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QuSoft events

QuSoft seminars

february 2019

*15 feb*

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

### Event Details

A single semiconductor

more

### 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

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### 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

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### 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

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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

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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

october 2018

*19 oct*

*11:00 am- 12:00 pm*A Converse Quantum Expander Mixing LemmaFARROKH LABIB (QUSOFT/CWI)

### Event Details

The classical expander mixing lemma

more

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The classical expander mixing lemma (EML) connects two notions of pseudorandomness for graphs. The EML states that spectral expansion (the adjacency matrix having “small second eigenvalue”) implies uniformity (having roughly “the right” number of edges between pairs of vertex subsets). In this talk, we look at a known quantum analogue of the EML, which shows that if a quantum channel is a quantum expander, then it is also an approximate 1-design. In particular, we show a quantum analogue of a recent result of Conlon and Zhao showing that, while converse of the classical EML is false in general, it holds true for all vertex-transitive graphs. Similarly, super-operators (and in particular channels) with sufficient symmetry turn out to allow for a converse quantum EML. Our proof uses the non-commutative Grothendieck inequality.

Based on joint work with Tom Bannink and Jop Briët.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

*12 oct*

*10:00 am- 12:00 pm*Cirq HackathonArjan Cornelissen and Farrokh Labib (QUSOFT/CWI)

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Arjan Cornelissen and Farrokh Labib

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### Event Details

Arjan Cornelissen and Farrokh Labib will be running a little hackathon to teach quantum programming on the Google Cirq platform (https://github.com/quantumlib/Cirq).

Cirq is effectively a Python library, so if you already know Python, it would help, but even if you don’t (like me), it should still be accessible.

All you need to do is to bring along your laptop (or desktop??) computer. We will go all the way from getting everything installed to programming and running simple quantum algorithms.

We’re doing this as a test run for Arjan’s platform that tests quantum algorithms, since it will be used in my upcoming course in November.

There might be prizes for those who solve the most problems.

### Time

(Friday) 10:00 am - 12:00 pm

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Events

### Event Details

Recent advances in Reinforcement Learning

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### Event Details

Recent advances in Reinforcement Learning (RL) consist in building agents that can learn to solve complex tasks, such as mastering the game of Go, in relatively few trial-and-error attempts. This number of attempts is commonly compared to the dimensionality of the space of states they can be in or the space of actions they can perform in those states. The ability to efficiently solve tasks for which state/action-spaces grow exponentially with the number of parameters describing them is called “tackling with the curse of dimensionality” or “generalization” in the literature. Projective Simulation (PS) [1], a physics-inspired framework for the design of intelligent agents, provides through its Episodic Compositional Memory (ECM) some mechanisms to enable generalization [2].

On the other hand, Reflecting PS (RPS), an extension of the basic PS model, achieves a quadratic quantum speed-up of the underlying deliberation process of agents with a restricted non-generalizing form of ECMs [3]. But there are currently no known applicable methods that achieve a similar quantum speed-up for PS agents with generalization. In this work, inspired by a solution to the curse of dimensionality first introduced in [4], which relies on Boltzmann machines, an energy-based recurrent neural network, and Monte Carlo Markov Chain (MCMC) methods, we first establish a direct connection between RPS and MCMC methods for Reinforcement Learning. We then explore the design of quantum algorithms to gain a quantum speed-up of the deliberation process of our newly defined RPS agents.

[1] Briegel, Hans J., and Gemma De las Cuevas. “Projective simulation for artificial intelligence.” Scientific reports 2 (2012): 400.

[2] Melnikov, Alexey A., et al. “Projective simulation with generalization.” Scientific reports 7.1 (2017): 14430.

[3] Paparo, Giuseppe D., et al. “Quantum speedup for active learning agents.” Physical Review X 4.3 (2014): 031002.

[4] Sallans, Brian, and Geoffrey E. Hinton. “Reinforcement learning with factored states and actions.” Journal of Machine Learning Research 5.Aug (2004): 1063-1088.

### Time

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

### Location

CWI Room L120

Science Park 123, Amsterdam

september 2018

### Event Details

It is widely believed that

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It is widely believed that randomness does not increase the computational power of polynomial-time algorithms (i.e. P = BPP). In this talk, we discuss the non-deterministic version of this problem (NP vs. MA), and we show that if a PCP theorem for MA holds, then MA = NP.

Technically, the result is achieved by showing that an NP-verifier can distinguish if a stoquastic Hamiltonian has groundstate-energy 0 or at least a constant.

