Jens Eisert

I have been impressed by the ease and efficiency with which we have been able to put this together. Warm thanks to John for the great collaboration and wonderful team work.

There are several gaps ahead of us, and we try to faithfully and honestly hint at how one may be able to "mind those gaps", and suggest a few important intermediate steps along the way.

In this perspectives article, we try to sketch the fraught road to quantum advantage — the path toward fault-tolerant, application-scale quantum (#FASQ) computers.

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...

No way?!

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...

Exactly.

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.

Classical shadows are obtained by random measurements.

You got the joke.

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.

The dream team involved @timohillmann.bsky.social, @qec.codes, @lucasberent.bsky.social, Armanda Quintavalle, and Robert Wille.

Localized statistics decoding for quantum low-density parity-check codes - Nature Communications Quantum low-density parity-check (QLDPC) codes offer lower overhead than topological quantum error-correcting codes, but decoding remains a key challenge for scalable fault-tolerant quantum computing....

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...

For #CRC183 it is relevant as it once again showcases the power of #measurements.

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...

This is also relevant for @dfg.de #CRC183 and #ML4Q.

www.quantum-randomness.com/clifford-wor...

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.