Quantum Error Correction with Multispecies Superconducting Circuits

Objective

In this project, we will build quantum-physical devices based on superconducting circuits and investigate approaches towards error -corrected quantum computing, which are both hardware-efficient and scalable. To this goal we envision to address errors hierarchically by multiple error-correcting layers and by using multispecies architectures in which data qubits and ancillary qubits are optimized for their respective purposes. Despite the tremendous progress in building quantum computers, all of today’s existing devices suffer from errors. All known quantum algorithms with a proven speed-up, however, rely on their near-perfect execution. To close this gap we need to learn to efficiently protect quantum information from decoherence and to process it faultlessly. While the theory of quantum error correction was developed in the 1990’s, experimental exploration of error correcting codes has only recently become possible due to the stringent quantum hardware requirements. Furthermore, realizations using conventional surface code architectures result in a massive hardware overhead requiring thousands of physical qubits per single logical qubit, which is considered a major obstacle towards practical quantum computing. To overcome this limitation, we will study multispecies concatenated architectures, in which every qubit is implemented as a hardware-efficient logical qubit tailored to its functional role. Such hardware-efficient logical qubits allow to detect and suppress the most frequent errors hardware-efficiently – promising a substantial reduction of the required size of an overarching code. Demonstrating quantum error correction in such multispecies and concatenated architectures, which we aim for in this project, would be a major breakthrough towards the realization of errorless superconducting quantum computers.