University of Denver, Department of Physics & Astronomy
Abstract: Entangled photons are a valuable resource for quantum logic, imaging, and information theory. While measuring entangled state amplitudes is relatively straightforward with coincidence-based correlation filters, the entangled state phases have received relatively little attention – despite the important role that phases play in defining and altering quantum states. In contrast to classical light, for which phase can be easily measured using interference with an ancillary reference beam, the reliance of coincidence detection for biphoton measurements makes it unclear how to implement the requisite reference. Furthermore, phase measurement of entangled states is not as simple as combining separate phase measurements of signal and idler photons, or of interfering them together. In short, a phase-measurement counterpart to direct amplitude measurements has remained elusive. I will show a method to directly measure the phase of biphoton states that uses the broader entanglement spectrum as a resource for interferometry. The technique is demonstrated with entangled photonic spatial modes in the Laguerre-Gaussian basis, and it is applicable to any quantum system that has multiple orthogonal modes. Two different implementations are demonstrated with measurements on entangled photons: a simple version that works in the case of a particular sparse entanglement spectrum, and another that works for general entangled states (including polarization entanglement). As one particularly useful application, we use the new methodology to directly measure the geometric phase accumulation of entangled photons.
All lectures in Hill Hall 202 unless otherwise specified