Direct measurements of quantum states by exploiting diffused photon state
KyeoReh Lee, YongKeun Park · arXiv (Cornell University) · 2017
Measuring the state of a physical system provides a complete understanding of the past, present, and future behavior of the system. Accordingly, techniques for measuring intact physical states are required in all subfields of physics. In quantum systems, however, measuring the exact state of a system is a challenging task due to the complex and uncertain nature of quantum systems. The conventional way of measuring a quantum state is the quantum tomographic approach. However, this is a challenging task because of the extreme vulnerability of the interferometric setup. Recently, direct measurement of a quantum state was realized utilizing the weak measurement. Though this alleviates the difficulty of measuring quantum states, the introduction of a pointer state still limits the generality of the technique. Here, we propose a general but straightforward measurement technique for the quantum state of a photon. At the heart of our idea is an optical diffuser. Based on the random feature of the diffused state, we theoretically show that the density matrix of a photon can be directly reconstructed from a single intensity image after the diffuser. In experimental demonstrations, we successfully measured the density matrices in the position-polarization basis for both pure and mixed states of photons.