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QuSoft events

QuSoft seminars

august 2019

*2 aug*

*11:00 am- 12:00 pm*Variational Quantum Fidelity EstimationAlexander Poremba

*Events:**QuSoft seminars*

### Event Details

Computing quantum state fidelity will

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### Event Details

Computing quantum state fidelity will be important to verify and characterize states prepared on a quantum computer. In our recent work, we propose novel lower and upper bounds for the fidelity based on the “truncated fidelity” which is projecting an input state onto its $m$-largest eigenvalues. Our bounds can be refined, i.e., they tighten monotonically with $m$. To compute our bounds, we introduce a hybrid quantum-classical algorithm, called Variational Quantum Fidelity Estimation, that involves three steps: (1) variationally diagonalize $\rho$, (2) compute matrix elements of $\sigma$ in the eigenbasis of $\rho$, and (3) combine these matrix elements to compute our bounds. Our algorithm is aimed at the case where $\sigma$ is arbitrary and $\rho$ is low rank, which we call low-rank fidelity estimation, and we prove that a classical algorithm cannot efficiently solve this problem. Finally, we demonstrate that our bounds can detect quantum phase transitions and are often tighter than previously known computable bounds for realistic situations.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

june 2019

### Event Details

Kloosterman sums are an important

### Event Details

Kloosterman sums are an important kind of complex-valued “special functions” on finite fields. They are analogous to Bessel functions and occur in Fourier analysis on Euclidean spaces (over finite fields in this case) in the presence of rotational symmetries. I will speak about

quantum algorithms to compute Kloosterman sums, with an application to the hidden radius problem, where the goal is to find the radius of a family of translates of a sphere in a Euclidean space over a finite field that is hidden by a black-box function.

### Time

(Friday) 11:00 am - 12:00 am *CEST*

### Location

L017 @CWI

Science Park 123, Amsterdam

### Event Details

Neural networks have been remarkably

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### Event Details

Neural networks have been remarkably successful for a variety of practical problems, ranging from computer vision to quantum error correction. However, they are often applied as a black box, which limits their utility for discoveries in the foundations of physics. I will present a neural network architecture that can be used to extract simple physical models from experimental data without any additional prior knowledge. Specifically, the network learns to compress experimental data to a simple representation and uses the representation to answer questions about the physical system. In examples, the network finds the physically relevant parameters, exploits conservation laws to make predictions, and can be used to gain conceptual insights. For example, given a time series of the positions of the Sun and Mars as observed from Earth, the network discovers the heliocentric model of the solar system – that is, it encodes the data into the angles of the two planets as seen from the Sun. This work provides a first step towards answering the question whether the traditional ways by which physicists model nature naturally arise from the experimental data without any mathematical and physical pre-knowledge, or if there are alternative elegant formalisms, which may solve some of the fundamental conceptual problems in modern physics, such as the measurement problem in quantum mechanics.

Joint work with Raban Iten, Henrik Wilming, Lidia del Rio, and Renato Renner; arxiv:1807.10300

### Time

(Friday) 10:00 am - 11:00 am *CEST*

### Location

L017 @CWI

Science Park 123, Amsterdam

may 2019

### Event Details

Entanglement renormalization is a circuit

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### Event Details

Entanglement renormalization is a circuit architecture (or a tensor network Ansatz, known as MERA) that reorganizes the entanglement of a state on a one-dimensional lattice over different scales, inspired by real-space renormalization methods. There is numerical and heuristic evidence that this type of circuit is a good method to approximate ground states of hamiltonians which have a scale invariance property in the continuous limit (in physics language: the limit is a conformal field theory) and which satisfy a logarithmic area law.

However, a rigorous understanding of this relation is still missing. In this talk I will explain a simple case, that of the free fermion, where explicit circuits can be constructed using wavelet theory, and where rigorous error bounds can be shown, both for the lattice theory and its continuous limit.

### Time

(Friday) 11:00 am - 12:00 am *CEST*

### Location

L0.16 @CWI

Science Park 123, Amsterdam

*3 may*

*2:00 pm- 3:00 pm*Tsirelson's problem, an overviewGerrit Vos (TU Delft)

*Events:**QuSoft seminars*

### Event Details

We discuss the setting of

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### Event Details

We discuss the setting of quantum correlations arising from 2-player games, and state Tsirelson’s problem asking whether two different quantum-mechanical models lead to the same set of quantum correlations. In finite dimensions, this is true. After a quick introduction on

C*-algebras, we give a short proof of this fact using C*-algebra theory. In the general case, this problem was proven to be equivalent to several other notorious open problems in the theory of C*-algebras and von Neumann Algebras, including the Connes Embedding Problem and Kirchberg’s conjecture. For the latter equivalence, we give a sketch of the proof.

