Past Quantum Lunches

1 July 2020, 12:0013:00
QLunch: Efficient simulation of random states and random unitaries

13 May 2020, 12:0013:00
ONLINE QLunch: Finite group velocity implies quasilocality of interactions

8 Jan. 2020, 12:0013:00
QLunch: Tensor network representations from the geometry of entangled states

27 Nov. 2019, 12:0013:00
QLunch: Quantum isomorphism is equivalent to equality of homomorphism counts from planar graphs

6 Nov. 2019, 12:0013:00
QLunch:Varieties of sum of powers, Stiefel manifolds and their degrees

16 Oct. 2019, 12:0013:00
QLunch: Faster quantum and classical SDP approximations for quadratic binary optimization

2 Oct. 2019, 12:0013:00
QLunch: Quantum correlations under restricted transfer of information

18 Sept. 2019, 12:0013:00
QLunch: Compatibility of quantum measurements and inclusion constants for free spectrahedra

21 Aug. 2019, 12:0013:00
QLunch: A polynomialtime algorithm for ground states of spin trees

14 Aug. 2019, 12:0013:00
QLunch: Preparation and Compression of Symmetric Pure Quantum States

3 July 2019, 12:0013:00
QLunch: Exact correlation functions of the principal chiral model

12 June 2019, 12:0013:00
QLunch: Nonlocal and nonabelian properties of Majorana bound states

6 June 2019, 12:0013:00
QLunch: KacRice fixed point analysis for large complex systems

29 May 2019, 12:0013:00
QLunch: Hamiltonian Learning on Superconducting Qubits Using Bayesian Inference

2 May 2019, 12:0013:00
QMATHOpAlg Seminar: Computational complexity and the quantum value of nonlocal games

11 Apr. 2019, 15:0016:00
QMATH Seminar: Generalized geometric Bogoliubov theory for the BoseHubbard model

3 Apr. 2019, 12:0013:00
QLunch: Faces of the Stabiliser Polytope and Robustness Measures

20 Mar. 2019, 12:0013:00
QLunch: The Quantum Information Bottleneck: Properties and Applications

20 Feb. 2019, 12:0013:00
QLunch: Construction of Wannier functions for insulators and metals

13 Feb. 2019, 12:0013:00
QLunch: Propagators on curved spacetimes and balanced geometric Weyl quantization

24 Jan. 2019, 14:1515:15
GAMP/QMATH Seminar: Schmidt number of bipartite and multipartite states under local projections

16 Jan. 2019, 12:0013:00
QLunch: Oneway quantum repeaters with photonic cluster states

19 Dec. 2018, 12:0013:00
QLunch:The KeylWerner theorem and the spin of a meanfield state

12 Dec. 2018, 12:0013:00
QLunch: A quantum code for quantum homomorphic encryption and malleable quantum shared secrets

5 Dec. 2018, 12:0013:00
QLunch: Lieb–Thirring inequalities and Weyltype asymptotics for difference operators

7 Nov. 2018, 12:0013:00
QLunch: Optimal Upper Bound for the Correlation Energy of the MeanField Fermi Gas

31 Oct. 2018, 12:0013:00
QLunch: Quantum ciphertext authentication and key recycling with the trap code

24 Oct. 2018, 12:0013:00
QLunch: Formulas of Szegő type for the periodic Schrödinger operator

3 Oct. 2018, 12:0013:00
QLunch: A simple 2nd order lower bound to the energy of dilute Bose gases

5 Sept. 2018, 12:0013:00
QLunch: Constructing local frustration free Lindbladians with given MPDOs as stable space

19 July 2018, 14:1515:15
GAMP/QMATH Lecture: Containment between LMI domains and the existence of quantum channels

18 July 2018, 12:0013:00
GAMP/QMATH Lecture: Generic Representations of quantum coordinate algebras

13 June 2018, 12:0013:00
QLunch: Quantum advantage of unitary Clifford circuits with magic state inputs

6 June 2018, 12:0013:00
QLunch: On the construction of exponentially localized Wannier functions

23 May 2018, 12:0013:00
QLunch: : Multivariate operator means and the barycenter of relative entropy

17 May 2018, 15:1516:00
GAMP/QMATH Seminar: Tsirelson's problems and the entanglement breaking rank

16 May 2018, 12:0013:00
QLunch:Dephrasure channel and superadditivity of coherent information

25 Apr. 2018, 12:0013:00
QLunch: Distinguished selfadjoint extensions of operators with gaps

7 Feb. 2018, 12:0013:00
QLunch: HardyLiebThirring Inequalities for Fractional Pauli Operators

11 Jan. 2018, 15:1516:15
GAMP/QMATH Lecture: Semidefinite Optimization for Quantum Information Processing

29 Nov. 2017, 12:0013:00
Quantum Lunch: Benchmarking purity and correlations for quantum states

1 Nov. 2017, 12:0013:00
QLunch: On the interplay between algebraic geometry and complexity theory

