Edition Q2/2019

Overview

Welcome to the Q2/2019 newsletter!

Enjoy our latest summary of news and know-how from the applications that we serve:

Quantum Technologies

Lock-in Amplifiers

Impedance

Company & Community

We hope that you enjoy reading and wish you all a happy and productive summer time.

And don't forget - feel free to provide us with your feedback regarding the newsletter. What do you like? Where can we improve?

Best wishes from Zurich!

Application note: Bell state preparation of superconducting qubits

Learn how the Quantum Device Lab at ETH Zurich, Switzerland, controls their 4-qubit experiment using the Zurich Instruments High-Density AWG (HDAWG) and Ultra-High Frequency Quantum Analyzer (UHFQA) to generate Bell states.

Get started here.

3 journeys to single spin detection

Rendering view of membrane AFM optical detection with nanoparticle spin probing. Image courtesy of Alexander Eichler, ETH Zurich.

At the most recent Zurich Instruments User Meeting, we had the chance to host 3 great contributors to the nano-MRI community (i.e. Magnetic Resonance Imaging at the nanoscale), namely Professors Christian Degen, Martino Poggio and Tjerk Oosterkamp.

Their 3 inspirational stories began 10 years ago at IBM Almaden with Dan Rugar but after that each took a very different route to get remarkably close to the grand goal of 3D magnetic resonance imaging with atomic resolution (D. Rugar et al., 2004).

Starting with a common Magnetic Resonance Force Microscopy (MRFM) toolkit - a magnetically sensitive tip with high force sensitivity, a MW source and a scanning sample - they reached breakthroughs with 3 different techniques:

1. ETH Zurich, Eichler/Degen’s inverted AFM: membrane based AFM promises to achieve high force sensitivity due to Q factor well above 100 million (Y. Tsaturyan et al., 2017). Instead of a vibrating tip, the sample membrane acts as the sensor with reduced loss. Two specially extended vibrational modes can be parametrically coupled to the flipping of the nuclear spin at the difference of these 2 frequencies, thus requiring frequency modulation techniques over 2 PLLs (W. M. Dougherty et al., 1996). This approach, focused on the sample, allows for more geometrical flexibility to add an interferometric cavity in the same measurement.
   
2. University of Basel, Poggio’s focus on the tip: a cantilever with low stiffness is needed for good force sensitivity, but this requires complex nanofabrication and has low mechanical resonance frequencies, exposing the measurement to 1/f noise. Scaling the mechanical element down to a nanowire transducer yields high sensitivity combined with high-frequency operation. Magnetic tips can also be integrated into the growth process. Because of the nearly perfect cross-sectional symmetry of a nanowire, flexural resonance modes are nearly degenerate, allowing for 2D force mapping. (N. Rossi et al., 2017; N. Rossi et al., 2019)
   
3. University of Leiden, Oosterkamp’s focus on ultra-low temperature: when it comes to ultimate force sensitivity, all key parameters of a sensor are worth tuning, and temperature is one way to significantly reduce noise. Challenges on the way are enormous because all parts of the MRFM experiment must be redesigned to minimize heat production. Measurements are slow and require a small PLL bandwidth to pick up the smallest changes in force (M. de Wit et al., 2019).

Ultimately, the common thread in these journeys is the resonance enhancement technique where the measure of the smallest frequency shift (or dissipation) of a mechanical resonator, coupled with a magnetically actuated nano object, leads to the smallest volume element with a single spin inside. Current state-of-the-art force sensitivity is limited to 1000 nuclear spin per voxel. We are happy that the MFLI and HF2LI platforms, with their PLL modules, are part of this exciting research, making contributions in the grand scheme of such complex experiments.

Interview: Ying He

Ying He researches novel trace gas detection techniques at the Harbin Institute of Technology, China

Y. He, Y. Ma, Y. Tong, X.Yu, and F. Tittel, "Ultra-high sensitive light-induced thermoelastic
spectroscopy sensor with a high Q-factor quartz
tuning fork and a multipass cell
" in Optics Letters, Vol. 44, Issue 8, 2019.

Y. Ma, Y. Tong, Y. He, X. Jin, and F. Tittel, "Compact and sensitive mid-infrared all-fiber quartz-enhanced photoacoustic spectroscopy sensor for carbon monoxide detection" in Optics Express, Vol. 27, Issue 6, 2019.
Hello Ying He, can you introduce yourself and your group?

