Lauritz van Luijk
@lvanluijk.bsky.social
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lvanluijk.bsky.social
With Simon Becker, Niklas Galke and Robert Salzmann.

The paper is inspired by doi.org/10.1103/Phys..., where Burgarth et al show unexpectedly slow Trotter convergence rates of N^{-¼} for the Coulomb dynamics of certain states. We quantitatively link such slow rates to certain regularity properties.
Strong error bounds for Trotter and strang-splittings and their implications for quantum chemistry
Efficient error estimates for the Trotter product formula are central in quantum computing, mathematical physics, and numerical simulations. However, the Trotter error's dependency on the input state ...
doi.org
Reposted by Lauritz van Luijk
arrr.de
Like embezzlement of entanglement but not von Neumann algebras?

Check out
arxiv.org/abs/2509.15749

where we show explicitly that generic Gaussian fermionic states provide universal embezzling families.

Plus: A novel bound relating trace distance of Gaussian states to their covariance matrices.
Gaussian fermionic embezzlement of entanglement
Embezzlement of entanglement allows to extract arbitrary entangled states from a suitable embezzling state using only local operations while perturbing the resource state arbitrarily little. A natural...
arxiv.org
lvanluijk.bsky.social
Main takeaway:

Haag duality and the uniqueness of purifications are equivalent, but not automatic in bipartite systems with infinitely many DoF. E.g., they can fail in certain bipartitions of topologically ordered systems.
lvanluijk.bsky.social
By our result, the Uhlmann property must also fail. But can we understand this explicitly?

Yes: Creating a pair of anyons in the two cones leaves the B-marginal unchanged. With unitaries in A, the anyons can't be removed. The resulting states remain perfectly distinguishable from the ground state.
lvanluijk.bsky.social
Example: The ground state sector of the surface code on an infinite square lattice. Let A be two disjoint cones, and let B be the complement (see below). Then tomography holds, but it was shown by P. Naaijkens in doi.org/10.1063/1.48... that Haag duality fails.
lvanluijk.bsky.social
For systems with finitely many DoF, all three are equivalent. In the general case, where subsystems are modeled by von Neumann factors on the full system’s Hilbert space, we prove: 

Haag duality ⇔ Uhlmann property ⇒ tomography. 

The converse to the second implication does not hold.
lvanluijk.bsky.social
Uhlmann property: Pure states with equal A-marginals are connected by unitaries of Bob, up to arbitrarily small error. In other words: Purifications of A-states are unique, modulo their obvious symmetries.
lvanluijk.bsky.social
A bipartite system is a system composed of two subsystems. We investigate three formalizations of what "composed of" means:

Tomography: States are uniquely determined by correlation experiments.

Haag duality: Observables belong to Alice if and only if they commute with all of Bob’s observables.
Reposted by Lauritz van Luijk
arrr.de
🥳I am very happy to have been awarded an ERC Starting Grant that I will use to start my own group and explore the large-scale entanglement properties of complex quantum systems.

This would not have been possible without my fantastic collaborators and supervisors. A big "thank you" to all of you! 🙏
erc.europa.eu
📣 The ERC Starting Grant call results are out!

Find out which early-career researchers will receive funding this year, what they will be investigating, where they will be based... plus lots of other #ERCStG facts & figures for 2025!

➡️ buff.ly/IsafuFh

#FrontierResearch 🇪🇺#EUfunded #HorizonEurope
Reposted by Lauritz van Luijk
improbabilitydrive.bsky.social
Glad someone took the time to debunk the (obviously nonsensical) claim that Bell inequalities could be violated w/o entanglement. It is astonishing (to say the least) that this claim was made by experienced authors & that it passed peer review in the first place, does not reflect well on the journal
Bell Inequality Violations Without Entanglement? It's Just Postselection
Recently Wang et al. have reported a violation of a Bell inequality without entanglement [arXiv:2507.07756]. We show that their result is an artifact of postselection. It is well known that postselect...
arxiv.org
Reposted by Lauritz van Luijk
arrr.de
Small paper w/ @lvanluijk.bsky.social and @stotti-alex.bsky.social: We revisit the amazing operator inequality by Lin et al. (arXiv:2211.13372), which implies strong sub-additivity of entropy and find that it's a special case of Connes' theory of spatial derivatives:

arxiv.org/abs/2508.03731
An inequality between density operators: \rho_A \otimes \sigma_{BC}^{-1} \geq \rho_{AB} \otimes \sigma_C^{-1}
Reposted by Lauritz van Luijk
qit-cqt.bsky.social
Quantum Toolbox (8): Hadamard's Three-Lines Theorem (1/6)
Reposted by Lauritz van Luijk
andreealefterovici.bsky.social
Henrik will soon talk about entanglement in the thermodynamic limit at LUH :).
Reposted by Lauritz van Luijk
hippoquantus.bsky.social
I am currently looking for a PhD student who would like to work on position-based cryptography. Details can be found here: andreasbluhm.eu/wp-content/u...

Please spread the word!
andreasbluhm.eu
Reposted by Lauritz van Luijk
stotti-alex.bsky.social
Today our paper on universal embezzlement of entanglement in critical fermion systems has been published in Nature Physics:
www.nature.com/articless415...
Another intense collaboration with the great Lauritz (@lvanluijk.bsky.social) & Henrik (@arrr.de).
Below is the former Twitter thread.
www.nature.com
Reposted by Lauritz van Luijk
arrr.de
For this year’s #QIP2025 we sadly had to give our talk as a video.

The upshot: Everyone can already watch @lvanluijk.bsky.social’s nice talk on pure state entanglement and von Neumann algebras!

https://m.youtube.com/watch?v=U70p9sauZ_E

#entanglement #quantum @stotti-alex.bsky.social
Pure state entanglement and von Neumann algebras (QIP 2025)
m.youtube.com
Reposted by Lauritz van Luijk