On-Demand, Direct Printing of Nanodiamonds at the Quantum Level

Principal Investigators: Dr. Ji Tae Kim, Associate Professor (Department of Mechanical Engineering) & Dr. Zhiqin Chu, Assistant Professor (Department of Electrical and Electronic Engineering)

This project is showcased as the Research Highlight (2023 May – July) in the second exhibition – Digitization in Innovation Wing Two

Project information


Practical realization of quantum devices calls for the placement of individual qubits on complex nanophotonic circuits. However, this prerequisite continues to suffer from coarse positioning accuracy, low throughput, and process complexity. We developed a novel nanoprinting scheme that allows the controllable placement of nitrogen-vacancy (NV) center nanodiamonds at the quantum level. The scheme enables remarkable achievements that are not attainable by other approaches: (1) single-quantum level quantity control, (2) sub-wavelength positional accuracy, and (3) scalable, ‘lithography-free’ patterning capability. We believe this work to be a game-changer, as it directly addresses the key technological challenge associated with the realization of quantum devices. The patent for this invention has been filed (US 63/236,411, PCT Application No. PCT/CN2022/113516).

About the scholars

Dr. Ji Tae Kim is an Associate Professor of the Department of Mechanical Engineering at the University of Hong Kong (HKU). He received his B.S. and Ph.D. degrees from POSTECH in 2006 and 2011 and conducted postdoctoral research at the Max Planck Institute. He joined HKU in 2016 as an Assistant Professor and has been promoted to Associate Professor in 2023. His research interests focus on new-paradigm 3D printing methods for manufacturing electronic and photonic devices. He has published over 45 peer-reviewed papers in high-profile, cross-disciplinary journals such as Nature Communications, Advanced Materials, ACS Nano, Nano Letters, Advanced Science, and so on. He has been awarded highly competitive external research grants including 5 RGC GRF, 1 NSFC/RGC JRS, and 1 ECF grants.

Dr. Zhiqin Chu received his PhD degree in Physics from The Chinese University of Hong Kong in July 2012. Dr. Chu carried out his postdoctoral training (2014/04-2016/09) at The University of Stuttgart (Germany), and then worked as a Research Assistant Professor (2016/10-2018/10) in Department of Physics at The Chinese University of Hong Kong. Since November 2018, Dr. Chu has been an Assistant Professor in Department of Electrical and Electronic Engineering (Joint Appointment with School of Biomedical Sciences), and established the Precision Biosensing & Biophysics (PBB) Laboratory at The University of Hong Kong. Dr. Chu’s current research interests include Quantum sensing, Biophysics, Nanophotonics and Materials-Biology interface. Dr. Chu is the co-founder of a start-up company commercializing the quantum demonstration kit for promoting education of quantum technologies.

Press release

Direct printing of nanodiamonds at the quantum level: HKU Engineering makes breakthrough in quantum device manufacturing

The press release article can be founded in HKU Press release (https://www.hku.hk/press/press-releases/detail/24403.html)

Diamond is more than just a pretty gem, and furthermore, the imperfections in it are more attractive to physicists. Diamond nanocrystals, namely nanodiamonds, hosting point defects such as nitrogen-vacancy (NV) centers, have been emerging as one of the most promising quantum materials.

A central requirement to realise the practical applications is the placement of individual NV centers at will on integrated circuits. This is critical for implementing quantum technologies, leading to a number of exciting opportunities and emerging fields such as quantum computers, quantum communications, and quantum metrology.

However, a universal and flexible route is still in great demand for achieving nanoscale accuracy, scalability, cost-effectiveness, and efficient coupling with a wide range of nanophotonic circuitries.

Several methods, such as the sophisticated “pick-and-place” nanomanipulation approach, have been devised to position the nanodiamonds with NV centers on various substrates and circuits. However, this prerequisite continues to suffer from coarse positioning accuracy, low throughput, and process complexity.

The team led by Dr. Ji Tae Kim from the Department of Mechanical Engineering and Dr. Zhiqin Chu from the Electrical and Electronic Engineering of the University of Hong Kong (HKU) has developed a nano-precision printing method for nitrogen-vacancy (NV) centers in diamond at the quantum level, meeting the technological requirements.

This novel approach is practical and cost-effective, paving the way for manufacturing of quantum information processing device, quantum computing and biosensing devices.

The research achievement has been published in Advanced Science in an article titled “On-Demand, Direct Printing of Nanodiamonds at the Quantum Level”, and featured as a Back Cover story by the Journal. A US patent has been filed for the invention.

The NV center is a point-defect in the diamond lattice and is the most common defect in nanodiamonds. It has emerged as a powerhouse for quantum systems due to their robust quantum states even at room temperature while other quantum systems such as superconducting quantum interference device can only operate at cryogenic temperatures, i.e., from −150 °C (−238 °F) to absolute zero (−273 °C or −460 °F).

Specifically, this atom-like solid-state device with its optically addressable spin-degrees-of-freedom, provides the key functionalities for serving as the quantum bit and/or quantum sensor in solid-state quantum processors.

“Diamond is the hardest material, so it is difficult to craft”
The researchers have developed an innovative way to tackle this issue. They have utilised electrical dispensing of nanodiamond-laden liquid droplets with sub-attoliter (< 10−18 liter) volume for placing NV-centers directly on universal substrates.

“To the best of our knowledge, the developed technique, for the first time, shows sub-wavelength positional accuracy, single-defect-level quantity control, and freeform patterning capabilities, meeting the technological requirements which marks a significant breakthrough in quantum device manufacturing,” said Dr Chu Zhiqin.

For the article “On-Demand, Direct Printing of Nanodiamonds at the Quantum Level”

For the back cover story: https://onlinelibrary.wiley.com/doi/10.1002/advs.202270032

Media enquiries:
Ms Celia Lee, Faculty of Engineering, HKU (Tel: 3917 8519; Email: leecelia@hku.hk

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