by Jop Briët (CWI) and Simon Perdrix (CNRS, LORIA)

For more than a century now, we’ve understood that we live in a quantum world. Even though quantum mechanics cannot be ignored during the development of atomic scale components of everyday computers, the computations they perform are governed, like the Turing machine, by the laws of classical Newtonian mechanics. But the most striking and exotic features of quantum mechanics, superposition and entanglement, currently play no part in every-day information processing. This is about to change – and in some specialised applications, already has. In academia, the field of quantum computation has been growing explosively since its inception in the 1980s and the importance of these devices is widely recognised by industry and governments. Big players in the tech industry like IBM and Google frequently announce that they have built yet a larger rudimentary quantum computation device and in 2016 the European Commission launched a one-billion Euro Flagship Initiative on Quantum Technologies. 

by Georgios M. Nikolopoulos (IESL-FORTH, Greece)

Quantum cryptography is the science of exploiting fundamental effects and principles of quantum physics, in the development of cryptographic protocols that are secure against the most malicious adversaries allowed by the laws of physics, the “quantum adversaries”. So far, quantum cryptography has been mainly identified with the development of protocols for the distribution of a secret truly random key between two legitimate users, known as quantum key-distribution (QKD) protocols. Beyond QKD, quantum cryptography remains a largely unexplored area. One of the main ongoing projects at the Quantum Optics and Technology group of IESL-FORTH [L1], is the design and development of cryptographic solutions, which rely on fundamental quantum-optical systems and processes, and offer security against quantum adversaries.

by Damian Markham (LIP6, CNRS - Sorbonne Université)

The massive global investment in quantum technologies promises unprecedented boosts for security, computation, communication and sensing. In this article we explore the use of so-called ‘graph states’ – a family of multipartite entangled states which act as ubiquitous resources for quantum information, are easily adapted for different tasks and applications, and can be combined in ways that fuses different utilities.

by Alexandru Gheorghiu (University of Edinburgh) and Elham Kashefi (University of Edinburgh, CNRS)

Quantum computers promise to efficiently solve not only problems believed to be intractable for classical computers, but also problems for which verifying the solution is also intractable. How then, can one check whether quantum computers are indeed producing correct results? We propose a protocol to answer this question.

by Alex Neville and Chris Sparrow (University of Bristol)

Boson sampling has emerged as a leading candidate for demonstrating “quantum computational supremacy”. We have devised improved classic al algorithms to solve the problem, and shown that photon loss is likely to prevent a near-term demonstration of quantum computational supremacy by boson sampling.

by Fabian Laudenbach, Sophie Zeiger, Bernhard Schrenk and Hannes Hübel (AIT)

Photonic quantum computers promise compact, user-friendly packaging. The building blocks of such an implementation comprise of sources for efficient production of photons with high purity. To increase the clock speed of the computation, such sources need to operate in the GHz range.

by Serge Fehr (CWI)

Over the last few years, significant progress has been made in understanding the peculiar behaviour of quantum information. An important step in this direction was taken with the discovery of the quantum Rényi entropy. This understanding will be vital in a possible future quantum information society, where quantum techniques are used to store, communicate, process and protect information.

by Thijs Veugen (TNO and CWI), Thomas Attema (TNO), Maran van Heesch (TNO), and Léo Ducas (CWI)

In the post-quantum era, most of the currently used cryptography is no longer secure due to quantum attacks. Cryptographers are working on several new branches of cryptography that are expected to remain secure in the presence of a universal quantum computer. Lattice-based cryptography is currently the most promising of these branches. The new European PROMETHEUS project will develop the most secure design and implementations of lattice-based cryptographic systems. Exploitation of the project results will be stimulated by demonstrating and validating the techniques in industry-relevant environments.

by Peter Mueller, Andreas Fuhrer and Stefan Filipp (IBM Research – Zurich)

Scientific groups in industry and academia have made enormous progress in the implementation of first quantum computer prototypes. IBM’s quantum experience with five and 16 qubits are already publicly accessible in the cloud. Three “standard” software interfaces are available. Client systems with 20 qubits ready for use and the next-generation IBM Q system is in development with the first working 50 qubit processor.

by Gábor Ivanyos and Lajos Rónyai (MTA SZTAKI, Budapest)

Effective versions of some relaxed instances of the Chevalley-Warning Theorem may lead to efficient quantum algorithms for problems of key practical importance such as discrete logarithm or graph isomorphism.

by Alain Sarlette (Inria) and Pierre Rouchon (MINES ParisTech)

Despite an improved understanding of the potential benefits of quantum information processing and the tremendous progress in witnessing detailed quantum effects in recent decades, no experimental team to date has been able to achieve even a few logical qubits with logical single and two qubit gates of tunably high fidelity. This fundamental task at the interface between software and hardware solutions is now addressed with a novel approach in an integrated interdisciplinary effort by physicists and control theorists. The challenge is to protect the fragile and never fully accessible quantum information against various decoherence channels. Furthermore, the gates enacting computational operations on a qubit do not reduce to binary swaps, requiring precise control of operations over a range of values.

by David Petrosyan (IESL-FORTH)

In order to develop functional devices for quantum computing and analogue and digital quantum simulations, we need controlable interactions between the physical systems representing quantum bits – qubits. We explore strong, long-range interactions between atoms excited to high-lying Rydberg states to implement quantum logic gates and algorithms and to realise quantum simulators of various spin-lattice models to study few- and many-body quantum dynamics.

by Nicolas Augier (École polytechnique), Ugo Boscain (CNRS) and Mario Sigalotti (Inria)

The dynamics of a quantum mechanical system is described by a mathematical object called Hamiltonian. The possible results of an energy measure are known as the “eigenvalues” (or energy levels) of the Hamiltonian. After an energy measure, the system collapses into a particular state called the eigenstate corresponding to the measured energy. Adding corners to adiabatic paths can be used to generate superpositions of eigenstates with simple and regular control laws.

by Harry Buhrman (CWI and QuSoft) and Floor van de Pavert (QuSoft)

Researchers and industry specialists across Europe have launched a Quantum Software Manifesto. With the Manifesto, the group aims to increase awareness of and support for quantum software research.
Quantum computers, once just the dream of science fiction writers, are rapidly becoming a reality. Already, the first small quantum hardware devices are being put through their paces, with researchers probing for evidence that they really do work in a fundamentally different way, unlocking solutions to problems classical computers could never solve.

Next issue: April 2021
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