Nicolas Delfosse
Principal Researcher at IonQ
Update - Dec 2025: Why I am joining IonQ - Two years after.
As progress across the quantum computing stack is accelerating, the industry is transitioning from small noisy devices to large-scale fault-tolerant quantum computers. This requires a fundamental rethinking of the architecture, placing error correction at its core to guarantee that errors can be corrected faster than they accumulate during the execution of a quantum algorithm.
I have been working on quantum error correction since 2009, first in academia at Bordeaux University, Ecole polytechnique, University of Sherbrooke, Caltech and UCR, then in industry at Microsoft for six years and now at IonQ. I have worked on different kinds of quantum error correction codes including surface codes, color codes, Floquet codes, block codes and LDPC codes, and decoding algorithms for these codes such as the union-find decoder, the projection decoder for color codes and the beam decoder for LDPC codes.
In 2023, I joined IonQ to build and lead the quantum error correction team focused on the design of fault-tolerant quantum computer architectures. To learn more about our work, check our detailed blueprint for fault-tolerant quantum computing with trapped ions - see also the blogpost. For an overview of quantum error correction, you can watch my UCLA tutorial on the topic.
Over the past few years, I contributed the quantum community as a PC member for QEC26 TQC26, QIP26 (PC chair for QEC), QEC25, QIP25, QIP24, TQC24, QCTIP22 and an editor at Quantum Journal in 2022-2023.
Recent News
Sept. 2026 - Accepted talk: our work on High-Performance qLDPC Codes with Efficient Layouts on Flying Qubits was accepted for a talk at the TQC conference.
August 2026 - Summer school on QEC and QA: I will give a series of three lectures on quantum error correction at Amterdam CWI.
June 2026 - Tutorial: I will give a tutorial on quantum error correction with trapped ions at the QEC conference.
June 2026: Accepted talk: Our work on distributed quantum computing with slow interconnects was accepted for a talk at the QEC conference.
April 21st 2026 - New preprint: Fault-tolerant quantum computing with trapped ions: The walking cat architecture.
April 2026 - Conference talk: I will speak at the Monte Verita Quantum Codes conference.
April 2026 - Conference PC. I will be on the PC of QEC 2026.
March 2026 - Conference talk: I will present our work on distributed quantum memories at the march meeting in Denver.
Feb 2026 - Conference PC. I will be on the PC of TQC 2026.
Publications
Selected papers:
Low-Cost Noise Reduction for Clifford Circuits
N Delfosse and E Tham
Physical Review Letters. 134, 090603 (2025).
Constant-Overhead Quantum Error Correction with Thin Planar Connectivity
M Tremblay, N Delfosse, M Beverland
Physical Review Letters 129, 050504 (2022).
Almost-linear time decoding algorithm for topological codes
N Delfosse, NH Nickerson
Quantum 5, 595
Optimizing quantum error correction codes with reinforcement learning
HP Nautrup, N Delfosse, V Dunjko, HJ Briegel, N Friis
Quantum 3, 215 (2019)
Decoding color codes by projection onto surface codes
N Delfosse
Phys. Rev. A 89, 012317
Short resume
Background:
I obtained my PhD degree in pure mathematics from Bordeaux University in 2012, under the supervision of Gilles Zémor. My PhD work was about quantum error correction and quantum LDPC codes. Then, I joined Ecole polytechnique supported by the LIX-Qualcomm fellowship, where I worked with Alain Couvreur. I held a postdoc position at Sherbrooke University in the group of David Poulin and a postdoc position shared between Caltech and UCR in the groups of John Preskill. and Leonid Pryadko. Before joining IonQ, I was as a principal researcher at Microsoft, where I spent 6 years, working on fault-tolerant quantum computing. I am currently leading the quantum error correction team of IonQ.
Intern supervision:
I supervised the following PhD students for 12-weeks internship:
- Rui Chao, summer 2019 (Duke University)
- Poulami Das, summer 2019 (Georgia Tech)
- Christopher Pattison, Fall 2020 (Caltech)
- Maxime Tremblay, Fall 2020 (Sherbrooke University) co-supervised with Michael Beverland
- Shilin Huang, Summer 2021 (Duke University)
- Yue Wu, Summer 2023 (Yale University)
- Gregory Baimetov, Summer 2024 (University of Washington) co-supervised with Edwin Tham
- Nolan Coble, Summer 2025 (University of Maryland) co-supervised with Min Ye
- Aarda Aydin, Summer 2025 (University of Maryland) co-supervised with Edwin Tham
- Evan Dobbs, Summer 2025 (Aalto University) co-supervised with Aharon Brodutch
Postdoc supervision:
I supervised Nicholas Connolly for his postdoc working on quantum LDPC codes from Sept 2021 to Aug 2023 (in collaboration with Vivien Londe and Anthony Leverrier).
Teaching:
In 2008, I obtained the agrégation de Mathématiques. Between 2009 and 2013, I have been teaching mathematics (Algebra, Calculus, Discrete Math, Numerical Analysis and Cryptography) and computer science (Java, Python) classes at classes préparatoire Camille Jullian, Bordeaux University, Enseirb-Matmeca engineering school and Ecole polytechnique.
Quantum computing lectures:
More recently, I have been teaching lectures for grad students at the IBM summer school in 2022 and at the PCMI summer school in 2023. I gave tutorials on quantum error correction at UCLA for the IPAM quantum computing program.
Math circle:
I am regularly teaching for a math circle in the Seattle area (the northwest academy of sciences). In 2023, I taught a series of lectures on Shor's algorithm. In 2024, I gave lectures on fault-tolerant quantum computing. In 2025, I gave lectures on quantum chemistry.
Recent lectures:
IPAM Quantum computing program 2023 at UCLA:
Tutorials on quantum error correction.
IAS | PCMI Summer School 2023:
Lectures on quantum LDPC codes.
IBM Summer School 2022:
Lectures on quantum LDPC codes.