Jian-Wei Pan, China’s Top Computer Expert: “The Next Biggest Quantum Breakthrough Will Come in Five Years” | Science


Adán Cabello and Jian-Wei Pan, in Stockholm in June 2019.
Adán Cabello and Jian-Wei Pan, in Stockholm in June 2019.Sevilla University

Any advance in quantum computing multiplies the potential of a technology capable of performing calculations and simulations that are impossible with current computers and facilitating the study of phenomena that until now were only theoretical. Last year, a group of researchers, with Spanish participation, raised in Nature that an alternative to quantum theory based on real numbers can be experimentally falsified. The original proposal left open a challenge. An investigation led by the most relevant Chinese scientist in this field, Jian-Wei Pan, and with the participation of the physicist from the University of Seville Adán Cabello has demonstrated “the indispensable role of complex numbers [raíz cuadrada de menos uno, por ejemplo] in standard quantum mechanics. The results allow progress in the development of computers that use this technology and, according to Cabello, “verify quantum physics in regions that were inaccessible until now.”

Jian-Wei Pan, 51, a graduate of the University of Science and Technology of China (USTC) in 1987 and a Ph.D. from the University of Vienna, heads one of the largest and most successful quantum research groups in the world. Physics Nobel laureate Frank Wilczek described it as “a force of nature.” Regarding him, his thesis director at the University of Vienna, the physicist Anton Zeilinger, has stated: “I cannot imagine the appearance of quantum technology without Jian-Wei Pan”.

His leadership in the discovery has been fundamental. He sums it up this way: “The experiment can be seen as a game between two participants: real-valued quantum mechanics versus complex-valued quantum mechanics. The game takes place on a quantum computer platform with four superconducting circuits. By submitting random measuring bases and measuring the result, you get the game score, which is a mathematical combination of the measuring bases and the result. The rule of the game is that real value quantum mechanics is discarded if the game score exceeds 7.66, which is the case in our work.”

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The experiment, collected by Physical Review Letters, has been developed by a team from the USTC and the University of Seville to answer a fundamental question: Are complex numbers really necessary for the quantum mechanical description of nature? The results rule out an alternative to standard quantum physics that uses only real numbers.

Jian-Wei Pan, at the University of Science and Technology of China.
Jian-Wei Pan, at the University of Science and Technology of China.USTC

Jian-Wei Pan explains: “Physicists use mathematics to describe nature. In classical physics, the real number seems complete in describing physical reality in all classical phenomena, while the complex number is only sometimes used as a convenient mathematical tool. However, whether the complex number is necessary to represent the theory of quantum mechanics remains an open question. Our results refute the actual numerical description of nature and establish the indispensable role of the complex number in quantum mechanics.”

“Beyond the interest of excluding a specific alternative”, adds Cabello, “the importance of the experiment is that it shows how a system of superconducting qubits [los que se usan en los ordenadores cuánticos] It allows us to verify predictions of quantum physics that are impossible to verify in the experiments that we have been doing up to now. This opens up a very interesting range of possibilities, because there are dozens of interesting predictions that we have never been able to check, since they require very good control over several qubits. Now we are going to be able to put them to the test.”

Chao-Yang Lu, from the USTC and also a co-author of the experiment, adds: “The most promising short-term application of quantum computers is the testing of quantum mechanics itself and the study of many-body systems.”

The next advance in quantum computing will be to have a logical qubit with higher fidelity than the physical one and it will happen in about five years. In homes, quantum computers, if realized, will first be available through cloud services

Jian-Wei Pan, a physicist at the University of Science and Technology of China

In this way, the discovery provides not only a way forward in the development of quantum computers, but also a new way of approaching nature to understand the behavior and interactions of particles at the atomic and subatomic level.

And like all progress, the opening of new paths generates uncertainties. However, Jian-Wei Pan prefers to focus on the positive aspects: “Building a practically useful and fault-tolerant quantum computer is one of the great challenges for human beings. I am more concerned with how and when we will build one. The most formidable challenge in building a large-scale universal quantum computer is the presence of noise and imperfections. We need to use quantum error correction and fault-tolerant operations to overcome noise and scale the system. The next advance in quantum computing will be to have a logical qubit with higher fidelity than the physical one and it will happen in about five years. In homes, quantum computers, if realized, will first be available through cloud services.


In this sense, Cabello advances that “when quantum computers are large enough and have thousands or millions of qubits, they will make it possible to understand complex chemical reactions that help to design new drugs and better batteries or to carry out simulations that lead to the development of new materials or calculations that allow optimize the artificial intelligence and machine learning algorithms used in logistics, cybersecurity and finance, or that allow the deciphering of the codes on which the security of current communications is based”

“Quantum computers”, explains the scientist from the University of Seville, “use the properties of quantum physics to perform calculations. Unlike the computers we use, in which the basic unit of information is the bit (which can take two values), in a quantum computer, the basic unit is the quantum bit, or qubit, which has an infinite number of states. ”.

Cabello adds that “the quantum computers that have been built by companies such as Google, IBM or Rigetti take advantage of the fact that objects the size of a micron and produced using standard semiconductor manufacturing techniques can behave like qubits.”

The goal of computers with millions of qubits is still far away, since most current quantum computers, according to the physicist from the University of Seville, “only have a few qubits and not all of them are good enough”. However, the discovery of the Chinese and Spanish team, allows to expand the uses of existing computers and understand physical phenomena that have puzzled scientists for years.

crystal of time

In this sense, Google Quantum AI has published in Nature the observation, for the first time, of a time crystal through the quantum processor Sycamore. A time crystal is similar to a grain of salt made up of sodium and chlorine atoms. However, while the layers of atoms of that salt form a physical structure based on repetitive patterns in space, in the crystal of time it is configured from an oscillating pattern. Google’s processor has been able to observe those oscillatory wave patterns of stable time crystals.

This finding, as Pedram Roushan and Kostyantyn Kechedzhi explain, shows “how quantum processors can be used to study new physical phenomena.” And they add: “Moving from theory to real observation is a critical leap and is the basis of any scientific discovery. Research like this opens the door for many more experiments, not just in physics, but hopefully inspiring future quantum applications in many other fields.”

In Spain, a consortium made up of seven companies, five research centers (BSC, CSIC, DIPC, ICFO and Tecnalia) and the Polytechnic University of Valencia (UPV) have launched the CUCO project to apply quantum computing in strategic Spanish industries : energy, finance, space, defense and logistics. The CUCO project, subsidized by the Center for Industrial Technological Development (CDTI) and with the support of the Ministry of Science and Innovation, is the first large quantum computing project in Spain in the business field and aims to “progress in knowledge scientific and technological development of quantum computing algorithms through public-private collaboration between companies, research centers and universities” to implement these technologies in the medium term. Seven companies participate in it (Amatech, BBVA, DAS Photonics, GMV, Multiverse computing, Qilimanjaro Quantum Tech and Repsol), five research centers (BSC, CSIC, DIPC, ICFO and Tecnalia) and the UPV.

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George Holan

George Holan is chief editor at Plainsmen Post and has articles published in many notable publications in the last decade.

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