### Time

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

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Event Details

Relaxing the assumptions about the

more

### Event Details

Relaxing the assumptions about the experimental setup in Quantum Key Distribution protocols lays the foundation for Device Independent Quantum Key Distribution (DIQKD). In the finite key regime of DIQKD, the protocols employ the use of only the CHSH inequality, so far. A natural question therefore arises whether are there other Bell inequalities that help achieve better results (in terms of higher rates, greater noise tolerance and lower number of minimum rounds required for positive rates) than those achieved using CHSH inequality? For the inequalities considered, we find that CHSH fares the best on account of noise tolerance. However, considering the other two parameters of interest we present two bipartite Bell-inequalities with three outcomes per party that perform better than CHSH for a certain range of noise involved.

### Time

(Wednesday) 2:00 pm - 3:00 pm

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

*7 sep*

*11:00 am- 12:00 pm*Quantum activities at KPNCorsin Pfister (KPN)

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This talk presents past, ongoing

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### Time

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

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

august 2018

*24 aug*

*11:00 am- 12:00 am*Leakage-Deterring Public-Key EncryptionPatrick Towa (IBM, Zurich)

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Preventing users from sharing their

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### Event Details

Preventing users from sharing their decryption capabilities is a notoriously difficult problem. It naturally arises in the context of paid services or of access to confidential information. Traitor tracing schemes were introduced to tackle this issue, but this approach is contingent on the detection of rogue decryption devices. Kiayias and Tang were the first to address the problem pre-emptively: they introduced leakage-deterring encryptions scheme, in which a secret valuable to a user is embedded in her public key, and can be recovered by anyone with access to a decryption device. Users are thereby dissuaded from sharing their decryption capabilities lest they share their valuable secret as well.

In this talk, Kiayias and Tang’s model and construction will be first discussed, as well as their respective shortcomings. Secondly, a new model, guaranteeing full user-privacy and overcoming the aforementioned shortcomings, will be exposed. Lastly, efficient constructions proved secure in the new model are to be presented. This solves the problem of devising an efficient and privacy-friendly leakage-deterring encryption scheme.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

july 2018

### Event Details

Which precise features of quantum

more

### Event Details

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Reinforcement learning (RL) is an

more

### Event Details

Reinforcement learning (RL) is an aspect of machine learning often

utilized in the context of robotics and artificial intelligence. In

comparison to other canonical machine learning modes, namely supervised

and unsupervised learning, RL has received comparatively little

attention from the quantum information processing (QIP) community.

In this review-style talk, I will discuss this interactive mode of

learning, and briefly present its basics, bottlenecks and perspectives.

Following this, I will discuss the potential of the interplay between RL

and QIP, and present a few results discussing how RL methodology can help in

quantum information settings, and, conversely, how QIP methods may

provide enhancements for this increasingly relevant learning model.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

SURFsara positions itself as a

more

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SURFsara positions itself as a national compute centre aiming to provide support and access to latest technologies for the Dutch research community. In recent years, parallel with multiple scientific and engineering breakthroughs on quantum hardware development, various simulators have attracted attention as research and development platforms for quantum algorithms. These require significant classical memory resources. Therefore, it becomes important to use a High Performance Computing environment where a large distributed memory can be used. In this presentation we’ll see what is presently available in the software stack of the Cartesius supercomputer. In addition, SURFsara is currently hosting a Quantum Learning Machine appliance for 30 qubits. The presentation will aim to give a soft introduction to the concepts behind the QLM appliance, some practical examples, as well as information about access to it and availability. Finally, we’ll look at a few of the ambitions and directions SURFsara will take in the future.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Understanding the computational power of

more

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Understanding the computational power of multi-prover interactive proofs where the provers may share entanglement — the complexity class MIP* — is a central question in quantum computation. In 2012, Ito and Vidick showed that this model is at least as powerful as MIP, i.e. NEXP is contained in MIP*. The original motivation for the introduction of multi-prover interactive proofs, however, was studying unconditional zero knowledge: while single-prover interactive proofs with unconditional zero knowledge are limited to the complexity class SZK, which is not believed to contain NP, with non-communicating provers unconditional zero knowledge is ‘for free’: ZK-MIP = NEXP. A natural question, then, is: what is the power of ZK-MIP*? This is not immediately clear from the other results, because the techniques used to obtain them seem to be incompatible. In this work, we show that ZK-MIP* contains NEXP, developing new algebraic tools for zero knowledge which are compatible with the Ito-Vidick framework.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

