| Abstract [eng] |
In the present master’s thesis, we demonstrate how quantum light can be used for spectroscopy. We propose two schemes that allow one to use advanced filtering technology at one frequency band (Telecomm window around 1550 nm) to perform high-resolution frequency measurements at another frequency band (810 nm) where this technology is not commercially available. In the first scheme we show, in a proof of concept experiment, that this can be achieved by measuring the coincidences between highly frequency-entangled signal/idler photon pairs generated via spontaneous parametric down-conversion (SPDC). We performed two measurements, in the first one we measured the spectral shape of a filter (Semrock) centered at 810 nm using a narrowband filter at 1550 nm. The bandwidth measured by the filter (FWHM) was 2.75 nm, which is within the margin of error provided by the manufacturer. In the second measurement, we designed and measured filters with arbitrary shapes, designed using a programmable filter at 1550 nm. The shape of the filters was measured using a monochromator centered at 810 nm. The shape of the filters and the different levels of attenuation were successfully retrieved. These experiments show the versatility of the method considered and the possibilities that arbitrary spectral shaping offers for spectroscopy at any frequency band, where key optical elements might not exist. Notwithstanding, the heart of the first scheme is the measurement of coincidences between signal and idler photons for which good optical detectors (sensitive enough) at both frequency bands are fundamental. The second scheme considered avoids this limitation and allows doing absorption spectroscopy at the idler wavelength range without making any measurement at this wavelength. All measurements are made at the signal wavelength range where advanced technology exists. The key element of this second scheme is a SU(1,1) interferometer. In the second part of the project, we demonstrate theoretically that the use of SU(1,1) interferometers for quantum spectroscopy is a step forward compared with spectroscopy based on the use of direct quantum correlations of pairs photons generated in SPDC. We showed that filters with arbitrary shapes can be easily recovered in both the high and low parametric gains. We showed, with the derivation of simple expressions and some examples, that in the high parametric gain regime, the photon fluxes generated are higher, so measurements can be faster (shorter detection times), and the optical detectors used can show lower sensitivity. |
