Julian Kelly
Experimental Quantum Computing researcher with over a decade of experience working on design, fabrication, calibration, and benchmarking of superconducting quantum processors. Julian Kelly is the Director of Quantum Hardware at Google Quantum AI. He previously led the System Control Team which was responsible for building the hardware and software to operate and manipulate quantum computers. He began his career in quantum computing in 2008 where he joined John Martinis' physics research group at UCSB as an undergraduate and researched qubit control and benchmarking techniques. Julian stayed at UCSB and completed his PhD in 2015 in experimental quantum computing. His thesis focused on the development of highly controllable, coherent, and scalable "Xmon" transmon systems that demonstrated record fidelity entangling gate and measurement operations, culminating in a demonstration of experimental quantum error correction. Since joining Google, Julian worked to improve, scale, and integrate quantum processors and was the lead designer for the 72 qubit Bristlecone processor. Julian also developed the automated calibration framework "optimus" which is a software backbone of operating quantum processors at Google. The above technologies were critical in the team's "Quantum Supremacy" demonstration in 2019, and the first experimental demonstration of scalable quantum error correction in 2022.
Google Scholar.
Research Areas
Authored Publications
Sort By
Reinforcement Learning Control of Quantum Error Correction
Cameron Maxfield
Guifre Vidal
Bob Buckley
Jonathan Waltz
Christopher Wood
Reza Molavi
John Mark Kreikebaum
Rajeev Acharya
David Sobel
Abeer Vaishnav
Ali Hadjikhani
Ryuho Kudo
Wendy Leung
Brett Buchea
Ningfeng Zhu
Shirin Montazeri
Jamie Yao
Bicheng Ying
Eric Mascot
Lenny Fuste
Zhenjie Zou
Rodrigo Cortinas
Matt Lloyd
Clarke Smith
Kris Ottosson
Emma Ropes
Felix Borjans
Rebecca Potter
Sean Harrington
Jeremy Hilton
David Enriquez
Stephen Heslin
Paula Heu
Daniel Lundahl
Elliot Young
Alex Crook
Fedor Kostritsa
Roberto Rodriguez
Chia Ni
Kim Ming Lau
Priyanka Thiruraman
Martin Damyanov
Logan Oas
Dmitry Abanin
Oscar Higgott
Aaron Shorter
Steve Habegger
Aniket Maiti
Ryan Kaufman
Valerie Ehimhen
Sayra Alcaraz
Marcos Flores
Elizabeth Rossi
Aria Shahingohar
Dario Rosenstock
Travis Weidel
Steven Waltman
Kristi Wong
Murat Sarihan
Arun Kumar
Vladimir Shvarts
Matt Reagor
Alfredo Torres
Michael Qian
Anthony Megrant
Charles Neill
Christopher Hudspeth
Michael Hamilton
Bill Huggins
Laura De Lorenzo
Tan Ha
Ran Zhang
Dar Gilboa
Nicholas Bushnell
Sherman Peek
David Rhodes
Leigh Martin
Mike Shearn
Vlad Kurilovich
David Browne
Spencer Small
Brian Ballard
Will Oliver
Lior Ella
Orion Pritchard
Josh Cogan
Rachel Resnick
Dmitri Maslov
Jose Guerrero
Paul Masih Das
Theodore White
Helge Gehring
Nikita Astrakhantsev
Can Knaut
Maddy Woodson
Brooks Foxen
Frank Arute
Alejo Grajales Dau
Yaxing Zhang
Aaron Szasz
Alexander Lill
Justin Ledford
Xiaoxuan Jin
Andreas Kabel
Sid Madhuk
Orion Martin
Catherine Vollgraff Heidweiller
Gabrielle Roberts
Juan Campero
Juhwan Yoo
Robert Salazar
Michael Newman
Arpit Ranadive
James Goeders
William Giang
Gonzalo Garcia
Agnetta Cleland
Maddie Taylor
Dogan Timucin
Ross Alcaraz
Hui Kang
Johannes Bausch
William Courtney
Robert Gasca
Kevin Satzinger
Meghan Voorhees
Silas Chen
Laleh Beni
Andrew Dunsworth
Jamal Busnaina
Pavel Laptev
Kiseo Kang
Shannon Wang
Paul Donohoe
Paul Conner
Vadim Smelyanskiy
James Spencer
Benjamin Chiaro
