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.
Hi all,
Apologies for the late email. This afternoon Diane Saint Aubin will tell us
about her semester project, entitled "Lower and upper bounds on quantum key
distribution protocols". See below for the abstract. We'll start as usual
at 2pm in/at https://ethz.zoom.us/j/362994444.
Best,
Joe
Abstract:
The 3-state quantum key distribution protocol has two entanglement-based
descriptions, raising the question of which one is best used to compute the
key rate. We show that the descriptions are equivalent, and that
symmetrising the state used in the protocol can give a lower bound on the
secret key rate. In addition, we provide an upper bound for the BB84
protocol using the intrinsic information which just outperforms a recent
bound by Xing Wang. For the device independent protocol based on the CHSH
game, thresholds on the key rate are found depending on the observed
parameters. We find an upper bound for protocols using one way-classical
communication, which is much tighter than the previous two-way classical
communication bound for low values of the Bell violation.
Hi all,
Tomorrow our new postdoc Christopher Chubb will tell us about his research,
in particular his latest paper "General tensor network decoding of 2D Pauli
codes". See below for the abstract, or the full paper at
https://arxiv.org/abs/2101.04125. We start at 2pm in zoom:
https://ethz.zoom.us/j/362994444.
Best,
Joe
Abstract:
In this work we develop a general tensor network decoder for 2D codes.
Specifically, we propose a decoder which approximates maximally likelihood
decoding for 2D stabiliser and subsystem codes subject to Pauli noise. For
a code consisting of $n$ qubits our decoder has a runtime of $O(n\log
n+n\chi^3)$, where $\chi$ is an approximation parameter. We numerically
demonstrate the power of this decoder by studying four classes of codes
under three noise models, namely regular surface codes, irregular surface
codes, subsystem surface codes and colour codes, under bit-flip, phase-flip
and depolarising noise. We show that the thresholds yielded by our decoder
are state-of-the-art, and numerically consistent with optimal thresholds
where available, suggesting that the tensor network decoder well
approximates optimal decoding in all these cases. Novel to our decoder is
an efficient and effective approximate contraction scheme for arbitrary 2D
tensor networks, which may be of independent interest.