Overcoming leakage in quantum error correction
Authors: Miao Kevin C. , McEwen Matt , Atalaya Juan , Kafri Dvir , Pryadko Leonid P. , Bengtsson Andreas , Opremcak Alex , Satzinger Kevin J. , Chen Zijun , Klimov Paul V. , Quintana Chris , Acharya Rajeev , Anderson Kyle , Ansmann Markus , Arute Frank , Arya Kunal , Asfaw Abraham , Bardin Joseph C. , Bourassa Alexandre , Bovaird Jenna , Brill Leon , Buckley Bob B. , Buell David A. , Burger Tim , Burkett Brian , Bushnell Nicholas , Campero Juan , Chiaro Ben , Collins Roberto , Conner Paul , Crook Alexander L. , Curtin Ben , Debroy Dripto M. , Demura Sean , Dunsworth Andrew , Erickson Catherine , Fatemi Reza , Ferreira Vinicius S. , Burgos Leslie Flores , Forati Ebrahim , Fowler Austin G. , Foxen Brooks , Garcia Gonzalo , Giang William , Gidney Craig , Giustina Marissa , Gosula Raja , Dau Alejandro Grajales , Gross Jonathan A. , Hamilton Michael C. , Harrington Sean D. , Heu Paula , Hilton Jeremy , Hoffmann Markus R. , Hong Sabrina , Huang Trent , Huff Ashley , Iveland Justin , Jeffrey Evan , Jiang Zhang , Jones Cody , Kelly Julian , Kim Seon , Kostritsa Fedor , Kreikebaum John Mark , Landhuis David , Laptev Pavel , Laws Lily , Lee Kenny , Lester Brian J. , Lill Alexander T. , Liu Wayne , Locharla Aditya , Lucero Erik , Martin Steven , Megrant Anthony , Mi Xiao , Montazeri Shirin , Morvan Alexis , Naaman Ofer , Neeley Matthew , Neill Charles , Nersisyan Ani , Newman Michael , Ng Jiun How , Nguyen Anthony , Nguyen Murray , Potter Rebecca , Rocque Charles , Roushan Pedram , Sankaragomathi Kannan , Schurkus Henry F. , Schuster Christopher , Shearn Michael J. , Shorter Aaron , Shutty Noah , Shvarts Vladimir , Skruzny Jindra , Smith W. Clarke , Sterling George , Szalay Marco , Thor Douglas , Torres Alfredo , White Theodore , Woo Bryan W. K. , Yao Z. Jamie , Yeh Ping , Yoo Juhwan , Young Grayson , Zalcman Adam , Zhu Ningfeng , Zobrist Nicholas , Neven Hartmut , Smelyanskiy Vadim , Petukhov Andre , Korotkov Alexander N. , Sank Daniel , Chen Yu 
Published: October 2023

The leakage of quantum information out of the two computational states of a qubit into other energy states represents a major challenge for quantum error correction. During the operation of an error-corrected algorithm, leakage builds over time and spreads through multi-qubit interactions. This leads to correlated errors that degrade the exponential suppression of the logical error with scale, thus challenging the feasibility of quantum error correction as a path towards fault-tolerant quantum computation. Here, we demonstrate a distance-3 surface code and distance-21 bit-flip code on a quantum processor for which leakage is removed from all qubits in each cycle. This shortens the lifetime of leakage and curtails its ability to spread and induce correlated errors. We report a tenfold reduction in the steady-state leakage population of the data qubits encoding the logical state and an average leakage population of less than 1 × 10−3 throughout the entire device. Our leakage removal process efficiently returns the system back to the computational basis. Adding it to a code circuit would prevent leakage from inducing correlated error across cycles. With this demonstration that leakage can be contained, we have resolved a key challenge for practical quantum error correction at scale.