Anusua Chatterjee’s fridge
The QuTech lab is empty, apart from a cylindrical cryostat hanging from the ceiling, along with a large metal chiller that keeps the temperature inside the cryostat near absolute zero. The ‘fridge’, as she lovingly calls it, is indispensable for Dr Anasua Chatterjee’s research. When she joined QuTech as a researcher in February, she bought the equipment right away. “It saved me two years of applying for research grants.” Chatterjee’s academic journey has been impressive, taking her from Calcutta to Princeton University, where she worked on nanowires of superconductors and semiconductors. She did her PhD research at University College London, after which she set up her own research group at the Niels Bohr Institute, part of the University of Copenhagen. What brought her to Delft?
Ambitious workplace
“TU Delft has long been at the forefront of quantum technologys. There are few institutes in Europe that can compare. TU Delft sends a clear message to interested researchers that they will support the best person for the job, making it both an ambitious and internationally oriented workplace,” says Chatterjee. What happens when you combine superconductivity (conduction without resistance) with semiconductors (whose conduction is changed by an electrical voltage)?
Chatterjee’s research revolves around the combination of superconductivity and semiconductors at temperatures close to absolute zero. What makes this such an interesting combination? “Like many hybrid technologies, you want to harness the advantages of both platforms without any of the disadvantages,” she explains. “The end goal is to develop a kind of switchable superconductivity, which would pave the way for superconducting amplifiers or lasers, or better models of natural quantum systems.” Chatterjee expressly rules out the prospect of developing another quantum bit, pointing at the wealth of qubit expertise already available at TU Delft. Fortunately, QuTech also has ample experience in working with semiconductors and superconductors. “I hope to bridge the gap between those fields, and bring about something greater than the sum of its parts.”
Stefan Witte creates lensless images
His office at Applied Physics is still entirely empty, bar a few chairs and tables. When asked for an example of his work (nanostructures imaged with extreme ultraviolet (EUV) light), Professor Stefan Witte reaches for his laptop and pulls up two images showing the rectangular details of a microchip. One is sharp and black and white, the other slightly blurrier, but with colour information reflecting depth. The first was made with an electron microscope, the other with EUV light reconstruction. “The reconstruction technique harnesses the unique properties of EUV”, says Witte, “as it can penetrate about 1 micrometre into the material and has a short wavelength (approx. 20 nanometres, ed.), producing a high resolution.” This makes it possible to create three-dimensional images of nanostructures. Because optical instruments and EUV radiation do not match well, Witte turned to lensless imaging, using the scattering patterns in the shadow produced by the EUV beam. To reconstruct an image, you need hundreds of patterns, slightly shifting the object every time. Witte uses a computational method that was developed some 20 years ago, but remained unfeasible in practice until the advent of powerful processors and cheaper data storage.