Grayson Young
Tim Burger
ILYA Drozdov
Peter Brooks
Jordan Suchard
Austin Fowler
Jimmy Chen
Alec Eickbusch
Francisco Heras
Hung-Shen Chang
Michael Broughton
Jeanne Hartshorn
Aviv Elbag
Martin Bigdeli
Tanner Hadick
Juan Atalaya
Mahmoud Elzouka
Melvin Mathews
Alex Sztein
Markus Ansmann
Pavol Juhas
Bryan Cochrane
Murray Ich Nguyen
Ashley Maloney
Will Livingston
Roberto Collins
Ming Li
Élie Genois
Jeremiah Ford
Christopher Garrick
Sayan Das
David Peterson
Eifu Tomita
Suhas Ganjam
Reno Hiltermann
Dylan Bowers
Bryce Kobrin
Yu Chen
Dan Riley
Leon Brill
Barrett Spells
Ben Curtin
Mike Hucka
Seneca Meeks
Sebastian Molina
Tiano Lange-Dei
Georg Aigeldinger
Ashley Huff
Wing Li
ZLATKO MINEV
Monica Hansen
Sebastian Schroeder
Walt Askew
Dietrich Graumann
Elias Portoles
Stijn de Graaf
Matt Cockrell
Harold Cook
Masaya Fukami
Ed Gonzales
Robert Geiger
Amir Karamlou
Loick Le Guevel
Ebrahim Forati
Justin Vargas
Doug Thor
Joel Grebel
Lucia De Rose
LILY LI
Dave Landhuis
Emma Rosenfeld
Hsin-Yuan (Robert) Huang
Kenny Lee
Shaun Jevons
Ping Yeh
Amira Abbas
Kunal Arya
Henry Schurkus
Hector Bates
Ganesh Ramachandran
Sergey Vdovichev
Brayden Ware
Max Schaefer
Cheng Xing
Brandon Langley
Anthony Cabrera
Michel Devoret
Cody Jones
Vlad Sivak
Mert Torunbalci
Ben Kueffler
Chaitali Joshi
Raja Gosula
Joy Lee
Alexander Korotkov
Thomas Edlich
Aditya Locharla
Nathan Lacroix
George Sterling
Hao Tran
Kostyantyn Kechedzhi
Trond Andersen
Alexandre Bourassa
Aaron Lunt
Alan Fung
Alex Pizzuto
Salvatore Mandra
Alex Greene
Vitali Kutsko
Kannan Sankaragomathi
Sofia Springer
Vinicius Ferreira
Raymond Orosco
Nature (2026)
Preview abstract
The promise of fault-tolerant quantum computing is challenged by environmental drift that relentlessly degrades the quality of quantum operations. The contemporary solution, halting the entire quantum computation for recalibration, is unsustainable for the long runtimes of the future algorithms \cite{reiher2017elucidating,gidney2025factor}. We address this challenge by unifying calibration with computation, granting the quantum error correction process \cite{ryan2021realization,krinner2022realizing,sivak2023real,acharya2024quantum, bluvstein2024logical,bluvstein2025architectural,lacroix2025scaling} a dual role: its error detection events are not only used to correct the logical quantum state, but are also repurposed as a learning signal, teaching a reinforcement learning (RL) agent \cite{silver2017mastering,mnih2015human,levine2016end, shalev2016safe,ouyang2022training} to continuously steer the physical control parameters and stabilize the quantum system during the computation. We experimentally demonstrate this framework on a Willow superconducting processor, improving the logical stability of the surface code 3.5-fold against injected drift. By synthesizing our full suite of technological advances, including RL fine-tuning of the entire system and near-optimal decoding \cite{senior2025scalable, beni2025tesseract}, we achieve record performance of the surface and color codes, with average logical error per cycle of $\varepsilon_L=7.7\times10^{-4}$ and $\varepsilon_L=8.2\times10^{-3}$ respectively. Simulations of surface codes up to distance-15 with tens of thousands control parameters confirm the scalability of our RL framework, revealing an optimization speed that is independent of the system size. This work thus enables a new paradigm: a quantum computer that learns to self-improve directly from its errors and never stops computing.
