Tools and Services by and for the GiRyd Community

Digital laser frequency and intensity stabilization based on the STEMlab platform (originally Red Pitaya)

The Birkl group (Technical University of Darmstadt) developed a digital PID controller based on the commerically available FPGA controller 'Red Pitaya (now renamed to STEMlab)'. Details are published in Review of Scientific Instruments 91, 083001 (2020) and design details are available as open source projects on Github (see abstract below):

Tilman Preuschoff, Malte Schlosser, Gerhard Birkl
"Digital laser frequency and intensity stabilization based on the STEMlab platform (originally Red Pitaya)"
Review of Scientific Instruments 91, 083001 (2020)
https://arxiv.org/abs/2009.00343

Abstract:
We report on the development, implementation, and characterization of digital controllers for laser frequency stabilization as well as intensity stabilization and control. Our design is based on the STEMlab (originally Red Pitaya) platform. The presented analog hardware interfaces provide all necessary functionalities for the designated applications and can be integrated in standard 19-in. rack mount units. Printed circuit board layouts are made available as an open-source project (T. Preuschoff et al., https://github.com/TU-Darmstadt-APQ/RedPitaya-Lockbox, 2020 and T. Preuschoff et al., https://github.com/TU-Darmstadt-APQ/RedPitaya-IntStab, 2020). A detailed characterization shows that the bandwidth (1.25 MHz) and the noise performance of the controllers are limited by the STEMlab system and not affected by the supplementary hardware. Frequency stabilization of a diode laser system resulting in a linewidth of 52(1) kHz (FWHM) is demonstrated. Intensity control to the 1 × 10−3 level with sub-microsecond rise and fall times based on an acousto-optic modulator as actuator is achieved.

Pairinteraction - A Rydberg Interaction Calculator

The pairinteraction software simulates systems of one or two Rydberg atoms, taking into account electric and magnetic fields in arbitrary directions as well as multipole interaction up to arbitrary order. The software consists of a high-performance C++ library, a Python3 library as a convenient API, and an easy-to-use graphical user interface for pair potential calculations.

The software is hosted on Github. It can be installed from pre-built binaries or using the Python package manager pip.

Sebastian Weber, Christoph Tresp, Henri Menke, Alban Urvoy, Ofer Firstenberg, Hans Peter Büchler, Sebastian Hofferberth
"Tutorial: Calculation of Rydberg interaction potentials"
J. Phys. B: At. Mol. Opt. Phys. 50, 133001 (2017)
https://arxiv.org/abs/1612.08053

Abstract
The strong interaction between individual Rydberg atoms provides a powerful tool exploited in an ever-growing range of applications in quantum information science, quantum simulation and ultracold chemistry. One hallmark of the Rydberg interaction is that both its strength and angular dependence can be fine-tuned with great flexibility by choosing appropriate Rydberg states and applying external electric and magnetic fields. More and more experiments are probing this interaction at short atomic distances or with such high precision that perturbative calculations as well as restrictions to the leading dipole–dipole interaction term are no longer sufficient. In this tutorial, we review all relevant aspects of the full calculation of Rydberg interaction potentials. We discuss the derivation of the interaction Hamiltonian from the electrostatic multipole expansion, numerical and analytical methods for calculating the required electric multipole moments and the inclusion of electromagnetic fields with arbitrary direction. We focus specifically on symmetry arguments and selection rules, which greatly reduce the size of the Hamiltonian matrix, enabling the direct diagonalization of the Hamiltonian up to higher multipole orders on a desktop computer. Finally, we present example calculations showing the relevance of the full interaction calculation to current experiments. Our software for calculating Rydberg potentials including all features discussed in this tutorial is available as open source.