Lawrence Livermore National Laboratory



Y. J. Rosen

Overview

For quantum computing to be fault tolerant, the underlying quantum bits must be effectively isolated from the noisy environment. Including an electromagnetic bandgap around the qubit operating frequency is known to improve coherence for superconducting circuits. However, investigations into extending the use of bandgaps to other environmental coupling mechanisms remain largely unexplored.

Our feasibility study explored the viability of enhancing the coherence of superconducting circuits by introducing a phononic bandgap around the device operating frequency. We constructed a multi-scale model that derives the decrease in the density of states due to the bandgap and the resulting increase in defect state relaxation times. We demonstrated that emission rates from in-plane defect states can be suppressed by up to two orders of magnitude. We combined these simulations with theory to show that improvements in quality factors are expected by up to the enhancement in defect relaxation times. We also developed a full master equation simulation to demonstrate the suppression of qubit energy relaxation even when interacting with 200 defects states. We concluded the study with an exploration of device implementation and fabrication strategies.

Impact on Mission

This project advanced Lawrence Livermore National Laboratory’s core competencies in high-performance computing, simulation and data sciences as well as advanced materials and manufacturing. As simulation is a foundation for nearly every Livermore mission focus area, advances in computing will impact programs across the Laboratory including high-energy-density science, materials science, and advanced sensors.

Publications, Presentations, Etc.

——— . 2019. “Protecting Superconducting Qubits from Phonon Mediated Decay.” Applied Physics Letters 114, 202601 (2019). doi: 10.1063/1.5096182. LLNL-JRNL-760620.

Rosen, Y. 2019. “Probing Two Level Systems at the Material Interfaces of Superconducting Devices.” TLSQU19, Dresden, Germany. LLNL-PRES-768212.