From nonholonomic quantum constraint to canonical variables of photons I: true intrinsic degree of freedom

TL;DR

This paper identifies the true intrinsic degree of freedom of photons as a local property in momentum space, distinct from polarization or spin, achieved through a nonholonomic quantum constraint approach.

Contribution

It introduces a new intrinsic photon degree of freedom via a nonholonomic quantum constraint and generalizes Stokes parameters in a local momentum-space reference frame.

Findings

The intrinsic degree of freedom is represented by Pauli matrices in a local reference frame.

Generalized Stokes parameters depend on a momentum-space fixed reference called Stratton vector.

Optical rotation can change the Stratton vector without affecting the intrinsic quantum number.

Abstract

We report that the true intrinsic degree of freedom of the photon is neither the polarization nor the spin. It describes a local property in momentum space and is represented in the local representation by the Pauli matrices. This result is achieved by treating the transversality condition on the vector wavefunction as a nonholonomic quantum constraint. We find that the quantum constraint makes it possible to generalize the Stokes parameters to characterize the polarization of a general state. Unexpectedly, the generalized Stokes parameters are specified in a momentum-space local reference system that is fixed by another degree of freedom, called Stratton vector. Only constant Stokes parameters in one particular local reference system can convey the intrinsic degree of freedom of the photon. We show that the optical rotation is one of such processes that change the Stratton vector with the intrinsic quantum number remaining fixed. Changing the Stratton vector of the eigenstate of the helicity will give rise to a Berry's phase.