Journal Club

Seminar Room

If you want to propose a paper, you can contact Supratim Das Bakshi (sdb AT

Tuesday 23rd of May, 2023

Title: Suppressing quantum errors by scaling a surface code logical qubit 

Presented by:  Ivan Rosario 

Abstract: * Practical quantum computing will require error rates that are well below what is achievable with physical qubits. Quantum error correction offers a path to algorithmically-relevant error rates by encoding logical qubits within many physical qubits, where increasing the number of physical qubits enhances protection against physical errors. However, introducing more qubits also increases the number of error sources, so the density of errors must be sufficiently low in order for logical performance to improve with increasing code size. Here, we report the measurement of logical qubit performance scaling across multiple code sizes, and demonstrate that our system of superconducting qubits has sufficient performance to overcome the additional errors from increasing qubit number. We find our distance-5 surface code logical qubit modestly outperforms an ensemble of distance-3 logical qubits on average, both in terms of logical error probability over 25 cycles and logical error per cycle (2.914%±0.016% compared to 3.028%±0.023%). To investigate damaging, low-probability error sources, we run a distance-25 repetition code and observe a 1.7×10−6 logical error per round floor set by a single high-energy event (1.6×10−7 when excluding this event). We are able to accurately model our experiment, and from this model we can extract error budgets that highlight the biggest challenges for future systems. These results mark the first experimental demonstration where quantum error correction begins to improve performance with increasing qubit number, illuminating the path to reaching the logical error rates required for computation. 

Title:  Inflationary Schwinger dark matter production (continuation) 

Presented by: Paulo Bernardo 

Abstract:  I will follow-up one of the previous journal clubs on a mechanism to produce a possible multi-component dark matter comprised by dark bosons, fermions and/or vectors. I will present some phenomenology associated with the mechanism, mainly the computation of the associated currents.