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The Fascinating History and Future of Light According to Nobel Laureate Serge Haroche

  For primitive people, light means day and direction. For modern people, light is an essential element in daily work and life. It can be said that light has accompanied every stage of human evolution and civilization development. As an ancient subject in physics, optics is one of the most active subjects in current scientific research, promoting the continuous deepening of human understanding of nature and the progress of human society.
  For Serge Haroche, emeritus professor at the Collège de France and winner of the 2012 Nobel Prize in Physics, light has extremely rich connotations. From determined to become an astronomer to spending his life exploring the science of light, he finally turned the “Schrödinger’s Cat” thought experiment into reality. In 2012, Arrosh and American physicist David Wineland won the Nobel Prize in Physics for their research on groundbreaking experimental methods that can measure and manipulate individual quantum systems.
  Recently, Serge Aroche appeared in the fourth “Pujiang Science Master Forum”. With the title “Science of Light: From Galileo to Quantum Physics”, he told the audience about the scientific research progress of people over the past hundreds of years. A moving story about light, understanding light, and exploring the world with light. As a researcher who is passionate about light, scientific stories about light have inspired his curiosity about the world. As an experimental physicist who manipulates individual quantum systems, lasers are the best helper in his career.
  After the speech, a reporter from “Xinmin Weekly” talked with Arosh about light in the eyes of physicists. Do they view light differently from ordinary people?
“Light” in the eyes of scientists

  ”I have been impressed and fascinated by the science of light since I was young.” The first light that aroused the infinite curiosity in the young boy came from Galileo who pointed the telescope at the starry sky.
  Does light have speed? This question seems undoubted now, but in Galileo’s time, it was unknown. It is generally believed that light is infinitely fast. Galileo was curious about this problem and made some attempts. Although the attempts ended in failure, it opened the door to measuring the speed of light. At the same time, his observations of Jupiter’s satellites also provided a “natural clock” for later scientists to measure the speed of light. Galileo first proposed that “the speed of light can be measured”, thus taking the first step in human exploration of the speed of light. 70 years later, Ole Romer confirmed for the first time that the speed of light is finite through the observation of the “Io eclipse” phenomenon.
  Light has speed, so is light a particle or a wave?
  This controversial and protracted question began in the 17th century and lasted for two centuries. It is related to almost all the masters of physics that we are now familiar with. In this process of constant verification and refutation, people’s understanding of light gradually became clearer. The ever-changing aspects of light were jointly discovered by Huygens, Newton, Thomas Young, Fresnel, Maxwell, Hertz, Einstein and other scientists. It gradually became clear through exploration and debate, and people’s understanding of the world also moved from the Newtonian era to the quantum era.
  In the 17th century, the particle theory represented by Newton and the wave theory represented by Huygens were in a stalemate. In the early 19th century, Thomas Young used the double-slit experiment to prove that derived light waves obey the superposition principle, confirming the wave nature of light. It was not until the mid-19th century that Maxwell proposed the electromagnetic wave theory of light, which was verified by Heinrich Hertz’s experiments, thereby unifying electricity, magnetism and optics. The theory of electromagnetic waves sheds new light on the nature of light: light and magnetism are triggered by the same substance, and light is an electromagnetic disturbance that propagates in a field according to the laws of electromagnetism.
  At the beginning of the 20th century, Baron Kelvin’s “Two Dark Clouds” theory emerged, and mankind entered the era of relativity and the quantum era. Planck’s blackbody radiation law gave mankind a deeper understanding of the nature of electromagnetic radiation, and Einstein’s light quantum theory helped lay the foundation for quantum mechanics. The birth of quantum mechanics and the theory of relativity and the great innovations brought about by the study of light – with the joint efforts of many scientists thereafter, the “Pandora’s Box” of quantum physics was opened. The wave-particle duality of light has become the cornerstone of quantum theory, and people have reached a basic consensus on the nature of light. Since then, quantum theory has swept the entire physics world, and mankind has entered a higher stage of understanding and exploring light.
  Arosh pointed out that great breakthroughs in basic scientific research are inseparable from the exploration of light, and the greatest scientific achievements in the palace of science are all related to light. The study of light has evolved from the earliest telescopes and prisms to the later invention and use of light sources in various wavelength bands, until the birth and development of lasers. The invention of these instruments allows us to achieve more precise observations, not only allowing us to better understand Different aspects of light have also promoted research in other aspects of physics. “This is a long and fascinating history.”
  ”From Galileo to quantum physics, this is a fascinating scientific path.” Arrosh said, “Most of the knowledge we know about the external world actually comes from light. Although the particle nature and wave nature of light are in quantum theory, However, electrons, atoms, and photons exhibit entanglement and superposition characteristics that are even more confusing. Compared with classical physics, the quantum world appears more subtle.” Looking back at the history of
  science, it can be seen that all researchers are standing On the shoulders of giants, continuous revision and even overthrow of original theories can achieve continuous breakthroughs in the boundaries of human cognition. Therefore, “there are no eternal truths in scientific research, only humans’ constantly revised conclusions and gradually deeper understanding of the world.” .
Quantum technology around us

