# Quantum Computers and Quantum Internet

Are there limits to the development of the computer industry? Taking into account the pace of this development over the past half century, a rather rosy impression is formed about the prospects for further improvement of information technologies. Although no further than in 2007, the notorious Gordon Moore stated that his law, which predicts a doubling of the number of transistors on an integrated circuit chip every two years, seems to cease to act very soon due to the banal reason of the atomic nature of matter and the limitation of the speed of light …

So far we will not argue about the possibilities of overcoming the speed mentioned above, but with regard to atoms it is very possible that the situation is far from so sad. After all, as far back as the mid-1980s, when personal computers were just beginning their triumphal journey to replace mainframes, the even more famous American physicist, Nobel laureate Richard Feynman (1918-1988) claimed: “It seems that the laws of physics do not represent any limit to reducing size computers right up to the fact that bits become the size of atoms and quantum behavior will begin to rule. ”

In fact, quantum computers, which partly overcome the limitations of the atomic nature of matter and which were discussed in detail by ITC.UA a decade ago, have existed on paper for more than thirty years, thanks to studies of the same Feynman, who put forward the idea of such a device in 1981 year, – although even a little earlier and independently of it, the mathematician Yuri Manin, a native of Simferopol, did it. Recall that in “ordinary” computers, media from punch cards and transistors contain information encoded in a binary number system: the presence or absence of a hole, the induction of a magnetic field is greater or less than a threshold value and just a state of “on. on / off ”are converted to bits consisting of zeros and ones.

Inside view of the “quantum computer” from IBM.

The quantum analogs of “bits” called “qubits” (from quantum bit – which, incidentally, in many languages successfully coincides in sound with the ancient Greek and Roman unit of measurement of length, the analogue of the “elbow”), as computer media of a qualitatively different type are distinguished by their ability to the so-called “superposition” – the ability to be in both states at once (relatively speaking, “1” and “0”) at the same time, but only until such a state is measured. In theory, such a strange feature of subatomic particles has been the subject of many debates and difficult hypothetical situations for almost a century, such as the famous (and very unhappy) “Schrödinger cat”, which is forced to be both alive and dead in a box with radioactive material, in which possible decay one of the atoms causes the activation of a deadly poison. However, in practice, such obscure properties of atoms have long been used – and the field of computer technology is no exception.

The trick is that if, at the very beginning of the calculations, the system consisting of quantum information carriers with the input data entered is transferred to the superposition state, such calculations will be performed for the entire obtained data set in parallel – that is, with tremendous speedup in solving the problem. True, the problem arises of measuring such calculations – since, like the Schroдингdinger cat, if you open the box and “look” at its state, it will always turn out to be either alive or dead, and “qubits” when measuring their data can we have only one answer, in spite of all the “parallelism” of the calculations preceding this dimension. And therefore, with all the advantages and unprecedented advantages of this kind of computer, using it will turn out far from any calculations.

In the 1990s, several possible schemes for the operation of a quantum computer were proposed at once, called the names of the scientists who nominated them. So, the algorithm of Peter Shore from Bell Laboratories provides that we may not be interested in the entire sequence of values of a function, but only its period, which is much more accessible for measurement. But with the help of this algorithm on a quantum computer it is possible with unprecedented speed – somewhere 100 million times faster! – solve the factorization problem, that is, determine simple prime factors of large numbers, which, in turn, allows you to almost instantly decrypt cryptographic algorithms with a public key, since the existing RSA-cryptosystems are built on the inaccessibility of this task to the current capacities of conventional computers.