### Time

(Friday) 2:00 pm - 3:00 pm *CEST*

### Location

L0.16 @CWI

Science Park 123, Amsterdam

april 2019

### Event Details

Finding the lowest energy of

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### Event Details

Finding the lowest energy of a Hamiltonian is a hard problem in general, however for many physical systems quantum Monte Carlo methods can often be effectively applied to determine the lowest energy of a Hamiltonian, and it is commonly understood that the absence of a sign problem is a requisite condition for the success of these methods. The notion of stoquastic Hamiltonians was introduced with the aim of categorizing those Hamiltonians which do not suffer from the sign problem. Indeed, the study of stoquastic Hamiltonians in the context of computational complexity theory has lent support to the notion that stoquastic Hamiltonians are somehow “simpler” than generic Hamiltonians. Importantly, the property of being stoquastic makes itself manifest only in a particular basis choice. In this work we explore how hard it is, from a computational complexity perspective, to find such a choice of basis. I will present an outline of an efficient algorithm for deciding if a 2-local Hamiltonian, with no 1-local terms, is stoquastic in some local basis.

### Time

(Friday) 11:00 am - 12:00 am *CEST*

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Event Details

Non-malleability is an important security

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### Event Details

Non-malleability is an important security property for public-key encryption (PKE). Its significance is due to the fundamental unachievability of integrity and authenticity guarantees in this setting, rendering it the strongest integrity-like property achievable using PKE only, without digital signatures. In this talk, we demonstrate how to generalize non-malleability to the setting of public-key cryptography. We do this by starting from a well-known classical definition, comparison-based non-malleability, and replacing components of this definition with their natural quantum counterparts.

This generalization comes with difficulties also seen in other integrity-like security notions, mainly the “recording barrier” that prevents a challenger from providing an input state for an adversary and later comparing her output to this input. We will show how to overcome these difficulties and present an argument for the correctness of our definition as well as a hybrid quantum-classical scheme that satisfies it.

### Time

(Friday) 11:00 am - 12:00 am *CEST*

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Event Details

In the preseminar, I will

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### Event Details

In the preseminar, I will focus on the group isomorphism problem, which is to decide whether two ﬁnite groups are isomorphic (given their Cayley tables). I will introduce necessary definitions about finite groups and show a 80-year-old reduction from a bottleneck case of the group isomorphism to the pseudo-isometry test of alternating matrix tuples. (No group-theoretic background is needed.)

In the seminar, we present an average-case efficient algorithm which, for almost all alternating matrix tuples, tests pseudo-isometry with any other alternating matrix tuples. Our algorithm is based on a linear-algebraic analogue of the individualization and refinement technique used in [Li-Qiao 2017], combined with concepts from isomorphism of low-genus groups [Brooksbank-Maglione-Wilson 2017]. Notably, the algorithm has been implemented in MAGMA, which in experiments improves over the default (brute force) algorithm for this problem.

### Time

(Friday) 11:00 am - 12:00 am *CEST*

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Event Details

Chattopadhyay, Mande and Sherif (to

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### Event Details

Chattopadhyay, Mande and Sherif (to appear in STOC 2019)

recently exhibited a total Boolean function, the sink function, that has

polynomial approximate rank and polynomial randomized communication

complexity. This gives an exponential separation between randomized

communication complexity and logarithm of the approximate rank, refuting

the log-approximate-rank conjecture. We show that even the quantum

communication complexity of the sink function is polynomial, thus also

refuting the quantum log-approximate-rank conjecture.

Our lower bound is based on the fooling distribution method introduced

by Rao and Sinha (Theory of Computing 2018) for the classical case and

extended by Anshu, Touchette, Yao and Yu (STOC 2017) for the quantum

case. We also give a new proof of the classical lower bound using the

fooling distribution method.

