The term has started again at Freie Universität Berlin. This term, I am teaching my favourite subject, quantum information and quantum technologies. www.physik.fu-berlin.de/en/einrichtu...

We introduce a method for achieving high-threshold decoding of non-Pauli codes aimed at two-dimensional universality. Our results suggest that genuinely non-Clifford quantum operations in two-dimensional codes can perform comparably to those of a simple quantum memory. scirate.com/arxiv/2604.0...

In the absence of quantum error correction, circuits of #quantumcomputers can be logarithmically deep. www.nature.com/articles/s41...

📢 New paper. 𝐐𝐆𝐏𝐔: 𝐏𝐚𝐫𝐚𝐥𝐥𝐞𝐥 𝐥𝐨𝐠𝐢𝐜 𝐢𝐧 𝐪𝐮𝐚𝐧𝐭𝐮𝐦 𝐋𝐃𝐏𝐂 𝐜𝐨𝐝𝐞𝐬. A great collaboration w/ Boren Gu, Andi Lui, Armanda Quintavalle, Xian Xu, & @jenseisert.bsky.social 𝐭𝐥𝐝𝐫; Quantum LDPC codes are an exciting architecture for fault-tolerant ... 1/n scirate.com/arxiv/2603.0...

New #QML paper alert! 📝🧠⚛️ 🧐 A PAC-Bayesian approach to generalization for quantum models arxiv.org/abs/2603.22964 This collaboration involved some seriously hard and fun work by @pablones8.bsky.social, Matthias Caro, Carlos Bravo-Prieto, @fjschreiber.bsky.social, and @jenseisert.bsky.social

Measurement-induced non-commutativity in adaptive fermionic linear optics We show that mid-circuit measurements of fermions with internal degrees of freedom can induce the equivalent of "magic" to free fermionic circuits and render them classically hard to sample. scirate.com/arxiv/2603.2...

What a week. A highlight for me has been the #quantumtechnologies segment of the Grand Challenges conference of the @berlinualliance.bsky.social. Jerry Chow blew everybody away with his talk.

QGPU: Parallel logic in quantum LDPC codes scirate.com/arxiv/2603.0... We introduce #clusteredcycliccodes for #quantumerrorcorrection and show how to pursue highly parallelized surface-code style quantum logic with quantum low density parity check codes featuring simple logicals.

Tight inapproximability of max-LINSAT and implications for decoded quantum interferometry. scirate.com/arxiv/2603.0... Warm thanks to @mxkramer.bsky.social and Carsten Schubert for this collaboration.

The unbearable hardness of deciding about magic We show that determining membership in the stabilizer polytope, which defines the free states of magic-state resource theory, requires super-exponential time exp(n2) in the number of qubits n, even approximately. scirate.com/arxiv/2602.2...

There are interesting separations in quantum learning theory depending on whether or not one has access to post-measurement states in quantum measurement. scirate.com/arxiv/2602.2...

Mid-circuit measurements are a powerful tool for state preparation. In contrast, their usefulness for #quantumcomputation remains comparatively less well understood. We demonstrate that #midcircuitmeasurementscan enable quantum advantages even in shallow circuits. journals.aps.org/prl/abstract...

Variational #quantumalgorithms and classical variational methods, such as #tensornetworks, provide upper bounds on ground-state energies. This work provides guarantees for lower bounds. journals.aps.org/pra/abstract...

We're excited to have kicked off a new project - together with Freie Universität Berlin, Technische Universität Berlin and NXP Semiconductors, and led by @jenseisert.bsky.social. Our goal is to advance the performance of quantum algorithms to solve real problems in semiconductor chip manufacturing.

This is a paper I very much like, for its foundational and somewhat "rebellious" character: We show that notions channel capacities are strongly altered if one simply assumes that all operations one can implement are efficient. scirate.com/arxiv/2601.1...

This is a paper I very much like, for its foundational and somewhat "rebellious" character: We show that notions channel capacities are strongly altered if one simply assumes that all operations one can implement are efficient. scirate.com/arxiv/2601.1...

It has been a great pleasure—and both fun and insightful—to speak with Dr. Thomas Ramge about the future of quantum technologies, broader aspects of science and technology, and what makes science so exciting in the first place. m.youtube.com/watch?si=mh2...

This is the most technological paper I have been involved in for a while. It presents a below-threshold error reduction in single photons through photon #distillation. scirate.com/arxiv/2601.0...

Variational optimization of projected entangled-pair states on the triangular lattice. journals.aps.org/prb/abstract... The “meta-message” is that the use of tools such as #automaticdifferentiation, and the co-design of the ansatz class and the physical system can improve #tensornetwork methods.

To what extent can noisy quantum circuits be classically simulated? And at what point is this no longer true, so that one can hope for a quantum advantage? This is a compelling research question. Here, we suggest frames to do so, extending known Monte Carlo methods. scirate.com/arxiv/2601.0...

Do Bose-Hubbard type systems have a speed of sound for particle propagation? scirate.com/arxiv/2601.001… Yes. This work proves a strikingly simple bound of this kind for particle propagation for generalized Bose–Hubbard models defined on general lattices.

We suggest a shift in emphasis—namely, putting it on the representability of #functions—when thinking about quantum models aimed at achieving a quantum advantage for machine learning tasks. scirate.com/arxiv/2512.1...

How can we classically simulate large-scale open quantum systems—effectively dequantizing them? I am delighted to see the results of this wonderfully fruitful collaboration published in @natureportfolio.nature.com Communications. www.nature.com/articles/s41...