View details
Correlated Error Bursts in a Gap-Engineered Superconducting Qubit Array
John Mark Kreikebaum
Leigh Martin
Vlad Kurilovich
Wojtek Mruczkiewicz
Lara Faoro
Gabrielle Roberts
Alex Opremcak
Kevin Satzinger
Alec Eickbusch
Igor Aleiner
Yu Chen
arXiv (2025)
Preview abstract
One of the roadblocks towards the implementation of a fault-tolerant superconducting quantum processor is impacts of ionizing radiation with the qubit substrate. Such impacts temporarily elevate the density of quasiparticles (QPs) across the device, leading to correlated qubit error bursts. The most damaging errors – T1 errors – stem from QP tunneling across the qubit Josephson junctions (JJs). Recently, we demonstrated that this type of error can be strongly suppressed by engineering the profile of superconducting gap at the JJs in a way that prevents QP tunneling. In this work, we identify a new type of correlated error that persists in the presence of gap engineering. We observe that impacts shift the frequencies of the affected qubits, and thus lead to correlated phase errors. The frequency shifts are systematically negative, reach values up to 3 MHz, and last for ~1 ms. We provide evidence that the shifts originate from the QP-qubit interactions in the JJ region. Further, we experimentally demonstrate these correlated phase errors are detrimental to the performance of quantum error correction protocols.
View details
Visualizing dynamics of charges and strings in (2 + 1)D lattice gauge theories
Tyler Cochran
Bernhard Jobst
Yuri Lensky
Gaurav Gyawali
Norhan Eassa
Melissa Will
Aaron Szasz
Dmitry Abanin
Rajeev Acharya
Laleh Beni
Trond Andersen
Markus Ansmann
Frank Arute
Kunal Arya
Abe Asfaw
Juan Atalaya
Brian Ballard
Alexandre Bourassa
Michael Broughton
David Browne
Brett Buchea
Bob Buckley
Tim Burger
Nicholas Bushnell
Anthony Cabrera
Juan Campero
Hung-Shen Chang
Jimmy Chen
Benjamin Chiaro
Jahan Claes
Agnetta Cleland
Josh Cogan
Roberto Collins
Paul Conner
William Courtney
Alex Crook
Ben Curtin
Sayan Das
Laura De Lorenzo
Paul Donohoe
ILYA Drozdov
Andrew Dunsworth
Alec Eickbusch
Aviv Elbag
Mahmoud Elzouka
Vinicius Ferreira
Ebrahim Forati
Austin Fowler
Brooks Foxen
Suhas Ganjam
Robert Gasca
Élie Genois
William Giang
Dar Gilboa
Raja Gosula
Alejo Grajales Dau
Dietrich Graumann
Alex Greene
Steve Habegger
Monica Hansen
Sean Harrington
Paula Heu
Oscar Higgott
Jeremy Hilton
Robert Huang
Ashley Huff
Bill Huggins
Cody Jones
Chaitali Joshi
Pavol Juhas
Hui Kang
Amir Karamlou
Kostyantyn Kechedzhi
Trupti Khaire
Bryce Kobrin
Alexander Korotkov
Fedor Kostritsa
John Mark Kreikebaum
Vlad Kurilovich
Dave Landhuis
Tiano Lange-Dei
Brandon Langley
Kim Ming Lau
Justin Ledford
Kenny Lee
Loick Le Guevel
Wing Li
Alexander Lill
Will Livingston
Aditya Locharla
Daniel Lundahl
Aaron Lunt
Sid Madhuk
Ashley Maloney
Salvatore Mandra
Leigh Martin
Orion Martin
Cameron Maxfield
Seneca Meeks
Anthony Megrant
Reza Molavi
Sebastian Molina
Shirin Montazeri
Ramis Movassagh
Charles Neill
Michael Newman
Murray Ich Nguyen
Chia Ni
Kris Ottosson
Alex Pizzuto
Rebecca Potter
Orion Pritchard
Ganesh Ramachandran
Matt Reagor
David Rhodes
Gabrielle Roberts
Kannan Sankaragomathi
Kevin Satzinger
Henry Schurkus
Mike Shearn
Aaron Shorter
Vladimir Shvarts
Vlad Sivak
Spencer Small
Clarke Smith
Sofia Springer
George Sterling
Jordan Suchard
Alex Sztein
Doug Thor
Mert Torunbalci
Abeer Vaishnav
Justin Vargas
Sergey Vdovichev
Guifre Vidal
Catherine Vollgraff Heidweiller
Steven Waltman
Shannon Wang
Brayden Ware
Kristi Wong
Cheng Xing
Jamie Yao
Ping Yeh
Bicheng Ying
Juhwan Yoo
Grayson Young
Yaxing Zhang
Ningfeng Zhu
Yu Chen