Joint work with Ronald de Wolf.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Quantum computing is gaining more

### Event Details

Quantum computing is gaining more and more interest from the aerospace community. In particular NASA, Airbus, Lockheed Martin, etc. The German Aerospace Center (DLR) investigates near-term quantum computing devices with respect to their applicability for aerospace research. Our research includes the identification of use cases as well as the development of algorithms and software for near-term quantum computers. We will report on our recent efforts to solve hard planning and scheduling problems from aerospace research with near term quantum computers.

### Time

(Friday) 10:00 am - 11:00 am

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

march 2019

### Event Details

The constraint satisfaction problems k-

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### Event Details

The constraint satisfaction problems k-SAT and Quantum k-SAT (k-QSAT)

are canonical NP-complete and QMA1-complete problems (for k>=3),

respectively, where QMA1 is a quantum generalization of NP with

one-sided error. Whereas k-SAT has been well-studied for special

tractable cases, as well as from a parameterized complexity perspective,

much less is known in similar settings for k-QSAT. Here, we study the

open problem of computing satisfying assignments to k-QSAT instances

which have a “matching” or system of distinct representatives; this is

an NP problem whose decision variant is trivial, but whose search

complexity remains open.

Among other results, our main contribution is the first known

parameterized algorithm for k-QSAT (which currently applies only to a

certain non-trivial class of instances), which allows us to obtain

exponential speedups over brute force methods in some cases. The

techniques behind our work stem from algebraic geometry, although no

background in the topic is required for this presentation. Along the

way, we will require the new concept of transfer filtrations on

hypergraphs, for which we leave certain complexity theoretic questions open.

Joint work with Marco Aldi (Virginia Commonwealth University), Niel de

Beaudrap (University of Oxford), and Seyran Saeedi (Virginia

Commonwealth University).

Bio:

Sevag obtained his Ph.D. in 2012 from the University of Waterloo in

Canada under the supervision of Dr. Richard Cleve. He taught as a

Visiting Lecturer at the University of Illinois at Chicago in Fall 2012,

and from 2013-2014 was a Postdoctoral Fellow in the group of Dr. Umesh

Vazirani at the University of California, Berkeley. He was awarded

Canada’s top postdoctoral fellowship in 2013, the NSERC Banting

Postdoctoral Fellowship, and was also a Simons Research Fellow at the

Simons Institute for the Theory of Computing at UC Berkeley. From 2014

to 2018, he was an Assistant Professor in Computer Science at Virginia

Commonwealth University in the USA, and since 2018 is a Junior Professor

in Computer Science at Universität Paderborn, Germany. He served from

2016 to 2018 as Secretary on the Board of Trustees of the Computational

Complexity Conference (CCC) (currently acts as Past Secretary from 2018

to 2019), and is a Founding Editor of the open-access journal Quantum.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

*14 mar*

*12:45 pm- 5:30 pm*Distinguished Lectures on Quantum Software

### Event Details

Featuring an all-star line-up, the

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### Event Details

Featuring an all-star line-up, the first edition of QuSoft’s Distinguished Lectures on Quantum Software will take place on 14 March 2019. Experts from throughout the field of quantum cryptology and quantum foundations will share their views and expertise.

Notable for his pioneering work on quantum informatics, Gilles Brassard (Université de Montréal) will discuss his recent breakthroughs. Brassard has made remarkable progress in aligning quantum theory with Albert Einstein’s perspective on local realism – with no need for what Einstein colorfully dismissed as ‘spooky action at a distance’. During his lecture, Brassard will discuss how quantum theory can be completed, including entanglement, but without resorting to nonlocality, Bell’s theorem notwithstanding.

Brassard is regarded by many as one of the founding fathers of quantum informatics. In 2018, Brassard won the prestigious Wolf Prize in Physics for his contribution to the creation and development of quantum cryptography and quantum teleportation. Currently, Brassard is a visiting scientist at QuSoft, the Dutch research center for quantum software.

PROGRAM

12.45-13.15

Registration

13.15-13.30

Opening

13.30-14.10

Christian Schaffner (UvA/CWI/QuSoft)

“The Quantum-Random-Oracle Model”

14.10-14.50

Nicolas Gisin (University of Geneva)

*“Quantum Non-Locality in Networks”
*Quantum non-locality, i.e. the violation of some Bell inequality, has proven to be an extremely useful concept in analyzing entanglement, quantum randomness and cryptography, among others. In particular, it led to the fascinating field of device-independent quantum information processing. Historically, the idea was that the particles emitted by various quantum sources carry additional variables, known as local hidden variables. The more modern view, strongly influenced by computer science, refers to these additional variables merely as shared randomness. This, however, leads to ambiguity when there is more than one source, as in quantum networks. Should the randomness produced by each source be considered as fully correlated, as in most common analyses, or should one analyze the situation assuming that each source produces independent randomness, closer to the historical spirit? The latter is known, for the case of n independent sources, as n-locality. For example, in entanglement swapping there are two sources, hence “quantumness” should be analyzed using 2-locality (or, equivalently, bi-locality). The situation when the network has loops is especially interesting. Recent results for triangular networks will be presented.

