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Publications & Talks
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Phase Space Compression
Kristina Giesel
Abstract coming soon...
Talk
Phase Space Compression
Kristina Giesel
Abstract coming soon...
TBD
Biao Lian
TBD
Talk
TBD
Biao Lian
TBD
Hyperinvariant Spin-Network
Hanno Sahlmann
Abstract coming soon...
Talk
Hyperinvariant Spin-Network
Hanno Sahlmann
Abstract coming soon...
Can the quantum switch be deterministically simulated?
Jessica Bavaresco
Higher-order transformations acting on input quantum channels in an indefinite causal order—such as the quantum switch—cannot be described by quantum circuits using the same number of calls to the input channels. A natural question is whether they can be simulated, i.e., whether their action can be exactly and deterministically reproduced by a quantum circuit with more calls to the input channels. Here, we prove that the quantum switch acting on two n-qubit channels cannot be simulated by any quantum circuit using k calls to one channel and one to the other, if k < 2^n. This establishes an exponential separation in quantum query complexity between processes with indefinite causal order and quantum circuits. Moreover, even with one extra call to both input channels, such a simulation remains impossible. We further demonstrate the robustness of this separation by extending the result to probabilistic and approximate simulations scenarios. Based on Nat. Commun. 16, 10216 (2025), arXiv:2409:18202 [quant-ph].
Talk
Can the quantum switch be deterministically simulated?
Jessica Bavaresco
Higher-order transformations acting on input quantum channels in an indefinite causal order—such as the quantum switch—cannot be described by quantum circuits using the same number of calls to the input channels. A natural question is whether they can be simulated, i.e., whether their action can be exactly and deterministically reproduced by a quantum circuit with more calls to the input channels. Here, we prove that the quantum switch acting on two n-qubit channels cannot be simulated by any quantum circuit using k calls to one channel and one to the other, if k < 2^n. This establishes an exponential separation in quantum query complexity between processes with indefinite causal order and quantum circuits. Moreover, even with one extra call to both input channels, such a simulation remains impossible. We further demonstrate the robustness of this separation by extending the result to probabilistic and approximate simulations scenarios. Based on Nat. Commun. 16, 10216 (2025), arXiv:2409:18202 [quant-ph].
Black holes, singularities, and quantum reference frames
Josh Kirklin
One version of the black hole information problem is the apparent incompatibility of unitarity with the fact that generalized entropy along semiclassical time appears to inevitably increase. But in quantum gravity, time must be defined relative to a quantum clock, and I will argue that accounting for this fundamentally changes the usual picture. In particular, when the clock’s quantum fluctuations are non-negligible, generalized entropy need not be monotonic with respect to the clock reading. This relaxes a key assumption underlying information-loss arguments and suggests a resolution based on quantum reference frames. I will also describe related consequences for the formation of singularities and the quantum focusing conjecture.
Talk
Black holes, singularities, and quantum reference frames
Josh Kirklin
One version of the black hole information problem is the apparent incompatibility of unitarity with the fact that generalized entropy along semiclassical time appears to inevitably increase. But in quantum gravity, time must be defined relative to a quantum clock, and I will argue that accounting for this fundamentally changes the usual picture. In particular, when the clock’s quantum fluctuations are non-negligible, generalized entropy need not be monotonic with respect to the clock reading. This relaxes a key assumption underlying information-loss arguments and suggests a resolution based on quantum reference frames. I will also describe related consequences for the formation of singularities and the quantum focusing conjecture.
Why Wigner’s friend matters for quantum gravity
Renato Renner
An emerging insight in quantum gravity is that observable quantities gain meaning only when defined relative to explicitly modelled observers. These observers must themselves be physical and, hence, are subject to the laws of quantum theory. On a different front, it has long been understood in quantum foundations that treating observers as quantum systems leads to conceptual challenges, exemplified by Wigner’s friend thought experiments. In my talk, I will show how recent insights from these thought experiments can help clarify questions that arise when incorporating observers into quantum-gravitational scenarios. Related paper: arXiv:2504.03835
ETH Zurich
Talk
Why Wigner’s friend matters for quantum gravity
Renato Renner
An emerging insight in quantum gravity is that observable quantities gain meaning only when defined relative to explicitly modelled observers. These observers must themselves be physical and, hence, are subject to the laws of quantum theory. On a different front, it has long been understood in quantum foundations that treating observers as quantum systems leads to conceptual challenges, exemplified by Wigner’s friend thought experiments. In my talk, I will show how recent insights from these thought experiments can help clarify questions that arise when incorporating observers into quantum-gravitational scenarios. Related paper: arXiv:2504.03835
ETH Zurich
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