Hi all,
Tomorrow Ladina Hausmann will tell us about her master thesis, entitled
''Axiomatic Black Hole Thermodynamics''. See below for the abstract. We
start at 2pm in zoom: https://ethz.zoom.us/j/362994444.
Best,
Joe
Abstract:
In order to establish under which conditions specific results from black
hole thermodynamics hold, it is important to know which assumptions were
made on the thermodynamic theory. This can be accomplished through the use
of a rigorous phenomenological axiomatic framework, such at that proposed
by Kammerlander [1]. However, existing frameworks only consider energy as a
conserved quantity. This means that the applicability of these frameworks
to systems which have multiple conserved quantities is limited. As black
holes have internal angular momentum and charge, this limitation also
extends to them. In this work, we address this by extending Kammerlander's
framework to describe multiple conserved quantities.
To do so, we first consider microscopic thermodynamics to extend
Kammerlander's framework and then to verify our generalisations. Next, we
apply our extended framework to black holes, and we successfully confirm
all previously established results which we took under consideration.
[1] Philipp Kammerlander. Tangible Phenomenological Thermodynamics. PhD
thesis, ETH Zurich, 2019
Hi all,
Tomorrow Julia Karlen will tell us about her semester project with Jinzhao,
entitled "Entropy and entanglement wedge reconstruction in holography". See
below for the abstract. We start at 2pm on zoom:
https://ethz.zoom.us/j/362994444.
Best,
Joe
Abstract:
Holography states that gravitational physics in the bulk can be
equivalently described as an ordinary quantum theory on its boundary. We
review some recent developments of the AdS/CFT correspondence in the
semiclassical limit. We take a closer look at the derivation of the
holographic entanglement entropies, using the gravitational replica method.
With the cosmic brane prescription, we can deduce, that the refined Rényi
entropy has an area law such as the Ryu-Takayanagi (RT) formula for the von
Neumann entropy. A black hole in Jackiw–Teitelboim (JT) gravity is examined
to elaborate the RT formula. AdS/CFT bears some mysterious features, which
hint at a quantum error correction viewpoint, where the bulk information
can be redundantly encoded into the boundary using error correcting codes.
>From this perspective, the equivalence of the RT formula, entanglement
wedge reconstruction and the matching of the relative entropies in bulk and
boundary can be demonstrated. Within the framework of universal recovery
channels, exact and approximate entanglement wedge reconstruction are
examined more carefully.
Hi all,
Tomorrow Mischa will tell us about one of his recent projects, entitled
"How to tell the time with a clock that's always off." See below for the
abstract. We'll start at 2pm in zoom: https://ethz.zoom.us/j/362994444.
Best,
Joe
Abstract:Conventional wisdom suggests that in order for a clock to be able
to tell the time, the clock cannot be a static device, since if it were,
the clock at different times would be indistinguishable. In other words,
the clock must be switched on. This widely held belief is indeed true for
all classical clocks. We show however, that somewhat counter-intuitively, a
quantum clock can be proven to measure to arbitrary high precision how much
time has passed between two events, even though it has always been off
during and before these events took place. Our results use counterfactual
reasoning to show that the mere fact that a clock could have been switched
on allows us to predict time even if it was never switched on in the past,
present, or future. Our protocols provide fresh insight into an over 2000
year old debate regarding the nature of time | lending support for the
substantival theory of time.
Hi all,
Tomorrow our new postdoc Ramona Wolf will tell us about her research, in
particular "Fusion categories and lattice models". See below for the
abstract. We start at 2pm on Zoom: https://ethz.zoom.us/j/362994444
Best,
Joe
Abstract:
While fusion categories are already an interesting subject from a purely
mathematical perspective, they can furthermore be used in physics to study
conformal field theories via 1D and 2D lattice models. In my talk I will
explain the basic theory of fusion categories and explain their connection
to conformal field theory. I will also discuss how to construct a lattice
model from a fusion category (and the context in which this problem arises)
via the Levin-Wen stringnet model.
Hi all,
Tomorrow Julian Arnold will tell us about his master's thesis project, on
"Entropy production in ticking clocks". See below for the abstract. We
start at 2pm in zoom: https://ethz.zoom.us/j/362994444
Best,
Joe
Abstract:
The concept of time and its role in physics, in particular quantum theory,
remains an active field of research. The act of timekeeping is linked to
the usage of clocks as reference systems. Thus, many open questions about
time can be addressed through the study of these devices. Ticking clocks
provide information about the flow of time in terms of discrete ``ticking''
events. In this thesis, we studied autonomous ticking clocks based on a
model derived from axiomatic principles [M. P. Woods, Quantum 5, 381
(2021)]. We tried to answer the question whether the theory of quantum
information imposes any constraints on the relation between the entropy
production per tick of a ticking clock and its accuracy. Here, the entropy
production serves as a measure for the exchanged information between a
ticking clock and its outside. We find that there exist quantum ticking
clocks with coherent internal dynamics that approach infinite accuracy at
zero entropy production per tick. In contrast, ticking clocks whose state
remains incoherent at all times must produce a minimal amount of entropy in
each tick that increases with increasing accuracy. For such clocks the
entropy production per tick acts as a fundamental resource for measuring
time.
