Past Quantum Lunches

Speaker: Mark Rudner, QDEV/NBIA.
Either: Berry curvature and a more beautiful classical mechanics.
Or: Survival, decay, and topological protection in non-Hermitian quantum transport.

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1 June 2016, 12:00-13:00

Quantum Lunch: Introduction to fermionic observables

Speaker: Jakob Björnberg, QMath.

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25 May 2016, 12:00-13:00

Quantum Lunch: Scalar Field Theories with Polynomial Shift Symmetries

Speaker: Kevin John Torres Grosvenor, NBI.
OBS: Aud 105, NOT 04.4.20.

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18 May 2016, 12:00-13:00

Quantum Lunch: Landauer's principle and the energy cost of measurement

Speaker: David Reeb, Leibniz Universität Hannover.

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11 May 2016, 14:00-15:00

After Quantum Lunch: Entropy power inequalities for qudits

Speaker: Māris Ozols, University of Cambridge.

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11 May 2016, 12:00-13:00

Quantum Lunch: Stahl's Theorem

Speaker: Fabien Clivaz, University of Geneva.

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4 May 2016, 12:00-13:00

Quantum Lunch: Quantum gate learning in engineered qubit networks: Toffoli gate with always-on interactions

Speaker: Leonardo Banchi, UCL.

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27 Apr. 2016, 12:00-13:00

Quantum Lunch: Topological edge states are monogamous

Speaker: Konstantinos Meichanetzidis, Center for Topological Quantum Information (Leeds).

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20 Apr. 2016, 12:00-13:00

Quantum Lunch: Geometry of random planar maps with high degrees

Speaker: Timothy Budd, NBI.

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13 Apr. 2016, 12:00-13:00

Quantum Lunch: Color Codes are cool

Speaker: Benjamin James Brown.

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6 Apr. 2016, 12:00-13:00

Quantum Lunch: Describing non-Markovian open quantum systems

Speaker: Jake Iles-Smith, DTU.

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30 Mar. 2016, 12:00-13:00

Quantum Lunch: Key Distillation

Speaker: Roberto Ferrara.

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23 Mar. 2016, 12:00-13:00

Quantum Lunch: Dirac operators with magnetic link

Speaker: Jeremy Sok.

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16 Mar. 2016, 12:00-13:00

Quantum Lunch: Quantum many-body fluctuations around nonlinear Schrödinger dynamics

Speaker: Chiara Boccato, UZH.

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9 Mar. 2016, 12:00-13:00

Quantum Lunch: Towards experimentally feasible unbounded violation of quantum steering inequality

Speaker: Magdalena Stobinska, University of Gdansk.

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2 Mar. 2016, 12:00-13:00

Quantum Lunch: Tradeoff bounds for local error correction

Speaker: Michael Kastoryano, NBIA.

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24 Feb. 2016, 12:00-13:00

Quantum Lunch: Pattern formation in biological systems & Electroweak baryogenesis in 2HDMs

Speaker: Nils Hermansson Truedsson, Dep. of Astronomy and Theoretical Physics, Lund University.

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17 Feb. 2016, 12:00-13:00

Quantum Lunch: Device-independent two-party cryptography secure against sequential attacks.

Speaker: Jed Kaniewski (QMath), ArXiV:1601.06752.

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10 Feb. 2016, 12:00-13:00

Quantum Lunch: Trace inequalities for arbitrary many matrices via pinching

Speaker: Mario Berta, Caltech.

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3 Feb. 2016, 12:00-13:00

Quantum Lunch: Tandem Talk

Speakers: Alexander Müller-Hermes and Roberto Ferrara.

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27 Jan. 2016, 12:00-13:00

Quantum Lunch: Gaussian optimizers in quantum information

Speaker: Giacomo De Palma, NEST and CNR-NANO.

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20 Jan. 2016, 12:00-13:00

Quantum Lunch: Topological States in Graphene

Speaker: Birger Brietzke.

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13 Jan. 2016, 12:00-13:00

Quantum Lunch: A Pfaffian formula for monomer-dimer partition functions

Speaker: Ian Jauslin.

