Quantum-entangled SPectrometer using Infra-Red Interference Technology (Q-SPIRIT)

We demonstrate a Quantum-entangled SPectrometer using Infra-Red Interference Technology (Q-SPIRIT) platform aims to realize a low Size, Weight, and Power (SWaP) spectroscopy unit for detecting IR-wavelength gas-absorption spectra by leveraging quantum entanglement and interference techniques. We create a source of highly non-degenerate VIS/IR photon pairs via spontaneous parametric downconversion (SPDC). We retroreflect the pump and the photons produced in the first pass back through the crystal, such that the pairs originating from the pump's first or second pass through the crystal are indistinguishable. The pairs interfere, leading to destructive interference, whereby no VIS or IR photons are produced. If an IR-absorbing material is placed in the IR photon's arm of the interferometer, the visibility at the VIS detector will be degraded, causing VIS photons to be produced, an example of quantum interrogation. We detect the visible light using a VIS low-light level spectrometer, quantifying the IR absorption without the need for cryogenically cooled detector. In order to compensate for unbalanced loss or absorption in interfering processes, we also incorporate the quantum eraser effect into our spectroscopy setup by specific polarization control.