Mr. Mohammed Daoud who is Professor of Theoretical Physics and National Coordinator of the Moroccan Network for Research in Quantum Computing (*), gave an interview to Lte Magazine (Khaouja) on the advent of the quantum computer.

Question from Lte magazine: Can you tell us the origin of this interest in what is commonly referred to in specialized literature as “quantum computer”?

Response from Si Mohammed Daoud: A second revolution in quantum physics has been preparing for a few years. Many projects are being tested behind the scenes of laboratories around the world and no doubt this research will bring results that will revolutionize the field of information technology. But before talking about what today is called new quantum technologies or quantum information sciences, it is interesting to note that the general public is sometimes unaware that it is thanks to the first quantum revolution that current advancements in digital technologies have been possible. In fact, this progress would never have been possible without quantum mechanics, which offers a very specific description of the laws of nature which govern the microscopic world (atoms, nuclei, electrons, etc.). By explaining electrical conduction in materials, quantum mechanics gaves birth to the semiconductor and transistor industry and our phones and computers are populated by millions of microchips . This physics leds to the invention of the laser, which is now known to have multiple applications in many fields.

Quantum physics is based on two fundamental pillars: the concept of superposition and the postulate of measurement. Superposition allows a quantum system (an electron, for example) to exist simultaneously in several different “states”. In other words, it can be in different states at the same time. There is also the postulate of measurement which makes it impossible to perform a measurement without disturbing the state of the system. Modern computing was therefore created by exploiting the physical properties of the microscopic world. It is unnecessary to recall the role of microprocessor transistors in computers which can allow an electric current to pass or, conversely, prevent it from flowing and thus retain type 1 or 0 binary information. This information is embodied in the states of matter and any transformation is governed by physical laws which are classic in nature in today’s computers. However, it turns out that today’s computers will quickly reach their limits when it comes to performing fairly large calculations, for example in the field of theoretical chemistry and solid-state physics (multi-body systems). It is therefore essential to seek solutions and it is in this spirit that the great physicist and Nobel Prize winner Richard Feynman was one of the first in 1980 to suggest the idea of taking advantage of the laws of quantum mechanics to simulate and better understand complex quantum systems using other quantum systems. Since then many researchers have looked at the advantages of encoding information in quantum states of matter and using the strange and counterintuitive properties of the microscopic world such as superposition or entanglement which is a particular type of correlation between two quantum systems.

To encode and process quantum information, we must use quantum bits such as the polarization of a photon or the spin of an electron, implement quantum logic gates that operate on these qubits and acquire practical tools to control quantum superposition and the phenomenon of quantum entanglement which could help us to process a large volume of data in relatively acceptable times on a human scale. The machine that is talked about most often in this regard and which is able to perform a large number of calculations in parallel is the quantum computer.

Question from Lte magazine: Can you give us the working principle of a quantum computer?

Response from Si Mohammed Daoud: In a quantum computer the physical media of information are quantum bits (qubits) such as the spin states of an electron (up / down). The principle of superposition allows a qubit to appear as a linear combination of quantum states (up / down) of the system chosen to encode information. In a quantum computer, the qubits are arranged in the form of blocks to constitute registers in a manner more or less similar to current computers. The manipulation of qubits and the various operations performed on these qubits are governed by the laws of quantum physics, whereas a classical computer manipulates bits of information, which are either 0s or 1s with operations governed by physics. classic. It is therefore thanks to the phenomena of superposition and entanglement that the quantum computer would be able to perform a series of operations in parallel and have all the possible results of a calculation in a single step to retain only the good. It is this ability to perform multiple operations simultaneously that is an advantageous advantage of these computers over conventional machines. The operational and physical realization of a quantum computer depends on the practical implementation of qubits. The latter is intimately dependent on the nature of the quantum algorithms that we have to execute and therefore on the type of calculation that we want to do.