We propose to generalise

more

### Event Details

We propose to generalise classical maximum likelihood learning to density matrices. As the objective function, we propose a quantum likelihood that is related to the cross entropy between density matrices. We apply this learning criterion to the quantum Boltzmann machine (QBM), previously proposed by Amin et al.. We demonstrate for the first time learning a quantum Hamiltonian from quantum statistics using this approach. For the anti-ferromagnetic Heisenberg and XYZ model we recover the true ground state wave function and Hamiltonian. The second contribution is to apply quantum learning to learn from classical data. Quantum learning uses in addition to the classical statistics also quantum statistics for learning. These statistics may violate the Bell inequality, as in the quantum case. Maximizing the quantum likelihood yields results that are significantly more accurate than the classical maximum likelihood approach in several cases. We give an example how the QBM can learn a strongly non-linear problem such as the parity problem. The solution shows entanglement, quantified by the entanglement entropy.

### Time

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

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

june 2018

### Event Details

One of the questions that

more

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One of the questions that drove early work on quantum computing was whether quantum mechanics can be used to produce machines which provide experimental evidence against the extended Church-Turing thesis. The most straightforward way to do so would be to construct a quantum machine that outperforms a classical computer at some well-defined computing task. Such a demonstration goes under the name of quantum advantage in the literature.

A few years ago, it was shown that passive linear optical quantum systems can be used to implement such a problem. This problem, known as boson sampling, has since attracted a great deal of interest from the quantum photonics community, and continues to be one of the driving open problems in our field.

One of the major open theoretical problems in this field is to understand how errors affect the integrity of a boson sampling experiment. Recently, Jelmer Renema has demonstrated an algorithm that exploits one such imperfection, namely distinguishability, to classically simulate a boson sampler. In those regions of the parameter space where this algorithm is efficient, a quantum advantage is excluded.

Jelmer’s talk will consist of two parts. In the first part, he will introduce boson sampling with an emphasis on experimental challenges. He will then move on to a discussion of the classical simulation algorithm in detail.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Networks of coupled nonlinear optical

more

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Networks of coupled nonlinear optical resonators offer unprecedented opportunities for exploring novel phases of strongly correlated light and matter with potential applications to simulation, computation, and optoelectronics. In this talk, I will discuss the nonlinear and quantum physics of the fundamental building-blocks of such networks: single and coupled nonlinear optical resonators.

First I will discuss the steady-state and dynamical behavior of nonlinear optical resonators influenced by quantum fluctuations. I will present measurements of dynamic hysteresis and stochastic trajectories of light in a microcavity. I will explain how to measure and control the reaction time of a nonlinear microcavity across arbitrarily long time scales using light. This control allows us to probe adiabatic and non-adiabatic dynamics of photons across a wide range of time scales by tuning the microcavities and/or a driving laser.

In the second part of the talk, I will introduce the experimental platforms we are currently developing at AMOLF, and the perspectives that these open for exploring phase transitions of interacting photons in tunable multicavity systems. I will map an array of bistable cavities to an Ising model, and I will discuss perspectives for solving challenging problems in combinatorial optimization with stochastic (quantum) optical hardware.

### Time

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

### Location

zaal D1.112

Science Park 904, Amsterdam

### Organizer

Qusoft Seminars

*8 jun*

*11:00 am- 12:00 am*Asymptotic performance of port-based teleportationCHISTIAN MAJENZ (QUSOFT)

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Port-based teleportation (PBT) is

more

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Port-based teleportation (PBT) is a variant of the well-known task of quantum teleportation where the receiver Bob, instead of having to apply a non-trivial correction unitary, merely has to pick up the right quantum system at a “port” specified by the classical message he received from Alice. While much more resource-demanding than standard teleportation, PBT has applications to instantaneous non-local computation and can be used to attack position-based quantum cryptography. A perfect PBT protocol would violate the linearity of quantum theory, so there is a trade-off between error and entanglement consumption (or the number of ports) which can be analyzed using representation theory of the symmetric and unitary groups. In particular the resource state has a “purified” Schur-Weyl duality symmetry. I will give an introduction to the task of PBT and its symmetries, and show how the asymptotics of existing formulas for the optimal performance for a given number of ports can be derived using a connection between representation theory and the random matrix ensemble GUE_0.

### Time

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

### Location

Room L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Motivated by problems in algebraic

more

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### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

may 2018

### Event Details

There are many methods to

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There are many methods to manage risks. However they all result in trying to determine the likelihood and impact of a risk. The presentation is about an approach to determine the likelihood of the quantum “threat” by investigating the requirements to run Shor’s algorithm on a fault-tolerant quantum computer. The results of this approach are used to make a suggestion on how an highly ICT dependent society should act regarding the quantum “threat”.