  If early quantum theory mostly benefited from the study of light, then in the last century, quantum theory began to feed back into optics, promoting the invention and innovation of a series of breakthrough technologies.
  At the beginning of the 20th century, many of the “utopias” that people had that now seem naive and childish have now become a reality. From the earliest transistors to later lasers, they have been widely and practically used. The electronic computers, nuclear magnetic resonance scanners, atomic clocks used in GPS, etc. that people take for granted in modern life are all based on quantum theory.
  This was completely unforeseen when quantum theory was born in 1900.
  Of all these inventions, the laser is the most special. The essence of laser is the fusion and evaporation of matter, and the cooling and capture of atoms. The development of laser technology has brought the study of the interaction between light and media to a new stage, and the “capture”, “storage” and “imprisonment” of light have changed from impossible to possible. “If a laser beam is fired from the earth to the moon and then reflected back from the moon, the phase of the light will not change.” Aroosh gave an example of the ultra-stability of lasers.
  With its unique characteristics such as monochromaticity, collimation, high power, and stability, lasers are widely used in basic research in physics, chemistry, and biology, as well as in fields such as metrology, medicine, and communications, and have become the first choice for scientists in many fields to explore the world. tool.

  Nowadays, the second quantum revolution has begun. Compared with the first quantum revolution, which “just asked what quantum theory can do”, humans now have to explore more “why” and give full play to their subjective initiative and use superposition. and entanglement and other quantum properties, which can be used in fields such as quantum metrology, quantum communication, quantum simulation, and quantum computing.

  As an epoch-making achievement in the mid-20th century, the invention of the laser in 1960 and the subsequent development of laser technology allowed scientists to control the duration of the laser beam and focus the laser beam to an atomic size range by changing the frequency of the laser. . Since then, experimental techniques and methods have developed greatly. Lasers can be used to cool atoms or ions to close to absolute zero, that is, to reduce their movement speed to a very small level until they almost stop.
  The famous Bose-Einstein condensate was produced in the laboratory with the help of lasers. With the help of lasers, scientists can make the measurement of time more and more precise, make the detection of gravitational waves a reality, and can also imprison atoms and explore the infinite possibilities of quantum computing. For example, the 429 terahertz visible quantum clock can measure the rate change caused by a height difference of 1 mm, which is 100,000 times more accurate than GPS time; another example is the laser interference gravitational wave observatory that can detect two objects 1.3 billion light years away. Gravitational waves produced by the merger of black holes. “This is a masterpiece, it can detect the relative displacement of mirrors (4 kilometers apart) with a diameter smaller than one billionth of the diameter of an atom,” Arrosh commented.

Members of the Kastler-Brossell Laboratory pose for a photo. Castler is third from the left, Brossell is the second from the left, and Aroche is the fourth from the left.

  As an expert in the manipulation of single quantum systems and cavity quantum electrodynamics, Arosh has always had a special affection for lasers and photons. Using a laser beam and the superconducting material niobium, Arrosh trapped a microwave photon for 1/10 second. He used a series of Rydberg atoms as detectors to pass through the cavity and couple with the cavity field. Arrosh Non-destructive measurement of single photons is achieved, that is, the information of the captured photons is taken away, but the photons are not absorbed. In cooperation with light, Arrosh achieved what Schrödinger thought was impossible more than half a century ago – creating “Schrödinger’s cat” in the laboratory.
  ”There is a symbiosis between basic science and technology.” He concluded that the invention of the Galilean telescope and the Huygens pendulum clock made precise measurements of space and time possible, and on this basis, the properties of light were discovered. People’s new understanding of light continues to lead to the invention of more precise equipment. The virtuous cycle formed between basic research and technological innovation helps physicists observe, confirm or falsify more efficiently and accurately.
  Nowadays, the second quantum revolution has begun. Compared with the first quantum revolution, which “just asked what quantum theory can do”, humans now have to explore more “why” and give full play to their subjective initiative and use superposition. and entanglement and other quantum properties, which can be used in fields such as quantum metrology, quantum communication, quantum simulation, and quantum computing.
  In the future, as measurement methods continue to improve, basic research can be advanced to the molecular level, atomic level, or even finer. Arrosh expects: “We can also use this research capability to explore some of the most cutting-edge technologies in the fields of electromagnetic science and biological science.” As for when quantum computers will appear, Arrosh admitted, “I really don’t know.” , but dancing with “uncertainty” is the characteristic and the most beautiful thing about scientific research.
“Passion, curiosity, intuition, opportunity”

