Jens Eisert

Warm thanks to the dream team of @sfeoliviero.bsky.social and Lorenzo Leone for this wonderful 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...

Once again, notions of #measurement feature strongly, which I find interesting.

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...

ParityQC joins PraktiQOM project, developing advanced quantum algorithms for semiconductor chip design - ParityQC ParityQC is a member of the PraktiQOM project, aiming to advance quantum algorithms to solve real-world optimization problems.

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.

A compellingly simple proof of the speed of sound for interacting bosons On physical grounds, one expects locally interacting quantum many-body systems to feature a finite group velocity. This intuition is rigorously underpinned by Lieb-Robinson bounds that state that loca...

Here the correct link to the paper. scirate.com/arxiv/2601.0...

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...

For @mathplusberlin.bsky.social this is a collaboration involving @freieuniversitaet.bsky.social, @zuseinstitute.bsky.social and @weierstrassinst.bsky.social.

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...

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