In fact, the architectures of quantum computers depend on the characteristics of the qubits chosen as a vector of information (ions, atoms, photons) and the algorithms used are not necessarily the same depending on the architectures. For a computer with a specific function, you need qubits whose characteristics are well known and whose quantum properties can be controlled during the calculation process. The transformations of the qubits are carried out by a set of universal quantum gates with activation times which must be much greater than the computation times. It is important to note that the physical architecture of qubits conditions the nature of the quantum gates that act on the qubits. It should be noted that at the present time of our knowledge, quantum computers are implemented as co-processors of conventional computers that power them. A quantum computer is still a coprocessor of a traditional computer as can be a GPU (Graphic Processing Unit) for video games for example. The traditional computer closely controls the operation of the quantum computer by triggering the operations to be performed and therefore executing the programs intended for the quantum processors to translate them into physical operations to be performed on the qubits and to extract the results.

Question from Lte magazine: Where are we in the mastery of technologies for the generation of qubits and the implementation of logic gates?

Response from Si Mohammed Daoud: This mastery is essential to achieve the technological realization of a quantum computer. But, this is not the case at the stage of current research in this area. Today, knowing how to produce individual quantum systems (photons, ions, ..) is encouraging for future applications in the field of quantum information. However, a lot of work remains to be done in controlling and manipulating these qubits. The fact of observing a quantum system disturbs it and generates errors requiring extreme stabilization conditions such as for example for a certain class of solid qubits for which stabilization requires the use of temperatures of around – 273 ° C with a device. A certain number of technological challenges and constraints must therefore be overcome and we are only at the beginning of a scientific and technological adventure which suggests on the horizon a new digital era with gigantic technological progress (as for the first transistors). . Researchers in this field are convinced of this. For example, the quantum computer would be a threat to current encryption systems like the RSA protocol widely used in banking transactions. Its computational abilities could help easily break any secret codes and so you have to be prepared for this eventuality.

We are already talking about post-quantum cryptography, which in such a short time has become an intensively studied theme in order to have the means to prevent against cybernetic attacks that could be carried out using a quantum computer. It is indisputable that the performance of quantum information technologies will be boosted to reach capacities whose limits and implications no one can predict today.

Question from Lte magazine: We know that quantum physics is based on non-deterministic processes. So how can we trust the probability to run a computer

Response from Si Mohammed Daoud: In a quantum computer, the qubits are arranged in the form of blocks to constitute registers in a more or less similar way to the 32 or 64 bit registers of current classical processors. In a register of n qubits, information can be manipulated simultaneously. This simultaneity is possible in the quantum case thanks to the principle of superposition which allows a qubit to be in a linear combination state of states 0 and 1. It is the superposition which therefore offers the possibility of performing exponential combinatorial calculations. It is essential to note that the 2n states do not correspond to a greater information storage capacity than in the conventional case.

But the qubit register offers a capacity for superposing states to which we then apply a set of operations and treatments to bring out the combinations that we are looking for according to a given algorithm. The use of qubits therefore makes it possible to simultaneously verify a multitude of hypotheses in order to reach the best solution in a very short period of time compared to conventional algorithms. Also, the relevant information is that which is extracted after the execution of the calculation and which is in the form of a conventional register of bits. The probabilistic character occurs when the states of the n qubits are combined to ensure parallel processing during the computation. But it does not intervene on input or output. In other words, a quantum algorithm will create a state of superposition of values in a quantum register. The superposed states of the registers satisfy a probabilistic distribution law. A quantum computation will change over time the probability of each of the combinations of qubit states to reach some and bring out one in particular which is the answer to the question asked. So at the output, the retrieved result is therefore not 2n values, but n bits.

Question from Lte magazine: What is the added value of the quantum computer? That is to say compared to a conventional computer? What more could a quantum computer achieve?

