Hi all,
Tomorrow Sven Jandura will tell us about his master thesis with Ernest,
entitled "De Finetti Theorems for Quantum Conditional Probability
Distributions with Symmetry". See below for the abstract. We start at 2pm
on zoom: https://ethz.zoom.us/j/362994444.
Best,
Joe
Abstract: In device independent quantum key distribution (DIQKD) Alice
and Bob try to establish a shared secret key without trusting the
devices used in key generation. The setup must therefore be treated as a
black box and is mathematically described by a conditional probability
distribution. Security proofs of DIQKD protocols can be simplified if
the attacker can be restricted to attack each round in the key
distribution process in an identical fashion (collective attacks). For
many protocols such a reduction is available through the entropy
accumulation theorem (EAT), but there are interesting protocols where
the EAT is not applicable. In this presentation we introduce two de
Finetti theorems that relate the properties of an arbitrary
Clauser-Horne-Shimony-Holt (CHSH) symmetric quantum black box to a
convex combination of iid quantum black boxes (de Finetti boxes). We
further discuss how these theorems could be used in DIQKD security
proofs, even if the EAT is not applicable, to impose restrictions on the
attacker.
Dear all,
Happy World Quantum Day! Join us today for a lunch interview with Renato
and Yiwen Chu at 12:00.
Best,
Lídia
———————————————————————————————————————————————————
>
> Dear all,
> April 14th is*World Quantum Day*! On the occasion of the launch of
> this initiative, the Quantum Center, ETH Zurich invites you, your
> family and friends to an online interview with Professors*Yiwen Chu
> and Renato Renner*, moderated by Chiara Decaroli. We will talk about
> what does it mean to be a Quantum Scientist, what is Quantum Science
> and what kinds of research are carried out by Quantum Center members.
> Join us on*April 14th, 2021 at 12:00*Zurich time at the following zoom
> link:https://ethz.zoom.us/j/68223543732
> <https://ethz.zoom.us/j/68223543732>
> ———————————————————————————————————————————
> /What is the World Quantum Day?/
> //
> The World Quantum Day is a new decentralised outreach initiative to
> promote the public understanding of quantum science and technology. We
> invite all quantum scientists, engineers, educators, communicators
> andentrepreneursto promote their own activities, such as outreach
> talks, lab tours, debates, lectures or interviews at a global scale.
> This year we celebrate the first World Quantum Day, on the 14th of
> April. Find out more and register your own events
> athttps://worldquantumday.org <https://worldquantumday.org/>
> /What is the Quantum Center, ETH Zurich?/
> //
> The freshly launchedQuantum Center <http://www.qc.ethz.ch/>is a
> network of 28 research groups from ETH Zurich and PSI. The Center
> coordinates the various scientific and structural activities in
> quantum science and technology at ETH Zurich. In particular, it
> interconnects research and teaching across ETH departments and further
> strengthens current activities by leveraging the broad competencies
> available at ETH Zurich. You can follow us on Twitter: @ETHQuantumCntr
> and sign up to theQuantum Center Newsletter
> <https://qc.ethz.ch/news-events/mailing-list.html>to stay in touch and
> learn about upcoming activities.
> Best regards,
> Chiara Decaroli, Lidia del Rio & Francesca Bay
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.