The Red Pitaya [1] is an affordable (<; 250 Euros) field-programmable gate array (FPGA) board with fast analog inputs and outputs (sampled at 125 MHz). This makes it useful for quantum optics experiments, in particular as a digital feedback controller for analog systems. Based on the open source software provided by the board manufacturer, we have created the software package PyRPL [2] (Python RedPitaya Lockbox) which implements many devices that are needed for optics experiments with the Red Pitaya. The user interface and all high-level functionalities are written in Python, but an essential part of the software is contained in a custom FPGA design written in the hardware description language (HDL) Verilog. The HDL part of PyRPL implements various digital signal processing (DSP) modules: a two-channel oscilloscope for measurement and diagnostics; two arbitrary function generators for waveform synthesis and noise generation; four proportional-integral-derivative (PID) controllers with up to fourth-order filters for feedback control; three demodulation modules for the generation of Pound-Drever-Hall-like error signals and the realization of narrow, phase-tunable band-pass filters; an infinite impulse response (IIR) filter able to realize transfer functions with up to 24 poles and 24 zeros; a network analyzer for the characterization of analog and digital systems and in-loop tuning of feedback parameters; a spectrum analyzer for the measurement and minimization of noise in closed-loop systems.
The Red Pitaya [1] is an affordable (<; 250 Euros) field-programmable gate array (FPGA) board with fast analog inputs and outputs (sampled at 125 MHz). This makes it useful for quantum optics experiments, in particular as a digital feedback controller for analog systems. Based on the open source software provided by the board manufacturer, we have created the software package PyRPL [2] (Python RedPitaya Lockbox) which implements many devices that are needed for optics experiments with the Red Pitaya. The user interface and all high-level functionalities are written in Python, but an essential part of the software is contained in a custom FPGA design written in the hardware description language (HDL) Verilog. The HDL part of PyRPL implements various digital signal processing (DSP) modules: a two-channel oscilloscope for measurement and diagnostics; two arbitrary function generators for waveform synthesis and noise generation; four proportional-integral-derivative (PID) controllers with up to fourth-order filters for feedback control; three demodulation modules for the generation of Pound-Drever-Hall-like error signals and the realization of narrow, phase-tunable band-pass filters; an infinite impulse response (IIR) filter able to realize transfer functions with up to 24 poles and 24 zeros; a network analyzer for the characterization of analog and digital systems and in-loop tuning of feedback parameters; a spectrum analyzer for the measurement and minimization of noise in closed-loop systems.
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.
We present PyRPL, an open source software package that allows the implementation of automatic digital feedback controllers for quantum optics experiments on commercially available, affordable 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.
In this paper, we present NQontrol, a digital feedback-control solution based on the ADwin platform that delivers eight simultaneous feedback loops running with 200 kHz sampling frequency and offers five second-order filtering sections per channel for flexible shaping of the feedback loop. With this system, we demonstrate a Pound-Drever-Hall lock of an optical resonator and compare its performance to an analog reference implementation. A comprehensive support package written in Python, together with a web-based graphical user interface, makes the system quick to setup and easy to use, while maintaining the full flexibility of open-source platforms.
Modern experiments with fundamental quantum systems - like ultracold atoms, trapped ions, and single photons - are managed by a control system formed by a number of input/output electronic channels governed by a computer. In hybrid quantum systems, where two or more quantum systems are combined and made to interact, establishing an efficient control system is particularly challenging due to the higher complexity, especially when each single quantum system is characterized by a different time scale. Here we present a new control apparatus specifically designed to efficiently manage hybrid quantum systems. The apparatus is formed by a network of fast communicating Field Programmable Gate Arrays (FPGAs), the action of which is administrated by a software. Both hardware and software share the same tree-like structure, which ensures a full scalability of the control apparatus. In the hardware, a master board acts on a number of slave boards, each of which is equipped with an FPGA that locally drives analog and digital input/output channels and radiofrequency outputs up to 400 MHz. The software is designed to be a general platform for managing both commercial and home-made instruments in a user-friendly and intuitive graphical user interface. The architecture ensures that complex control protocols can be carried out, such as performing of concurrent commands loops by acting on different channels, the generation of multi-variable error functions, and the implementation of self-optimization procedures. Although designed for managing experiments with hybrid quantum systems, in particular with atom-ion mixtures, this control apparatus can in principle be used in any experiment in atomic, molecular, and optical physics.
In this paper we present a flexible, high-performance, integrated qubit control system using modular PXIe equipment. To manipulate qubits, a classical control system is required to generate and acquire a mix of baseband, radio frequency, and/or optical signals, with the specific mix different for each qubit technology. Typically, a quantum system requires many of these signals with a high degree of synchronization and phase coherence, and increasingly needs real-time data processing and on-the-fly sequencing capabilities for feedback experiments. The proposed system is scalable to hundreds of channels, all of them being phase coherent and fully time-synchronized.The system includes a programmable real-time sequencer for precise execution timing and decision making; and open FPGA capabilities for custom Digital Signal Processing (DSP) by hardware. Using the latter, we present FPGA IP to generate one-/two-qubit gates efficiently with the AWG, and to analyze high-frequency signals to measure the qubit states in real time on the digitizers. This IP features very low latencies for Quantum Error Correction (QEC) and Frequency Division Multiplexing (FDM) capabilities, among others.
Optical atomic clocks utilizing strontium are the gold standard of timekeeping. Generating entanglement by spin-squeezing has the potential to continue pushing the limits of clock stability below the fundamental performance limit for unentangled ensembles, the standard quantum limit (SQL). One way to do so is by using an optical cavity to transduce interactions between the atoms and to improve the cavity readout, one needs to minimize the noise of the stabilized cavity length. Noise in a control loop can arise from many different sources, including mechanical resonances of the piezo (PZT) used to control the cavity length, so addressing this noise can improve clock stability and maximize the capabilities of quantum sensing. For this project, I measured the transfer function of the piezo-cavity system, inverted this transfer function, and extracted the poles and zeros. I then programmed this tailored digital filter on a Red Pitaya using an open-source Python package, PyRPL. Challenges still remain with the device implementation into the control loop, but afterwards this would ultimately contribute to improved clock precision and attain better spin-squeezing generated by the cavity.