Open position MEP: Superconducting interconnects for spins in diamond and cryo-CMOS

25.07.2025Open Position MEP/BEP

Open position MEP: Superconducting interconnects for spins in diamond and cryo-CMOS

Ryoichi Ishihara

Associate Professor, Group leader

Qutech, Dep. Quantum and Computer Engineering, Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology

Ishihara-lab focuses on the integration technologies for unconventional electronic systems; quantum computers, quantum sensors, neuromorphic computers, and biodegradable sensors. Our work involves new materials, scalable fabrication of electronic and photonic devices, and 3D heterogeneous integration, aiming to realize unconventional electronic systems.

Superconducting interconnects for spins in diamond and cryo-CMOS

Current research on quantum computer chips have been focused on scaling the total number of qubits to enable advanced quantum algorithms and truly unlock the full potential of quantum computers. Modular quantum computer chips is an approach based on optical links between individual modules, each with a single quantum bit, or qubit. This enables high connectivity between modules with low crosstalk [1]. Each module has a single color-center in diamond with an electron spin (spin qubit) and an integrated photonics chip with several optical links to other modules. A cryo-CMOS chip provides the classical analog and digital electronic framework to control multiple modules.

The integration between all the components of a modular quantum computer chip should enable a high density of interconnects and a small footprint. These requirements are easily achieved through a three-dimensional (3D) integration scheme, in which the cryo-CMOS chip is stacked on top of the integrated photonics chip and vertically connected to it through a solder bump or other material (Figure 2). The choice of the interconnect material significantly influences the performance of the quantum computer chip. Ideally, this material should be a superconductor at the operating temperature of the quantum chip, as well as a good thermal insulator to thermally isolate the cryo-CMOS chip from the integrated photonics chip.

Figure 2. – Schematic representation of the 3D integration of a cryo-CMOS chip and an integrated photonics chip via an Indium solder bump. Other materials will be investigated.
This project focuses on the three-dimensional integration of the cryo-CMOS chip and the integrated photonics chips, more specifically the design, fabrication, and testing of superconducting interconnects. The student will conduct a thorough literature review on the topic and select the proper material based on their properties (Figure 3) and availability. At the same time, the student will be trained on various micro fabrication techniques and processes in the cleanroom, which will enable them to actually manufacture samples, characterize, and test them.

Figure 3. – Thermal conductivity and critical temperature of several materials.

The results of this research will be crucial to scaling the number of spin qubits in diamonds and to the overall development of the quantum computer field. Students who are interested in material sciences with a strong interest in micro fabrication in the cleanroom are encouraged to apply, as this will be a terrific opportunity to get familiar with several processes routinely used in the microelectronics industry.

References:

[1] Ishihara, R., Hermias, J., Neji, S., Yu, K.Y., Van Der Maas, M., Nur, S., Iwai, T., Miyatake, T., Miyahara, S., Kawaguchi, K. and Sato, S., 2023, May. 3D Integration for Modular Quantum Computer based on Diamond Spin Qubits. In 2023 IEEE International Interconnect Technology Conference (IITC) and IEEE Materials for Advanced Metallization Conference (MAM)(IITC/MAM) (pp. 1-3). IEEE.

Interested? Please contact Ryoichi Ishihara r.ishihara@tudelft.nl or Wagno Bragança <W.Braganca@tudelft.nl>

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