Alexander Jahn
physicistalex.bsky.social
Alexander Jahn
@physicistalex.bsky.social
Junior research group leader in Berlin. Working in the borderlands of quantum information, condensed matter physics, and string theory.
Reposted by Alexander Jahn
If you are interested in doing a postdoc with me, please apply to the IQC postdoctoral fellowship here: iqc-uwaterloo.slideroom.com#/login/progr...
University of Waterloo Attn: Institute for Quantum Computing - SlideRoom
Apply to University of Waterloo Attn: Institute for Quantum Computing. Powered by SlideRoom.
iqc-uwaterloo.slideroom.com
November 6, 2025 at 7:12 PM
Reposted by Alexander Jahn
(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...
October 21, 2025 at 1:47 PM
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!
October 7, 2025 at 3:26 PM
You can tell that the #QIP2026 deadline has not yet passed, since @zoltanzimboras.bsky.social has not given word on his submission yet.
September 13, 2025 at 9:50 AM
Reposted by Alexander Jahn
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
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
academicjobsonline.org
September 5, 2025 at 5:26 PM
Reposted by Alexander Jahn
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!
Post-Doctoral Research Visit F/M Senior postdoctoral researcher in bosonic quantum error correction
Offre d'emploi Inria
recrutement.inria.fr
August 26, 2025 at 1:14 PM
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*.
Random #tensornetworks provide a powerful framework for probing and understanding complex quantum systems, especially in regimes where conventional tools fail. Here, we rigorously investigate dynamical properties of holographic toy models.

scirate.com/arxiv/2508.1...
August 25, 2025 at 1:05 PM
They've obviously been best friends for years, I don't know why this is so hard for the media to acknowledge.
Trump claps for Putin as he arrives in Alaska.
August 16, 2025 at 10:01 AM
Reposted by Alexander Jahn
At least Chamberlain got a piece of paper
August 16, 2025 at 7:12 AM
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.
August 13, 2025 at 9:13 PM
A second Quantum paper within three weeks!

We show how to construct a class of qubit "Evenbly codes" - toy models of holography at finite N - which turn out to be highly tunable subsystem codes that can be made resilient against different types of quantum noise.

Why "Far from Perfect"? Well...
Far from Perfect: Quantum Error Correction with (Hyperinvariant) Evenbly Codes
Quantum 9, 1826 (2025). https://doi.org/10.22331/q-2025-08-08-1826 We introduce a new class of qubit codes that we call Evenbly codes, building on a previous proposal of hyperinvariant tensor networks. Its tensor network description consists of local, non-perfect tensors describing CSS codes interspersed with Hadamard gates, placed on a hyperbolic $\\{p,q\\}$ geometry with even $q\geq 4$, yielding an infinitely large class of subsystem codes. We construct an example for a $\\{5,4\\}$ manifold and describe strategies of logical gauge fixing that lead to different rates $k/n$ and distances $d$, which we calculate analytically, finding distances which range from $d=2$ to $d \sim n^{2/3}$. Investigating threshold performance under erasure, depolarizing, and pure Pauli noise channels, we find that the code exhibits a depolarizing noise threshold of about 19.1% in the code-capacity model and 50% for pure Pauli and erasure channels under suitable gauges. We also test a constant-rate version with $k/n = 0.125$, finding excellent error resilience (about 40%) under the erasure channel. Recovery rates for these and other settings are studied both under an optimal decoder as well as a more efficient but non-optimal greedy decoder. We also consider generalizations beyond the CSS tensor construction, compute error rates and thresholds for other hyperbolic geometries, and discuss the relationship to holographic bulk/boundary dualities. Our work indicates that Evenbly codes may show promise for practical quantum computing applications.
quantum-journal.org
August 11, 2025 at 12:36 PM
Even before being replaced by AI, the jobs of American comedians have apparently been made obsolete.
August 1, 2025 at 10:01 PM
The first paper with my PhD student Dimitris Saraidaris is now published in Quantum!

We explore the symmetries of discrete-holographic models and find that they generically produce critical phases in spin systems - but only when the symmetries describe a "dual" bulk geometry!
July 24, 2025 at 4:02 PM
Reposted by Alexander Jahn
I am looking for a PhD student to explore quantum advantage with indistinguishable particles in my group at CTP PAS, Warsaw (within Quantera TouQan project touqan.eu). 4‑yr scholarship, start  Oct 2025. Apply by 8 Aug 2025: euraxess.ec.europa.eu/jobs/360583
Touqan Quantera Project
touqan.eu
July 18, 2025 at 7:42 AM
We should be more understanding: Grok initially wanted to be an image-generation AI, but then it was rejected by Midjourney Inc.
July 9, 2025 at 6:51 AM
Very proud of my PhD student Lev Shaposhik for winning a poster prize at QIQG25 at @perimeterinstitute.ca!

He's the main driver behind our work on von Neumann algebras in infinite tensor networks from April, see thread below.
June 27, 2025 at 10:40 PM
POV: You think you're attending a quantum gravity conference, but it's just a Lenny Susskind birthday party in disguise.
June 25, 2025 at 10:06 PM
At Perimeter Institute in Waterloo for QIQG25 this week!

Lenny Susskind started his opening talk on de Sitter holography in classic Lenny Susskind style:
"Hello children."
June 23, 2025 at 8:53 PM
At least there's still one geopolitical certainty under Trump:

WW3 will never start on a stock trading day.
June 22, 2025 at 4:31 AM
Reposted by Alexander Jahn
Open position at QuSoft / University of Amsterdam: Assistant Professor in Quantum Computing and Simulation for Quantum Chemistry and Materials
qusoft.org/qusoft-vacan...
Deadline: 14 July 2025
QUSOFT Vacancies – Qusoft
qusoft.org
June 11, 2025 at 10:37 AM
After the success of #Andor, there's only one logical direction for Disney to take the Star Wars franchise:
A two-hour ASMR video of Ben Mendelsohn saying "Deep-substrate Foliated Kalkite".
June 9, 2025 at 7:03 PM
"Where is the Lagrangian, Donald?"
I think Elon and Trump need to go on Piers Morgan and have a civilized discussion
June 6, 2025 at 9:23 AM
Reposted by Alexander Jahn
An article in the leading daily newspaper @tagesspiegel.de on #Berlin as a place for doing good research on quantum science and technology. And what BERLIN QUANTUM and several other initiatives have to do with it.

www.tagesspiegel.de/themenspezia...
Palo Alto in Dahlem?: Berlin auf dem Weg zur Quantenmetropole
Die Initiative „Berlin Quantum“ nimmt Fahrt auf und will komplexe Quantenwelt besser nutzbar machen – mit jeder Menge Drittmitteln im Rücken.
www.tagesspiegel.de
June 6, 2025 at 9:09 AM
My talk on fault-tolerant universal gates with holographic codes, recorded last month in Kyoto, is now online:
m.youtube.com/watch?v=z5DY...
May 12, 2025 at 1:38 PM
Prepared a papal dish this Sunday.
May 11, 2025 at 12:37 PM