I am a second-year Ph.D. student at the National Key Laboratory of Science and Technology on Tunable Laser, Harbin Institute of Technology, China. Under the supervision of Prof. Xin Yu and Yufei Ma, I focus on exploring novel trace gas detection techniques, such as Tunable Diode Laser Absorption Laser Spectroscopy (TDLAS), Photoacoustic Spectroscopy (PAS), and Quartz-Enhanced Photoacoustic Spectroscopy (QEPAS). Our group has worked on laser-based trace gas sensors for years. Prof. Ma brought the techniques to our group after his stay in Prof. Frank K. Tittle’s group at Rice University.

What are the principles of TDLAS/PAS/QEPAS, and what are potential applications?

PAS/QEPAS evolved from TDLAS, and the underlying principles are similar; it measures the absorption of light passing through a gas chamber. Wavelength-tunable light sources allow us to investigate the absorption spectroscopy. The fingerprints in the spectroscopy indicate the presence and the concentration of certain species. In order to achieve better signal-to-noise ratio, especially to avoid 1/f noise, we modulate the laser current in the kilohertz range, and demodulate the signal by using the harmonic detection method.

These techniques enable real-time trace gas monitoring and quantification. They could be applied in various fields, such as environmental monitoring, combustion field analysis, and medical diagnostics. They’re used, for example, in sensing atmospheric pollutants, measuring the concentration of methane in underground coal mines, identifying hazardous gases in automobile exhaust fumes, and analyzing the combustion field of rocket engines.

What is the role of the MFLI in your TDLAS/QEPAS systems? How does it make your life easier?

The MFLI is far more than just a lock-in amplifier – the test and measurement tools that come along with it are game-changers. Using the MFLI and LabOne, we can easily generate the modulated signal for the light source, demodulate the response of the photodetector/quartz tuning fork, and stream the results to the computer. In our QEPAS system, the MFLI is also used to obtain the frequency response of the quartz tuning fork, from which we fit the resonance frequency and Q-factor, using built-in functionality. This can be done very neatly with the Sweeper tool. The Sweeper sweeps any parameter of the drive signal in the experiment, not just the frequency; sweeping the amplitude and offset voltage is also extremely useful. We use the amplitude sweep to optimize the modulation depth in our experiments, and the offset voltage for wavelength tuning.

The MFLI’s oscilloscope is helpful when troubleshooting – I can examine any signal in the box, which helps to quickly identify the cause of any issues. I can also use the Plotter’s analysis tools to measure the peaks, noise floor, and signal statistics such as the average and standard deviation. All of these features help speed up the tuning process, and take the tediousness out of optimization. Thanks to the toolset, I don’t need to do any programming, and the amount of data saved for offline analysis is reduced significantly.

What have you achieved so far? What’s your favorite piece of work?

I have co-authored a few publications in some leading journals, such as Sensors and Actuators B, Applied Physics Letters, Optics Express, as well as proceedings in the Conference on Lasers and Electro-Optics (CLEO). My favorite piece is our recent report on Light-Induced Thermo-Elastic Spectroscopy (LITES) sensors. Conventionally, a quartz tuning fork in the QEPAS system functions as an acoustic wave detector. The detector is in contact with the gas under test. The gas may consist of corrosive elements, vapor, and other impurities, which can reduce the lifetime of the detector: the vapor and impurities can condense on the detector surface, which leads to instability and even failure. The LITES utilizes a novel mechanism to avoid this scenario, using light rather than acoustic waves. After passing through an isolated gas cell, the light is absorbed by the quartz tuning fork; this induces thermal elastic expansion, which in turn induces a piezoelectric signal in the tuning fork. This means that the turning fork doesn’t have to be in contact with the gases themselves, and can be placed outside of the gas cell. In our report, we experimentally demonstrate the function of LITES sensor for the first time. The detection sensitivity is better than conventional TDLAS and QEPAS by a factor of 5 to 20.

The LITES technique is nominated for ‘China’s Top 10 Optical Breakthroughs’ in 2019.

How did you come up with the LITES method?

