Doctoral thesis

The main goal of this thesis is to build a rubidium D1 line-resonant squeezed light source capable of overcoming the limitations of the previous system, whose initial squeezing was 2.5 dB (1), which was later improved to 3.2 dB (2). The theoretical prediction by Predojevic suggests that the maximum achievable value is 10 dB (3) and we set this value as our target. The new device will use the same method for squeezing light: spontaneous parametric down-conversion (SPDC) inside an Optical Parametric Oscillator (OPO), since this approach has proven to be the most efficient method for generating squeezed light (4; 5). The following objectives are envisioned:

Optimal choice of the nonlinear medium used for SPDC. χ2 nonlinear coefficient, refractive index, and other material-dependent properties greatly affect system performance, making the selection of an optimal material the first objective. A determining factor in this selection is blue light-induced infrared absorption (BLIIRA), as it poses a detrimental effect in nonlinear media (6; 7). A detailed analysis of the achievable squeezing will be conducted, aiming to maximize it for given values of χ2 and BLIIRA. This will be followed by the selection of a crystal based on the mentioned analysis and currently available technologies.

• Design the resonator geometry. The OPO will operate below threshold in the degenerate regime (8; 9) to produce squeezed vacuum at 795 nm. These requirements, along with the optimal utilization of the pump source, define the geometry of the resonator and the wave-equation description of the beams involved in SPDC, determining the optical components required for beam shaping and transmission to ensure proper oscillation.
• After squeezed-light is obtained, a quantum noise locking system (10) is required to control the level of squeezing. Therefore, the design and implementation of an efficient locking system is a key objective of this work and will require significant effort. A common approach is the use of PID controllers, but the performance of the system could benefit from the use of more advanced techniques such as those found in (11; 12).
• Test the system in an atomic ensemble. Optically Pumped Magnetometers (OPMs) are sensors capable of measuring extremely weak magnetic fields with femtotesla sensitivity (13), making them an ideal test bed for squeezed light. A cell containing isotopically enriched rubidium vapor will be used to induce D1 line atomic transitions and measure the noise reduction achieved by squeezed light, following a procedure similar to (14).