  In 1966, at the age of 20, he entered the Castler-Brossell Laboratory of the Ecole Normale Supérieure in Paris and started his research career. This laboratory is full of masters – before Arroche, his mentor Castler won the Nobel Prize in Physics in 1966, and another scientist in the laboratory, Brossel, laid the foundation for the French school of quantum optics. people.
  These academic leaders gave young people ample freedom and encouragement, which Aroosh still remembers. “I am very happy and very lucky to be nurtured in such an environment.”
  Another thing that made him feel lucky was the invention of the laser. Arrosh started researching physics after the invention of laser technology. As an experimental physicist who manipulates individual quantum systems, “lasers have opened the way to advances in fundamental and applied physics that were unimaginable in the 1960s.” He said.

  Serge Haroche,
   French physicist, was born in Morocco in September 1944. Honorary professor of the Collège de France, academician of the French Academy of Sciences, academician of the European Academy of Sciences, foreign academician of the US National Academy of Sciences, foreign academician of the American Academy of Arts and Sciences, and foreign academician of the Brazilian Academy of Sciences. His research direction is quantum optics and quantum information. He has made important contributions to the study of quantum electrodynamics in quantum optics. He is well-known in the field of experimental quantum mechanics and is hailed as the experimental founder of cavity quantum electrodynamics in the industry.

  In 2012, Arrosh and American physicist David Wineland won the Nobel Prize in Physics for “breakthrough experimental methods that make it possible to measure and manipulate individual quantum systems.” As an expert in cavity quantum electrodynamics, Arosh used quantum technology to design a realistic experiment using atoms and light, successfully taming atoms and photons and observing quantum superposition.
  The detection method he invented does not intervene while observing, which makes the thought experiment envisioned by the founder of quantum physics come true. It seems that the “Schrödinger’s cat” that has troubled the physics community for many years can finally be “caught” in reality.
  What is the driving force behind this initiative? Arosh shared the secrets of doing scientific research at the scene.
  “If you want to be a scientist, you must first have passion and enthusiasm, have a curiosity to explore the outside world, be able to do very in-depth research in certain fields, and have a very strong pursuit of knowledge exploration and thirst. .” Arosh believes that personal investment is indispensable in scientific innovation and exploration.
  In addition, to truly bring innovation to existing science, we must not only communicate and cooperate with contemporary researchers, but also learn from the great scientific pioneers in history. “If you want to do science, you must work with a group of talented scientists. Working in a group, those star-studded scientists in history will become your motivation to continuously inspire your enthusiasm and explore new scientific frontiers.”
  ”Passion, curiosity, intuition, and opportunity.” Aroosh summed up the four key words for his own scientific research. Looking at the long history, it is impossible for scientists with bright eyes to make accurate judgments forever. Science can surprise everyone. In the 1960s, Arrosh believed that lasers would definitely become a new tool. But today, what lasers can do is far beyond what he imagined at the time.
  ”This is the charm of science – on the one hand, the scientific research I engage in comes from the past, on the other hand, it can also extend to the future. History has given us many opportunities to have ideological collisions with many great scientists. We are all because of Fascinating with light, scientific undertakings span time. At the same time, our interest and efforts in science, our curiosity, enthusiasm, knowledge, and our exploration of truth can all be shared with scientists around the world. I deeply We feel that we are part of the entire community, so science also spans space.”
  Arrosh told reporters that the scientists who had the greatest impact on him in his career were Galileo and Einstein. As he expresses in his new book “The Exploration of Light: From Galileo’s Telescope to the Strange Quantum World” (Chinese version), one of them used a telescope to look up at the sky for the first time, and the other discovered something based on many studies on light. The theory of relativity helps people re-understand the relationship between matter and space-time. The long history between the two is a fascinating history of people’s profound understanding of the world. “These scientists, like artists of the same period, played a very important role in history. The scientific and technological revolution and the literary and artistic revolution were born together and progressed together, and people found some new ways to look at the world.”

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