Our group has conducted research on quartz-based gas sensors for years, so we have a lot of experience, and are constantly searching for novel approaches. Together with my supervisors, I did a thorough literature review on the use of quartz tuning forks, and found that they’re widely used in scanning probe microscopy (SPM), gyroscopes, and displacement sensors. It was reported in the SPM community that the incident radiation was able to actuate a quartz tuning fork, which was attributed to radiation pressure. We were inspired by the idea, and were curious whether it was possible to harness this effect for other uses. We collected some preliminary data and found that, in principle, it worked, but wasn’t in line with the radiation pressure theory. After a systematic investigation, we figured out that the response of the quartz tuning fork is better described by the light-thermo-elastic conversion mechanism. We proposed the LITES technique and did a benchmark against conventional TDLAS and QEPTAS techniques; we found that the LITES outperformed the conventional methods by a large margin.

What is your ongoing work about?

There are still open questions about the LITES technique. Our ultimate goal is to increase the detection limit of LITES. We’re working on enhancing its performance by optimizing the parameters overlooked in our previous work. We’re also considering how to adapt it to industry applications, which may result in a commercial product.

What are your interests outside of your lab?

I like listening to music, swimming, cycling, and other outdoor sports. I also like playing with aeromodelling, especially maneuvering fixed-wing planes.

Blog post: Frequency-domain response of lock-in filters

Are you curious about the spectral response of demodulator filters inside lock-in amplifiers and how to measure them? Are you wondering how the time constant of demodulation filters relates to their 3-dB and noise-equivalent power (NEP) bandwidths for various filter orders? In Mehdi’s recent blog post, you will find analytical formulas to obtain 3-dB and NEP bandwidths in terms of time constant for any filter order. Moreover, you will see how to measure the filter response using the sweeper module of LabOne user interface. In the end, measurement and theory demonstrate an impressive agreement.

Application note: 2D nanomechanical force field sensing with SiC nanowires

Have you considered using nanowires as sensors and the HF2LI for measurement enhancement in scanning probe microscopy?

In the Olivier Arcizet's group at Institut Néel Grenoble, the HF2PLL dual phase-locked loop is used to track two nearly orthogonal vibrational modes of a SiC nanowire and record 2D force fields on the nanoscale. With this highly sensitive method, imaging of Casimir forces or weak magnetic structures like Skyrmions might be within reach.

Get started here.

Application note: Noise reduction by parallel cross-correlation measurements

Did you know that when the device’s intrinsic noise is lower than that of the measurement apparatus, two lock-in amplifiers can do better than one?

By using two MFLI Lock-in Amplifiers on a sensitive SQUID device, Michael Thompson and Jonathan Prance from the University of Lancaster, UK lowered the noise floor by a factor of 10, to 0.3 nV/√Hz. They made two simultaneous independent measurements and calculated the cross-correlation of their outputs. By averaging measured signals uncorrelated noise is attenuated, while persistent signals that are correlated are preserved. Find out more about this generic method in the new Application note titled Noise reduction by parallel cross-correlation measurements.

Get started here and let us know what you think!

Blog post: Measuring low ESR & ESL with the MFIA

In the latest impedance blog, Tim Ashworth demonstrates how the MFIA Impedance Analyzer can be used to measure the equivalent series resistance (ESR) and equivalent series inductance (ESL) of a commercially available DC-Link capacitor down to levels unattainable with standard impedance analyzers.

DC-Link capacitors are typically used in power-inverters, for example in electric vehicles. Increased ESR will lead to unwanted power losses and the ESL leads to unwanted voltage spikes when switching. Reducing both ESR and ESL is of high importance when optimizing these critical components. Using the MFIA and a custom low-ESL fixture, along with careful fixture compensation, we demonstrate a very low baseline and repeatable measurements of ESR and ESL for the three different sets of electrodes of the DC-Link capacitor. The measured values for ESR 0.7 mΩ, and 9.5 nH for ESL agree with, and confirm the manufacturer's stated values. Read more about these measurements here.

Student travel grants: apply by June 30, 2019

The submission deadline for our annual Zurich Instruments Student Travel Grants award is just around the corner. Don't miss your chance to be one of the 3 winners of 1'500 Swiss Francs each.

The ground rules are simple - do you have a paper mentioning one of Zurich Instrument's products and are you a PhD student or PostDoc researcher? Then apply before June 30, 2019. For more details, click here!

3rd SPM Zurich Instruments User Meeting

"Jamais 2 sans 3", as the French say, where number three works a charm. At the 3rd SPM User Meeting, which we conducted in our home city with our hosts from the ETH Zurich - Prof. Christian Degen and Alex Eichler - more users than ever before joined us to share their experiences using Zurich Instruments!

Read Romain Stomp's blog, where he shares his impressions, provides links to materials presented at the meeting and other useful resources.

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