Dual fiber spectrometer for highly non-degenerate entanglement source

Abstract

NASA is developing quantum metrology capabilities for potential space-based quantum components in future navigation and communications systems. Innate knowledge of component operation is key for the space qualification of these components. This paper focuses on the measurement and analysis of an important characteristic of an entanglement source, the joint spectrum. We describe a spectrometer based on dispersive optical fibers and present experimental measurements of the joint spectrum of a highly non-degenerate SPDC-based entanglement source that emits entangled photons in the near-infrared and telecommunications bands. How the analysis of such a joint spectrum could be applied to the modeling and simulation of entanglement swapping operations as possible extensions of quantum networks is examined. Lastly, we discuss how the separability of the two-photon state is quantified via Schmidt decomposition and how the degree of separability impacts the spectral purity of heralded single-photon emissions.

Overview of NASA’s quantum metrology laboratory and quantum communications analysis suite for degenerate source verification and validation within aerospace network applications

“…In this article, we discuss the measurement of the joint spectral intensity (JSI) of a time-energy Spontaneous Parametric Down Conversion (SPDC) entanglement source implemented in a periodically poled potassium titanyl phosphate (pp-KTP) waveguide. The source is like other non-degenerate sources our team has previously reported on [11]; however, the main difference is that the source in this paper is degenerate at 1550 nm. We report on the JSI and Schmidt decomposition of our source with different optical filtering conditions.…”

“…Measuring the degree of signal-idler correlation involves finding the JSI of the down converted photons. Example JSI images of strong and weak correlations are provided in Figures 1b and 1c in Reference [11].…”

“…The data from fiber spectroscopy was retrieved in the form of raw time tags on three channels: (1) a trigger channel measured directly from the 775 nm pulsed laser pump, (2) a count channel from signal photon emission, and (3) a count channel from idler photon emission. The three-fold coincidence measurement we used for JSI recovery is described in detail in Section Two of Reference [11]. In this report we evaluate the JSI of a source with two different optical filtering conditions: (1) no filtering, and (2) 1.8nm bandpass.…”