Vadim Smelyanskiy
Adam Gammon-Smith
Frank Pollmann
Michael Knap
Nature, 642 (2025), 315–320
Preview abstract
Lattice gauge theories (LGTs) can be used to understand a wide range of phenomena, from elementary particle scattering in high-energy physics to effective descriptions of many-body interactions in materials. Studying dynamical properties of emergent phases can be challenging, as it requires solving many-body problems that are generally beyond perturbative limits. Here we investigate the dynamics of local excitations in a LGT using a two-dimensional lattice of superconducting qubits. We first construct a simple variational circuit that prepares low-energy states that have a large overlap with the ground state; then we create charge excitations with local gates and simulate their quantum dynamics by means of a discretized time evolution. As the electric field coupling constant is increased, our measurements show signatures of transitioning from deconfined to confined dynamics. For confined excitations, the electric field induces a tension in the string connecting them. Our method allows us to experimentally image string dynamics in a (2+1)D LGT, from which we uncover two distinct regimes inside the confining phase: for weak confinement, the string fluctuates strongly in the transverse direction, whereas for strong confinement, transverse fluctuations are effectively frozen. We also demonstrate a resonance condition at which dynamical string breaking is facilitated. Our LGT implementation on a quantum processor presents a new set of techniques for investigating emergent excitations and string dynamics.
View details
Visualizing Dynamics of Charges and Strings in (2+1)D Lattice Gauge Theories
Jamie Yao
Ping Yeh
Bicheng Ying
Juhwan Yoo
Grayson Young
Yaxing Zhang
Ningfeng Zhu
Yu Chen
Vadim Smelyanskiy
Adam Gammon-Smith
Frank Pollmann
Michael Knap
Tyler Cochran
Bernhard Jobst
Yuri Lensky
Gaurav Gyawali
Norhan Eassa
Melissa Will
Aaron Szasz
Dmitry Abanin
Rajeev Acharya
Laleh Beni
Trond Andersen
Markus Ansmann
Frank Arute
Kunal Arya
Abe Asfaw
Juan Atalaya
Brian Ballard
Alexandre Bourassa
Michael Broughton
David Browne
Brett Buchea
Bob Buckley
Tim Burger
Nicholas Bushnell
Anthony Cabrera
Juan Campero
Hung-Shen Chang
Jimmy Chen
Benjamin Chiaro
Jahan Claes
Agnetta Cleland
Josh Cogan
Roberto Collins
Paul Conner
William Courtney
Alex Crook
Ben Curtin
Sayan Das
Laura De Lorenzo
Paul Donohoe
ILYA Drozdov
Andrew Dunsworth
Alec Eickbusch
Aviv Elbag
Mahmoud Elzouka
Vinicius Ferreira
Ebrahim Forati
Austin Fowler
Brooks Foxen
Suhas Ganjam
Robert Gasca
Élie Genois
William Giang
Dar Gilboa
Raja Gosula
Alejo Grajales Dau
Dietrich Graumann
Alex Greene
Steve Habegger
Monica Hansen
Sean Harrington
Paula Heu
Oscar Higgott
Jeremy Hilton
Robert Huang
Ashley Huff
Bill Huggins
Cody Jones
Chaitali Joshi
Pavol Juhas
Hui Kang
Amir Karamlou
Kostyantyn Kechedzhi
Trupti Khaire
Bryce Kobrin
Alexander Korotkov
Fedor Kostritsa
John Mark Kreikebaum
Vlad Kurilovich
Dave Landhuis
Tiano Lange-Dei
Brandon Langley
Kim Ming Lau
Justin Ledford
Kenny Lee
Loick Le Guevel
Wing Li
Alexander Lill
Will Livingston
Aditya Locharla
Daniel Lundahl
Aaron Lunt
Sid Madhuk
Ashley Maloney
Salvatore Mandra
Leigh Martin
Orion Martin
Cameron Maxfield
Seneca Meeks
Anthony Megrant
Reza Molavi
Sebastian Molina
Shirin Montazeri
Ramis Movassagh
Charles Neill
Michael Newman
Murray Ich Nguyen
Chia Ni
Kris Ottosson
Alex Pizzuto
Rebecca Potter
Orion Pritchard
Ganesh Ramachandran
Matt Reagor
David Rhodes
Gabrielle Roberts
Kannan Sankaragomathi
Kevin Satzinger
Henry Schurkus
Mike Shearn
Aaron Shorter
Vladimir Shvarts
