Jens Eisert

Quantifying unknown quantum states: Study explores effectiveness of existing methods Reliably quantifying and characterizing the quantum states of various systems is highly advantageous for both quantum physics research and the development of quantum technologies.

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

PS: Posted again with the correct link.

Huge thanks to my co-authors for this fantastic collaboration: @antonioannamele.bsky.social,
@francescoannamele.bsky.social, Lennart Bittel, Vittorio Giovannetti, @ludovicolami.bsky.social, Lorenzo Leone, and Salvatore F. E. Oliviero.

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 …

Danke, das hat viel Spaß gemacht.

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/...

Ich finde diesen Sprachduktus schon zu einem Grade zu streng. So heftig auszuteilen, geht zu weit, zumal, wenn man um Unterstützung zum Bahnfahren bittet. Das ich selber auch gerne und sehr viel mache - wir sahen uns schon im Zug. Eine etwas moderatere Reaktion wäre angemessener.

Wow. Stunning indeed.

…

arxiv.org/abs/2502.09514
arxiv.org/abs/2509.20472

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 …

Thanks for posting.

Thanks.

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.