QuIT Physics

Emergence of Classicality in Wigner's Friend Scenarios The Wigner's Friend (WF) thought experiment concerns quantum measurements by a 'superobserver' of an observer measuring a quantum system. Variations on the setup and its extended versions have seen a ...

New preprint! Really excited about this. It's some of my best work ever, IMO: an analytic and numerical study of the Wigner's Friend problem(s) with a specific model of the measurement process and a decohering environment.

arxiv.org/abs/2507.21221

Experimental composable key distribution using discrete-modulated continuous variable quantum cryptography - Light: Science & Applications We demonstrate the first four-state DM CVQKD system generating composable secure keys over 20 km fiber, marking progress toward practical, high-performance, cost-effective, and highly secure QKD netwo...

New in Light: Science & Applications: Florian joins a team presenting experimental results for a quantum key distribution method that relies on discretely-modulated continuous variables, including security proofs and more

www.nature.com/articles/s41...

Thanks to Physics World for this fab write-up of the work by our group members, including some lovely quotes from lead author Florian

(1/3) Updated on the arXiv this morning! No more painful typos and new appendices. One comparing our sample complexity with that of classical probabilistic approaches and another providing a recipe for oracles to prepare thermal machines.

arxiv.org/abs/2505.15887

Nice piece that ends with a nice quote from our very own Max!

Congrats to QuITter Phila Rembold on being awarded an FWF ESPRIT award! Among other things, she'll be using her expertise in quantum optimal control to develop new techniques for entanglement estimation, sensing and metrology 🥳🥳

www.fwf.ac.at/forschungsra...

New PRL! Here, Florian and Marcus propose a new framework for computing key rates in quantum key distribution, for the tricky case of high-dimensional entanglement

journals.aps.org/prl/abstract...

An information-theoretic proof of the Planckian bound for thermalization We demonstrate that quantum mechanics entails a fundamental lower bound on the thermalization time $τ$ of any system. At finite temperature, we show that $τ$ is bounded by half the Planckian dissipati...

New preprint from Alberto: how long do quantum systems take to thermalise? Here the authors show that quantum theory imposes a fundamental lower bound on this time!

arxiv.org/abs/2506.19188

New preprint: Moha and colleagues get into the swing of things with a study of the thermodynamics of... pendulum clocks?

...oh, right! QUANTUM pendulum clocks!

arxiv.org/abs/2506.10666

(1/n) Today on the arXiv, we examine the folklore that cooling a quantum system with access to another requires one to order their joint state eigenvalues in decreasing order and find that this sorting is actually dictated by a simple set of inequalities.

scirate.com/arxiv/2506.1...

This paper is now out in Nature Communications! www.nature.com/articles/s41...

This paper is now out in PRL! journals.aps.org/prl/abstract...

Deep congratulations to the whole team but especially to Florian on what I'm sure is only his first Nature Physics paper.

I am also super happy to see the Malta - Vienna connection crystallized in such a paper facilitated by @aspects-quantum.bsky.social

Copyright by Alexander Rommel / TU Wien.

What started as informal discussions on the Danube beach in Vienna during QTD2023 has been published at last. Trying to come up with an experimentally feasible quantum clock we came across a rich model – the ring clock – that overturned a common wisdom in the community. doi.org/10.1038/s415...

Verborgene mathematische Verbindung zwischen gegensätzlichen Teilchen entdeckt Bosonen und Fermionen hängen auf bisher unbekannte Weise zusammen. Die einen ähneln eher Schneeflocken, die anderen Sandkörnern

And here you can read Yuri explain the result in his own words to Der Standard (auf Deutsch!)

www.derstandard.at/story/300000...

Unified Interface Model for Dissipative Transport of Bosons and Fermions Dissipative transport of both fermionic and bosonic particles in a one-dimensional lattice belongs to the Kardar--Parisi--Zhang universality class.

Congrats to Yuri for having his new PRL be an Editors' Suggestion! A model of boson transport with dissipation turns out to have surprising connections to a fermionic scenario, via its link to a universality class for surface growth models

journals.aps.org/prl/abstract...