(Quantum “threat” is defined as the impact of quantum computing on public-key cryptosystems and symmetric key systems.)

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Quantum computing is powerful because

more

### Event Details

Quantum computing is powerful because unitary operators describing the time-evolution of a quantum system have exponential size in terms of the number of qubits present in the system. Recent developments in Hamiltonian simulation provide a rich toolbox to perform matrix arithmetics directly harnessing the exponential nature of quantum mechanics.

We develop a new algorithm that we call “Singular value transformation” that can apply polynomial transformations to the singular values of a block of a unitary, which is a generalization of the optimal Hamiltonian simulation results of Low and Chuang. The proposed quantum circuits have a very simple structure, often give rise to optimal algorithms and have appealing constant factors, while typically only use a constant number of ancilla qubits.

We show that singular value transformation leads to novel algorithms. For example we show how to use it for solving a “non-commutative” measurement problem required for efficient ground-state-preparation of certain local Hamiltonians, and propose a new method for singular value estimation. We also show how to exponentially improve the complexity of implementing fractional queries to unitaries with a gapped spectrum.

Our “Singular value transformation” algorithm is conceptually simple and efficient, and leads to a unified framework of quantum algorithms incorporating a variety of quantum speed-ups. We illustrate this by showing how it generalizes a number of prominent quantum algorithms, and quickly derive the following algorithms: optimal Hamiltonian simulation, implementing the Moore-Penrose pseudoinverse with exponential precision, fixed-point amplitude amplification, robust oblivious amplitude amplification, fast QMA amplification, fast quantum OR lemma and certain quantum walk results.

In order to exploit the strengths of the presented method it is useful to know its limitations too, therefore we also prove a lower bound on the efficiency of singular value transformation, which often gives optimal bounds.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

Randomized Benchmarking is an experimental

more

### Event Details

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

How can we make sure

more

### Event Details

How can we make sure that a quantum message remains unaltered when we send it over an insecure channel? How do we protect a quantum state from being corrupted when it is stored someplace where adversarial parties can potentially access it? And, especially relevant in the current era of cloud computing, how can we have an untrusted third party perform computations on such authenticated data?

The main protagonist of this talk will be a specific quantum authentication code called the “trap code” (Broadbent et al., 2013), which has proven to be very useful in several quantum cryptographic tasks. It also has a weakness, however: an adversary can learn information about the ciphertext structure by altering the ciphertext in a specific way, and observing whether or not the corrupted ciphertext is still accepted by the authentication protocol. The trap code is vulnerable to these types of attacks, because it lacks a property called strong purity testing (Portmann, 2017). I will discuss the strengths of authentication codes that do have this property, and I will also show how the trap code can be adjusted to become a strong-purity-testing code.

The talk is based on joint work with Florian Speelman (University of Copenhagen, QMATH).

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

### Organizer

Qusoft Seminars

### Event Details

In analogy with the classical

more

### Event Details

In analogy with the classical complexity class Total Functions from NP (TFNP), we introduce the complexity class of Total Functions from QMA (TFQMA). In this complexity class one is given a family of quantum circuits Qn that takes as input a classical string x of length n and a quantum state psi, such that for all x, there exists a witness, i.e. a psi such that Q_n(x,psi)=1 with probability > 2/3. The functional problem is then, given Q_n and x, find a psi such that Q_n(x,psi)=1 with probability > 2/3. The complexity of this class lies between the functional analogs of BQP and QMA, denoted FBQP and FQMA respectively. We provide examples of problems that lie in FQMA, coming from areas such as the complexity of k-local Hamiltonians and public key quantum money. In the context of black-box groups, we note that Group Non Membership, which was known to belong to QMA, in fact belongs to TFQMA. We conclude by discussing the relation between TFQMA, public key quantum money, and the complexity of quantum states.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam

april 2018

### Event Details

A basic question about non-local

more

### Event Details

A basic question about non-local games is: how much entanglement is required to play optimally or near-optimally? There are non-local games which cannot be played optimally with any finite amount of entanglement. For such games, we’d like to understand the amount of entanglement required to play epsilon optimally, as a function of epsilon. In particular, it seems interesting to find games where the amount of entanglement required grows as fast as possible. For two-player non-local games, the best known lower bounds on this function are polynomial in 1/epsilon. Recently, Ji, Leung, and Vidick have given a three-player game where the amount of entanglement required grows subexponentially in 1/epsilon. In this talk, I will explain how to get a two-player game where the amount of entanglement required grows subexponentially, using a connection with hyperlinear profile of groups.

### Time

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

### Location

L0.16 @CWI

Science Park 123, Amsterdam