Vlad Sivak
Spencer Small
Clarke Smith
Sofia Springer
George Sterling
Jordan Suchard
Alex Sztein
Doug Thor
Mert Torunbalci
Abeer Vaishnav
Justin Vargas
Sergey Vdovichev
Guifre Vidal
Catherine Vollgraff Heidweiller
Steven Waltman
Shannon Wang
Brayden Ware
Kristi Wong
Cheng Xing
Nature, 642 (2025), 315–320
Preview abstract
Lattice gauge theories (LGTs) can be used to understand a wide range of phenomena, from elementary particle scattering in high-energy physics to effective descriptions of many-body interactions in materials. Studying dynamical properties of emergent phases can be challenging, as it requires solving many-body problems that are generally beyond perturbative limits. Here we investigate the dynamics of local excitations in a LGT using a two-dimensional lattice of superconducting qubits. We first construct a simple variational circuit that prepares low-energy states that have a large overlap with the ground state; then we create charge excitations with local gates and simulate their quantum dynamics by means of a discretized time evolution. As the electric field coupling constant is increased, our measurements show signatures of transitioning from deconfined to confined dynamics. For confined excitations, the electric field induces a tension in the string connecting them. Our method allows us to experimentally image string dynamics in a (2+1)D LGT, from which we uncover two distinct regimes inside the confining phase: for weak confinement, the string fluctuates strongly in the transverse direction, whereas for strong confinement, transverse fluctuations are effectively frozen. We also demonstrate a resonance condition at which dynamical string breaking is facilitated. Our LGT implementation on a quantum processor presents a new set of techniques for investigating emergent excitations and string dynamics.
View details
Optimizing quantum gates towards the scale of logical qubits
Alexandre Bourassa
Andrew Dunsworth
Kevin Satzinger
Will Livingston
Vlad Sivak
Trond Andersen
Yaxing Zhang
Desmond Chik
Jimmy Chen
Charles Neill
Alejo Grajales Dau
Anthony Megrant
Alexander Korotkov
Vadim Smelyanskiy
Yu Chen
Nature Communications, 15 (2024), pp. 2442
Preview abstract
A foundational assumption of quantum error correction theory is that quantum gates can be scaled to large processors without exceeding the error-threshold for fault tolerance. Two major challenges that could become fundamental roadblocks are manufacturing high-performance quantum hardware and engineering a control system that can reach its performance limits. The control challenge of scaling quantum gates from small to large processors without degrading performance often maps to non-convex, high-constraint, and time-dynamic control optimization over an exponentially expanding configuration space. Here we report on a control optimization strategy that can scalably overcome the complexity of such problems. We demonstrate it by choreographing the frequency trajectories of 68 frequency-tunable superconducting qubits to execute single- and two-qubit gates while mitigating computational errors. When combined with a comprehensive model of physical errors across our processor, the strategy suppresses physical error rates by ~3.7× compared with the case of no optimization. Furthermore, it is projected to achieve a similar performance advantage on a distance-23 surface code logical qubit with 1057 physical qubits. Our control optimization strategy solves a generic scaling challenge in a way that can be adapted to a variety of quantum operations, algorithms, and computing architectures.
