qubits in their spin up state) is presented and we show why such an effect cannot be observed in a standard SU(2) interferometer. The quantum phase representation of such an interferometer provides clues as to how its apparatus might be modified in order to demonstrate these phenomena. The same representation is then used to provide insight on the range and sensitivity that one can expect from quantum phase statistical inference algorithms which can surpass the Heisenberg limit.