iiinova — where your digital self keeps evolving

Alexander Jahn @physicistalex.bsky.social · 01/10/2026

Exactly, the legendary chalk that's nowadays made solely in Korea! After years of office whiteboards, I feel like I'm going back to an old artisanal craft...

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Alexander Jahn @physicistalex.bsky.social · 01/10/2026

With a beautiful view and a full box of hagoromo in my new office, I'm off to a perfect start at APCTP in Pohang, South Korea!

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Alexander Jahn @physicistalex.bsky.social · 13/08/2026

Politics in Berlin is such a mess that one could call it a... mission impossible?

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Alexander Jahn @physicistalex.bsky.social · 12/08/2026

Per popular request, I've extended the application deadline for both postdoc positions to *Aug 19*.

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Alexander Jahn @physicistalex.bsky.social · 12/08/2026

Our work only introduces a very simple model without locality or an explicit decoding/recovery circuit, showing the basic consistency between overlapping qubits and black hole evaporation. So there are many more details to explore and check in future work!

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Alexander Jahn @physicistalex.bsky.social · 12/08/2026

But if we wait longer, our overlapping exterior basis becomes more and more overcomplete, allowing us to recover the interior with a simpler circuit! That is, the complexity barrier between interior and exterior modes is gradually, and very slowly, broken down.

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Alexander Jahn @physicistalex.bsky.social · 12/08/2026

The resolution is to assume "black hole complementarity": Rather than Hawking modes being entangled with the interior, both live in the *same* Hilbert space!

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Alexander Jahn @physicistalex.bsky.social · 12/08/2026

Naively, overlapping qubits don't help here: An old black hole should have lots of overlap between the many qubits describing the interior, but not necessarily between interior and exterior - so no information leaks.

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Alexander Jahn @physicistalex.bsky.social · 12/08/2026

In our universe, black holes are probably the closest we can get to testing quantum-gravitational effects. If they are truly described by quantum gravity, we expect that their Hawking radiation gradually reveals information about their interior!

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Alexander Jahn @physicistalex.bsky.social · 12/08/2026

Adding gravity to quantum degrees of freedom affects their spatial independence: A qubit at point X no longer perfectly commutes with a qubit at a different point Y. We previously suggested that this is described by the quantum information notion of overlapping qubits: arxiv.org/abs/2304.02673

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Alexander Jahn @physicistalex.bsky.social · 12/08/2026

Three years ago, we proposed "overlapping qubits" as a description of information encoding in quantum gravity. In our new paper with Charles Cao's group at @virginiatech.bsky.social, we finally apply overlapping qubits to evaporating black holes! arxiv.org/abs/2608.10085

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Alexander Jahn @physicistalex.bsky.social · 26/07/2026

Big news: I'll be moving to APCTP in Pohang, South Korea, starting a new group in October! I'll be hiring two postdocs on a range of topics from high-energy to quantum information theory, collaborating across the Asia-Pacific region and beyond. Deadline Aug 12. More: www.apctp.org/bbs/board.ph...

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Alexander Jahn @physicistalex.bsky.social · 29/05/2026

"Holographic storage"? Has someone finally found an application for HaPPY codes? 😅

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Alexander Jahn @physicistalex.bsky.social · 12/05/2026

Better move to Vienna a month before the deadline, just in case they like your research statement!

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Alexander Jahn @physicistalex.bsky.social · 11/05/2026

TU Vienna has an interesting tenure-track faculty opening: Deadline May 14, start of position on June 1. I wonder how they'll find someone that quickly. 🙄 jobs.tuwien.ac.at/Job/266522

jobs.tuwien.ac.at

Assistant Professorship - Tenure Track

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Alexander Jahn @physicistalex.bsky.social · 26/04/2026

Clearly in a disordered phase, as children tend to be.

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Alexander Jahn @physicistalex.bsky.social · 13/04/2026

Gave a talk at the University of Vienna today, in a room once used by the great logician Kurt Gödel! However, my treatment of the subject - holographic fault tolerance - remains incomplete.

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Alexander Jahn @physicistalex.bsky.social · 25/03/2026

Why does this charging station remind me of a certain American president?

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Alexander Jahn @physicistalex.bsky.social · 21/03/2026

Since Rydbergs work at room temperature, they're literally much hotter than all the dilution-refrigerated qubits out there! I hope they still build some golden chandeliers around them for promo photos, though.

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Ben Brubaker @benbenbrubaker.bsky.social · 18/03/2026

It's not often that I do breaking news! Today, Charles Bennett and Gilles Brassard received the Turing Award for helping lay the foundations of quantum information science. Read more in @quantamagazine.bsky.social!

quantamagazine.org

Quantum Cryptography Pioneers Win Turing Award | Quanta Magazine

Charles Bennett and Gilles Brassard were recognized for their foundational work in quantum information science.

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Alexander Jahn @physicistalex.bsky.social · 16/03/2026

Berlin's pubs are already adjusting to new geopolitical realities: "Beer now cheaper than gasoline - Don't drive away, drink and stay!"

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Alexander Jahn @physicistalex.bsky.social · 17/01/2026

Indeed, because he's still missing the Dulwich Peace Prize.

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Graeme Smith @graemesmith.bsky.social · 06/11/2025

If you are interested in doing a postdoc with me, please apply to the IQC postdoctoral fellowship here: iqc-uwaterloo.slideroom.com#/login/progr...

iqc-uwaterloo.slideroom.com

University of Waterloo Attn: Institute for Quantum Computing - SlideRoom

Apply to University of Waterloo Attn: Institute for Quantum Computing. Powered by SlideRoom.

