Dr Jan-Theodoor (JT) Janssen, NPL Research Director, talks to AZoM about a new quantum resistance standard based on graphene to dramatically reduce transport uncertainty allowing customers to calibrate its standards more regularly thereby reducing the drift effects. It also reduces down-time for the customer and so productivity can be significantly increased.
What are your current research areas?
My field of expertise is solid-state quantum physics. In recent years I’ve studied the quantum Hall effect in graphene which can be used a primary standard for resistance. I’ve also done a lot of work on single-electron pumping which can be used as primary standard for electrical current. However, since January this year I’ve been appointed Research Director at NPL and so unfortunately haven’t been in lab much.
Can you tell us about your collaboration with Oxford Instruments NanoScience?
My collaboration with OI goes a long way back. Working in the field of low-temperature and high magnetic field research you naturally come across OI a lot. We have a lot of equipment supplied by them and know the people very well. When we were developing the idea for a new quantum resistance standard based on graphene we started talking with OI and the joint project was conceived.
How do you aim to achieve a dramatic reduction in the calibration traceability chain?
At the moment users of our resistance calibration service have to bring a standard resistor to us once a year or so. We measure it against our primary standard which is based on the quantum Hall effect in GaAs heterostructures and send the resistor back to the customer. The transport of the standard resistor adds some uncertainty as well as the fact that the value of these resistors drifts in time. As result the customer needs to use a significantly reduced uncertainty for his work (as much as an order of magnitude). With our graphene based quantum Hall system you can use a much simpler cryostat which is cryogen-free and simple to operate. Such a system does not require the advanced facilities at NPL and can be operated in a calibration laboratory of the customer. This eliminates the transport uncertainty and means the customer can calibrate its standards as much as they like thereby reducing the drift effects. A final benefit is that there is very little down-time for the customer and so productivity can be much increased.
What are the main challenges you face?
Cryogen-free cryostats tend to be noisier in terms of electrical noise and vibrations. When you want to measure a resistor to parts in 10^9 (one in a billion) this becomes quite a challenge. We’ve done a lot of work on eliminating all the sources of noise.
How do you plan on developing a simple turnkey calibration system, based on the unique properties of graphene?
Graphene is a very special material and a lot of its properties are unique. It’s a two-dimensional crystal and exhibits a beautiful quantum Hall effect like that observed in traditional semiconductor devices such as GaAs and Silicon. The beauty of the quantum Hall effect in graphene is that the quantisation is very strong. This means that you don’t need such a low temperature (a few Kelvin) and also don’t need a very high magnetic field (a few Tesla). This makes the technology a lot simpler and can be achieved in a simple cryogen-free table-top system.
How will this be incorporated into the high-end electronics instrumentation industry and what benefits will it bring?
The first market for these systems is other metrology laboratories around the world. At the moment the number national metrology labs who have access to a quantum Hall system is limited. This is because traditional quantum Hall systems are complex and expensive and require highly trained staff to operate (they use high magnetic field and ultra-low temperatures >10T and <1K). The next market will be the high-end calibration laboratories around the world. Some of these laboratories already use a primary Josephson system for calibrating voltage standards. These calibrations laboratories have enough experience to also operate a quantum Hall system.
What is the market value and impact of technology on existing techniques?
This is a difficult one to answer. The original outlay for a primary quantum Hall system is very significant compared to sending a few resistors to NPL each year for calibration. However, being able to calibrate resistors to a higher accuracy will have significant benefits for calibration laboratories as it gives them a competitive advantage and will also feed through more innovate products.
What challenges do you need to overcome for the technology to be successfully adopted?
We don’t know yet enough about the reliability of graphene quantum Hall devices. So far it’s looking good but it is still a relatively young technology compared to semiconductors. Also device technology keeps improving and so more needs to be done on this.
What are the main risks preventing the adoption of the technology?
It’s linked to the point made above. If we can’t guarantee that graphene devices will work well for decades, customers could be nervous about this and stick with existing approaches.
What other applications do you think will benefit from this technology?
Many more people want to work with cryogen-free systems because of their low running costs and simplicity. The solutions we’ve developed for our graphene quantum Hall system can be applied to many more experiments which require a low noise environment. All sorts of quantum technologies come to mind.
What are the next steps for the project over the next few years?
The next step is to integrate a cryogenic current comparator into the same cryogen-free graphene quantum Hall system. The CCC is the device which is used to measure the quantum Hall resistance with extremely high precision. It’s operations it uses SQUIDS (superconducting quantum interference device) which again require a low temperature to operate.
What expertise has Oxford Instruments NanoScience brought to the project?
OI have wealth of experience in designing magnets and cryostats. They have brought many innovative ideas to this project and I believe we now have a pretty unique measurement system. The project has been a lot fun to do,
About Dr Jan-Theodoor (JT) Janssen
Dr Jan-Theodoor (JT) Janssen’s research interest is focused around low temperature solid-state physics and in particular quantum electrical effects with application in metrology. In this respect, JT has studied single electron transport in nanoscale semiconductor devices, the quantum Hall effect and the Josephson effect. JT has also done extensive research in the properties of low-dimensional systems such as graphene and other 2D materials.
JT is a Chartered Physicist and a Fellow of the National Physical Laboratory (NPL), the Institute of Physics (UK) and the Institute of Engineering and Technology.
JT was born in the Netherlands, where he studied at the Catholic University of Nijmegen (now called Radboud University). He specialised in experimental solid-state physics and received his Master's degree in 1989. He then started his PhD at the High Field Magnetic Laboratory, also at the University in Nijmegen, studying electronic nanostructures. His doctoral thesis was on the far-infrared magneto-optical properties of low dimensional semiconductor structures and organic conductors.
In 1994, JT moved to the UK under a Human Capital Mobility Fellowship of the EU. He worked as a Research Fellow at the University of Bristol, investigating the Fermi surface properties of heavy Fermion metals and superconductors using the de Haas-van Alphen effect. He won a Leverhulme Fellowship to continue this work for another two years.
JT joined the National Physical Laboratory (NPL) in 1998, where he is responsible for the research on quantum electrical standards. In 2006 he was promoted to NPL Fellow.
At NPL, his research involves a wide range of topics in solid-state physics applied to electrical metrology. Key topics are: the behaviour and transport of electrons in nanostructured devices with the aim of developing a quantum standard for electrical current; the quantum Hall effect in both traditional semiconductor systems, as well as graphene, as a primary standard for resistance; and the Josephson effect for a quantum voltage standard. He has co-authored more 100 scientific publications on these topics.
In 2015, JT launched and now heads the National Graphene Metrology Centre (NGMC), whose role it is to develop metrology and standardisation for the nascent graphene industry. JT is also a Scientific Co-Director of the Quantum Metrology Institute (QMI), which covers all of NPL's leading-edge quantum science and metrology research and provides the expertise and facilities needed for academia and industry to test, validate and ultimately commercialise new quantum research and technologies. In December 2015, JT was appointed Head of Science at NPL for SI Metrology. In this role he was leading with the in the strategic rebalancing of the NPL science portfolio.
From 2008 to 2016, JT was the contact person for NPL on the Technical Committee for Electricity and Magnetism (TC-EM) of the European Association of National Metrology Institutes (EURAMET), and convenor of the EURAMET DC quantum metrology experts group from 2010-2016, and a member of several international working groups.
In 2017, JT was appointed as our new NPL Research Director.
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