Locking optics experiments with a microcontroller

Optics experiments critically require the stable and accurate locking of relative phases between light beams or the stabilization of Fabry-Perot cavity lengths.
We have developped a simple and inexpensive technique based on a stand-alone microcontroller unit to perform such tasks. Easily programmed in C language, this reconfigurable digital locking system also enables automatic relocking and sequential functioning. We have developed Different algorithms and applied to fringe locking and to low- and high- finesse optical cavity stabilization, without the need of external modulations or error signals. We provide here the codes for the ADUC7020.

This techique has been published in
Review of Scientific Instruments 85, 123112 (2014)  arXiv version
Locking a Mach-Zehnder interferometer. (code)
Locking a cavity. (code)


During the Kun Huang’s PhD, we developed a versatile software for quantum state engineering. A general conditional preparation strategy is considered : two arbitrary modes impinge on a tunable beamsplitter and one port is measured. Based on numerical calculations with truncated density matrices, the soft provides the output conditional state. The user can either select typical input states (Fock states, squeezed states,..) and measurements (APD, PNRD, homodyning) or input any density matrices and POVM. Various panels are given: photon number distribution, marginal distributions, Wigner function, fidelity with a targeted state.
Initially programmed in LabView, QMixer can now be run on any computer.

QMixer can be downloaded in Windows version or Mac version. (readme)


Engineering non-classical states of light is a central quest for quantum optics. Beyond their fundamental significance, such states are the resources for implementing a variety of protocols, ranging from enhanced metrology to quantum communication and computing.

Over the recent years, the team has demonstrated very efficient techniques to generate such states with continuous-wave optical parametric oscillators. These sources are based on non-linear crystals inserted inside optical cavities, and can generate pair of photons or squeezed light. Noise reduction by more than 90% (11 dB measured) below the shot noise level has been obtained. By adding to single-photon detections operated by superconducting detectors, Fock states (single photon or two-photon) and optical Schrödinger cat states have also been generated with unprecedented fidelities. The well-controlled spatiotemporal mode in which they are produced will facilitate their use in subsequent protocols where such states need to interfere with other optical resources, e.g. in quantum gate implementations or cascaded state-engineering procedures. 

This is summarized in a video article published in JoVE - Journal of Visualized Experiments.