Linien: A versatile, user-friendly, open-source FPGA-based tool for frequency stabilization and spectroscopy parameter optimization

A Versatile Board for Event-Driven Data Acquisition

Event-driven data acquisition is used to capture information from fast transient phenomena typically requiring a high sampling speed. This is an important requirement in the ITER Neutral Beam Test Facility for the development of one of the heating systems of the ITER nuclear fusion experiment. The Red Pitaya board has been chosen for this project because of its versatility and low cost. Versatility is provided by the hosted Zynq System on Chip (SoC), which allows full configuration of the module architecture and the OpenSource architecture of Red Pitaya. Price is an important factor, because the boards are installed in a hostile environment where devices can be damaged by EMI and radiation. A flexible solution for event-driven data acquisition has been developed in the Zynq SoC and interfaced to the Linux-based embedded ARM processor. It has been successfully adopted in a variety of data acquisition applications in the test facility.

Python Red Pitaya Lockbox (PyRPL): An open source software package for digital feedback control in quantum optics experiments

We present the Python Red Pitaya Lockbox (PyRPL), an open source software package that allows the implementation of automatic digital feedback controllers for quantum optics experiments on commercially available, affordable Field-Programmable Gate Array (FPGA) boards. Our software implements the digital generation of various types of error signals, from an analog input through the application of loop filters of high complexity and real-time gain adjustment for multiple analog output signals, including different algorithms for resonance search, lock acquisition sequences, and in-loop gain optimization. Furthermore, all necessary diagnostic instruments, such as an oscilloscope, a network analyzer, and a spectrum analyzer, are integrated into our software. Apart from providing a quickly scalable, automatic feedback controller, the lock performance that can be achieved by using PyRPL with imperfect equipment, such as piezoelectric transducers and noisy amplifiers, is better than the one achievable with standard analog controllers due to the higher complexity of implementable filters and possibilities of nonlinear operations in the FPGA. This drastically reduces the cost of added complexity when introducing additional feedback loops to an experiment. The open-source character also distinguishes PyRPL from commercial solutions, as it allows users to customize functionalities at various levels, ranging from the easy integration of PyRPL-based feedback controllers into existing setups to the modification of the FPGA functionality. A community of developers provides fast and efficient implementation and testing of software modifications.

Field-programmable-gate-array-based digital frequency stabilization of low-phase-noise diode lasers

We present the comparison of a field-programmable-gate-array (FPGA) based digital servo module with an analog counterpart for the purpose of laser frequency stabilization to a high-finesse optical cavity. The transfer functions of both the digital and analog modules for proportional-integral-derivative control are measured. For the lasers stabilized to the cavity, we measure the singe-sideband power spectral density of fast phase noise by means of an optical beat with filtered light transmitted through the cavity. The comparison between the digital and analog modules is performed for two low-phase-noise diode lasers at 1120 and 665 nm wavelengths. The performance of the digital servo module compares well to the analog one for the lowest attained levels of 30 mrad for the integrated phase noise and 10-3 for the relative noise power. The laser linewidth is determined to be in the sub-kHz regime, only limited by the high-finesse cavity. Our work exploits the versatility of the FPGA-based servo module (STEMlab) when used with open-source software and hardware modifications. We demonstrated that such modules are suitable candidates for remote-controlled low-phase-noise applications in the fields of laser spectroscopy and atomic, molecular, and optical physics.

Multiplexed random-access optical memory in warm cesium vapor

The ability to store large amounts of photonic quantum states is regarded as substantial for future optical quantum computation and communication technologies. However, research for multiplexed quantum memories has been focused on systems that show good performance only after an elaborate preparation of the storage media. This makes it generally more difficult to apply outside a laboratory environment. In this work, we demonstrate a multiplexed random-access memory to store up to four optical pulses using electromagnetically induced transparency in warm cesium vapor. Using a Λ-System on the hyperfine transitions of the Cs D1 line, we achieve a mean internal storage efficiency of 36% and a 1/e lifetime of 3.2 µs. In combination with future improvements, this work facilitates the implementation of multiplexed memories in future quantum communication and computation infrastructures.