14.50-15.30

Break for coffee/tea

15.30-16.10

Renato Renner (ETH Zürich)

*“Quantum theory cannot consistently describe the use of itself”
Can quantum mechanics be used to describe a physicist who herself uses quantum mechanics? Clearly, if quantum mechanics was a universally valid physical theory, the answer should be yes. In my talk, I will present an extension of Schrödinger’s cat thought experiment, with the cat replaced by a quantum physicist (or, maybe preferably, a computer that is programmed to make predictions based on the laws of quantum physics). This allows us to provide an answer to the question posed above. The talk is based on the recent paper “Quantum theory cannot consistently describe the use of itself” by Frauchiger and Renner (Nature Communications 9, 3711, 2018).
*

16.10-16.50

Stacey Jeffery (CWI/QuSoft)

*“Quadratic speedup for finding marked vertices by quantum walks”
*A quantum walk algorithm can detect the presence of a marked vertex on a graph quadratically faster than the corresponding random walk algorithm (Szegedy, FOCS 2004). However, quantum algorithms that actually find a marked element quadratically faster than a classical random walk were only known for the special case when the marked set consists of just a single vertex, or in the case of some specific graphs. We present a new quantum algorithm for finding a marked vertex in any graph, with any set of marked vertices, quadratically faster than the corresponding classical random walk. This is joint work with Andris Ambainis, András Gilyén, and Martins Kokainis.

16.50-17.30

Gilles Brassard (University of Montreal)

*“Could Einstein have been right after all?”
One of the most surprising aspects of quantum theory is that it tells us that we live in a nonlocal universe. This idea was completely abhorrent to Einstein, who dismissed it as “spooky action at a distance”. Recent so-called loophole-free experiments (the first one having been performed in the Netherlands) have confirmed nonlocality beyond any reasonable doubt. But have they really? In this talk, I shall argue that no experiment whose purpose is to confirm the predictions of quantum theory can possibly be used as an argument in favour of nonlocality because any theory of physics that does not allow instantaneous signalling to occur and has reversible dynamics (such as unitary quantum theory) can be explained in a purely local and realistic universe. And if Einstein was right after all… once again? (This is joint work with Paul Raymond-Robichaud)
*

17.30-17.40

Closing

17.40-18.40

Drinks

Participation is free after registration.

The number of places is limited, so registration is mandatory!

You can register by email to

silvia.benschop at cwi.nl

Please mention your name and your affiliation.

### Time

(Thursday) 12:45 pm - 5:30 pm

### Location

Oudemanhuispoort, Zaal D1.09

Oudemanhuispoort 4-6, 1012 CN Amsterdam

### Organizer

Qusoft Events

### Event Details

Transporting quantum information between various

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### Event Details

Transporting quantum information between various (parts of) quantum computers is an essential ingredient for quantum technologies, and is stated as one of DiVincenzo’s criteria. Still, high-fidelity transport over significant distances remains challenging for most platforms that are not based on photons.

Koen will consider a network of sites (you may think of them as qubits) laid out in real space, whose allowed interactions are given by a graph.

It turns out that, under certain graph restrictions, quantum information can be transferred between certain sites. This requires only local control over the interactions connecting the sender/receiver, thus allowing passive “cables” to be laid between the communicating parties.

This generalizes previous work, which was mostly limited to linear chains, to a much broader set of graphs, and to transport between more than two parties. The protocol turns out to inherit all robustness features that helped the conventional linear protocol (so-called STIRAP) to become a widely adopted experimental technique.

The talk is based on a work in progress together with Carla Groenland and Reinier Kramer, and to a lesser extend on

https://scipost.org/SciPostPhys.6.1.011.

