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  1. Ferdinand-Braun-Institut
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  4. Nonlinear Quantum Optics

Nonlinear Quantum Optics

Our Joint Lab Nonlinear Quantum Optics researches and develops concrete applications of quantum light for photonic quantum sensing and quantum communication. To this end, we use methods of generating and converting quantum light based on nonlinear optics and focus on various application-relevant topics:

  • Mid-infrared (MIR) sensing with entangled photons
  • Photon-pair sources for quantum communication
  • Converter modules for quantum communicatio
The illustration shows scientific representations, including a graphic presentation with colorful rings and a screen. Further sections show microscope images with different magnifications and a diagram depicting absorption over wave numbers.
We use undetected photons for imaging purposes, such as hyperspectral microscopy (medical diagnostics) and MIR spectroscopy in environmental analysis (gas and microplastic analysis).
The image shows a microscopic view of a semiconductor chip with fine lines and structures. The embedded detail illustrates a process for manufacturing or analyzing these structures.
Our sources for quantum communication are based on integrated nonlinear optics in semiconductors. Semiconductor waveguides such as AlGaAs, GaAs, or InGaP enable ultra-bright SPDC sources with more than 10 GHz photon pairs per milliwatt pump power. They can be mass-produced and easily integrated with other photonic and optoelectronic elements such as pump lasers and frequency filters.
The image shows a schematic diagram of an optical system that includes a cw 1064 nm laser, a monolithic ppKTP resonator, and various components such as an isolator, oven, and temperature controller. The main components are arranged for wavelength conversion and system monitoring.
Quantum frequency conversion converts single photons from NV centers in diamonds into telecommunications wavelengths, combining high efficiency (>70% intrinsic) with low noise. The converter uses a thermally self-stabilizing monolithic ppKTP resonator pumped by a low-cost, commercially available 3 W 1064 nm Nd:YAG laser.

Mid-infrared (MIR) sensing with entangled photons

The goal is to completely circumvent technological hurdles for classical MIR sources and MIR detectors by using the quantum measurement principle of “sensing with undetected photons.” For our approach, we only need lasers and detectors in the visible and near-infrared range. This enables compact, robust, and cost-efficient solutions that can be used, among other things, in hyperspectral microscopes for medical diagnostics, for MIR spectroscopy in environmental analysis (gas and microplastic analysis), and for 3D imaging using optical coherence tomography in the MIR spectral range (MIR-OCT) for 3D imaging, for example within highly scattering ceramics. Demonstrators developed at the FBH thanks to its many years of expertise in micromodule construction are used to validate the practical suitability of these quantum technology approaches.

Sources for quantum communication

High-efficiency photon pair sources play a key role in entanglement-based quantum key distribution (QKD). The requirements include the highest possible pair-rate, full telecommunications-band coverage for wavelength multiplexing, with simultaneously low pump power requirements. We are researching suitable new approaches using semiconductor waveguides based on AlGaAs, GaAs, or InGaP, among others. Important factors here are the extremely high optical nonlinearities of these materials and the possibility of co-integrating the pump laser on the same chip. We are pursuing the goal of scalable, high-performance pair sources for large-scale QKD deployment in close collaboration with the institute’s optoelectronics department.

Converters for quantum communication

In quantum repeater networks, photons must be converted between different wavelength ranges while preserving their entanglement. To enable low-loss distribution of these photons in fiber optic networks, we are developing highly efficient, low-noise converter modules optimized specifically for entangled photons from diamond defect centers, based on monolithic ppKTP resonators.

The Joint Lab Nonlinear Quantum Optics is run jointly with the Nonlinear Quantum Optics (NIQO) working group at the Department of Physics at Humboldt-Universität zu Berlin.