Today’s Brief Commentary
The word of the day is:
Quantum Error Correction (QEC) and Fault Tolerance
Okay, maybe that’s longer than one word. The more I dug into the latest quantum news and articles, the more QEC kept coming up.
Let’s look at the question, “How should we change our approach to QEC when we have networked quantum processor units?”. Nu Quantum’s paper addresses this. While it’s easy to conclude prematurely that the problem simply becomes harder, maybe that extra connectivity allows us to employ different techniques, taking advantage of this additional degree of freedom, so to speak.
Next, rather than one company trying to do it all while building their quantum computers, doesn’t it make sense to partner with someone else with deep expertise in error correction? Riverlane certainly thinks so, and now we have QC Design working with Quantum Source in the photonic modality. In my comments below, I ding these companies a bit about how partnership announcements don’t take much effort compared to doing the actual work, but I like their lining up together.
Finally, why would we think there will be one error-correcting code to rule them all? IBM has investigated using more than one, and now we have researchers working with Alpine Quantum Technologies (AQT) demonstrating how they can use two codes for different kinds of gates. Here’s the strategy for advancing new technology, be it quantum, AI, or anything else: divide and conquer. Mixture-of-Experts, anyone?
Stay tuned for Friday’s newsletter for a special announcement.
Don’t forget to check out and bookmark my new sortable list of upcoming quantum technology conferences.
Conference and Event Talks
Q2B24 Silicon Valley | Carmen Palacios-Berraquero, Founder & CEO, Nu Quantum
https://youtu.be/buSit-PcUJI?feature=shared
Author: Carmen Palacios-Berraquero
Date: Wednesday, December 11, 2024
Excerpt: Carmen is the CEO of Nu Quantum and discusses the company’s approach to quantum networking via the Entanglement Fabric.
Earnings Announcements and Financial Dealings
Alice & Bob Closes €100M Series B Led by Future French Champions (FFC), AVP and Bpifrance to Advance Towards a Useful Quantum Computer
https://alice-bob.com/newsroom/alice-bob-100m-series-b-fundraising-press-release/
Author: Niccolò Coppola
Date: Tuesday, January 28, 2025
Commentary: Also see my previous investment news Research Note for Qolab, Quantum Brilliance, and SEEQC in the Related section below.
Excerpt: Alice & Bob will use the funding to enhance the performance of its system, improve error correction, and create its first error-corrected logical qubit. Nearly half of the funds will be used to finance the ongoing construction of a state-of-the-art lab and production facility, and additional funds will be used to further expand the team, which has doubled in the past year.
Quantum Error Correction and Fault Tolerance
Quantum Source Pilots QC Design’s Plaquette to Accelerate Photonic Fault-Tolerance
https://www.qc.design/news/quantum-source-pilots-plaquette
Date: Thursday, January 23, 2025
Commentary: Announcing partnerships is easy, but demonstrating results is harder. I’m looking forward to the demo and the quantitative output from the collaboration. I would love to see more solid partnerships of complementary technologies such as this. Note the funding news in the press release.
Excerpt: Quantum Source, a company developing technology for powerful, cost-effective, practical photonic quantum computers, today announced its pilot engagement with QC Design’s Plaquette, a state-of-the-art software tool for designing and optimizing fault-tolerant quantum computing architectures. This collaboration will boost Quantum Source’s capabilities to rigorously simulate, analyze, and refine the photonic fault-tolerance architectures integral to its proprietary large-scale quantum computing platform.
Nu Quantum Redefines Distributed Quantum Scalability with Hyperbolic Codes | Quantum Insider
Author: Cierra Choucair
Date: Monday, January 27, 2025
Excerpt: Distributed quantum computing, with its promise of scalable architectures, is seen as a way to overcome the limitations of current quantum systems. But as researchers and companies explore this modular approach, one unassailable challenge continues to rear its head: error correction. In a recently published preprint on arXiv, researchers form Nu Quantum propose a fresh solution, using hyperbolic Floquet codes to address the shortcomings of traditional methods and enable scalable, distributed quantum computation.
Quantum Error Correction and Fault Tolerance | Technical
[2403.13732] Experimental fault-tolerant code switching | arXiv
https://arxiv.org/abs/2403.13732
Date: Wednesday, March 20, 2024
Commentary: This is the open access preprint of the final Nature Physics paper below.