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Richard Kueng @richardkueng.bsky.social · 21/10/2025

(I/III) We're excited to announce a new tenure track opening! The position is called 'quantum informatics' and is affiliated with our QUICK group within the CS+AI division at @jku.at 🇦🇹. Application deadline is November 30th, 2025: www.jku.at/en/the-jku/w...

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Alexander Jahn @physicistalex.bsky.social · 07/10/2025

This week, we're in beautiful Kraków for a conference on tensor networks and all their applications. My PhD students Dimitris and Lev already gave amazing talks about discrete-holographic boundary symmetries and von Neumann algebras in holographic codes!

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Alexander Jahn @physicistalex.bsky.social · 23/09/2025

Or dare we say... Engineering? 😬

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Alexander Jahn @physicistalex.bsky.social · 13/09/2025

You can tell that the #QIP2026 deadline has not yet passed, since @zoltanzimboras.bsky.social has not given word on his submission yet.

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Sean Carroll @seanmcarroll.bsky.social · 05/09/2025

Postdoc job! I expect to have an opening at Johns Hopkins for a postdoctoral researcher working somewhere in the broad realms of physics, philosophy, and complexity. Apply at Academic Jobs Online: academicjobsonline.org/ajo/jobs/30496

academicjobsonline.org

Johns Hopkins University, Physics and Astronomy

Job #AJO30496, Postdoctoral Fellow in Foundations of Physics, Complexity, and Emergence, Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland, US

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Alexander Jahn @physicistalex.bsky.social · 31/08/2025

Thanks Zoltan! You should petition the museum to add some hyperbolic tilings as well, there's plenty of material in our papers. 😁

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Alexander Jahn @physicistalex.bsky.social · 29/08/2025

It would be a lost opportunity if they didn't call it the Ministry of Magic (state distillation).

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Francesco Arzani @frarzani.bsky.social · 26/08/2025

Looking for a postdoc to work on bosonic quantum error correction! Join me and the QAT team at ENS & INRIA Paris — flexible start date. Details here 👉 recrutement.inria.fr/public/class... or feel free to reach out!

recrutement.inria.fr

Post-Doctoral Research Visit F/M Senior postdoctoral researcher in bosonic quantum error correction

Offre d'emploi Inria

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

This suggests a deep relationship between equilibration strength and entanglement phases in many-body quantum systems! The main idea: More entanglement = stronger equilibration.

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

For the condensed-matter theorists among you, our work also leads to an interesting conjecture: RTNs on different geometries describe different phases of entanglement scaling. We show that D_eff follows a sharp hierarchy between area- and volume-law phases.

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

This means that random tensor networks know a lot more about holographic dynamics than we expected, and may be able to hold more insights into (holographic) quantum gravity.

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

And surprisingly, the result matches gravitational degree-of-freedom counting in holography: If we "fuse" tensors together, i.e., replace part of the bulk geometry by a "black hole", D_eff always *increases*. Just as in gravity, where a black hole is the highest-entropy state!

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

This brings us to holography: For holographic RTNs, we can now compute the minimum effective dimension D_eff that describes late-time dynamics! From the geometry and bond dimension of the RTN alone, we can determine how complex its dynamics must be.

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

Now here's the kicker: For random ensembles, we can strictly lower-bound D_eff *without knowing H*! In a sense, the randomness cancels out its exact eigenstate structure. This is a trick we learned from Haferkamp et al., who used it on random MPS: arxiv.org/abs/2103.02634

arxiv.org

Emergent statistical mechanics from properties of disordered random matrix product states

The study of generic properties of quantum states has led to an abundance of insightful results. A meaningful set of states that can be efficiently prepared in experiments are ground states of gapped ...

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

The key quantity to describe the strength of equilibration is the "effective dimension" D_eff, which basically counts how many (energy) states are needed to describe late-time dynamics.

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

Here's how it works: In a quantum system, expectation values of observables fluctuate. At late times, even a pure state will *equilibrate*, meaning that local expectation values will fluctuate within a fixed window. This happens for all Hamiltonians H with "non-degenerate gaps".

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

In our paper, we bring in ideas from quantum statistical mechanics to show that the opposite is true: Thanks to the randomness in RTNs, we can probe late-time dynamics without knowing the explicit Hamiltonian! The key concept that enables this is called *equilibration*.

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

That makes choosing a Hamiltonian that performs time evolution on the boundary difficult: Any choice, e.g. motivated from AdS/CFT arguments, would time-evolve different RTN samples differently. Thus, it seemed that randomness made time evolution impossible to describe!

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

This sparked hundreds of follow-up papers - many of which refined the original proposal - but there was one limitation: Random tensor networks (RTNs) produce an *ensemble* of states, with every random sample looking quite different locally.

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

Some background: In a seminal paper from 2016, Hayden et al. showed that tensor networks with locally random tensors, if put on a hyperbolic geometry, reproduce quantum states that very closely resemble boundary states of the AdS/CFT duality. arxiv.org/abs/1601.01694

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Alexander Jahn @physicistalex.bsky.social · 25/08/2025

Very happy to have this paper with @jenseisert.bsky.social and his PhD student Shozab Qasim out on the @arxiv.bsky.social! It achieves something that, until recently, I thought to be impossible: To use random tensor networks to study holographic *dynamics*.

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Alexander Jahn @physicistalex.bsky.social · 16/08/2025

They've obviously been best friends for years, I don't know why this is so hard for the media to acknowledge.

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Matt Green @mattgreencomedy.com · 16/08/2025

At least Chamberlain got a piece of paper

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Alexander Jahn @physicistalex.bsky.social · 13/08/2025

Back from an exciting week visiting the great @zoltanzimboras.bsky.social in Budapest! As you can see, I was also very busy pensively staring at Platonic solids at the Hungarian National Museum.

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