Alexander Jahn

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

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.

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

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

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

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!

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

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*.

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

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*.

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.

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*.

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.

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*.

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.

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*.

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*.

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*.

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.

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*.

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...

Our conclusion: Holographic codes aren't just cool physical models, but might actually be useful! We've already shown they have more nice features in two further papers: 1) Reaching the Hashing bound: arxiv.org/abs/2408.06232 2) Building fault-tolerant logic: arxiv.org/abs/2504.10386

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...

We look at different error models - erasures, depolarizing, and biased-Pauli - and find *thresholds* for all of them: If you scale up the code, errors below a certain rate get suppressed arbitrarily well!

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...

The resulting codes - Evenbly codes! - behave similar to HaPPY codes, but don't use perfect tensors and model small quantum gravity corrections. arxiv.org/abs/2304.02732

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...

That gives you a number of neat holography features, but rather impractical codes: Building code states with a lot of entanglement is hard! Plus, describing the *quantum* gravity regime of holography ("finite N") should give you less entangled states. So we want less-than-perfect tensors.

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...