In the pre-seminar, at 10.30 AM, Koen will give an introduction about quantum dynamics (the evolution of states in time), targeting an audience of computer scientists and mathematicians who have little experience working with Hamiltonians or Schroedinger’s equation.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

february 2019

### Event Details

In 1974, Ralph Merkle proposed

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### Event Details

In 1974, Ralph Merkle proposed the first unclassified protocol for secure communications over insecure channels. When legitimate communicating parties are willing to spend an amount of computational effort proportional to some parameter N, an eavesdropper cannot break into their communication without spending a time proportional to N^2, which is quadratically more than the legitimate effort. In a quantum world, however, Merkle’s protocol is immediately broken by Grover’s algorithm, but it is easily repaired if we are satisfied with a quantum protocol against which a quantum adversary needs to spend a time proportional to N^{3/2} in order to break it.

Can we do better? I shall discuss two key establishment protocols in the spirit of Merkle’s. The first one, which requires the legitimate parties to have access to a quantum computer, resists any quantum adversary who is not willing to make an effort at least proportional to N^{7/4}, except with vanishing probability. If we only care about query complexity rather than computing time, we can almost recover in an all-quatum world the quadratic advantage that Merkle had secured in an all-classical world. Our second protocol is purely classical, yet it requires any quantum adversary to work asymptotically harder than the legitimate parties, again except with vanishing probability. In either case, security is proven for a typical run of the protocols: the probabilities are taken over the random choices made by the legitimate participants in order to establish their key as well as over the random choices made by the adversary who is trying to be privy to it.

IMPORTANT NOTE ABOUT THE 10:30 PRE-SEMINAR:

I shall explain the notion of key establishment and the fascinating history of this momentous discovery in the 1970s (if not earlier!). If you think it comes from Diffie and Hellman celebrated 1976 paper “New Directions in Cryptography”, think again! I shall also say a few words about the main quantum tools involved, namely Grover’s algorithm, its generalization known as BBHT, and quantum walks in Markov chains.

### Time

(Friday) 11:00 am - 12:00 pm *CET*

### Location

L0.16 @CWI

Science Park 123, Amsterdam

*15 feb*

*11:00 am- 12:00 pm*Quantum dots, cavities and photonsWolfgang Löffler (Leiden University)

### Event Details

A single semiconductor

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### Event Details

**Pre-seminar will start at 10:30 AM.**

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Even though, in itself, classical

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### Event Details

Even though, in itself, classical simulation of quantum circuits is inherently limited, trying to push it further can yield mathematical tools which are then useful in other contexts, like compilation or optimization of quantum resources. Instances include the stabilizer formalism, decision diagrams (QMDDs) or tensor networks. After quickly reviewing these techniques, we will focus on the simulation of quantum circuits by tensor network contraction. In this case, the quantum circuit itself is seen as a tensor network, and its contraction complexity depends on its underlying graph structure. This technique therefore constitutes an invitation to study the structure of quantum circuits, seen as graphs.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

*1 feb*

*11:00 am- 12:00 pm*Optimal circuits based on Euclidean path integralsMichal P. Heller (AEI/NCBJ)

### Event Details

The talk will first

### Event Details

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

january 2019

*25 jan*

*11:00 am- 12:00 pm*Self-embezzlement using C*-dynamicsLi Liu (University of Waterloo)

### Event Details

The notion of locality of

more

### Event Details

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

*18 jan*

*11:00 am- 12:00 pm*Power series in stochastic processesTom Bannink (CWI/QuSoft)

### Event Details

Tom Bannink will talk

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### Event Details

Tom Bannink will talk about the Bak-Sneppen process, a random process on a graph, introduced in 1993. This talk is about work done together with András Gilyén, Harry Buhrman and Mario Szegedy. Tom Bannink will explain what a phase transition is and define some functions related to this phase transition. The power series of these functions turn out to have interesting properties, which is proven in the article. He’ll explain these properties and give a short sketch of one of the proofs.

