Hi all,
Next week we will have two seminars.
On Monday at 15:00 in HIT E41.1:
(1) Yuma Stäubli will talk about “Observers in Black Holes”
(2) Benjamin Asch Ruiz will talk about “Renyi-Entropy Bounds for Randomness Extraction”
On Friday at 14:00 in HIT E41.1, our visitor Liuhang Ye will talk about “Strong Converse Bounds for Classical Identification over Quantum Channels”
See below for the abstracts.
Best,
Ladina
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Title:
Observers in Black Holes
Abstract:
In quantum gravity, emergent spacetime has been described using codes that map between the effective gravitational theory and the fundamental description. When describing the interior spacetime of old black holes, the code becomes highly non-isometric, as the fundamental space is much smaller than the effective space. This causes disagreements between the effective theory and the fundamental description, even in regimes where we would expect the effective theory to hold. To amend this problem, an observer has been added to the encoding in recent work, leading to codes that are approximately isometric.
In this talk, we first review the concepts of emergent spacetime and encoding maps, and then investigate the role of the observer in these codes. We explore to what extent it captures common intuitions about the notion of an observer, and argue that they act as an interface between the fundamental and effective description.
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Title:
Renyi-Entropy Bounds for Randomness Extraction
Abstract:
Randomness is a fundamental resource in cryptography, randomized algorithms, simulation, and quantum information processing, but real random sources are often imperfect: they may be biased, correlated, or partly known to an adversary. Randomness extraction asks when such imperfect sources can still be converted into bits that are close to uniform and secure.
We introduce and explain the difficulties of randomness extraction in the presence of quantum side information and explain how entropy is used to quantify the amount of usable randomness in a source. We then focus on a simple two-source extraction procedure based on the inner product function, using it to illustrate the standard proof strategy. We present two main improvements: a sharper binary-source entropy bound and a mixed order Renyi bound obtained through interpolation.
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Title:
Strong Converse Bounds for Classical Identification over Quantum Channels
Abstract:
Message identification is a communication task introduced by Ahlswede and Dueck in which the receiver does not aim to recover the transmitted message, but only to determine whether a particular message was sent. This seemingly weaker task exhibits a striking phenomenon: while the number of reliably transmissible messages grows exponentially with the number of uses of the channel, the number of reliably identifiable messages can grow doubly exponentially. In this talk, I will first introduce the identification problem and explain its relation to ordinary message transmission. I will then present two recent results for the depolarizing channel. First, I will discuss a new strong converse bound for the identification capacity, obtained by relating identification codes to coverings of the channel output geometry. Second, if time permits, I will discuss a more restricted version of the task called simultaneous identification, and show that under product-basis measurements the identification capacity for the depolarizing channel coincides with its transmission capacity.