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6 Jan. 2016, 12:00-13:00

Quantum Lunch: Determinism and causality. Which aspects are shared between classical physics and quantum physics?

Speaker: Peter Harremoes

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16 Dec. 2015, 12:00-13:00

Quantum Lunch

Speaker: Chris Perry

Title: TBA

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9 Dec. 2015, 12:00-13:00

Quantum Lunch: Variational Expressions for Quantum Relative Entropies

Speaker: Marco Tomamichel (Joint work with Mario Berta and Omar Fawzi.)

Abstract: Distance measures between quantum states like the trace distance and the fidelity can naturally be defined by optimizing a classical distance measure over all measurement statistics that can be obtained from the respective quantum states. In contrast, Petz showed that...

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2 Dec. 2015, 12:00-13:00

Quantum Lunch

Speaker: Magnus Goffeng

Title: K-theory and topological insulators

Abstract: This will be an introductory seminar aimed at showing some basic facts in index theory and K-theory in the context of topological insulators.

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25 Nov. 2015, 12:00-13:00

Quantum Lunch

Speaker: n.n.

Title: TBA

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18 Nov. 2015, 12:00-13:00

Quantum Lunch

Speaker: Courtney Brell

Title: Error-correction in non-abelian anyon models

Abstract:

Scalable anyonic topological quantum computation requires the error-correction of non-abelian anyon systems. In contrast to abelian topological codes ...

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11 Nov. 2015, 12:00-13:00

Quantum Lunch

Speaker: Ulrich Linden, University of Stuttgart

Title: On the Fermi Polaron in Two Dimensions

Abstract: We investigate the quantum system of a Fermi gas interacting
attractively with a single impurity by contact interaction in a
two-dimensional box. The contact interaction is implemented by a
limiting procedure ...

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4 Nov. 2015, 12:00-13:00

Quantum Lunch: Extensions of the entanglement entropy for symmetry protected topological order

Title: Extensions of the entanglement entropy for symmetry protected topological order

Speaker: Shunji Matsuura

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28 Oct. 2015, 12:00-13:00

Quantum Lunch: Interaction Effects in Spin-Wave Theory

Title: Interaction Effects in Spin-Wave Theory

Speaker: Niels Benedikter

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21 Oct. 2015, 12:00-13:00

Quantum Lunch: Random permutations and the mean-field Heisenberg model

Title: Random permutations and the mean-field Heisenberg model

Speaker: Jakob Björnberg

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14 Oct. 2015, 12:00-13:00

Quantum Lunch: Renormalising entanglement distillation

Speaker: Earl Campbell

Title: Renormalising entanglement distillation

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7 Oct. 2015, 12:00-13:00

Quantum Lunch: Entanglement Measures

Title: Entanglement Measures

Speaker: Roberto Ferrara

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30 Sept. 2015, 12:00-13:00

Quantum Lunch: Accurate atomic radii from Thomas-Fermi Theory

Title: Accurate atomic radii from Thomas-Fermi Theory

Speaker: Jan Philip Solovej

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23 Sept. 2015, 12:00-13:00

Quantum Lunch: Bogoliubov correction to the mean-field dynamics of interacting bosons

Title: Bogoliubov correction to the mean-field dynamics of interacting bosons

Speaker: Marcin Napiórkowski

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16 Sept. 2015, 12:00-13:00

Quantum Lunch: Quantum Circuits for Isometries

Title: Quantum Circuits for Isometries

Speaker: Raban Iten

Abstract: Every quantum operation can be decomposed into a sequence of single-qubit and Controlled-Not (C-NOT) gates. In many experimental architectures, single-qubit gates are relatively ‘cheap’ to perform compared to C-NOTs (for instance, being less susceptible to noise), and hence it is desirable to minimize the number of C-NOT gates required to implement a circuit. I will consider the task of constructing an arbitrary isometry from m qubits to n qubits, while trying to minimize the number of C-NOT gates required. I will show a lower bound and then give an explicit gate decomposition that gets within a factor of about two of this bound. Through Stinespring’s theorem this points to a C-NOT-efficient way to perform an arbitrary quantum operation.

