The quantum internet – the second quantum revolution

It is there for all to see that the emergence of the internet has allowed computers and digital electronics to realise their full potential. Now, with the emergence of the entirely new type of quantum technologies, whose early demonstration is becoming a reality, their full potential is expected to be inevitably disclosed by networking them. This is just the central topic of The Quantum Internet – The Second Quantum Revolution, by Peter. P. Rohde. The quantum era is just at its inception, but it already shows how countless industries will be revolutionised, starting from quantum computing. The book then presents an early formulation and analysis of quantumnetworking protocols, by depicting a possible future quantum internet where resources can be shared and communicated. Starting from a description of classical networks, the author then introduces the key concepts of quantum internet protocols, quantum cryptography and cloud quantum computing, by examining in some detail the technology required as well as the implications it will have economically and politically. Indeed, the superclassical scaling in the computational power of quantum computing forces to give the required attention tomany important economic and strategic considerations. The classical-equivalent power of a quantum computer may grow exponentially with the number of qubits, so that economic indicators are likely expected to exhibit different scaling characteristics and dynamics with respect to those of classical computers, resulting in a fundamental alteration of the economic landscape of the post-quantumworld. The author appropriately addresses all such issues throughout the book, allowing ‘to inspire new research directions, encourage future work and stimulate lively and rigorous scientific debate about future technology’. The onset of quantum computing also carries with it somewhat deep ‘philosophical’ implications. A game theory approach shows, indeed, that strong motivations exist for quantum computing vendors to cooperate in order to globally maximise net utility and remain competitive: they are boosted to contribute their resources to the quantum internet (rather than go it alone), due to the superlinear leverage. As a matter of fact, facilitating cloud quantum computing is of key importance for allowing very expensive quantum computers to be accessible to end users, thus favouring early widespread adoption of quantum computation. Possiblemarket structures are also envisaged by the author, which clearly show interesting and largely unexplored avenues for future research at the intersection between economics and quantum information theory. Of course, however, the main attention of the present book is devoted to technical issues and, aside from quantum computing, which is the most exciting of the emerging quantum technologies, a central use for them is – expectedly – in cryptography, given its fundamental relevance in the area of the general security of information transmission in the internet age. Here, while classical encryption protocols mainly refer to computational security (for example, classical random generators are actually deterministic, but so difficult to predict that can be regarded as good as random), quantum ones are typically information theoretically secure. The laws of quantum information bound the amount of information that can be extracted from a system (ultimately due to the Heisenberg uncertainty principle), irrespective of an adversary’s computational resources. Hacking attacks are then expected to exploit weaknesses in the physical implementation, rather than weakness of the theory. In this respect, a key point appropriately addressed in the book is the fact that, while classical digital data are discretised, so that data transmission is highly robust against noise, this is not necessarily true in the quantum case (the coefficients in quantum superpositions are continuous), so that errors accumulate during transmission and states will inevitable deteriorate. Also, future quantum internet will require the communication of quantum information over arbitrarily long distances, well beyond the attenuation length of the optical fibres connecting them or the line of sight of satellites in orbit, thus introducing another issue to take into due account. These and many other interesting technical topics are thoroughly discussed along the present book, which gradually introduces the reader into the power and versatility of universal quantum computers interconnected via a quantum internet. ‘Our goal, first and foremost, is to inspire future science’, Rohde ambitiously declares, but, firmly planted with his feet on the ground, he as well recognises that