In this blog post we want to present a lesser known but very powerful LabOne® tool freely available to all Zurich Instruments users: multi-device synchronization (MDS).
Although all Zurich Instruments lock-ins and impedance analyzers are equipped with multiple demodulators either natively or through upgrade options, and most instruments have multiple physical channels, you may find yourself needing more than two physical inputs or 8 AWG outputs to cover your requirements. In that case, simply adding more instruments addresses the problem but also adds complexity without the infrastructure to synchronize them effectively.
The LabOne multi-device synchronization functionality handles this complexity: it provides clock synchronicity while aligning in time sampling rates and time stamps across up to 8 instruments. With this, all measurement data recorded from any of the synchronized devices is perfectly aligned in time, greatly simplifying its post-processing.
This alignment is not only available at the instruments' inputs: MDS provides sample-wise synchronization of all output channels and, with arbitrary waveform generators (AWGs), an AWG linked mode that gives you control over multiple AWG channels from a single sequencer program.
Most Common Applications for MDS
There are many situations that require the simultaneous measurement of many physical signals, for instance when characterizing a multi-port network: a test signal is injected in one of the ports and the others are measured. If the test signal's frequency is swept, the full transfer functions can be acquired. In many situations this measurement is possible with only one measurement instrument by measuring each port in series, but at a significant cost in time.
Other common applications that benefit from MDS for measurements include multi-point impedance measurements in microfluidics, nuclear magnetic resonance and multi-sensor measurement systems.
One example of the latter is the Hall effect measurement, used for material characterization and magnetic field sensing. This application page describes the technique and shows how it can be performed using 2 MFLI Lock-in Amplifiers linked through MDS; this application note (written in collaboration with the Quantum Optoelectronics group at the ETH Zurich) goes into even more details about it. It also shows how 2 MFLIs were used to measure the quantum Hall effect of a sample, with one of them providing the driving current and measuring the transverse (Hall) voltage and the other one measuring the longitudinal voltage (see Figure 1, taken from the application note). MDS allows to perform the two measurements in parallel and associate immediately the values of the two voltages and the driving current to each other.
Figure 1. Configuration to measure the Hall effect using 2 MFLI Lock-in Amplifiers synchronized with MDS.
Another use for MDS is to perform cross-correlations on the measured signal to improve its signal-to-noise ratio and enable sensitive measurements of very small signals. The technique is discussed in detail in this blog post using a single UHFLI Lock-in Amplifier, while this application note shows how to implement the technique using two MFLI Lock-in Amplifiers synchronized through MDS. Both implementations show a decrease of the noise floor level by an order of magnitude or more. The application note, written by a research group at Lancaster University, demonstrates the characterization of the noise in a superconducting quantum interference device (SQUID). This measurement would be extremely challenging without MDS, as the input noise of any commercial lock-in amplifier is higher than the noise floor of the SQUID, measured at 0.5 nV/√Hz. By probing the SQUID simultaneously with 2 MFLI Lock-in Amplifiers linked through MDS and averaging the cross-correlated spectra, the authors were able to reduce their input noise well below this value, making the measurement possible (see Figure 2).
Significantly, cross-correlation has a stronger effect in the frequency region most affected by the 1/f noise, enabling very sensitive measurements at low frequencies.
Figure 2. SQUID noise measurement comparison: in red the single channel spectrum and in black the cross-correlated one. Both measurements were averaged 105 times
So far, we have seen how MDS can be used to synchronize multiple input channels of Zurich Instruments' lock-in amplifiers, boxcar averagers and impedance analyzers, but this tool can also be used to synchronize the outputs of up to 8 of our arbitrary waveform generators for applications such as phased-array radars or multi-qubit quantum computing. As the HDAWG Arbitrary Waveform Generator has up to 8 channels, you can build a system with up to 64 sample-synchronized AWG channels with MDS. As each platform has its own cable configuration for MDS, please refer to the diagrams on the MDS page for further details.
MDS and LabOne
MDS is available both through the LabOne APIs, for easy implementation in your own code, and in the LabOne user interface. The latter provides a simple set-up interface and a schematic that shows the correct cable configuration for your instruments.
The advantages of MDS in performing measurements are not limited to the synchronization of the instruments: LabOne tools such as the Sweeper, Data Acquisition, Plotter and Spectrum acquire new functionality with MDS, allowing them to visualize and save the data streams coming from all linked instruments as if they came from a single one, thus removing the need to post-process the data to realign it.