Response from Si Mohammed Daoud: One of the main motivations of current research in quantum information is the design of new information processing tools and to have theoretical and practical tools that would make it possible to solve problems that traditional computers cannot solve or would be unable to resolve. We think of the problems whose complexity increases exponentially with the amount of data to be processed where classical algorithms find their limits on traditional computers. The calculation times of exponential problems would remain exponential even if we manage to double the power of machines whose operation is governed by the laws of classical physics. Coding information in quantum systems and changing the states of these systems according to operations governed by quantum laws offers the possibility of drastically reducing these exponential calculation times. A quantum computer could, for example, allow the development of new drugs using the simulation of the synthesis of new molecules, the simulation of the behavior of new materials or chemical reactions or even the resolution of problems related to logistics and technology like optimization of transport systems. But using these machines, a long way to go and a lot of technological barriers sould be overcome.

Question from Lte magazine: At what stage are we today in the design of a reliable quantum computer and when will we have quantum computers on the market?

Response from Si Mohammed Daoud: Research on the possible applications offered by quantum information in general and the quantum computer and quantum calculations in particular has been well developed over the past ten years. But there is still some confusion reported in the media about what is possible to do with computers or quantum calculators. First of all, quantum computer and quantum computer are different and do not mean the same thing. A quantum computer should be able to run any type of quantum algorithm while a quantum computer (which is not a universal Turing machine programmable in theory to be able to perform any algorithm) is designed to run a single class of algorithms. It is not programmable to perform any type of calculation. A few quantum computers have been developed, but they are very basic. Also, many physicists believe that only quantum computers designed to solve very specific problems could compete with classical computers. A great effort is dedicated to the manufacture of quantum computers, but this is conditioned by the ability to implement and control the quantum properties of superposition and entanglement. It would be necessary to limit the influence of environmental disturbances which rapidly degrade the properties of the qubits involved in a calculation, especially when the latter uses a large number of qubits. Today, it is unclear how to overcome or at least limit the effects of these perturbations, and the most optimistic experts believe that building reliable quantum computers would not be possible until 2050.

Question from Lte magazine: But in the press, from time to time we read advertisements about the realization of quantum computers. What is it?

Response from Si Mohammed Daoud: Indeed, in the press, we read from time to time announcements on new achievements breaking the records achieved by the competitors. In fact, large international firms are interested in this subject and seek to achieve quantum supremacy which is defined as the threshold from which the quantum computer becomes an operational technology, capable of performing tasks that no classical computer does or will ever be able to accomplish. Several projects to arrange viable quantum bits in registers to develop quantum processors are underway. A race is on and IT giants like Google, Microsoft and IBM are in the game. In 2019, Google announced the realization of a 54-qubit quantum computer called “Sycamore” in which qubits that are kept near the absolute zero (−273.15 ° C) using cryogenic equipment. It seems that this new computer would have made it possible to perform a complex calculation in a period of 200 seconds instead of 10,000 years if the same calculation were performed on a conventional supercomputer. This result, which is difficult to verify, was quickly contested by Google’s competitors, in particular IBM. Still in this race to occupy the top of the podium, the American company Honeywell announced in March 2020 the manufacture of its first quantum computer with 64 qubits. According to company officials, the performance of this machine is currently being tested by a few companies doing their calculations on Honeywell’s quantum computer. Due to the lack of a business model, no one is able to verify whether this machine operates according to the laws of quantum mechanics or whether it is only a supercomputer whose operation is identical to conventional computers.

Question from Lte magazine: There has been media coverage of the launch of a satellite designed using quantum cryptography. What is the point of quantum cryptography?

Response from Si Mohammed Daoud: It is widely accepted that cryptography and quantum communications are key applications of quantum information. Quantum cryptography, also known as quantum key distribution (QKD: Quantum Key distribution), offers a physical method to distribute a secret key while guaranteeing unconditional security. A cryptographic protocol does not require any encryption of the information exchanged. It is the laws of physics that place a limit on the amount of information that would be accessible to a spy depending on the parameters of quantum transmission. Of course, the information exchanged would have to be encoded in qubit states and the exchange of encryption keys, generally symmetrical, can be done by optical means (optical fiber, air link or satellite). During the last two decades, experiences of implementing quantum cryptography protocols have multiplied both in the open air and on optical fibers.

