Hi all,
Next Monday, Elias Rothlin will tell us about “Exploring the Connection between Gauge Theory and Quantum Error Correction via Quantum Reference Frames”. See below for the abstract.
The talk will take place on Monday at 11:15 in HIT F 32.
Best,
Ladina
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Title:
Exploring the Connection between Gauge Theory and Quantum Error Correction via Quantum Reference Frames
Abstract:
How is physical information robustly preserved in quantum gauge theories? One possible way of addressing …
[View More]this question is by noticing that gauge systems share a key feature with quantum error correction codes (QECCs): in both cases, the relevant information is redundantly encoded in a larger space. In gauge theories, this ensures invariance under certain gauge symmetry transformations, while in QECCs, it protects logical data against noise by distributing it as entanglement across many subsystems. This connection has been made precise in prior work where stabilizer QECCs were interpreted as gauge systems and their error correction properties were investigated via the perspective-neutral framework of quantum reference frames (QRFs). Applying the tools of this formalism, we identify sets of correctable errors for general gauge systems viewed as QECCs. As an example, we analyze lattice quantum electrodynamics as a QECC and its correctable errors tied to QRFs and to syndrome measurements.
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Hi all,
This week, our visitor Richard Kueng will talk about “Quantum-enhanced shadow tomography of (very many) Pauli observables”. See below for the abstract. The talk will take place on Thursday at 14:00 in HIT E41.1
Best,
Ladina
****
Title:
Quantum-enhanced shadow tomography of (very many) Pauli observables
Abstract:
Shadow tomography protocols have recently emerged as powerful tools for efficient quantum state learning, aiming to reconstruct expectation values of observables with …
[View More]considerably fewer resources than traditional quantum state tomography. For the particular case of estimating Pauli observables, entangling two-copy measurement schemes can offer an exponential improvement in sample complexity over any single-copy strategy conceivable [Huang, Kueng, Preskill, PRL (2021)]. A recent refinement of these ideas by King et al. King, Gosset, Kothari, Babbush, SODA (2025)] does not only achieve polynomial sample complexity, but also maintains reasonable computational demands and utilizes joint measurements on only a small constant number of state copies. This ‘triple efficiency’ is achievable for any subset of n-qubit Pauli observables, whereas single-copy strategies can only be efficient if the Pauli observables in question have advantageous structure.
In this work, we complement existing theoretical performance guarantees with the empirical evaluation of triply efficient shadow tomography using classical, noise-free simulations. Our findings indicate that the empirical sample complexity aligns closely with theoretical predictions for stabilizer states and, notably, demonstrates slightly improved scaling for random Gibbs states compared to established theoretical bounds. In addition, we improve a central subroutine in the triply-efficient shadow protocol by leveraging insights from a refined quantum and quantum-inspired convex optimization algorithm [Henze et al. arXiv:2502.15426 (2025)].
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Hi all,
This week, Jakob Miller will talk about “Incoherent Feedback Protocols in Timekeeping Devices: Never touch your ticking clocks?”. The talk will take place on Thursday at 11:00 in HIT E41.1. See below for the abstract.
Best,
Ladina
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Title:
Incoherent Feedback Protocols in Timekeeping Devices: Never touch your ticking clocks?
Abstract:
From an operational perspective any physical system that allows one to measure the passage of time can be regarded as a clock. If one …
[View More]additionally demands that the clock is not influenced by the act of reading off the time, one is naturally lead to the formalism of ticking clocks that we introduce in this talk. In particular, we discuss ticking clocks that satisfy the properties of self-timing and clockwork independence. In order to quantify the quality of the clock’s time estimate, we study the signal-to-noise ratio. Motivated by the relevance of feedback mechanisms in atomic clocks, we propose a notion of incoherent feedback protocols for ticking clocks. We provide numeric evidence that feedback-controlled quantum clockworks can achieve fundamentally higher signal-to-noise ratios when compared to their non-controlled counterparts.
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Hi all,
This week, Leonardo Valente will talk about “Decoherence in Quantum Reference Frames”. The talk will take place on Thursday at 11:00 in HIT E41.1. See below for the abstract.
Best,
Ladina
****
Title:
Decoherence in Quantum Reference Frames
Abstract:
We explore the phenomenon of decoherence and how it changes under quantum reference frame (QRF) transformations. In particular, we simulate how gravitationally induced decoherence depends on the chosen QRF. In our model, we find that …
[View More]if a massive particle decoheres smoothly over a finite timescale in one QRF, then from the particle’s own QRF, the decoherence appears instantaneous. We analyse this asymmetry and show, using entropy-based tools, that it does not arise from the existence of a privileged QRF. Additionally, we introduce the notion of non-entangling states — a class of states that preserve entanglement and maintain the tensor product structure under QRF transformations — as a way to keep coherence frame-independent.
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