Full characterization of polarization states of light via direct measurement

By J. Z. Salvail, Megan Agnew, Allan S. Johnson, E. Bolduc, Jonathan Leach, R. W. Boyd. Nature Photonics, 2012

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Ascertaining the physical state of a system is vital in order to understand and predict its behaviour. However, due to their fragile nature, the direct observation of quantum states has, until recently, been elusive. Historically, determination of the quantum state has been performed indirectly through the use of tomography. We report on two experiments showing that an alternative approach can be used to determine the polarization quantum state in a simple, fast and general manner. The first experiment entails the direct measurement of the probability amplitudes describing pure polarization states of light, the first such measurement on a two-level system. The second experiment entails the direct measurement of the Dirac distribution (a phase-space quasi-probability distribution informationally equivalent to the density matrix), demonstrating that the direct measurement procedure is applicable to general (that is, potentially mixed) quantum states. Our work has applications to measurements in foundational quantum mechanics, quantum information and quantum metrology. Researchers report the first direct measurements of the wavefunction and Dirac distributions for polarization states of light. Their implementation determines the general description of the pure state of a qubit. This technique is simple, fast and general, and has an advantage over the conventional approach of performing quantum state tomography.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/5e87938018e9ebdb37ec0fe56918897310760b68