View details
Model-based Optimization of Superconducting Qubit Readout
Alex Opremcak
Alexandre Bourassa
Kevin Satzinger
Alexander Korotkov
Jimmy Chen
Physical Review Letters, 132 (2024), pp. 100603
Preview abstract
Measurement is one of the essential components of quantum algorithms, and for superconducting qubits it is often the most error prone. Here, we demonstrate a model-based readout optimization achieving low measurement errors while avoiding detrimental side-effects. For simultaneous and mid-circuit measurements across 17 qubits we observe 1.5% error per qubit with a duration of 500 ns end-to-end and minimal excess reset error from residual resonator photons. We also suppress measurement-induced state transitions and achieve a qubit leakage rate limited by natural heating.This technique can scale to hundreds of qubits, and be used to enhance performance of error-correcting codes as well as near-term applications
View details
Stable quantum-correlated many-body states through engineered dissipation
Xiao Mi
Alexios Michailidis
Sara Shabani
Jerome Lloyd
Rajeev Acharya
Igor Aleiner
Trond Andersen
Markus Ansmann
Frank Arute
Kunal Arya
Abe Asfaw
Juan Atalaya
Gina Bortoli
Alexandre Bourassa
Leon Brill
Michael Broughton
Bob Buckley
Tim Burger
Nicholas Bushnell
Jimmy Chen
Benjamin Chiaro
Desmond Chik
Charina Chou
Josh Cogan
Roberto Collins
Paul Conner
William Courtney
Alex Crook
Ben Curtin
Alejo Grajales Dau
Dripto Debroy
ILYA Drozdov
Andrew Dunsworth
Lara Faoro
Edward Farhi
Reza Fatemi
Vinicius Ferreira
Ebrahim Forati
Austin Fowler
Brooks Foxen
Élie Genois
William Giang
Dar Gilboa
Raja Gosula
Steve Habegger
Michael Hamilton
Monica Hansen
Sean Harrington
Paula Heu
Markus Hoffmann
Trent Huang
Ashley Huff
Bill Huggins
Sergei Isakov
Justin Iveland
Cody Jones
Pavol Juhas
Kostyantyn Kechedzhi
Marika Kieferova
Alexei Kitaev
Andrey Klots
Alexander Korotkov
Fedor Kostritsa
John Mark Kreikebaum
Dave Landhuis
Pavel Laptev
Kim Ming Lau
Lily Laws
Joonho Lee
Kenny Lee
Yuri Lensky
Alexander Lill
Wayne Liu
Aditya Locharla
Orion Martin
Amanda Mieszala
Shirin Montazeri
Ramis Movassagh
Wojtek Mruczkiewicz
Charles Neill
Ani Nersisyan
Michael Newman
JiunHow Ng
Murray Ich Nguyen
Tom O'Brien
Alex Opremcak
Andre Petukhov
Rebecca Potter
Leonid Pryadko
Charles Rocque
Negar Saei
Kannan Sankaragomathi
Kevin Satzinger
Henry Schurkus
Christopher Schuster
Mike Shearn
Aaron Shorter
Vladimir Shvarts
Jindra Skruzny
Clarke Smith
Rolando Somma
George Sterling
Doug Strain
Marco Szalay
Alfredo Torres
Guifre Vidal
Catherine Vollgraff Heidweiller
Cheng Xing
Jamie Yao
Ping Yeh
Juhwan Yoo
Grayson Young
Yaxing Zhang
Ningfeng Zhu
Jeremy Hilton
Anthony Megrant
Yu Chen
Vadim Smelyanskiy
Dmitry Abanin
Science, 383 (2024), pp. 1332-1337
Preview abstract
Engineered dissipative reservoirs have the potential to steer many-body quantum systems toward correlated steady states useful for quantum simulation of high-temperature superconductivity or quantum magnetism. Using up to 49 superconducting qubits, we prepared low-energy states of the transverse-field Ising model through coupling to dissipative auxiliary qubits. In one dimension, we observed long-range quantum correlations and a ground-state fidelity of 0.86 for 18 qubits at the critical point. In two dimensions, we found mutual information that extends beyond nearest neighbors. Lastly, by coupling the system to auxiliaries emulating reservoirs with different chemical potentials, we explored transport in the quantum Heisenberg model. Our results establish engineered dissipation as a scalable alternative to unitary evolution for preparing entangled many-body states on noisy quantum processors.
