Zurich Instruments Test & Measurement Newsletter - Edition Q4/2021

Accurate noise characterization is essential for many applications, especially when dealing with low-noise components and devices. In this blog post and through a hands-on example of thermal noise measurement, Mehdi Alem shows how to obtain the noise spectral density of a sample using the frequency sweeper tool offered by our lock-in amplifiers. The accompanying mathematical description discussed in the post helps you better understand the technique and avoid inaccurate results due to miscalculations.

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From the Archives: All about noise

We recently redesigned our company blog to provide you with a more enjoyable reading experience that also allows you to browse related blog posts and webpages more easily.

With this redesign came the idea of highlighting a complex topic that features often in our archives – noise. How to characterize, understand and tame the noise affecting the quality of laboratory measurements is relevant to most if not all of our customers: here are some resources covering different aspects of noise which we hope will inspire and help you.

Basics of signal analysis: In this blog post, Mehdi Alem writes about the relation between the noise of signal amplitude and phase and the noise of in-phase and quadrature components of the signal.

Input noise: Are you using one of our instruments in the laboratory and wondering how to measure the input noise level of your lock-in amplifier? Wei Yu's blog post answers exactly this question for the MFLI Lock-in Amplifier.

Low-pass filter settings: One of the central elements of any lock-in amplifier is the low-pass filter. To learn how to set this element appropriately to best reject noise in your measurements, watch this step-by-step video by Claudius Riek.

Noise and applications – Cross-correlation technique: If you rely on ultra-sensitive voltage measurements to characterize your quantum devices, this blog post by Jitesh Srinivas shows how cross-correlating the acquired signals can improve the signal-to-noise ratio (SNR).

Noise and applications – Optical imaging: In this blog post, Claudius Riek focusses on laser-scanning microscopy to discuss what can be done at the electronics level to increase the SNR with a lock-in amplifier.

Auto-ranging is one of the key features of all impedance analyzers, as it ensures a smooth sweep in most use cases. When the noise in your measurement setup is considerable, however, you may want to take advantage of some degree of manual control to adjust the ranging steps. In this blog post, Meng Li explains how you can achieve this with current zone ranging, a new feature available in the LabOne^® 21.08 release.

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Can you tell us about your journey as a researcher?

I started my academic career as a mechanical engineer at Hanyang University in South Korea. When I was a third-year undergraduate student, I took a course in electrical engineering for mechanical engineers where I was exposed to the field of micro-electromechanical systems (MEMS) for the first time. This field excited me because of how nanoscale and microscale force interactions significantly influence the dynamics of the mechanical devices. This experience then led me to study quantum mechanics, electrodynamics and condensed matter physics, which are all essential to understand nanoscale physics. With this background I moved to ETH Zurich in Switzerland for a master’s degree in Micro and Nanosystems, where I had fantastic opportunities to study and gain research experience on a wide range of nanoscale physics phenomena and devices. Once I completed my master’s degree, I joined the group of Prof. Chiara Daraio (now at Caltech in the USA) at ETH Zurich as a PhD student in Mechanical Engineering. During my PhD I worked on the development of micro and nanoscale phononic metamaterials by employing nano-electromechanical systems (NEMS) as a platform. Based on these NEMS metamaterials, we achieved the electrical tuning of elastic wave propagation and the experimental realization of nanomechanical topological insulators operating at radiofrequencies.

Following my PhD, I stayed at Caltech as a postdoctoral researcher for 6 months and I then came back to South Korea for personal reasons. My experience with nanofabrication and NEMS devices and my personal interest in quantum mechanics led me to work on superconducting electromechanical devices as a senior research scientist at the Quantum Technology Institute of the Korea Research Institute of Standards and Science (KRISS), which I joined in 2020.

Could you tell us a bit more about the research group where you currently work at KRISS?

The Quantum Technology Institute of KRISS is led by Dr. Heesu Park. At this institute, we develop a variety of quantum technologies based on single photons, ultracold atoms, NV centers, spintronics, and superconducting quantum circuits. I work in the Quantum Nanomechanics Team led by Dr. Junho Suh: our team studies and develops various types of hybrid quantum devices based on superconducting microwave circuits, NEMS, optomechanical systems, and novel nanomaterials. Some examples of our recent research activities include nanomechanical measurements of quantum interference in a topological insulator-nanowire and niobium-based superconducting nanoelectromechanical devices.

Our team will also work on a new project about quantum interconnects funded by the National Research Council of Science & Technology (NST) in South Korea. For this project, we will collaborate with researchers at the Korea Institute of Science and Technology (KIST) and at the Korea Advanced Institute of Science and Technology (KAIST) to develop quantum transducers by integrating nano-optoelectromechanical devices, superconducting microwave circuits and integrated photonic circuits. Our ultimate goal with this project is to realize efficient and reliable remote entanglement between two superconducting qubits through an optical fiber at telecommunication wavelengths.

You've used several Zurich Instruments’ products since your days at ETH. How do these instruments help you with your experiments?

I used the UHFLI Lock-in Amplifier to characterize my nanomechanical lattices operating at tens of MHz frequencies. The UHFLI is a really powerful addition to my experiments due to its large frequency bandwidth, the versatile sweeper function, and the additional UHF-AWG option. The LabOne software also made it easy to operate the instrument and provided useful coding guidelines when writing my own MATLAB^® and Python scripts to customize experimental settings. In the study of nanomechanical lattices, I used the output of the UHFLI to electromechanically excite my devices in the vacuum chamber and the UHFLI’s input to measure the vibration-induced laser intensity modulation coming from the photodetector. Then I performed steady-state response measurements using the sweeper functionality. The UHF-AWG option allowed me to design chirped pulses containing large frequency components, which I used to measure the transient responses of my devices.

Recently, we purchased an HDAWG for new experiments on superconducting quantum devices, and we hope to purchase other quantum-oriented products from Zurich Instruments for our project on quantum transduction. We really look forward to this journey, and to the scientific and technical achievements we will attain.

What trends do you see in the research and development of quantum computers in South Korea?

Just like other countries, South Korea is actively investing in quantum information science and technology (QIST). The National Research Foundation (NRF) of South Korea has run a scientific program for the development of quantum computing technologies with a total funding amounting to ~35 million CHF from 2019 to 2023. This program supports research on superconducting qubits, semiconductor quantum-dot qubits, trapped-ion quantum systems, photonic quantum computing and simulations, among others. Additionally, various research topics related to QIST have been supported through other programs offered by the NRF as well as by other funding agencies such as the Samsung Science & Technology Foundation.

The Government of South Korea also supports directly several national research institutes such as KRISS, KIST, and the Electronics and Telecommunications Research Institute (ETRI). These three institutions have their own research centers focused on developing a wide range of quantum technologies. In particular, with its Quantum Technology Institute KRISS has the largest quantum center consisting of a quantum spin team, a quantum nanomechanics team, a quantum information team, a quantum magnetic measurement team, a quantum magnetic imaging team, an ultracold atom quantum research team, and a fabrication infrastructure team.

Are there overseas institutions that you like to think of as references or models?

There are many institutes in the world that we would like to refer to. ETH Zurich is the foremost example I can mention. ETH Zurich is one of the institutes leading the field of quantum science and technology, with many faculty members working on various quantum systems. The Quantum Center at ETH gathers faculty members from different departments, and education programs such as the master’s degree in Quantum Engineering also show the institute’s effort to promote this field.