## Introduction

The promising field of quantum information technologies is evolving very rapidly and involves many players. Among these technologies, we find more particular applications or application concepts in the following areas:

- Information processing systems, universal or specialized;
- Telecommunications;
- Sensors.

However, quantum technologies are also a field filled with many obstacles and uncertainties. Two questions are therefore important: what is actually happening and what is the next step?

## The hope of quantum technologies

Quantum technology is the field of physics and engineering based on the principles of quantum physics. Applications range from computing to sensors and communication. Quantum computing itself has the potential to deal with many classes of problems: simulation and modeling, machine learning and natural language processing, optimization, etc.

Actors in this field include academics as well as large companies and small start-ups (which focus on certain categories of problems).

Much research is conducted on the software side; less on the hardware side. However, the field is evolving rapidly and is marked by uncertainties. The current horizon for real-life applications would be around 2025. Some players communicate a lot: IBM recently promised a 1000-bit quantum computer by 2023. Around the same time, Professor John Martinis, Google’s top quantum scientist, resigned from the company, creating a stir throughout the quantum community.

Many obstacles remain before quantum technologies can be used to solve real problems. In particular, the number and stability of qubits must be significantly increased.

## Not all promises will be kept

In reality, the prospects for development vary greatly depending on the type of quantum information technology, but also because, for example, the same word: “computer” is used to talk about mathematical ideas and information technology.

Thus, the first question when talking about a quantum computer is whether we are talking about a speculative concept based on a mathematical possibility or a technological concept based on a physical possibility. This is the old opposition between theory and practice: a mathematical possibility is proved by theoretical demonstration, where a technological concept is proved by experimental construction.

Secondly, in the case where it is really a question of technology, it is necessary to ascertain whether it is a question of a computer in the sense of a universal computer, capable in particular of carrying out all the computations performed by information technologies already existing today, or a computer in the sense of a computing technology exploiting a quantum mechanism applicable only to a special class of problems.

For example, it is quite permissible to consider that quantum computing is the most fundamental form of computing, that everything that can be computed classically can be computed on a quantum computer, that the qubit is the basic unit of computation, and not the bit. Similarly, it is possible to consider that certain categories of problems require quantum algorithms for their resolution. But it should be added that such considerations today refer in all cases only to the field of theoretical computing, and not to that of information technology. Quantum information technology must indeed operate on technological qubits and not on purely mathematical qubits. The realizations of technological qubits are today limited and face important physical challenges. The question of the realization of quantum information technology thus remains an open question, with a high degree of uncertainty.

Regarding the current challenge of quantum supremacy (cf. Google’s Sycamore computer, and the Chinese Jiuzhang more recently), let us note that these computers are specialized in a type of optimization. The goal is to establish the existence of types of computational problems in which the quantum computer has a unique advantage.

## So what are the real prospects for these technologies?

The first step of the rocket is to understand what really happens on the ground. What is the real current state of quantum technologies, compared to pure communication. What are the technologies, their level of maturity, the hurdle to be overcome to make them usable in an industrial context, and compatible with the targeted applications? For example, which problem classes are well suited to quantum computing? Which programming languages are suitable? What are the corresponding time horizons? What are the existing applications and scenarios? Who are the main actors, etc.? Even if companies do not wish to develop their own quantum technologies, as a user, it is essential to have a good understanding of these technologies.

The second step of the rocket is to think about post-quantum. Indeed, if a new quantum technology were owned by a state, telecommunications would become transparent to it, but the rest of the world would not know about it. It is therefore essential to think about post-quantum approaches as well.

## Conclusion

Integrating the impacts of future quantum information technologies is necessary because of the size of these impacts. But size must be weighted by probability – and this is where it becomes difficult to orient the technology roadmap. For few organizations have direct expertise, or (like Presans!) the expertise on expertise, to evaluate the announcements that are currently stirring up this technological field.

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