Day 2 Dec-3 2021
Session 4 17:15-18:00

Superconducting quantum computing chip with a vertically accessed two-dimensional array of qubits

Yasunobu Nakamura
RIKEN Center for Quantum Computing (RQC), Japan
Research Center for Advanced Science and Technology, The University of Tokyo, Japan

Superconducting circuits are one of the most promising platforms for quantum computing. Several groups have already demonstrated operations of quantum computing chips with tens of qubits integrated in a two-dimensional lattice. With the rapidly improving fidelities of the control gates and readouts, more and more advanced computation becomes achievable.

There are a few different architectures under intensive studies, roughly classified with tunable-frequency or fixed-frequency qubits and with tunable or fixed couplings. The less tunability tends to lead the longer coherence and less demands for wiring. On the other hand, the system could be vulnerable to the device parameter fluctuations in the fabrication as well as the energy coincidences with two-level fluctuators and the residual interactions between neighboring qubits. Apparently, there is a trade-off.

In this talk, we introduce our approach with a square lattice of fixed-frequency transmon qubits directly coupled with their nearest neighbors via capacitors. The circuit is controlled and read out only through microwave signals. To realize a tile-able design and mitigate the wiring issues in the planar approaches, we bring the control and readout lines vertically to the chip. We report the progress on the design and characterization of the chips and discuss the possible improvements and limitations.

Yasunobu Nakamura started his research career at NEC Fundamental Research Laboratories in 1992, where he demonstrated the first coherent manipulation of a superconducting qubit in 1999 and met quantum information science. He spent a year as a Visiting Researcher in TU Delft from 2001 to 2002. Since 2012, he has been a Professor in Research Center for Advanced Science and Technology (RCAST) of the University of Tokyo. He has also been leading his research team in RIKEN since 2014. He is currently the Director of RIKEN Center for Quantum Computing (RQC) as well as the Project Leader of the MEXT Q-LEAP Flagship project on Superconducting Quantum Computing. His current research area covers superconducting quantum computing, microwave quantum optics and hybrid quantum systems.