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9 Sept. 2015, 12:00-13:00

Quantum Lunch

Speaker: Douglas Lundholm

Title: Anyons in the average-field approximation

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2 Sept. 2015, 12:00-13:00

Quantum Lunch: Non-binding of strongly coupled many-polarons in dimensions two and three

Title: Non-binding of strongly coupled many-polarons in dimensions two and three

Speaker: Anton Samojlow

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19 Aug. 2015, 12:00-13:00

Quantum Lunch: Estimates for the lowest eigenvalue of magnetic Laplacians.

Title: Estimates for the lowest eigenvalue of magnetic Laplacians.

Speaker: Fabian Portmann

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1 July 2015, 12:00-13:00

Quantum Lunch: Localization from superselection rules in translation invariant systems

Speaker: Isaac Kim

Abstract: We study a translation invariant spin model in a three-dimensional regular lattice, called the cubic code model, in the presence of arbitrary extensive perturbations. Below a critical perturbation strength, we show that most states with finite energy are localized; the overwhelming majority of such states have energy concentrated around a finite number of defects, and remain so for a time that is near-exponential in the distance between the defects. This phenomenon is due to an emergent superselection rule and does not require any disorder. This is joint a joint work with Jeongwan haah.(1505.01480)

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24 June 2015, 12:00-13:00

Quantum Lunch: Bogoliubov theory at positive temperature

Speaker: Robin Reuvers

Abstract: I will discuss Bogoliubov theory in the translation invariant case of a Bose gas. The theory arises by restriction to translation invariant quasi-free states. I will introduce the positive temperature pressure functional and the corresponding ground state energy functional...

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17 June 2015, 12:00-13:00

Quantum Lunch: Quantum-information processing with solid-state single-photon sources

Speaker: Peter Lohdal (NBI)

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10 June 2015, 12:00-13:00

Quantum Lunch: The fractional Laplacian on bounded domains

Speaker: Gerd Grubb

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3 June 2015, 12:00-13:00

Quantum Lunch: Learning and testing of mixed state spectra

Speaker: John Wright

Abstract:

An experiment produces an unknown mixed state, and you would like to learn some property of this state. How do you do this? The standard approach is to rerun the experiment multiple times and perform some measurement on the copies produced. The goal is then to learn or test the property using the smallest number of copies possible. In some cases, such as performing tomography on rank one pure states, researchers have designed algorithms which are optimal in their copy complexity. However, for many basic properties, including things as basic as estimating a mixed state's spectrum, this remains an open problem.

In this talk, we consider learning and testing properties which depend only on the mixed state's spectrum. Natural problems in this space include learning its spectrum, estimating its von Neumann entropy, or testing whether it is low rank. Our results include (i) a new upper bound for learning a mixed state's spectrum and (ii) an optimal algorithm for testing whether a mixed state is equal to the maximally mixed state. We use techniques from the asymptotic theory of the symmetric group; in particular, we rely on Kerov's algebra of observables to help us study the moments of random Young diagrams.

Joint work with Ryan O'Donnell.

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20 May 2015, 12:00-13:00

Quantum Lunch: Defining work from operational principles

Speaker: Henrik Wilming

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13 May 2015, 12:00-13:00

Quantum Lunch: An adaptive attack on Wiesner's quantum money

Speaker: Daniel Nagaj (Slovak Academy of Sciences)

Abstract:

Unlike classical money, which is hard to forge for practical reasons (e.g. producing paper with a certain property), quantum money is attractive because its security might be based on the no-cloning theorem. The first quantum money scheme was introduced by Wiesner circa 1970. Although more sophisticated quantum money schemes were proposed, Wiesner's scheme remained appealing because it is both conceptually clean and relatively easy to implement.

We show efficient adaptive attacks on Wiesner's quantum money scheme (and its variant by Bennett et al.), when valid money is accepted and passed on, while invalid money is destroyed. We propose two attacks, the first is inspired by the Elitzur-Vaidman bomb testing problem, while the second is based on the idea of protective measurements. It allows us to break Wiesner's scheme with 4 possible states per qubit, and generalizations which use more than 4 states per qubit.