View details
Resisting high-energy impact events through gap-engineering in superconducting qubit arrays
Juan Atalaya
Alex Crook
John Mark Kreikebaum
Bicheng Ying
Hung-Shen Chang
Andrew Dunsworth
Yaxing Zhang
Ebrahim Forati
Rajeev Acharya
Justin Iveland
Wayne Liu
Anthony Megrant
Yu Chen
Charles Neill
Michel Devoret
Alex Opremcak
Physical Review Letters (2024)
Preview abstract
Quantum error correction (QEC) provides a practical path to fault-tolerant quantum computing through scaling, assuming that physical errors are rare and uncorrelated in time and space.
In superconducting qubit arrays, high-energy impact events produce correlated errors, violating this key assumption.
Following such an event, phonons with energy above the superconducting gap propagate throughout the device substrate, which in turn generate a temporary surge in quasiparticle (QP) populations across the array.
When these QPs tunnel across the qubits’ Josephson junctions, they induce correlated errors.
Engineering different superconducting gaps across the qubit's Josephson junctions (gap-engineering) provides a new method to resist QP tunneling.
By fabricating all-aluminum transmon qubits with both strong and weak gap-engineering on the same substrate, we observe a starkly different responses during single high-energy impact events.
Weakly-gap-engineered qubits show high rates of correlated $T_1$ errors, while the strongly-gap-engineered qubits do not show any degradation in $T_1$.
We also show strongly-gap-engineered qubits are robust to QP poisoning from increasing optical illumination intensity, whereas weakly-gap-engineered qubits display rapid degradation in coherence.
Based on these results, gap-engineering resolves high-energy impacts as a serious threat to QEC using superconducting qubit arrays.
View details
Dynamics of magnetization at infinite temperature in a Heisenberg spin chain
Trond Andersen
Rhine Samajdar
Andre Petukhov
Jesse Hoke
Dmitry Abanin
ILYA Drozdov
Xiao Mi
Charles Neill
Rajeev Acharya
Richard Ross Allen
Kyle Anderson
Markus Ansmann
Frank Arute
Kunal Arya
Abe Asfaw
Juan Atalaya
Gina Bortoli
Alexandre Bourassa
Leon Brill
Michael Broughton
Bob Buckley
Tim Burger
Nicholas Bushnell
Juan Campero
Hung-Shen Chang
Jimmy Chen
Benjamin Chiaro
Desmond Chik
Josh Cogan
Roberto Collins
Paul Conner
William Courtney
Alex Crook
Ben Curtin
Andrew Dunsworth
Clint Earle
Lara Faoro
Edward Farhi
Reza Fatemi
Vinicius Ferreira
Ebrahim Forati
Austin Fowler
Brooks Foxen
Gonzalo Garcia
Élie Genois
William Giang
Dar Gilboa
Raja Gosula
Alejo Grajales Dau
Steve Habegger
Michael Hamilton
Monica Hansen
Sean Harrington
Paula Heu
Gordon Hill
Markus Hoffmann
Trent Huang
Ashley Huff
Bill Huggins
Sergei Isakov
Justin Iveland
Cody Jones
Pavol Juhas
Marika Kieferova
Alexei Kitaev
Andrey Klots
Alexander Korotkov
Fedor Kostritsa
John Mark Kreikebaum
Dave Landhuis
Pavel Laptev
Kim Ming Lau
Lily Laws
Joonho Lee
Kenny Lee
Yuri Lensky
Alexander Lill
Wayne Liu
Aditya Locharla
Salvatore Mandra
Orion Martin
Steven Martin
Seneca Meeks
Amanda Mieszala
Shirin Montazeri
Ramis Movassagh
Wojtek Mruczkiewicz
Ani Nersisyan
Michael Newman
JiunHow Ng
Murray Ich Nguyen
Tom O'Brien
Seun Omonije
Alex Opremcak
Rebecca Potter
Leonid Pryadko
David Rhodes
Charles Rocque
Negar Saei
Kannan Sankaragomathi
Kevin Satzinger
Henry Schurkus
Christopher Schuster
Mike Shearn
Aaron Shorter
Vladimir Shvarts
Vlad Sivak
