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Christopher K. Long @christopher-k-long.bsky.social · 21/09/2026

Here is a practice version of my talk from last weeks Foundations of Quantum Technologies Conference at Girton College Cambridge. It is a brief overview of my PhD thesis. youtu.be/zRikXKlZ0dQ?...

youtu.be

Optimal Hamiltonian control for variational quantum algorithms

YouTube video by Christopher K. Long

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Christopher K. Long @christopher-k-long.bsky.social · 25/08/2026

Since finishing my PhD viva on the 6th, with minor corrections, life has been busy. The discussion with Alex Thom and Simon Benjamin during my viva was insightful, and I'll have a better thesis as a result—thank you! My corrections are now done, but were slowed down by an accident on the 17th.

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Christopher K. Long @christopher-k-long.bsky.social · 07/07/2026

I'm dyslexic; em dashes are great. I struggle to follow where I am in text: once I was asked, "What the f@!# is your reading age?" Visually distinct elements help me follow text—e.g., em dashes, varying paragraph shapes, and accents on imported words like "naïve", "rôle", "café", or "ansätze".

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Christopher K. Long @christopher-k-long.bsky.social · 02/07/2026

VQEs have 3 main problems: (i) excessive runtimes, (ii) susceptibility to noise, and (iii) optimizability. In our recent preprint (arxiv.org/abs/2606.17357), we address the first 2 without losing optimizability. We achieve this by designing pulses for 4-qubit gates that run up to 15 times faster.

arxiv.org

Pulse-optimised circuit elements for scalable and noise-resilient quantum chemistry

Useful chemistry calculations on near-term quantum processors are hindered by current algorithmic runtimes. We develop a methodology to significantly reduce these runtimes. Typically, variational quan...

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Christopher K. Long @christopher-k-long.bsky.social · 16/06/2026

For many quasiprobability distributions, the set of positive (“classical”) states is difficult to characterize. However, for a random Kirkwood–Dirac distribution, we completely characterized not only the positive states, but also the positive measurements and unitaries.

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Christopher K. Long @christopher-k-long.bsky.social · 11/06/2026

In our recent arXiv (arxiv.org/abs/2605.28936) we benchmarked QEC and magic state factories for spin qubits. By computing magic state production overheads as a function of initialization, gate, measurement, and decoherence times we estimated the runtimes for typical algorithms—see Fig.

$Figure 2 from Songqinghao Yang, Christopher K. Long, Rubén M. Otxoa, Prakash Murali, Crispin H. W. Barnes, & David R. M. Arvidsson-Shukur, Hardware-Tailored Resource Estimation for Magic-State Distillation on Silicon Spin Qubits, arXiv preprint arXiv:2605.28936 (2026). Used under a CC-BY-4.0 license: https://creativecommons.org/licenses/by/4.0/ Caption: Algorithmic resource requirements. We plot the wall-clock time (horizontal axis) and the number of physical qubits (vertical axis) needed to run three different quantum algorithms. The color map indicates the fraction of the qubits used for MSD. The circles label the sparse SpinBus architecture with the standard surface code; the triangles label the SpinBus architecture with the XZZX surface code; and the squares label the dense architecture with the standard surface code. The logical operations are implemented with lattice surgery and the ‘grow-and-distill’ MSD protocol is chosen to minimize the space-time overhead.$

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Christopher K. Long @christopher-k-long.bsky.social · 01/06/2026

On Friday, I submitted my PhD thesis! I'm looking forward to defending in August and sharing the thesis with the rest of you.

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Christopher K. Long @christopher-k-long.bsky.social · 10/04/2026

The University of Cambridge is hosting a Foundations of Quantum Technologies conference on September 15–18th to mark the 100-year anniversary of the discovery of modern quantum mechanics. Abstract submissions for talks and posters close May 4th. More details: www.girton.cam.ac.uk/events/found...

girton.cam.ac.uk

Foundations of Quantum Technologies

Girton College, University of Cambridge, is hosting a conference to mark the 100-year anniversary of the discovery of modern quantum mechanics.

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Christopher K. Long @christopher-k-long.bsky.social · 07/04/2026

Screenings are happening across the UK over the next few months and are free to attend. You can find your closest screening here: www.nebriefing.org/screening-map

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Christopher K. Long @christopher-k-long.bsky.social · 22/12/2025

Now is not a good time for citations: Miss-citing online-only journals and Google Scholar indexing non-existent articles cited by hallucinating LLMs. Maybe the silver lining is that this will undermine metrics such as citation counts and h-indices, forcing academics to be judged more holistically.

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Christopher K. Long @christopher-k-long.bsky.social · 12/10/2025

With a long transfer from the Sahara to Fes, I finally finished going through the starter packs below. It was great to see everything you all have been working on! I like to spend some time reading through each profile, so I start to remember who's working on what. Please comment more starter packs!

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Reposted by Christopher K. Long

EU Science, Research & Innovation @scienceinnovation.ec.europa.eu · 30/09/2025

The European Commission is pleased to launch this new Science, Research & Innovation account. We look forward to connecting with the community on Bluesky! 🧪 Here you will find: - EU scientific news - Horizon Europe funding opportunities - Innovative EU-supported projects - Events, tools & resources

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Christopher K. Long @christopher-k-long.bsky.social · 04/10/2025

Last academic year, I reviewed my first paper. To any other PhD student considering whether to accept or decline this opportunity: I found it insightful to be on the other side of the process. It will help me anticipate future reviewer questions and prepare responses.

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Christopher K. Long @christopher-k-long.bsky.social · 18/09/2025

Ever wanted to use virtual Z gates with arbitrary powers of SWAP? Introducing the virtual Z pulse: arxiv.org/abs/2509.13453. In our new article, we present a method for distorting a pulse sequence to implement single-qubit Z controls virtually.

arxiv.org

From virtual Z gates to virtual Z pulses

Virtual $Z$ gates have become integral for implementing fast, high-fidelity single-qubit operations. However, virtual $Z$ gates require that the system's two-qubit gates are microwave-activated or nor...

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Christopher K. Long @christopher-k-long.bsky.social · 05/07/2025

How fast can quantum processors run? My coauthors and I answer in our new npj Quantum Information article! Utilising pulse engineering, we prepare molecular ground states in a few nanoseconds, ~100× faster than with gates. Back-of-the-envelope: Simulations can now tolerate T₁ and T₂ ~100× smaller.

nature.com

Minimal state-preparation times for silicon spin qubits - npj Quantum Information

npj Quantum Information - Minimal state-preparation times for silicon spin qubits

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Christopher K. Long @christopher-k-long.bsky.social · 17/06/2025

Hi all! I am excited to finally share this suite of quantum optimal control libraries that run up to 100× faster than QuTiP for some tasks. We developed these libraries while working on our preprint arxiv.org/abs/2406.10913, which was recently accepted into npj Quantum Information—keep tuned! (1/7)

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Christopher K. Long @christopher-k-long.bsky.social · 07/06/2025

Open for responses until Sunday 15th June 2025, 11:30pm BST.

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Christopher K. Long @christopher-k-long.bsky.social · 25/05/2025

Hi! Those who know me might be surprised to see me here—I’m something of a social media hermit. However, academia has taught me the value of connecting with the community, so I’m giving this a go. I’m excited to share my work and hear your thoughts, and I look forward to collaborating with you!

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