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6 May 2015, 12:00-13:00

Quantum Lunch: an introduction to Hypercontractivity and Log-Sobolev inequalities, and their applications in Mathematical Physics and Quantum Information

Speaker: Michael Kastoryano

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29 Apr. 2015, 12:00-13:00

Quantum Lunch: Factorizable completely positive maps and Quantum Information Theory

Speaker: Magdalena Musat

Title: Factorizable completely positive maps and Quantum Information Theory

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22 Apr. 2015, 12:00-13:00

Quantum Lunch: Energy Levels of Dipoles in Graphene

Title: Energy Levels of Dipoles in Graphene

Speaker: Simone Rademacher

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15 Apr. 2015, 12:00-13:00

Quantum Lunch

Speaker: TBA

Title: TBA

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8 Apr. 2015, 12:00-13:00

Quantum Lunch

Speaker: Min-Hsiu Hsieh

Title: A Classical Analog to Entanglement Reversibility

Abstract:

In this letter we introduce the problem of secrecy reversibility. This asks when two honest parties can distill secret bits from some tripartite distribution pXYZ and transform secret bits back into pXYZ at equal rates using local operation and public communication (LOPC). This is the classical analog to the well-studied problem of reversibly concentrating and diluting entanglement in a quantum state. We identify the structure of distributions possessing reversible secrecy when one of the honest parties holds a binary distribution, and it is possible that all reversible distributions have this form. These distributions are more general than what is obtained by simply constructing a classical analog to the family of quantum states known to have reversible entanglement. An indispensable tool used in our analysis is a conditional form of the G\'{a}cs-K\"{o}rner Common Information.

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25 Mar. 2015, 12:00-13:00

Quantum Lunch: Two results in topology, motivated by quantum computation

Title: Two results in topology, motivated by quantum computation

Speaker: Gorjan Alagic

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18 Mar. 2015, 12:00-13:00

Quantum Lunch

Speaker: Olga Bershtein

Title: TBA

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11 Mar. 2015, 12:00-13:00

Quantum Lunch: Heralded quantum gate with integrated error detection

Speaker: Johannes Borregaard

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4 Mar. 2015, 12:00-13:00

Quantum Lunch: Error distributions on large entangled states with non-Markovian dynamics

Speaker: Dara McCutcheon

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25 Feb. 2015, 12:00-13:00

Quantum Lunch: A flea on Schrödinger's cat

Speaker: Robin Reuvers

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18 Feb. 2015, 12:00-13:00

Quantum Lunch: Cryptography

Speaker: Gorjan Alagic

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11 Feb. 2015, 12:00-13:00

Quantum Lunch: Ground state entanglement constrains low energy excitations

Speaker: Benjamin Brown

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4 Feb. 2015, 12:00-13:00

Quantum Lunch

Title: Dynamical Mean-Field Theory of Fermionic Systems

Speaker: Niels Benedikter

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28 Jan. 2015, 12:00-13:00

Quantum Lunch

Title: Capacities for quantum memories

Speaker: Alexander Mueller-Hermes

Abstract: Quantum memories can be regarded as quantum channels that transmit information through time without moving it through space. Aiming at a reliable storage of information we may thus not only encode at the beginning and decode at the end, but also intervene during the transmission - a possibility not captured by the ordinary capacities....

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21 Jan. 2015, 12:00-13:00

Quantum Lunch

Title: A mean-field approximation of QED

Speaker: Jeremy Sok

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14 Jan. 2015, 12:00-13:00

Quantum Lunch: Finding large gaps between tensor rank and border rank via algebras

Speaker: Jeroen Zuiddam

Abstract: In quantum information theory, it is well-known that the GHZ-state 000+111 cannot be (SLOCC-)transformed into the W-state 000+101+011, but the W-state can be approximated with states from the GHZ-orbit. The W-state is thus an example of a tensor of tensor rank 3 that can be approximated by tensors of tensor rank 2....

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