Jindra Skruzny
Clarke Smith
Rolando Somma
George Sterling
Doug Strain
Marco Szalay
Doug Thor
Alfredo Torres
Guifre Vidal
Catherine Vollgraff Heidweiller
Cheng Xing
Jamie Yao
Ping Yeh
Juhwan Yoo
Grayson Young
Yaxing Zhang
Ningfeng Zhu
Jeremy Hilton
Anthony Megrant
Yu Chen
Vadim Smelyanskiy
Vedika Khemani
Sarang Gopalakrishnan
Tomaž Prosen
Science, 384 (2024), pp. 48-53
Preview abstract
Understanding universal aspects of quantum dynamics is an unresolved problem in statistical mechanics. In particular, the spin dynamics of the one-dimensional Heisenberg model were conjectured as to belong to the Kardar-Parisi-Zhang (KPZ) universality class based on the scaling of the infinite-temperature spin-spin correlation function. In a chain of 46 superconducting qubits, we studied the probability distribution of the magnetization transferred across the chain’s center, P(M). The first two moments of P(M) show superdiffusive behavior, a hallmark of KPZ universality. However, the third and fourth moments ruled out the KPZ conjecture and allow for evaluating other theories. Our results highlight the importance of studying higher moments in determining dynamic universality classes and provide insights into universal behavior in quantum systems.
View details
Readout of a quantum processor with high dynamic range Josephson parametric amplifiers
Aaron Shorter
Aditya Locharla
Alejandro Grajales Dau
Alex Crook
Alex Opremcak
Alexander Korotkov
Alexander Lill
Alexandre Bourassa
Alfredo Torres
Andrew Dunsworth
Ani Nersisyan
Anthony Megrant
Ashley Anne Huff
Ben Curtin
Benjamin Chiaro
Bob Benjamin Buckley
Brooks Riley Foxen
Charles Neill
Christopher Schuster
Dave Landhuis
Ebrahim Forati
Fedor Kostritsa
Frank Carlton Arute
Grayson Robert Young
Jamie Yao
Jeremy Patterson Hilton
Jimmy Chen
JiunHow Ng
John Mark Kreikebaum
Josh Godfrey Cogan
Juhwan Yoo
Justin Thomas Iveland
Kannan Aryaperumal Sankaragomathi
Kenny Lee
Kevin Satzinger
Kunal Arya
Leon Brill
Lily MeeKit Laws
Marco Szalay
Marika Kieferova
Markus Ansmann
Markus Rudolf Hoffmann
Michael C. Hamilton
Mike Shearn
Murray Nguyen
Nicholas Bushnell
Ningfeng Zhu
Pavel Laptev
Ping Yeh
Rajeev Acharya
Rebecca Potter
Reza Fatemi
Roberto Collins
Sean Harrington
Shirin Montazeri
Tim Burger
Trent Huang
Trevor Johnathan Mccourt
Vladimir Shvarts
Wayne Liu
William Giang
Xiao Mi
Yu Chen
Applied Physics Letters, 122 (2023), pp. 014001
Preview abstract
We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in which the active nonlinear element is implemented using an array of rf-SQUIDs. The device is matched to the 50 $\Omega$ environment with a Klopfenstein-taper impedance transformer and achieves a bandwidth of 250-300 MHz, with input saturation powers up to $-95$~dBm at 20 dB gain. A 54-qubit Sycamore processor was used to benchmark these devices, providing a calibration for readout power, an estimate of amplifier added noise, and a platform for comparison against standard impedance matched parametric amplifiers with a single dc-SQUID. We find that the high power rf-SQUID array design has no adverse effect on system noise, readout fidelity, and qubit dephasing, and we estimate an upper bound on amplifier added noise at 1.6 times the quantum limit. Lastly, amplifiers with this design show no degradation in readout fidelity due to gain compression, which can occur in multi-tone multiplexed readout with traditional JPAs.
View details