11 Oct. 2017, 12:0013:00
Quantum Lunch: The diatomic repulsion in reduced HartreeFock Theory

4 Oct. 2017, 12:0013:00
Quantum Lunch: Entanglement and Chaos: Linear entropy production at instabilities

27 Sept. 2017, 12:0013:00
Quantum Lunch: The LeeHuangYang Formula for Dilute Bose Gases

22 Aug. 2017, 15:0016:00
QMATH Lecture: LiebThirring inequality and gradient correction

16 Aug. 2017, 12:0013:00
QLunch: The excitation spectrum of Bose gases interacting through singular potentials

28 June 2017, 12:0013:00
QLunch: On the stability of the quantum DarmoisSkitovich theorem

22 June 2017, 14:0015:00
QMATH Lecture: Logical paradoxes in deterministic quantum state injection

21 June 2017, 12:0013:00
Quantum Lunch: PeierlsBogolyubov's inequality for deformed exponentials

20 June 2017, 14:0015:00
QMATH/GAMP Lecture: Contextuality and Noncommuative Geometry in Quantum Mechanics

31 May 2017, 12:0013:00
Quantum Lunch: Topological Matter and Why You Should be Interested

10 May 2017, 12:0013:00
QLunch: Symmetry and Combinatorics for Identical Quantum Systems

19 Apr. 2017, 12:0013:00
QLunch: Quantum framework from simple physical principles for single systems

18 Apr. 2017, 13:0014:00
QMATH Lecture: Asymptotic entanglement concentration of W states

29 Mar. 2017, 12:0013:00
Quantum Lunch: Ultimate data hiding in quantum mechanics and beyond

15 Mar. 2017, 12:0013:00
Quantum Lunch: Local boundary states imply gap for the parent Hamiltonian of PEPS

1 Mar. 2017, 12:0013:00
Quantum Lunch: Quantum simulations with noisy quantum computers

22 Feb. 2017, 12:0013:00
Quantum Lunch: Ground states and excitations of homological codes

3 Feb. 2017, 13:0014:00
QMATH Lecture: On the dynamics of multicomponent condensates: mixtures and spinors

18 Jan. 2017, 12:0013:00
Quantum Lunch: FeynmanKac formulas for the ultraviolet renormalized Nelson model

12 Jan. 2017, 15:1516:15
Joint QMATH/GAMP Seminar: Limit shapes in statistical mechanics

11 Jan. 2017, 12:0013:00
Quantum Lunch: To what extent can information propagation decouple from energy propagation?

7 Dec. 2016, 12:0013:00
Quantum Lunch: Universality in interacting topological insulators

30 Nov. 2016, 12:0013:00
Quantum Lunch: Instantaneous nonlocal quantum computation using the gardenhose model

23 Nov. 2016, 12:0013:00
Quantum Lunch: Semideviceindependent quantum randomness generation

16 Nov. 2016, 12:0013:00
Quantum Lunch: MarchenkoPastur distributions and hypergeometric Hurwitz numbers

19 Oct. 2016, 12:0013:00
Quantum Lunch: Informationtheoretic nonmalleability and authentication

12 Oct. 2016, 12:0013:00
Quantum Lunch: Picking holes and cutting corners to achieve Clifford gates with the surface code

28 Sept. 2016, 12:0013:00
Quantum Lunch: Periodically driven impurity in the XX quantum spin chain

21 Sept. 2016, 12:0013:00
Quantum Lunch: Random tensor networks and multipartite entanglement

14 Sept. 2016, 12:0013:00
Quantum Lunch: The martingale method meets the detectability lemma

7 Sept. 2016, 12:0013:00
Quantum Lunch: Schrödinger Operators in Some Curvature Problems

10 Aug. 2016, 12:0013:00
Quantum Lunch: An outsider's view on the mathematical foundations of machine learning

6 July 2016, 12:0013:00
Summer Quantum Lunch: Sandwiches and Sandwiched Renyi Divergences

25 May 2016, 12:0013:00
Quantum Lunch: Scalar Field Theories with Polynomial Shift Symmetries

18 May 2016, 12:0013:00
Quantum Lunch: Landauer's principle and the energy cost of measurement

20 Apr. 2016, 12:0013:00
Quantum Lunch: Geometry of random planar maps with high degrees

16 Mar. 2016, 12:0013:00
Quantum Lunch: Quantum manybody fluctuations around nonlinear Schrödinger dynamics

24 Feb. 2016, 12:0013:00
Quantum Lunch: Pattern formation in biological systems & Electroweak baryogenesis in 2HDMs

17 Feb. 2016, 12:0013:00
Quantum Lunch: Deviceindependent twoparty cryptography secure against sequential attacks.

10 Feb. 2016, 12:0013:00
Quantum Lunch: Trace inequalities for arbitrary many matrices via pinching

13 Jan. 2016, 12:0013:00
Quantum Lunch: A Pfaffian formula for monomerdimer partition functions

9 Dec. 2015, 12:0013:00
Quantum Lunch: Variational Expressions for Quantum Relative Entropies
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...