In Europe, a lot of progress has been made such as the demonstration of QKD carried out by a team led by Anton Zeilenger in 2007 and then in 2010. The aim was to establish a distribution of quantum keys over a distance of 144 km connecting the islands of La Palma and Tenerife in the Canaries. The range of QKD transmission over fiber has also improved, and many telecom operators are paying special attention to privacy modes that exploit the properties of the microscopic world. We can quote, for example, the Swiss company IDQ which offers secure transmission services using QKD protocols or the French group Orange which announced in May 2019 that it was launching tests for a communication protected by QKD. Other projects are underway, such as the European Open-QKD consortium aiming to test a terrestrial QKD network on the continent.

In the USA, a QKD network was tested in Ohio in 2013, and tests were also carried out in 2015 at MIT to link two sites 43 km away.

A commercial deployment of QKD on an unused 800 km fiber-optic network connecting Boston to Washington DC is also being deployed to connect Wall Street financial firms with their offices in New Jersey. An 85 km facility was also deployed in Chicago in 2019. In July 2020, the US Department of Energy announced it was expanding this QKD network to link all the sites of these research laboratories.

In China, a deployment had been carried out for a fiber optic link secured by QKD between Shanghai and Beijing, covering 2000 km. This line is operating by banks and government departments in the financial sector. China is considering a QKD network on an additional 33,000 km network that will be ready by 2025. But China’s outstanding performance in this area concerns satellite QKD for the teleportation of quantum states of photons optically to 1400 km distance between the Micius satellite and the Earth. Although this first experience has its limits, China continues to develop QKD by satellite and therefore to ensure a mastery of the communications of the future offered by the second quantum revolution.

Today, investing in QKDs is a strategic choice for developed countries for the obvious reasons of sovereignty and for better protection of secret data and sensitive communications

Question from Lte magazine: In addition to cryptography, what can a quantum computer bring us? Power?

Response from Si Mohammed Daoud: What seems easy today in quantum physics was hardly easy a few years ago. Indeed, even the founders of quantum mechanics believed that microscopic reality could only be experienced with the help of collective effects induced at the macroscopic scale. This was coomonly accepted until 1970 when researchers began to produce, study, control and use individual quantum systems. This increasingly fine-grained mastery of the microscopic world will undoubtedly lead to new applications other than those very familiar today such as lasers, transistors, nuclear magnetic resonance…. Current research in quantum physics offers exciting new perspectives for building machines that perform tasks beyond the performance of classical (non-quantum) machines. In addition to cryptography and quantum communications, there are other very promising future applications of quantum information. We can cite for example (i) quantum computing which could help to solve certain complex problems, (ii) quantum simulators which and (iii) quantum metrology. Indeed with unique quantum objects, it is possible to go closer and closer to the object to be measured and this will allow us to make extraordinarily small sensors. Thus by exploiting the quantum properties of these microscopic systems we can improve the precision of our measurements and go beyond the standard quantum limit. Better exploitation of quantum resources for complex and varied tasks will lead to practical, integrated and flexible quantum information processing systems that provide maximum security, speed and precision. Many researchers are convinced that ongoing research in this area will certainly lead to a rich range of applications beyond those expected.

(*): Mohammed Daoud is professor of theoretical physics in the physics department of the Faculty of Sciences of IbnTofail University (Kénitra-Morocco). He is also the national coordinator of the Moroccan Network for Quantum Information and vice-president of the Moroccan Society of Mathematical Physics. His recent work focuses on the mathematical and physical aspects of quantum information. Mohammed Daoud was elected, in 2009, regular associate member at the International Center for Theoretical Physics (ICTP-Trieste-Italy) and was appointed, in 2012 and then in 2017 by the Minister of Higher Education, expert at the National Center of Scientific and Technical Research. He has been invited as a researcher, professor or associate member by several international universities or research centers. Mohammed Daoud is a member of several scientific expert committees (CNRST-Maroc, CONICYT-Chile, CNCS-Romania). He is a member editor and referee for several international journals of theoretical physics, mathematical physics and quantum physics.