Hi all
Next Monday (March 15) at 4 pm we welcome Tom Purves and Tony Short from
the University of Bristol who will speak to us about their recent important
result, *"Quantum theory cannot violate a causal inequality"*,
https://arxiv.org/abs/2101.09107.
The talk will take place in the usual QIT seminar zoom room,
https://ethz.zoom.us/j/362994444, at 16:00 Zürich time (3 pm U.K. time).
*Abstract:*
*Within quantum theory, we can create superpositions of different causal
orders of events, and observe interference between them. This raises the
question of whether quantum theory can produce results that would be
impossible to replicate with any classical causal model, thereby violating
a causal inequality. This would be a temporal analogue of Bell inequality
violation, which proves that no local hidden variable model can replicate
quantum results. However, unlike the case of non-locality, we show that
quantum experiments can be simulated by a classical causal model, and
therefore cannot violate a causal inequality.*
Regards
Ralph
Hi all,
Tomorrow our new postdoc Esteban Castro will tell us about his research,
specifically "Regular representation approach to quantum reference frame
transformations". See below for the abstract. We start at 2pm on zoom:
https://ethz.zoom.us/j/362994444
Best,
Joe
------
Recent works on quantum reference frames outline a promising research
direction to study space and time from an inherently quantum point of view.
In this talk, I will summarise some important aspects of these works and
present a new method for quantum reference frame transformations, which
complements previous approaches. As an application of the method, I will
discuss quantum reference frame transformations for the (centrally
extended) Galilei group.
Hi all,
Tomorrow Anian Altherr will present his master's thesis, entitled "Quantum
metrology for non-Markovian processes". See below for the abstract. We
start at 2pm on zoom: https://ethz.zoom.us/j/362994444
Best,
Joe
---------------------
Quantum metrology is concerned with finding precision bounds in
parameter estimation of a given sample. Whereas classical strategies
allow the precision to scale at most linearly with the number of
resources used, quantum strategies can achieve a quadratic scaling.
Noise, however, in general reduces the quadratic scaling to a linear
scaling. Most work so far has dealt with assessing Markovian noise, but
in the future, assessing time-correlated noise, e.g. in deep quantum
circuits, will be of increasing interest. A general framework to assess
such non-Markovian noise has been missing. In this work, we use quantum
combs to model non-Markovian noise and express its quantum Fisher
information in terms of a semidefinite program and the conditional
min-entropy. We apply the semidefinite program to collision models,
which serve as an instance of non-Markovian noise. Numerics show that
the non-Markovian setting allows for more precise estimators than the
Markovian setting. Finally, we employ variational circuits to find an
explicit metrological setup that achieves the maximal precision.
Hi all,
Tomorrow Elias Huber will present his semester project, entitled "Maxwell's
Demon". See the abstract below. Usual time and place, 2pm at
https://ethz.zoom.us/j/362994444.
Best,
Joe
Abstract:
Maxwell's demon has been proclaimed exorcised more than once but continues
to fascinate in many ways. In this talk I will first give an introduction
to the theory of phenomenological thermodynamics presented by Dr. Philipp
Kammerlander in his PhD thesis [https://doi.org/10.3929/ethz-b-000413414].
I then talk about the role of phenomenological thermodynamics in the
discussion of Maxwell’s demon and go on to give a detailed description of
the Szilard engine. This description will be based on Landauer’s principle
and in agreement with the postulates of thermodynamics. Finally, we will
look at another thought experiment of an automated (Szilard engine-like)
demon and talk about the importance of fluctuations.
Hi all,
Tomorrow Roman Wixinger will present his semester project “Uncomputation
and Entanglement in High-level Quantum Programming Languages”, conducted
under the supervision of Prof. Christian Mendl at TU München. See below for
the abstract. We start as usual at 2pm on zoom:
https://ethz.zoom.us/j/362994444.
Best,
Joe
Quantum programming languages traditionally focus on the hardware level
and are therefore not really good at representing the intentions of the
programmer. Explicit formulation of uncomputation, which is essential
for the safe and efficient use of the qubits, makes the code
unnecessarily complex. In recent work, Vechev et al. (2020) introduced
Silq, a high-level language that allows for safe, automatic
uncomputation just using its type system. This feature makes the code
significantly shorter and more intuitive. The type system can also
ensure that any program that compiles is physical. In this project, we
compared Silq’s solution of handling uncomputation with other approaches
and give an overview of the features of quantum languages. We have also
tried to understand whether a qubit can be safely discarded by directly
looking at the entanglement.