Compare Papers

Paper 1

Demonstrating real-time and low-latency quantum error correction with superconducting qubits

Laura Caune, Luka Skoric, Nick S. Blunt, Archibald Ruban, Jimmy McDaniel, Joseph A. Valery, Andrew D. Patterson, Alexander V. Gramolin, Joonas Majaniemi, Kenton M. Barnes, Tomasz Bialas, Okan Buğdaycı, Ophelia Crawford, György P. Gehér, Hari Krovi, Elisha Matekole, Canberk Topal, Stefano Poletto, Michael Bryant, Kalan Snyder, Neil I. Gillespie, Glenn Jones, Kauser Johar, Earl T. Campbell, Alexander D. Hill

Year

2024

Journal

arXiv preprint

DOI

arXiv:2410.05202

arXiv

2410.05202

Quantum error correction (QEC) will be essential to achieve the accuracy needed for quantum computers to realise their full potential. The field has seen promising progress with demonstrations of early QEC and real-time decoded experiments. As quantum computers advance towards demonstrating a universal fault-tolerant logical gate set, implementing scalable and low-latency real-time decoding will be crucial to prevent the backlog problem, avoiding an exponential slowdown and maintaining a fast logical clock rate. Here, we demonstrate low-latency feedback with a scalable FPGA decoder integrated into the control system of a superconducting quantum processor. We perform an 8-qubit stability experiment with up to $25$ decoding rounds and a mean decoding time per round below $1$ $μs$, showing that we avoid the backlog problem even on superconducting hardware with the strictest speed requirements. We observe logical error suppression as the number of decoding rounds is increased. We also implement and time a fast-feedback experiment demonstrating a decoding response time of $9.6$ $μs$ for a total of $9$ measurement rounds. The decoder throughput and latency developed in this work, combined with continued device improvements, unlock the next generation of experiments that go beyond purely keeping logical qubits alive and into demonstrating building blocks of fault-tolerant computation, such as lattice surgery and magic state teleportation.

Open paper

Paper 2

Quasi-Majorana modes in the $p$-wave Kitaev chains on a square lattice

S. Srinidhi, Aayushi Agrawal, Jayendra N. Bandyopadhyay

Year

2024

Journal

arXiv preprint

DOI

arXiv:2410.04955

arXiv

2410.04955

The topological characteristics of the $p$-wave Kitaev chains on a square lattice with nearest-neighbor and next-nearest-neighbor inter-chains hopping and pairing are investigated. Besides gapless exact zero-energy modes, this model exhibits topological gapless phase hosting edge modes, which do not reside strictly at zero energy. However, these modes can be distinguished from the bulk states. These states are known as pseudo- or quasi-Majorana Modes (qMMs). The exploration of this system's bulk spectrum and Berry curvature reveals singularities and flux-carrying vortices within its Brillouin zone. These vortices indicate the presence of four-fold Dirac points arising from two-fold degenerate bands. Examining the Hamiltonian under a cylindrical geometry uncovers the edge properties, demonstrating the existence of topological edge modes. These modes are a direct topological consequence of the Dirac semimetal characteristics of the system. The system is analyzed under open boundary conditions to distinguish the multiple MZMs and qMMs. This analysis includes a study of the normalized site-dependent local density of states, which pinpoints the presence of localized edge states. Additionally, numerical evidence confirms the robustness of the edge modes against disorder perturbations. The emergence of topological edge states and Dirac points with zero Chern number indicates that this model is a weak topological superconductor.

Open paper