(1/7)On a train to Styria, headed for a weekend of hiking I kept thinking 𝘤𝘢𝘯 𝘢 𝘩𝘦𝘢𝘵 𝘦𝘹𝘤𝘩𝘢𝘯𝘨𝘦 𝘣𝘦 𝘶𝘴𝘦𝘥 𝘧𝘰𝘳 𝘢 𝘤𝘰𝘮𝘱𝘶𝘵𝘢𝘵𝘪𝘰𝘯?

In today's arXiv, I show that a heat exchange between a qubit and a thermal machine can be used to solve some old school query complexity problems.

scirate.com/arxiv/2505.1...

Very proud of the @univie.ac.at under grad physics society Roter Vektor for standing up for science today and peaceful distributing these flyers and picketing after the talk.

Shame on Uni Wien for using security to intimidate.

Cheers @graemesmith.bsky.social for the flyer inspiration 😉

If you've read this @sciencenews.bsky.social article and you're interested in learning more about the work Marcus and the rest of our research area does in quantum theory, check out our website here!

www.quitphysics.info

As quantum mechanics turns 100, a new revolution is under way With greater control over the quantum realm, physicists are poised to make major leaps in quantum computing, quantum gravity and more.

To us, every year is the International Year of Quantum Science and Technology, but it's nice that it's official now...

And this week, Marcus spoke to esteemed science journo Emily Conover about the future of quantum theory, with some hot takes 👀

www.sciencenews.org/article/quan...

New preprint: Marcus joins a team which managed to produce strongly entangled, high-dimensional quantum states of photons in a lab, expanding the range of entangled states that it's possible to study and use

arxiv.org/abs/2505.10035

Time crystals! There's been a lot of hype around them recently. In this new preprint, Marcus and others explore an overlooked aspect of them: how good are they as (quantum) clocks? The answer: potentially very good!

arxiv.org/abs/2505.08276

Distributed quantum sensing with measurement-after-interaction strategies We investigate multiparameter quantum estimation protocols based on measurement-after-interaction (MAI) strategies, in which the probe state undergoes an additional evolution prior to linear measureme...

New preprint from QuIT's Shuheng! He and his collaborators studied 'measurement after interaction' strategies in quantum estimation (for both discrete and continuous systems). These methods can increase both the sensitivity and robustness of sensing protocols

www.arxiv.org/abs/2505.05270

Composable Finite-Size Security of High-Dimensional Quantum Key Distribution Protocols Practical implementations of Quantum Key Distribution (QKD) extending beyond urban areas commonly use satellite links. However, the transmission of quantum states through the Earth's atmosphere is hig...

New preprint from Florian and Marcus: They show new security proofs for attacks against high-dimensional quantum key distribution platforms, and provide a security argument that yields higher key rates

arxiv.org/abs/2505.03874

YouTube video by PBS Space Time Quantum Energy Teleportation is REAL!

Check out the latest episode of PBS Space Time, which extensively quotes a paper by Nayeli from our group!
youtu.be/8CgquHFM_O8?...

...and check out the original paper here:
journals.aps.org/prl/abstract...

🦑⚛️🦑⚛️🦑

A few of us were involved in this beast of a preprint! Congrats to Moha, Alberto, and Pauli, and to the dozens of others on this wok. Check it out to get an amuse-bouche of a variety of quantum thermo topics!

Finally, Philipp and his collaborators study the theory of high harmonic generation using quantum optics, and in particular the notion of optical coherence

arxiv.org/abs/2504.13287

Third, Phila has a preprint working with experimentalists to verify entanglement between position and momentum degrees of freedom in electron-photon pairs using a transmission electron microscope

arxiv.org/abs/2504.13163

Next, Florian has a preprint on quantum key distribution, where he and colleagues succeed in transmitting quantum keys 10 km aways at over 1.2 Gbits per second

arxiv.org/abs/2504.08298