Phase sensitive amplifiers (PSAs) are gaining attention for their ability to mitigate noise limitations in amplification. They also offer advantages such as optical phase and amplitude regeneration, dispersion compensation, and improved imaging and sensing performance. Traditionally, PSAs have primarily relied on third-order nonlinearities (χ3) which involves four-wave mixing (FWM) for their operation. However, second-order nonlinearities (χ2) are stronger but have been less utilized in semiconductor-based PSAs due to challenges in effectively phase matching the interacting waves and countering two-photon absorption of the pump. Although, this second-order nonlinear (χ2) approach provides numerous benefits such as immunity to stimulated Brillouin scattering, larger nonlinear coefficient, better pump filtering, low noise, low cross talk, and no intrinsic frequency chirp.

Experimental setup

PSA in-phase gain measured as a function of external pump power

These benefits can be achieved by employing an efficient phase matching approach and utilizing a pulsed pump in an AlGaAs Bragg reflection waveguide. It demonstrates impressive on-chip in-phase gain of nearly 30 dB and a sensitivity of 0.005 photons per pulse. Additionally, its performance approaches the theoretical minimal noise figure of 0 dB. Importantly, the PSA operates in the single-mode regime, holds promise for the advancement of on-chip quantum circuits.

PSA gain measured as a function of wavelength

The noise figure (NF) as a function of amplifier gain

In conclusion, this development represents a significant step forward in leveraging second-order nonlinearities for semiconductor-based PSAs, with potential applications in both classical and quantum on-chip signal processing, as well as optical communication systems.

https://doi.org/10.1364/OPTICA.446674

Light Detection and Ranging (LiDAR) systems often struggle with noise, which can degrade the accuracy and reliability of the generated maps. However, Quantum-enhanced LiDAR systems hold promise for overcoming these limitations. By exploiting quantum phenomena such as entanglement and quantum superposition, these techniques can provide higher resolution, better sensitivity, and improved noise resilience compared to classical imaging method.

Experimental setup

Optics for LiDAR demonstration

Experimental measurement demonstrated that these quantum effects provide quantum lidar systems with a noise resilience advantage of over 40dB, making them highly promising for applications requiring precise measurements in noisy environments. However, the quantum-enhanced LiDAR system based on time-frequency entanglement demonstrates a remarkable 43dB higher signal-to-noise ratio (SNR) compared to a classical phase-insensitive quantum imaging system. This higher SNR indicates that the quantum-enhanced system can provide clearer and more accurate imaging results, even in noisy environments.

Signal-to-noise ratio for varying noise power

Signal-to-noise ratio for varying probe power

Hence, these advancements pave the way for the widespread adoption of quantum-enhanced imaging technologies in various applications, including non-reflecting target imaging in noisy environments.

https://doi.org/10.1038/s41467-022-33376-9