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Nicolas Delfosse

Principal Researcher at Microsoft

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It is exciting to work on the first generation of quantum computers. Unfortunately, current quantum hardware is not sufficiently reliable for industrial applications. The primary challenge for the quantum computing community is to transition from small noisy devices to large-scale fault-tolerant quantum computers capable of solving industrial problems. This requires designing a quantum computer around quantum error correction and fault-tolerance. Most of what a large-scale quantum computer will do is correcting faults!

I am an expert in quantum error correction and fault tolerance. The goal of my research is to use these techniques to make quantum bits and quantum operations good enough to run large-scale quantum algorithms and to solve practical problems.

I worked on different kinds of quantum error correction codes including surface codes, color codes, Floquet codes, block codes and LDPC codes. One of my favorite research problem is the design of fast decoders for these codes. I designed some popular decoding algorithms such as the Union-Find decoder, the projection decoder for color codes or the peeling decoder capable of correcting erasures. My goal is to make quantum error correction practical to enable large-scale fault-tolerant quantum computing.

Recent News

Feb 2024 - Workshop on QLDPC codes: I will be co-organizing a workshop on quantum LDPC codes at the Simons Institute at UC Berkeley. 

Sept. 2023 - Conference Talk: I will be speaking at the IEEE Quantum Week.

July 2023 - Lectures: I will be giving lectures on quantum LDPC codes at the PCMI summer school.

July 10th 2023 - Seminar talk: I will be speaking at the virtual QCDA seminar organized by Christophe Vuillot. Register here to this seminar series.

June 7th 2023 - Seminar talk: I will be speaking at the QEC seminar of Duke University.

April 2023 - New preprint: Spacetime codes of Clifford circuits

April 2023 - Conference Talk: I will be speaking at the QCTIP conference.

March 2023 - Conference Talk: I will be speaking at the APS March meeting.

Feb. 2023 - Seminar Talk: I will be speaking at the Caltech IQIM seminar.

Jan. 2023 - Publication: Our paper Performance of Planar Floquet Codes with Majorana-Based Qubit has been published in PRX Quantum.

Nov 2022 - Seminar talk: I will be speaking at the seminar of the math department of Bristol University.

Aug. 1st 2022 - New preprint: Fast erasure decoder for a class of quantum LDPC codes.

July 28th 2022 - Publication: Our paper Constant-Overhead Quantum Error Correction with Thin Planar Connectivity has been published in PRL.

July 2022 - QEC Summer School: I will give a lecture about quantum LDPC codes at the Quantum Error Correction summer school in July 2022.

March 2022 - Editor at Quantum Journal: I joined the journal Quantum as an editor. Quantum is non-profit, community-run and publishes excellent papers. Submit your best work to Quantum Journal!

Feb. 25th 2022 - New preprintPerformance of planar Floquet codes with Majorana-based qubits

Feb. 18th 2022 - Seminar talk: I will speak at the quantum information seminar of Cambridge University.

Jan. 18th 2022 - Talk: I will speak at the group meeting of the GRACE Team at Ecole polytechnique.

Jan. 14th 2022 - Publication: Our paper Toward a Union-Find decoder for Quantum LDPC codes has been published in IEEE Transaction on Information Theory.

Jan. 4th 2022 - Talk: I will speak at the quantum code meeting at Bordeaux University.

Jan. 11th 2022 - Conference: I am a member of the program committee for the conference QCTIP2022. Submit your recent work before January 11th, 2022.

Dec. 2nd 2022 - Publication: Our paper Almost-linear time decoding algorithm for topological codes has been published in Quantum.

Oct. 15th 2022 - Publication: Our paper Beyond Single-Shot Fault-Tolerant Quantum Error Correction has been published in IEEE Transaction on Information Theory.

Sept. 30th 2021 - Talk: I will speak at the QuICS seminar of University of Maryland and NIST.

Sept. 29th 2021 - New preprint: Constant-overhead quantum error correction with thin planar connectivity

Sept. 29th 2021 -New preprintBounds on stabilizer measurement circuits and obstructions to local implementations of quantum LDPC codes

July 28th 2021 - New preprintImproved quantum error correction using soft information


Selected papers:

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

Wigner function negativity and contextuality in quantum computation on rebits

N Delfosse, PA Guerin, J Bian, R Raussendorf

Physical Review X 5 (2), 021003


Short resume


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. Prior to joining Microsoft in 2017, I held a postdoc position at Sherbrooke University in the group of David Poulin and a postdoc position shared between UCR and Caltech in the groups of Leonid Pryadko and John Preskill.


Intern supervision:

Within the Microsoft internship program, I supervised the following PhD students for a three-month internship:

- Rui Chao, summer 2019 (Duke University)

- Poulami Das, summer 2019 (Georgia Tech)

- Christopher Pattison, Fall 2020 (Caltech)

- Maxime Tremblay, Fall 2020 (Sherbrooke University)

- Shilin Huang, Summer 2021 (Duke University)

- Yue Wu, Summer 2023 (Yale University)

Postdoc supervision:

I am currently supervising a postdoc (Nicholas Connolly) in collaboration with Vivien Londe at Microsoft Paris and Anthony Leverrier at INRIA Paris.


I obtained the agrégation de Mathématiques in 2008 and I have been teaching mathematics (Algebra, Calculus, Discrete Math and Cryptography) and computer science (Java, Python) classes at classes preparatoire Camille Jullian, Bordeaux University, Enseirb-Matmeca engineering school and Ecole polytechnique. 

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.

In 2023, I taught a series of lectures on Shor's algorithm for a non-profit teaching science to students in the Seattle area (Northwest academy of sciences).

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