[2501.14029] Distributed quantum error correction based on hyperbolic Floquet codes | arXiv
https://arxiv.org/abs/2501.14029
Authors: Sutcliffe, Evan; Jonnadula, Bhargavi; Gall, Claire Le; Moylett, Alexandra E.; and Westoby, Coral M.
Date: Thursday, January 23, 2025
Excerpt: Quantum computing offers significant speedups, but the large number of physical qubits required for quantum error correction introduces engineering challenges for a monolithic architecture. One solution is to distribute the logical quantum computation across multiple small quantum computers, with non-local operations enabled via distributed Bell states. Previous investigations of distributed quantum error correction have largely focused on the surface code, which offers good error suppression but poor encoding rates, with each surface code instance only able to encode a single logical qubit. In this work, we argue that hyperbolic Floquet codes are particularly well-suited to distributed quantum error correction for two reasons. Firstly, their hyperbolic structure enables a high number of logical qubits to be stored efficiently. Secondly, the fact that all measurements are between pairs of qubits means that each measurement only requires a single Bell state. Through simulations, we show that distributed hyperbolic Floquet codes offer good performance under local and non-local phenomenological noise. This shows that distributed quantum error correction is not only possible but efficiently realisable.
Experimental fault-tolerant code switching | Nature Physics
https://www.nature.com/articles/s41567-024-02727-2
Authors: Pogorelov, Ivan; Butt, Friederike; Postler, Lukas; Marciniak, Christian D.; Schindler, Philipp; Müller, Markus; and Monz, Thomas
Date: Friday, January 24, 2025
Commentary: The final author listed, Thomas Monz, is the founder of Alpine Quantum Technologies (AQT) in Innsbruck, Austria.
Excerpt: Quantum error correction is essential for mitigating hardware errors in quantum computers by encoding logical information into several physical qubits. However, no single error-correcting code intrinsically supports a fault-tolerant implementation of all the gates needed for universal quantum computing. One approach for addressing this problem is to switch between two suitable error-correcting codes that in combination provide a fault-tolerant universal gate set. Here we present the experimental implementation of fault-tolerant code switching between two different codes in a trapped-ion processor. We switch between the 7-qubit colour code, which features fault-tolerant CNOT and H quantum gates, and the 10-qubit code, which allows for a fault-tolerant T gate implementation. Together, these codes form a complementary universal gate set. We construct logical circuits and prepare 12 different logical states that are not accessible natively in a fault-tolerant way within a single code. Finally, we use code switching to entangle two logical qubits using the full universal gate set in a single logical quantum circuit. Our results experimentally demonstrate a route towards deterministic control over logical qubits with low auxiliary qubit overhead and without relying on the probabilistic preparation of resource states.
Sovereign Initiatives
NERSC Launches IBM Quantum Innovation Center
https://www.nersc.gov/news-publications/nersc-news/nersc-center-news/2025/nersc-launches/
Author: Elizabeth Ball
Date: Tuesday, January 21, 2025
Excerpt: Beginning in January 2025, users at the National Energy Research Scientific Computing Center (NERSC) at Lawrence Berkeley National Laboratory (Berkeley Lab) will be able to access IBM’s quantum computers over the cloud for their research, allowing users to take advantage of these next-generation systems for certain scientific applications.
Related Articles and Papers
Quantum in Context: Early-Stage Startups Are Still Finding Investors | The Futurum Group
Author: Dr. Bob Sutor
Date: Wednesday, January 22, 2025
Excerpt: During December 2024, the stock prices of public quantum computing companies IonQ, Rigetti Computing, and D-Wave Quantum rose dramatically by hundreds of percent despite the latter two publishing lackluster earnings results for the third quarter. Following remarks by NVIDIA CEO Jensen Huang saying that useful quantum computing was at least 15 to 30 years away, these stocks crashed. They each recovered somewhat, but how did this affect small quantum startups’ investment environment? Three such companies closed early-stage rounds despite the turmoil.
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Disclosures
Bob Sutor is a former employee of IBM and Infleqtion and holds equity positions or stock options in each company. He is a Non-Executive Director for Nu Quantum.
Previous Newsletter Edition
AI – Monday, January 27, 2025: Commentary with Notable and Interesting News, Articles, and Papers
