The Engineering Salon aims at communication, break- through, succession, innovation and development, which will provide a platform for exchange and demonstration, and encourage the engineer craftsman spirit of overcoming difficulties and striving for perfection in the engineering team.  All scientists, postdocs and engineers are welcome to join us!

Date: Jun 25, 2021 (Friday) 13:30-15:40

Venue: Room 526

Host: Tiefu Li, Director of Division of Quantum Engineering Research

1) Introduction to Fabrication of Josephson Junction

Keywords: Superconducting Qubit，Microfabrication

Yongchao Li,  Senior Engineer

Abstract: Josephson junctions are widely used in superconducting qubit circuits due to their lossless and nonlinear properties. In this report, we mainly discuss the fabrication of Al/Al2o3/Al Josephson junction and the problems encountered during the fabricating process of Multi-bits.

2) Image Techniques and Magnetic\Electrical Applications of Atomic Force Microscope

Keywords: Magnetic Measurement, Film Deposition, 2D Material Transfer,  Low-temperature Physical Property Measurement, Morphology Characterization.

Yu Zhang, Senior Engineer

Abstract: Atomic force microscope (AFM) is used to characterize the surface morphology and properties of materials by detecting the very weak interatomic force between the micro probe and the sample surface. In addition to the basic morphology characterization, it can also obtain the electrical, mechanical and magnetic properties of the sample, and achieve the atomic level resolution.  This report will introduce the points for attention and tips for high quality AFM imaging. At the same time, the property measurement function of AFM which is easily ignored are also introduced.

3) Process Exploration of Transmon Qubit

Keywords: Coating, Lithography, Etching, Superconducting Quantum Chip Preparation

Chenlu Wang, Senior Engineer

Abstract: Superconducting quantum computing (SQC) is one of the most promising candidates for building practical quantum computers. However, one of the drawbacks of SQC is its relatively short coherence time. As a result, there has been a long battle for improving the coherence time of superconducting qubits, since their birth in the end of the last century. Although we can reach a lifetime of tens or even hundreds of microseconds for superconducting qubits using the state-of-the-art Transmon design and fabrications, it still cannot meet the requirements of a practical SQC system, especially for the error threshold of quantum error correction. This report will explore ways to increase the decoherence time of Transmon qubit from the perspective of process improvement.

4) FET-Hall devices based on Si_m/Ge_n superlattice

Keywords: Material Synthesis, Device Fabrication, Low-temperature Physical Property Measurement

Jun Lu, Senior Engineer

Abstract: The valley splitting in Si can be tuned to several MeV by artificially designing the SiGe superlattice barrier. The inter-valley spin relaxation can be suppressed due to large valley splitting, so the coherent time of Si spin qubit is expected to increase. We will introduce MBE growth and material characterization of SiGe superlattices, and further discuss the electrical properties and existing problems of the FET-Hall devices based on SiGe superlattice.

5) Molecular Beam Epitaxy of Novel Low Dimensional Materials

Keywords: Molecular Beam Epitaxy, low temperature and quantum transport, ultra-high vacuum

Bingbing Tong, Senior Engineer

Abstract：Since graphene was discovered, novel low dimensional material has been the research focus in the world, and it has placed an important role in the development of future microelectronics technology and information technology. High quality low dimensional materials, such as topological film and novel heterostructure can be fabricated by molecular beam epitaxy (MBE). This report will give a brief introduction to the MBE growth of nanowire and nanowire network by selective area growth (SAG).

6) Quantum Capacitance Measurement Technique

Keywords: Quantum Capacitance Measurement, Low-temperature Physical Property Measurement, Transmission Electron Microscopy, Scanning Electron Microscopy, Atomic Force Microscopy.

Yuanjun Song, Senior Engineer

Abstract：In quantum computing and quantum communication, quantum capacitance is an urgent problem that must be considered and studied as the device size decreases. Quantum capacitance measurement can also give the information of density of state and Fermi velocity of the two-dimensional materials. The traditional capacitance measuring instrument cannot be used to measure the capacitance of the sample in the cryogenic equipment. Therefore, we developed an in-situ quantum capacitance measuring system in the whole temperature region.