2 Dec. 2015, 12:0013:00
Quantum Lunch
Title: Ktheory and topological insulators
Abstract: This will be an introductory seminar aimed at showing some basic facts in index theory and Ktheory in the context of topological insulators.

18 Nov. 2015, 12:0013:00
Quantum Lunch
Title: Errorcorrection in nonabelian anyon models
Abstract:
Scalable anyonic topological quantum computation requires the errorcorrection of nonabelian anyon systems. In contrast to abelian topological codes ...

11 Nov. 2015, 12:0013:00
Quantum Lunch
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
twodimensional box. The contact interaction is implemented by a
limiting procedure ... 
4 Nov. 2015, 12:0013:00
Quantum Lunch: Extensions of the entanglement entropy for symmetry protected topological order
Speaker: Shunji Matsuura

28 Oct. 2015, 12:0013:00
Quantum Lunch: Interaction Effects in SpinWave Theory
Speaker: Niels Benedikter

21 Oct. 2015, 12:0013:00
Quantum Lunch: Random permutations and the meanfield Heisenberg model
Speaker: Jakob Björnberg

14 Oct. 2015, 12:0013:00
Quantum Lunch: Renormalising entanglement distillation
Title: Renormalising entanglement distillation

30 Sept. 2015, 12:0013:00
Quantum Lunch: Accurate atomic radii from ThomasFermi Theory
Speaker: Jan Philip Solovej

23 Sept. 2015, 12:0013:00
Quantum Lunch: Bogoliubov correction to the meanfield dynamics of interacting bosons
Speaker: Marcin Napiórkowski

16 Sept. 2015, 12:0013:00
Quantum Lunch: Quantum Circuits for Isometries
Speaker: Raban Iten
Abstract: Every quantum operation can be decomposed into a sequence of singlequbit and ControlledNot (CNOT) gates. In many experimental architectures, singlequbit gates are relatively ‘cheap’ to perform compared to CNOTs (for instance, being less susceptible to noise), and hence it is desirable to minimize the number of CNOT 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 CNOT 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 CNOTefficient way to perform an arbitrary quantum operation.

2 Sept. 2015, 12:0013:00
Quantum Lunch: Nonbinding of strongly coupled manypolarons in dimensions two and three
Speaker: Anton Samojlow

19 Aug. 2015, 12:0013:00
Quantum Lunch: Estimates for the lowest eigenvalue of magnetic Laplacians.
Speaker: Fabian Portmann

1 July 2015, 12:0013:00
Quantum Lunch: Localization from superselection rules in translation invariant systems
Abstract: We study a translation invariant spin model in a threedimensional 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 nearexponential 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)

24 June 2015, 12:0013:00
Quantum Lunch: Bogoliubov theory at positive temperature
Abstract: I will discuss Bogoliubov theory in the translation invariant case of a Bose gas. The theory arises by restriction to translation invariant quasifree states. I will introduce the positive temperature pressure functional and the corresponding ground state energy functional...

17 June 2015, 12:0013:00
Quantum Lunch: Quantuminformation processing with solidstate singlephoton sources

3 June 2015, 12:0013:00
Quantum Lunch: Learning and testing of mixed state spectra
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. 
13 May 2015, 12:0013:00
Quantum Lunch: An adaptive attack on Wiesner's quantum money
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 nocloning 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 ElitzurVaidman 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. 
29 Apr. 2015, 12:0013:00
Quantum Lunch: Factorizable completely positive maps and Quantum Information Theory
Title: Factorizable completely positive maps and Quantum Information Theory

22 Apr. 2015, 12:0013:00
Quantum Lunch: Energy Levels of Dipoles in Graphene
Speaker: Simone Rademacher

8 Apr. 2015, 12:0013:00
Quantum Lunch
Title: A Classical Analog to Entanglement ReversibilityAbstract: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 wellstudied 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}csK\"{o}rner Common Information. 
25 Mar. 2015, 12:0013:00
Quantum Lunch: Two results in topology, motivated by quantum computation
Speaker: Gorjan Alagic

11 Mar. 2015, 12:0013:00
Quantum Lunch: Heralded quantum gate with integrated error detection

4 Mar. 2015, 12:0013:00
Quantum Lunch: Error distributions on large entangled states with nonMarkovian dynamics

11 Feb. 2015, 12:0013:00
Quantum Lunch: Ground state entanglement constrains low energy excitations

28 Jan. 2015, 12:0013:00
Quantum Lunch
Speaker: Alexander MuellerHermes
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....

14 Jan. 2015, 12:0013:00
Quantum Lunch: Finding large gaps between tensor rank and border rank via algebras
Abstract: In quantum information theory, it is wellknown that the GHZstate 000+111 cannot be (SLOCC)transformed into the Wstate 000+101+011, but the Wstate can be approximated with states from the GHZorbit. The Wstate is thus an example of a tensor of tensor rank 3 that can be approximated by tensors of tensor rank 2....