Recent analysis shows that quantum-state tomography faces significant challenges in accurately reconstructing continuous-variable quantum states, highlighting key limitations for quantum technologies. doi.org/hbdw67

This is a publication I am extremely happy about. It is a bit rebellious, and yet it touches upon an old and important question: How can we learn an unknown continuous quantum state from data? www.nature.com/articles/s41... We prove that quantum state tomography is a lot harder than anticipated.

The results of the evaluation of the submissions to #QIP2026 are out. I am very happy to see eight accepted submissions from our team so far. arxiv.org/abs/2504.12263 arxiv.org/abs/2505.15770 arxiv.org/abs/2502.12284 arxiv.org/abs/2510.07305 arxiv.org/abs/2503.15751 arxiv.org/abs/2510.05531 and …

Congratulations to Kiana Salehi, Perimeter PhD student who was awarded the Blue Apple Award for her talk, Influence of observer’s inclination and spacetime structure on photon ring observables. Learn more: indico.global/event/14302/...

Wow. Stunning indeed.

The results of the evaluation of the submissions to #QIP2026 are out. I am very happy to see eight accepted submissions from our team so far. arxiv.org/abs/2504.12263 arxiv.org/abs/2505.15770 arxiv.org/abs/2502.12284 arxiv.org/abs/2510.07305 arxiv.org/abs/2503.15751 arxiv.org/abs/2510.05531 and …

Over the recent weeks and months, John Preskill and I sat down to think about where we are in quantum computing. While the noisy intermediate-scale quantum (#NISQ) era is just unfolding as we speak, the time seems right to look ahead to the next steps to come. scirate.com/arxiv/2510.1...

This is a manuscript I am particularly happy with. It concerns topics I have been working on for my PhD, entanglement theory, going back to the work of Bennett et al. Yet it still has a fresh flavour, relating the subject to modern developments in quantum computing. www.nature.com/articles/s41...

In the shadow of the Hadamard test: Using the garbage state for good and further modifications journals.aps.org/prl/abstract... I am excited to see this improvement of the primitive of the Hadamard test in #quantumalgorithms in press in the PRL. We combine the unused output with shadow estimation.

Stability of digital and analog quantum simulations under noise scirate.com/arxiv/2510.084… How can one fairly compare the robustness of digital and analog quantum simulations? Immanuel Bloch, for we made an attempt to bring light into the question from a rigorous perspective.

How hard is it to verify a classical shadow? We look at the problem of establishing classical shadows from the perspective of computational complexity. scirate.com/arxiv/2510.0...

A data-driven heuristic method using tensor-network ansatze is shown to perform high-fidelity tomography of topological states. go.aps.org/4nVFFKy

Computational relative entropy We take steps towards a computationally efficient quantum information theory. scirate.com/arxiv/2509.2...

Efficient distributed inner-product estimation via Pauli sampling journals.aps.org/prxquantum/a...

Optimal trace distance bounds for free-fermionic states: Testing and improved tomography journals.aps.org/prxquantum/a... How can one optimally learn Gaussian fermionic states? A new trace distance bound is the key. Thanks to Lennart Bittel, @Antonio_ and Lorenzo Leone for this collaboration.

Localized statistics decoding for quantum low-density parity-check codes www.nature.com/articles/s41... A highly efficient and highly parallelizable decoder for qLDPC codes, overcoming a bottleneck in the field. Warm thanks to the team for the collaboration.

A fun discussion at the Oxford Union at #Seeqa2025 circled around the question whether we can reasonably expect quantum computers to have a bigger impact on our lives than classical computers. With Elham Kashefi, Terry Rudolph, Victor Albert, Nathan Wiebe, Graham Smith.

Quantum metrology in the finite-sample regime journals.aps.org/prxquantum/a... We propose an operational framework of #quantummetrology in the practically meaningful regime of a few measurement samples, introducing probably approximately correct (#PAC) metrology.

Random #tensornetworks provide a powerful framework for probing and understanding complex quantum systems, especially in regimes where conventional tools fail. Here, we rigorously investigate dynamical properties of holographic toy models. scirate.com/arxiv/2508.1...

Learning quantum states - aka #quantum state tomography - is strangely sample inefficient for #continuousvariable states. For #Gaussian states, it should be relatively easy. Here, we find an energy independent way, equipped with rigorous performance guarantees. scirate.com/arxiv/2508.1...

Two papers approach the question of how to better classically simulate quantum circuits at large scales and/or in the presence of noise. It turns out that one can go to large system sizes and even equip statements with rigorous guarantees. scirate.com/arxiv/2508.0... scirate.com/arxiv/2508.1...

Where do thermal states in nature come from? We present technical progress: we show that if initial states are slightly perturbed— anyway not known to arbitrary precision—then local thermalization can be rigorously proven, offering a novel perspective on typicality. www.nature.com/articles/s42...

Summer is back, and so are our garden seminars on #quantumerrorcorrection. Thanks so much, Virgile Guemard, for the compelling talk on lifted quantum Tanner codes.

Short-time simulation of quantum dynamics by Pauli measurements. journals.aps.org/pra/abstract...

Teaching is fun. Today, I have covered elements of the Pauli and Clifford groups. Cutely, at the very same moment when in Cologne, a #Berlin-#Cologne workshop is talking place on the Clifford commutant, triggered by two papers only, arxiv.org/abs/2504.12263, arxiv.org/abs/1712.08628.