The abstract of our paper:

We consider a class of random processes on graphs that include the discrete Bak-Sneppen (DBS) process and the several versions of the contact process (CP), with a focus on the former. These processes are parametrized by a probability 0 ≤ p ≤ 1 that controls a local update rule. Numerical simulations reveal a phase transition when p goes from 0 to 1. Analytically little is known about the phase transition threshold, even for one-dimensional chains. In this article we consider a power-series approach based on representing certain quantities, such as the survival probability or the expected number of steps per site to reach the steady state, as a power-series in p. We prove that the coefficients of those power series stabilize as the length n of the chain grows. This is a phenomenon that has been used in the physics community but was not yet proven. We show that for local events A, B of which the support is a distance d apart we have cor(A, B) = O(p^d). The stabilization allows for the (exact) computation of coefficients for arbitrary large systems which can then be analyzed using the wide range of existing methods of power series analysis.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

*11 jan*

*11:00 am- 12:00 pm*Title and abstract will follow a.s.a.p.Alessandro Danelon (Leiden University)

### Event Details

A talk about supersingular elliptic

### Event Details

A talk about supersingular elliptic curves and their appearances in cryptography, most notably in the NIST submission scheme SIKE. We’ll define the Diffie-Hellman problem and its variants for supersingular elliptic curve isogenies and discuss their reductions to problems about the arithmetic of quaternion algebras.

### Time

(Friday) 10:00 am - 11:00 am

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

*4 jan*

*11:00 am- 12:00 pm*Circuit Transformations for Quantum ArchitecturesEDDIE SCHOUTE (QUTECH)

### Event Details

Quantum computer architectures impose restrictions

more

### Event Details

Quantum computer architectures impose restrictions on qubit interactions.

We propose efficient circuit transformations that modify a given quantum

circuit to fit an architecture, retaining the original function up to a

permutation of the qubits. To achieve this, we first consider the qubit

movement subproblem and propose the Routing via Matchings framework to

prove tighter bounds on parallel routing.

In practice, we need to perform partial permutations, so we generalize Routing via

Matchings to thatsetting. We give new routing procedures for common architecture

graphs andfor the generalized hierarchical product of graphs, which produces

subgraphs of the Cartesian product. Second, for serial routing we consider

the Token Swapping framework and extend a 4-approximation algorithm for

general graphs to support partial permutations.

Using various heuristic

gate placement subroutines, we apply these qubit routing procedures to give

several circuit transformations. We implement these transformations in

software and compare their performance for large quantum circuits on grid

and modular architectures, identifying strategies that work well in

practice.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

november 2018

### Event Details

Since its first release, ProjectQ

### Event Details

Since its first release, ProjectQ has been extended with many new features, making it more useful and accessible. I will give an overview of the framework and highlight a few of these recent changes with a focus on mappers. Then, using the example of a Hoare based optimizer, I will demonstrate how simple it is to implement a custom compiler engine. Finally, I will give an outlook on features that are work in progress and on ProjectQ as a whole.

After the lunch, Thomas Häner will give a demonstration- and question/answer session about ProjectQ.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

*16 nov*

*11:00 am- 12:00 pm*Entanglement of completely symmetric quantum statesHans Maassen (KdVI, UvA)

### Event Details

The study of entanglement between

more

### Event Details

The study of entanglement between more than two systems, or particles, is complicated by the fact that the number of degrees of freedom of n-particles, each with a d-dimensional state space, increases steeply as a function of n an d. By requiring symmetry both under particle permutation and under joint unitary transformations, we simplify the situation considerably and yet retain a rich, fundamental structure, which might serve as a kind of “backbone” for the general theory. We lean heavily on the classical representation theory of finite and compact groups. The well-known Young diagrams occurring in the representation theory of finite permutation groups are seen in a new light. A connection is made with Lieb’s conjecture concerning the so-called immanants of positive definite matrices. A promising approach to characterize the set of all separable (non-entangled) states as a polytope in state space, breaks down in a strange way at n=5.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Conditional von Neumann entropy is

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### Event Details

Conditional von Neumann entropy is an intriguing concept in quantum information theory. In the present work, we examine the effect of global unitary operations on the conditional entropy of the system. We start with a set containing states with a non-negative conditional entropy and find that some states preserve the non-negativity under unitary operations on the composite system. We call this class of states the absolute conditional von Neumann entropy non-negative (ACVENN) class.

We characterize such states for 2×2 dimensional systems. From a different perspective the characterization accentuates the detection of states whose conditional entropy becomes negative after the global unitary action. Interestingly, we show that this ACVENN class of states forms a set which is convex and compact. This feature enables the existence of Hermitian witness operators. With these we can distinguish the unknown states which will have a negative conditional entropy after the global unitary operation. We also show that this has immediate application to superdense coding and state merging, as the negativity of the conditional entropy plays a key role in both these information processing tasks. Some illustrations followed by analysis are also provided to probe the connection of such states with absolutely separable states and absolutely local states.

### Time

(Friday) 11:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars