News and views (1&2)

1 2022 Nobel Prize in physics: Bell inequalities and quantum entanglement by Shang-Shu Li and Heng Fan

1.1 Background

Three physicists, Alain Aspect, John F. Clauser, and Anton Zeilinger, are awarded the Nobel Prize in physics in 2022 for “Experiments with entangled photons, establishing the violation of Bell Inequalities and pioneering quantum information science.” This will undoubtedly add impetus to the development of new quantum technology. Anders lrback, Chairman of the Nobel Committee for Physics, pointed out that “The laureates’ work with entangled states is of great importance, even beyond the fundamental questions about the interpretation of quantum mechanics.” It can be understood that the basic mechanism and principles of quantum computing and quantum information processing are based directly on this year’s Nobel Prize work.

In recent years, quantum technology has become one of the commanding heights of scientific and technological competition. A lot of countries around the world have invested huge resources in quantum computing, quantum metrology, quantum communication, and other quantum technological areas. On the other hand, quantum mechanics has always been of interests for public. People usually use quantum mechanics concepts such as “quantum entanglement” and “Schrödinger’s cat” to describe some daily phenomena in Internet. So, what is the meaning of quantum entanglement, and why did the experiments on Bell’s inequality win Nobel Prize in physics? We try to provide some interpretations of these results.

1.2 Quantum entanglement and EPR paradox

It all starts with the mysterious quantum entanglement. In 1935, Schrödinger found that under the framework of quantum mechanics, there would be such a quantum state that the wave functions of two particles could not be written as the direct product of the wave functions of single particles. Namely, the wave function of two particles cannot be separated, and we could only use the whole wave function to describe the two-particle state. This property seems not to be strange. However, when taking account of the quantum mechanics statements about measurement and spatial locality, it would lead to the EPR (Albert Einstein, Boris Podolsky, and Nathan Rosen) paradox [1] that confuses a lot of people. Consider that we can prepare a special entangled state, in which each particle can be measured to two states: “ + ” and “ − .” According to theory that wave function collapses, in such an EPR state, when we find the first particle as “ + ” in measurement, the second particle must be measured as “ − ” and vice versa. Note, however, that the collapse of the wave function in quantum mechanics is instantaneous. Even if we separate the two particles sufficiently far away, the measurement of one particle can also immediately determine the result of other. It is as if there exists an interaction with speed exceeding the speed of light (action at a distance). This result has been absurd to most people, even Einstein and the co-authors, hence named “EPR paradox.” Einstein believed that the world is local or realistic or both, where “local” means that no influence can be generated beyond the speed of light, while reality describes the objective existence of a physical element, and our measurements are all derived from this physical reality and cannot affect it. But in quantum mechanics, when we make a measurement, the wave function will collapse immediately, and the single-shot measurement result is random, even still constrained by the corresponding amplitudes. To illustrate this issue, Einstein et al. argued that this result of quantum mechanics is due to that its theory is incomplete.

This incompleteness is manifested in the hidden variable theory proposed by Boehm in 1952 [2]. In this theory, quantum mechanics is still local-realistic, and the EPR paradox is caused by our ignorance of hidden variables. To understand hidden variables, let us take a daily example. Suppose Alice has a pair of shoes, and she will give them to two people who are far apart from each other, Bob and Charlie. Alice has told them there is only one pair of shoes. Now, when Bob opens his package, he can determine immediately whether Charlie’s shoe is left or right, which seems to be much like quantum entanglement. However, on second thoughts, it is clear that this is not an action at a distance; it is just because Bob knows the implicit condition: there is only one pair of shoes. It is that implicit condition that makes relevant of Bob and Charlie’s results. Quantum mechanics in Boehm’s theory is more like that the world is still local-realistic, but the condition such as “one pair of shoes” is not known; perhaps in the EPR case, the separation of the two particles has already been determined to be opposite by hidden variables, rather than by the action at a distance in measuring. The question then becomes how can we know whether quantum mechanics is described by hidden variables? That is what Bell’s inequalities solve.

1.3 Bell’s inequalities

The significance of Bell’s inequality is to transfer the problem of whether the world is local-realistic into a mathematical formula. And, we can test it by designing specialized physical experiments. The key to solve the problem is that the correlation generated by local hidden variable theory has a bound. If this bound is violated, the world is not described by the local hidden variables; quantum mechanics is complete but nonlocal. The first Bell inequality was proposed by Bell in 1964 [3], and many similar inequalities have been developed in similar framework. The Nobel Prize of physics in this year was awarded for a series of experiments, such as those verified the violation of Clauser, Home, Shimony, and Holt (CHSH) inequalities [4].

CHSH inequality, consider that Alice and Bob are separated by a certain distance, and each has a particle. The state of these two particles may be described by quantum mechanics or by hidden variable theory. Suppose Alice measures the particle in two ways. Let us label it with$x$, and its value can be${x}_{0} \mathrm{and} {x}_{1}$. Bob also has two ways of measuring y, labeled as${y}_{0} \mathrm{and }{y}_{1}$. Moreover, it is assumed that the measurement can only obtain two outcomes: − 1 and + 1. Here, we use $a$ to represent the measured results of Alice and $b$ for that of Bob. Then after many measurements, we can find two facts: (1) when the measurement basis is fixed, the results can present a certain probability distribution. For example, when Alice measures ${x}_{0}$ and Bob measures${y}_{0}$, the values of $a$ and $b$ are always opposite. When Alice measures ${x}_{1}$ and Bob measures${y}_{0}$, there is no such correlation, and the probabilities of $b$ to get + 1 and − 1 are equal. In general cases, we can define the probability distribution of measurement outcomes. Here, we use $p\left(ab|xy\right)$ to represent the joint conditional probability distribution of outcomes when the measurement axes are $x$ and$y$. (2) No matter how far Alice and Bob are from each other, their measurement results always show correlation, that is as follows:

$$p\left(ab|xy\right)\ne p\left(a|x\right)p\left(b|y\right)$$

(1)

In the previous section, we mentioned that if the measurement depends on some hidden variable, the results will show a correlation. Let us think about the fact that we have a variable $\lambda$ in addition. We cannot observe it for some physical reason, and the value of $\lambda$ can vary in each measurement. Suppose it also satisfies a probability distribution $q\left(\uplambda \right)$. The measurement distribution of Alice and Bob is now determined by two variables, which are denoted by $p\left(a|x,\uplambda \right)$ and $p\left(b|y,\uplambda \right),$ respectively. What does the joint probability look like? If we introduce the local condition, the results of Alice and Bob cannot affect each other, and then, the joint probability must be the product form as follows:

$$p\left(ab|xy,\lambda \right)=p\left(a|x,\uplambda \right)p\left(b|y,\uplambda \right)$$

(2)

Note that under this assumption, due to our ignorance of the hidden variable $\lambda$, the observation results average over possible values of $\lambda$; the observation results can then be correlated, i.e., as follows:

$$\begin{aligned}p\left(ab|xy\right)&={\int}_{\lambda }q\left(\lambda \right)p\left(a|x,\lambda \right)p\left(b|y,\lambda \right)\\ &\ne {\int }_{\lambda }q\left(\lambda \right)p\left(a|x,\lambda \right){\int }_{\lambda }q\left(\lambda \right)p\left(b|y,\lambda \right)\\ &=p\left(a|x\right)p\left(b|y\right)\end{aligned}$$

Equation ($2$) is the joint probability distribution obtained under the local hidden variable theory. It can be seen that Alice’s (Bob’s) measurement results only depend on the local variable $x$($y)$ and the hidden variable $\lambda$. However, in quantum mechanics, Alice’s measurement results are correlated with that of Bob in some way, so that the joint probability of quantum mechanics may be beyond the expression ability of formula ($2$). Now let us try to figure out the limitation of the expression under localize hidden variable theory, which is Bell’s inequality.

Let us consider the relationship between the expectations of measurement results, under specified measurement axes. Define the correlation function as follows:

$$E\left({a}_{x},{b}_{y}\right)= \sum_{a,b}p\left(ab|xy\right)ab$$

(3)

Furthermore, define the observable $S=E\left({a}_{0},{b}_{0}\right)+E\left({a}_{0}{b}_{1}\right)+E\left({a}_{1},{b}_{0}\right)-E\left({a}_{1},{b}_{1}\right)$. Due to the existence of formula ($2$), formula ($3$) can be written as the sum of product of local expectation value, under the distribution of implicit variable, namely $E\left({a}_{x},{b}_{y}\right)={\int }_{\uplambda }\mathrm{q}\left(\uplambda \right)\mathrm{E}\left({a}_{\mathrm{x}};\uplambda \right)E\left({b}_{y};\uplambda \right)$. The local expectation $\mathrm{E}\left({a}_{x};\uplambda \right)={\sum }_{a}a p\left(a|x,\uplambda \right)$ is in the interval [− 1, 1], the same for $E\left({b}_{y};\uplambda \right)$.

Now, we have the following:

$$\begin{aligned}S&=\int \mathrm{d}\lambda \mathrm{q}\left(\uplambda \right)\left[\mathrm{E}\left({a}_{0};\uplambda \right)\left(E\left({b}_{0};\uplambda \right)+E\left({b}_{1};\uplambda \right)\right)+\mathrm{E}\left({a}_{1};\uplambda \right)\left(E\left({b}_{0};\uplambda \right)-E\left({b}_{1};\uplambda \right)\right)\right]\\ &\le \int \mathrm{d}\lambda \mathrm{q}\left(\uplambda \right)\left|E\left({b}_{0};\uplambda \right)+E\left({b}_{1};\uplambda \right)\right|+\left|E\left({b}_{0};\uplambda \right)-E\left({b}_{1};\uplambda \right)\right|\\ &\le \int \mathrm{d}\lambda \mathrm{q}\left(\uplambda \right)2\le 2\end{aligned}$$

We then obtain the famous CHSH inequality,

$$S=E\left({a}_{0},{b}_{0}\right)+E\left({a}_{0}{b}_{1}\right)+E\left({a}_{1},{b}_{0}\right)-E\left({a}_{1},{b}_{1}\right)\le 2$$

(4)

It is a variation of the original Bell inequality. In other words, under the probability distribution obtained by the local hidden variable hypothesis, the value of the correlation function $S$ must satisfy this inequality. If the actual measurement results violate this inequality, it means that the real world cannot be described by local hidden variable theory. So, does quantum mechanics violate this inequality? The answer is yes. For example, we prepare Alice and Bob’s particle pairs into the spin singlets $\left|{\uppsi }_{AB}\right.\rangle =1/\sqrt{2}(|01\rangle -|10\rangle$, where $\left|0\right.\rangle$ and $\left|1\right.\rangle$ are the eigenvectors of the Pauli operator ${\upsigma }_{z}$. For any particle, we can measure the eigenvalue in its quantized direction $\overrightarrow{x} \cdot \overrightarrow{\upsigma }$ in the experiment. Let the measured direction of Alice be $\overrightarrow{x}$ and Bob’s be $\overrightarrow{y}$. Then, the value of the correlation function obtained by quantum mechanics is $-\overrightarrow{x}\cdot \overrightarrow{y}$. Now, we use these results to test the CHSH inequality and let Alice’s two measurement directions be two orthogonal basis ${x}_{0}={\widehat{\mathrm{e}}}_{1},{x}_{1}={\widehat{\mathrm{e}}}_{2}$. Bob’s two measurement directions are also orthogonal but have an angle with Alice’s. If Bob selects the two directions as ${y}_{0}=-\left({\widehat{\mathrm{e}}}_{1}+{\widehat{\mathrm{e}}}_{2}\right)/\sqrt{2},{y}_{1}=\left(-{\widehat{\mathrm{e}}}_{1}+ {\widehat{\mathrm{e}}}_{2}\right)/\sqrt{2}$, the value of the correlation function in CHSH inequality can be given by simple vector multiplication as follows:

$$E\left({a}_{0},{b}_{0}\right)+E\left({a}_{0}{b}_{1}\right)+E\left({a}_{1},{b}_{0}\right)=1/\sqrt{2},E\left({a}_{1},{b}_{1}\right)=-1/\sqrt{2}$$

(5)

It follows that $S=2\sqrt{2}>2$, meaning that quantum mechanics indeed violate the CHSH inequality.

1.4 Experimental verification

Although Bell inequality is such a simple mathematical formula, experimental verification remains challenging. First of all, it requires that the entangled states are prepared with high fidelity experimentally and separated at a sufficiently long distance. The experimenter needs to make sure that the transmission of information below or equal the speed of light is excluded when measuring the two particles. The second challenge is the ability to measure particles in different arbitrary directions, since only in certain directions quantum mechanics can violate Bell’s inequality. In addition, the particle detection efficiency of the detector will also affect the verification of Bell inequality. Therefore, historically, the verification of Bell’s inequality has been carried out in the process of constantly closing the loopholes.

In 1972, John F. Clauser and Stuart Freedman performed the first Bell experiment [5]. They used the cascade transition of calcium atoms to produce entangled photon pairs. However, because the photon pair generation efficiency is very low, the measurement time reaches 200 h, and the distance between the two photons is too short; there is a loophole of locality. In addition, fixed measurement base is also one of the reasons for criticism.

In 1981 and 1982, Alain Aspect and his collaborators conducted a series of experiments that improved the measurement accuracy and reduced the loopholes in the verification of Bell’s inequality. In the first experiment [6], they used a double laser system to excite calcium atoms, producing pairs of entangled photons and improving the entanglement source. In the second experiment [7], a two-channel method was used to improve photon utilization. The measurement accuracy has been greatly improved. The third experiment [8] is the most important for closing the locality loophole. In the experiment, the two entangled photons are separated by about 12 m, and this distance needs 40 ns for the signal to travel at the speed of light. The distance between the photons and polarizer is 6 m. When performing measurement, polarizer rotates for no more than 20 ns. Using acousto-optical devices, photons can be switched to two measurement bases on even shorter time scales. The measurement time is much less than the time it takes for the signal to travel between two photons at the speed of light, closing the locality loophole.

In 1998, Anton Zeilinger’s team tested the Bell inequality under strict local conditions [9], with observers up to 400 m apart, closing the locality loophole completely. Subsequently, there have been a lot of experiments on the violation of Bell’s inequality. They are all aimed at closing the loopholes in the verification of quantum mechanics from various aspects, so that we are more and more confident in using quantum mechanics to describe the world. One interesting experiment is the Big Bell Test [10], which was designed to eliminate the effect of pseudo-randomness on the verification of Bell’s inequality. We know that random numbers generated by computers in simulations or experiments are pseudo-random numbers. As long as we give a certain seed, then the following series of random numbers are determined. This leads to the possibility that the correlation of experimental results measured in this way may exceed the limit represented by Bell’s inequality.

So how do you get a “true” random number? Big Bell Test proposes to solve this issue by using human’s free will to generate random numbers, as long as you believe that a person’s will is free and random. Okay, no, we do not believe it neither, maybe the experimenters have OCD (obsessive–compulsive disorder) or something related. To solve this problem, the researchers gathered more than 100,000 volunteers around the world and asked them to quickly and randomly press either 0 or 1 button in a game of tricks. They then uploaded the choices to the cloud and randomly sent them to different experimenters to use as random number generators for their experiments. Through the free will of a large number of participants, the Big Bell experiment closed the free choice loophole in a wider scope, strongly negating the localized hidden variable theory. So far, quantum mechanics has been almost perfectly demonstrated to be complete.

1.5 The second quantum revolution

Quantum mechanics has been verified to be correct, but some problems posed by non-locality need to be explained here. For example, can quantum entanglement transmit information faster than light? The answer is no; even though it looks like that the action at a distance travels faster than light, it does not transmit any information. Take the EPR pair as an example. First, since the collapse of the measurement is random, neither Alice nor Bob can encode the information into the EPR and decode it by measurement (without the help of classical means). Second, since there is no classical communication between Alice and Bob, the probability distribution of Alice’s measured results will not change regardless of whether Bob measures or not, namely regardless of whether Alice’s particles collapse. Therefore, Bob’s measurement operation will not transmit any information to Alice. In quantum mechanics, this is represented by the fact that the density matrix describing Alice’s particles does not change. So, does quantum entanglement make any sense? Of course, the violation of Bell’s inequality shows that entanglement is a kind of resource that transcends classical one, which indicates that even with infinite classical resources, we cannot achieve the results of quantum entanglement.

The research of such problems and all other efforts gave birth to the second quantum revolution which aims at the processing and application of quantum information. The first quantum mechanical revolution in history happens after the establishment of quantum mechanics. In this revolution, various classical applications based on quantum principles were developed, such as laser, semiconductor, and nuclear energy, which enabled mankind to quickly step into the information age, while the second quantum mechanical revolution is aimed to directly develop the applications of quantum coherence and quantum entanglement in quantum mechanics. Quantum information technology takes quantum bits as the basic unit, and the generation, transmission, processing, and detection of quantum information all follow the principle of quantum mechanics. In the last decades, the development of quantum computing theory and applications of quantum communication have made us see the potential of quantum technology to change the world. On the one hand, the development of quantum technology is to use the principles of quantum mechanics to process, transfer, and calculate quantum information; on the other hand, it also deepens our understanding of quantum mechanics.

2 53rd AAPPS video council meeting by AAPPS

The 53rd Council Meeting of the Association of Asia Pacific Physical Societies (AAPPS) was held online from 4:00 p.m. to 6:00 p.m. (UTC + 9 h) on November 28, 2022, via a Zoom session hosted by the Asia Pacific Center for Theoretical Physics (APCTP). The participants were Jun'ichi Yokoyama (president), Hyoung Joon Choi (vice president), Nobuko Naka (secretary), Gui-Lu Long (former president, ex officio member), and council members Xiu-dong Sun (the Chinese Physical Society, Beijing), Tao Xiang (the Chinese Physical Society, Beijing), Ruiqin Zhang (the Physical Society of Hong Kong), Rajdeep Singh Rawat (Institute of Physics Singapore), Fu-Jen Kao (the Physical Society located in Taipei), Meng-Fan Luo (the Physical Society located in Taipei), and Nguyen Quang Liem (Vietnam Physical Society). Present as observers were Reza Ejtehadi (the Physics Society of Iran), Yunkyu Bang (president of APCTP), Jae-Hyung Jeon (executive director of APCTP), and Dayoung Yang (AAPPS liaison and editorial staff member). Treasurer Keun-Young Kim and council members Jodie Bradby (Australian Institute of Physics (AIP)), Mio Murao (the Physical Society of Japan (JPS)), Akira Yamada (the Japan Society of Applied Physics (JSAP)), Woo-Sung Jung (the Korean Physical Society (KPS)), and Kurunathan Ratnavelu (Malaysian Institute of Physics) were absent.

(1) Secretary Naka reported the presence of 11 council members out of 17 council members. The quorum was declared as not fulfilled. President Yokoyama informed that we will have approval later in writing when necessary.

(2) Yokoyama opened the 53rd Council Meeting and welcomed the participants. The agenda was adopted as prepared by the president.

(3) Yokoyama introduced Prof. Reza Ejtehadi, the president of the Physics Society of Iran (PSI). Ejtehadi made a brief introduction to the society for application to join AAPPS as an associate member. PSI is a non-profit and non-governmental organization with the aim of establishing and strengthening scientific cooperation among physics researchers, physics teachers, and students studying physics. PSI is the largest and oldest professional and scientific society in Iran. The society was established in 1932 and formally founded in 1963. Activities ceased after the revolution in 1979 and resumed in 1984. The society presently has 11,933 members, including 2463 full members, 1304 associate members, 8158 student members, and 10 fellows.

The General Assembly is the highest decision-making body of PSI. The board of directors consist of seven members. A president, vice president, and treasurer are elected by the board of directors from among themselves. PSI has many branches in areas including condensed matter physics; particle and high-energy physics; computational physics; light, atomic, and molecular physics; statistical physics and complex systems; quantum information; and women in physics. In PSI, there are committees for conferences and events, publications, prizes and awards, international affairs, and industrial relations. Annual physics conferences have been held since 1985. Branch meetings and webinars are regularly organized. PSI publishes the Iranian Journal of Physics Research and the Journal of Applied Fluid Mechanics, in addition to books, reports, and proceedings. As outreach activities, PIS organizes the Physics Club, which has a 23-year history and is held monthly in 11 cities across the country, and publishes online newsletters in Persian. As a nonprofit society, the budget relies on membership fees, registration fees, publications, and donations, as support from the ministry is limited. PSI actively uses social media, such as Instagram, Youtube, Telegram, and Aparat, in addition to PSI’s own website, to share recorded meetings and events.

Yokoyama asked about the percentage of female physicists in PSI. Ejtehadi responded that 48% of physics students and 20% of faculty members are females. The graduating female students are now gaining faculty positions, and the percentage of female faculty members is expected to rapidly increase in the near future. Hyoung Joon Choi queried as to why PSI applied to become an associate member rather than a full member. Ejtehadi answered that PSI has difficulty transferring money for the payment of membership because of sanctions.

After Ejtehadi left the Zoom room, a discussion was made by the council. Yokoyama stated that the Iranian physics community is large, and they are producing excellent research outcomes. Therefore, it would be a good idea for PSI to be, for the moment, an associate member. Yunkyu Bang agreed that there is no reason not to accept. However, Bang expressed his concern about the current political environment. Although AAPPS is independent of any political organization, complete separation between politics and science is becoming unclear these days. Rajdeep Singh Rawat shared his experience as the president of the International Physics Olympiad and the research program for plasma fusion and related energy devices in Singapore. Fu-Jen Kao wondered about the rights of associate members. Yokoyama clarified that an associate member has no voting rights at ordinary general meetings (OGMs) and cannot send any candidate to become council members. Kao stated that as an associate member makes no effect on decisions by the AAPPS Council, the political considerations should be minimal. Tao Xiang suggested changing the name of “associate member” to “observer.” Yokoyama responded that the associate member status is defined in the constitution.

Yokoyama proposed to endorse the application, which was seconded by Long and Xiang. The proposal was unanimously agreed upon.

(4) Choi reported on APPC15, held in August 2022. He explained the list of committee chairs, 14 subjects, special sessions, and the number of presentations (963 presentations in total, consisting of 768 parallel talks, 168 posters, 15 plenary talks, and 12 special talks). The number of registrations was slightly over 1000, and there were a few no-shows in the poster sessions. Presently, 30 manuscripts were submitted for the proceedings. The manuscripts will be sent to the publisher in January 2023, after review and revision processes. At APPC15, there was small input from JSAP regarding the applied physics subjects; how to organize the applied physics session at the next APPC should be considered. Even though special sessions were open to the public and two plenary talks on Monday were open to all member societies, the audience was not large. This information might not be directly useful for APPC16, which will be held in a face-to-face manner. Nevertheless, we should strive to have bigger audiences at APPCs, and we should consider how we might open the sessions to a wider community. Choi commented that the Division of Plasma Physics organizes online meetings on a large scale, where each speaker can invite a free audience.

Yokoyama thanked Choi for all his efforts in making APPC15 a successful meeting. Yokoyama commented that the number of submitted manuscripts for the proceedings is rather small. Choi responded that submission is optional, and most of the participants would not need to provide a contribution as they did not have to travel internationally. The proceedings will be published in an online book dedicated to APPC15.

(5) On behalf of Treasurer Keun-Young Kim, Yokoyama briefly reported on the financial status of AAPPS. The total balance is US $67,028, in addition to the Leo Koguan Foundation’s US $36,500. The account statements include interest and the dues that 14 societies paid for the 2022 membership. Four societies supported the AAPPS Bulletin (AB) with contributions of US $5000 each. JSAP provided support of US $5000 to AAPPS for international activities, which was partially used for the meetings in Nepal and Thailand. The contribution of APCPT of US $545,360 in total is greatly appreciated and acknowledged. Yokoyama informed that he sent 1 million KRW, which he had received as an honorarium for writing an article in AB, to the representative of the activities for physicists in Myanmar by the Division of Nuclear Physics. The donation was appreciated by the representative, who is a professor at Gifu University in Japan.

Kao commented that any member society that does not pay membership fees has no right to vote at OGMs. Yokoyama explained that this was practically realized in the last OGM in August because member societies with unpaid fees did not attend the OGM. Nguyen Quang Liem requested to correct the record to reflect that the Vietnam Physical Society paid for their 2020 membership fee.

(6) Gui-Lu Long, the editor in chief of AB reported on the current status of AB. As of October 2022, 35 articles were published this year, including five articles in the News and Views section. The article with the highest citations was published in 2008, titled “Spin-transfer torque MRAM (STT-MRAM): Challenges and Prospects” by Prof. Yiming Huai. Other articles in early AB issues have generally low citations. The role of AB at the earliest stage was to serve the association, and joint publication with APCPT brought steady growth. Currently, articles are published in three ways; i.e., on the website by Springer Nature, AB’s direct website at www.aappsbulletin.org, and in printed form (6 issues/year). The printed copies are mailed every 2 months to the cooperate members who have paid for the subscription. The total surplus is US $138, with contributions from four member societies of AAPPS to AB. The article publication charge (APC) has been covered by APCPT last year and this year. The first article, whose APC will be paid by the author directly, will appear soon.

The citations of AB are recently improving, particularly in the fields of particle physics, nuclear physics, and quantum information. An expected impact factor is 6 or 7. Among 30 published articles this year with already 61 citations, 11 are original articles compared to only 2 original articles published in 2021. Therefore, the performance of AB in this respect is excellent.

Some of the editors have been refreshed regularly, and cooperation with Springer Nature will continue for the target of 40–100 articles to be published each year until 2025. Springer Nature decided to apply for indexing in SCOPUS next year, but application to the Web of Science has been pending.

Yokoyama expressed his thanks for Long’s dedication. He also commented that he agrees with the plan to enhance the News and Views section. Bang asked about the status of the article whose APC will be paid by the author. Long answered that the manuscript is under revision after the review, and publication in the December or February issue is expected. Bang stated that it is good to have this kind of article; however, maintaining the rather strict conditions for quality control is also important. Kao informed about a useful database of top journals in the world, https://exaly.com/journal.

Yokoyama explained that according to the discussion of the Editorial Board in October, the current editor-in-chief is ready to serve another term. Bang stated that no one would be able to compete with the current editor in chief’s dedication, passion, and energy. Yokoyama acknowledged APCTP for continued support to AB. The appointment of Long to continue as the next editor in chief of AB was endorsed by the council.

Yokoyama added that AAPPS endorsed the International Symposium on Trans-scale Quantum Science held at The University of Tokyo, Japan. At the symposium, Yokoyama gave a closing remark and introduced activities of AAPPS as well as AB. He found that the main organizer of the symposium already contributed to AB, indicating the increasing reputation of the journal.

(7) Yokoyama explained that he received an email from Prof. Youngah Park, who served as the chair of the Women-in-Physics Working Group (AAPPS-WIP) for 16 years. They had a working group meeting on August 23, 2022. The next chair will be Prof. Mihoko Nojiri from the Institute of Particle and Nuclear Physics, KEK, Japan, and Prof. Setsuko Tajima, the current president of JPS, will serve as the vice chair. This means that the Japanese community will be taking a leading role in AAPPS-WIP. Yokoyama suggested endorsing the decision. He also explained that the next chair requested AAPPS to designate one of the AAPPS council members to serve as the liaison to AAPPS-WIP. This matter will be one of the first items on the agenda of the new council that is starting next year.

(8) Yokoyama stated that the pilot program of a joint award of member societies has started with the Physical Society located in Taipei, as a presentation award. So far, the first award, which included commemorative gift, was given to three recipients. Establishing such an award to further promote cooperation between AAPPS and member societies as an early-career award has been discussed and approved in previous council meetings. On behalf of Mio Murao, Yokoyama explained and presented the scope and regulations of the AAPPS-JPS Award, which is becoming the second case of the joint award. The scope of the AAPPS-JPS Award is quite different from that of the Physical Society located in Taipei. Namely, the candidates for the award will be those who were nominated by the divisions of JPS to the CN Yang Award but were not selected as finalists. Up to five winners will be selected by the AAPPS committee inside JPS among candidates who conducted high-quality and impressive research.

Xiang wondered about the restriction on age. Yokoyama answered that the qualifications are the same as for the CN Yang Award. Bang expressed his slight worry that this new joint award might provide an impression of a kind of remedy for secondary prestige. Although there are both good and worrying aspects, he appreciated such efforts by JPS. Xiang considers that the AAPPS-JPS Award could be decoupled from the CN Yang Award, though the decision should be made by JPS. Yokoyama commented that they will try and amend it if necessary.

Yokoyama proposed to proceed with establishing the AAPPS-JPS Award, which was seconded by the council. Kao informed that the Physical Society located in Taipei intends to continue the joint award and that the next annual meeting will take place in January 2023.

(9) Naka explained that as reported at the last OGM in August, some typos in the constitution and bylaws were corrected. She suggested sharing some additional typos and possible inconsistencies (highlighted in orange and blue in circulated pdf files). As any amendments should be approved at an OGM, and the next one will be held in 2025; the issue will be transferred to the next council. Using Grammarly and having advice from native English speakers from the next council are suggested.

(10) Bang stated that there is no recent update on the status of APCTP. Yokoyama informed that Bang will continue to be the president of APCTP for the next 3 years. Yokoyama finally stated that this meeting is the last meeting of this council and expressed his gratitude to members for their support through the past 3 years of his term. Accordingly, each participant made a short farewell speech. The President-elect Choi informed that the first meeting of the new council will be held online in January or February, and the second one is scheduled in spring as an in-person meeting in Seoul. Ruiqin Zhang reminded that Hong Kong is still available to host a council meeting in the future.

Yokoyama closed the meeting.

3 2022 Nishina Memorial Prize by Nishina Memorial Foundation

Dr. Eiji Saitoh

Professor, Graduate School of Engineering, University of Tokyo

3.1 Pioneering contribution to the physics of spin current

The charge of an electron and its flow, the electric current, have always been the main physical quantities of interest in electronics. The angular momentum, or the spin, is another fundamental physical quantity of an electron that generates magnetic moment through its polarization and plays an important role in the physics of magnetism and related engineering. Spintronics has emerged as a research field that seeks to discover novel physical phenomena and functionalities through the control of spins, within which the flow of spins, or the spin current, has attracted particular interest.

The spins of conduction electrons in a conductor usually point either upward or downward in a 50–50 ratio, and thus, the spin transfer associated with the flow of electrons is averaged out to zero. The balance between the up- and down-spin flows can be changed to yield a net spin current, e.g., by the flow of spin-polarized electrons in magnetic materials and by the “spin Hall effect,” in which, due to spin–orbit interaction in the material, electrons are subject to a force perpendicular to the current’s direction depending on their spin orientations. However, a direct method for measuring the spin current with an external probe was elusive, and experiments were limited to indirect estimation, e.g., through the observation of “spin accumulation” generated at the sample’s edge by the spin current.

Dr. Saitoh discovered the “inverse spin Hall effect” in 2006 as a scheme for the direct measurement of spin current [11]. He used a bilayer metal film of platinum (Pt) and ferromagnetic alloy, permalloy (Ni₈₁Fe₁₉). When spin excitations were generated in the permalloy layer through ferromagnetic resonance and injected into the Pt probe layer through the interface, the spin current was converted into electric current due to the strong spin–orbit interaction in Pt, and a voltage signal was detected between the two ends of the Pt layer along the direction perpendicular to the magnetic field. This enabled the direct measurement of the spin current for the first time and led to the substantial development of related research.

Since then, Dr. Saitoh and his colleagues have discovered various physical phenomena involving spin currents by using this spin-current detection technique mentioned above. A major achievement among them is the “spin Seebeck effect,” in which a spin current is generated by a temperature gradient applied to a magnetic material and is injected into a probe electrode, e.g., made from Pt, to produce a voltage through the inverse spin Hall effect [12]. In conventional thermoelectric devices based on the Seebeck effect, two different conductors are combined in parallel under a thermal gradient, and the voltage is generated from the difference in the density of states and scattering properties of the conduction carriers in each conductor. The clever idea that led to the discovery of the spin Seebeck effect was to utilize the difference in the behavior of the two spin states of electrons in a single magnetic material.

Dr. Saitoh and his collaborators then extended the physics of spin current from conductors to insulators. They showed that the spin current, as a flow of angular momentum in solids, is carried not only by conduction electrons but also by spin excitations in insulators, a finding that greatly expanded the concept of spintronics. In ferromagnetic insulating oxides such as yttrium iron garnet (YIG), spin waves, which are collective excitation modes of ordered spins of localized electrons, or magnons as their elementary excitations, propagate over long distances without being scattered by conduction electrons. In their 2010 paper, Dr. Saitoh et al. reported that they injected a spin current into a YIG thin film by using the spin Hall effect in a Pt electrode and observed the propagation of the spin current using the inverse spin Hall effect in another Pt electrode [13]. This also revealed that angular momentum is transferred between conduction electrons in the metal electrodes and spin excitations in the insulator through the exchange interaction at the interface. Dr. Saitoh et al. also observed the spin Seebeck effect in YIG-related oxides [14], pioneering research on thermoelectric devices using insulating materials. In addition, they experimentally demonstrated that spin currents are carried not only by magnons in ferromagnets but also by various elementary excitations in solids, such as magnons in antiferromagnets, spinons in quantum spin liquids [15], magnons in nuclear spin wave modes [16], and magnetic polarons, coupled excitations of magnons and phonons. These achievements revealed the broad potential of spin current as a probe for the study of the physical properties of materials.

Dr. Eiichiro Komatsu

Director, Max Planck Institute for Astrophysics

3.2 Contribution to the standard cosmology based on cosmic microwave background

As a theory that explains the global homogeneity and isotropy of the universe, inflationary cosmology, which postulates that the universe experienced exponential accelerated expansion long before primordial nucleosynthesis, is a very attractive idea. However, in order to establish it as the standard cosmology, it is important not only to explain such qualitative observational facts but also to quantitatively verify its predictions. These include that the universe is spatially flat, has an almost scale-invariant spectrum originating from quantum fluctuations, and generates adiabatic curvature fluctuations and tensor fluctuations (quantum gravitational waves) that approximately follow Gaussian statistics.

Dr. Komatsu, under the advice of Professor Spergel at Princeton University, focused on the statistical nature of fluctuations and developed a methodology to quantitatively evaluate the deviation from the Gaussian distribution using cosmic microwave background radiation. While Gaussian distributions can be characterized only by their amplitude and variance, non-Gaussian distributions have infinite possibilities, making it difficult to quantitatively evaluate deviations from a Gaussian distribution. They proposed to constrain the deviation to a single parameter, the nonlinear parameter, and to limit it by observations of the cosmic microwave background radiation [17]. Dr. Komatsu established a methodology to measure this by using three-point correlations (bispectrum) of the cosmic microwave background radiation and applied it to the data observed by the COBE (COsmic Background Explorer) [18].

He also joined the research team of the Wilkinson Microwave Anisotropy Probe (WMAP), which was in progress at the time, and applied it to the first-year observation data, quantitatively verifying for the first time that the nonlinear parameter has no significant finite value and the curvature fluctuation is consistent with a Gaussian distribution. This was the first quantitative verification of this phenomenon in the world [19]. At the same time, he also performed a detailed analysis of the spectrum of the fluctuations and found the existence of nearly scale-invariant adiabatic curvature fluctuations, as predicted by standard inflationary cosmology.

WMAP also showed that the spatial curvature of the universe is below the limit of measurement, verifying that space is flat as predicted by inflationary cosmology. WMAP also measured the amount of cold dark matter and dark energy, which is responsible for accelerating the expansion of the universe, including error estimates, and found that the current universe consists of about 5% baryons, 22% cold dark matter, and 73% dark energy, although these values were updated by the subsequent observations of the Planck mission. In addition, the Hubble parameter, which expresses the rate of expansion of the universe, was precisely measured, and it was revealed for the first time that the universe is 13.7 billion years old. These results confirmed the validity of the cold dark matter model with a cosmological term, which was obtained at the end of the twentieth century based on a variety of observations. It can be said that with the achievement of WMAP, cosmology became a precision science. In the third year of the WMAP, Dr. Komatsu took charge of polarization analysis in addition to the responsibilities he had held since the 1st year and in the 5th year, became responsible for the entire analysis.

During this period, the system of each cosmological parameter measured gradually improved, and significant values were measured for the spectral index, which represents the deviation of the curvature fluctuation from the scale invariance of the spectrum. Theoretically, the standard single-field slow-roll inflation model predicts that the spectral exponent is slightly less than 1, and its value is a major clue to identifying the model. Signs of a spectral index deviating from 1 began to appear in the 5th year of WMAP data but were rejected with a 99.5% statistical confidence level in the 7th year of data [20].

As described above, WMAP played a decisive role in establishing today’s standard cosmology, which predicts that structure formation occurred in a universe filled with cold dark matter and dark energy, with curvature fluctuations that are nearly scale invariant and follow a Gaussian distribution as the initial conditions as predicted by inflationary cosmology. Dr. Komatsu played a leading role in the analysis of WMAP data and contributed greatly to the contemporary standard cosmology.

4 Young Scientist Award of the Physical Society of Japan, 2023 by JPS

Every year, the Physical Society of Japan presents its Young Scientist Awards to young researchers to recognize outstanding achievements in their early research careers. This year’s winners were recently decided by the board of directors of the JPS based on the recommendations of the selection committees established in 19 divisions of the JPS. The maximum number of winners from each division has been determined based on the number of talks given at the Annual Meetings in the past 3 years. Each winner is to give an award lecture at the next Annual Meeting of the JPS, which is scheduled for March 2023. Here is the list of winners and their research topics.

4.1 Theoretical particle physics

• Shinichiro Akiyama (Institute for Physics of Intelligence, Faculty of Science, The University of Tokyo): “Development of the tensor renormalization group approach for the lattice field theory”

• Zixia Wei (Yukawa Institute for Theoretical Physics, Kyoto University): “Causal structures and nonlocality in double holography”

• Masataka Watanabe (Yukawa Institute for Theoretical Physics, Kyoto University): “Development of the large charge expansion”

4.2 Experimental particle physics

• Tomoko Ariga (Kyushu University): “First neutrino interaction candidates at the LHC”

• Takuya Nobe (International Center for Elementary Particle Physics, The University of Tokyo): “Search for charginos and neutralinos in final states with two boosted hadronically decaying bosons and missing transverse momentum in pp collisions at √s = 13 TeV with the ATLAS detector”

• Yuto Minami (Research Center for Nuclear Physics, Osaka University): “New Extraction of the Cosmic Birefringence from the Planck 2018 Polarization Data”

4.3 Theoretical nuclear physics

• Yuki Kamiya (Helmholtz-Institut für Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Universität Bonn): “K^-p correlation function from high-energy nuclear collisions and chiral SU(3) dynamics

• Kazuki Yoshida (Advanced Science Research Center, Japan Atomic Energy Agency): “Alpha clustering in atomic nuclei probed by alpha knockout reactions”

4.4 Experimental nuclear physics

• Satoshi Adachi (Cyclotron and Radioisotope Center (CYRIC), Tohoku University): “Search for the α condensed state in 20Ne and systematic study of inelastic α scattering”

• Yuki Kubota (RIKEN Cluster for Pioneering Research): “Surface Localization of the Dineutron in 11Li”

• Niwase Toshitaka (High-Energy Accelerator Research Organization (KEK)): “First direct mass measurement of superheavy nuclide”

4.5 Cosmic ray and astrophysics

• Ken Ohashi (Graduate School of Science, Nagoya University): “Effects of diffractive dissociation on ultra-high energy cosmic rays and measurements of diffractive dissociation using ATLAS and LHCf detectors”

• Kawaguchi Kyohei (Institute for Cosmic Ray Research, University of Tokyo): “Theoretical studies on electromagnetic radiation from binary neutron star mergers”

• Hiromasa Suzuki (Department of Physics, Faculty of Science and Engineering, Konan University): “Study of time evolution of the efficiency of particle acceleration on supernova remnants with gamma-rays and thermal X-rays”

4.6 Beam physics

• Lei Guo (Nagoya University Synchrotron Research Center): “Photo-cathodes Studies for High Performance Electron Linear Accelerator”

• Katsuhiro Moriya (Japan Atomic Energy Agency, J-PARC center, Accelerator division): “Studies on Beam Instability in Circular Accelerators Using a Linear Paul Trap”

4.7 Atomic and Molecular physics, quantum Electronics, and radiation

• Yuki Takeuchi (NTT Communication Science Laboratories, NTT Corporation): “Quantum supremacy of measurement-based quantum computation and its verification”

• Hiroyuki Tajima (Graduate School of Science, The University of Tokyo): “Theoretical study of strongly-interacting multi-component Fermi gases”

• Ernst David Herbschleb (Institute for Chemical Research, Kyoto University): “Study of coherence in solid materials and its exploitation for quantum sensing”

4.8 Plasma

• Naoki Kenmochi (National Institute for Fusion Science): “Experimental study of non-local transport in magnetically confined plasmas”

• Kazuki Matsuo (EX-Fusion Inc.): “Experimental studies on electron thermal energy transport in magnetized high energy density plasma for fast ignition inertial confinement fusion”

4.9 Magnetism

• Yutaka Akagi (Department of Physics, Graduate School of Science, The University of Tokyo): “Theoretical studies on topological magnetism and its stabilization mechanism/emergent phenomena”

• Ishikawa Hajime (The Institute for Solid State Physics, The University of Tokyo): “Development of novel phases of quantum magnets via ligand field control”

• Toshihiro Nomura (The Institute for Solid State Physics, The University of Tokyo): “Ultrahigh-magnetic-field study on oxygen”

4.10 Semiconductors, mesoscopic systems, and quantum transport

• Nobuyuki Okuma (Yukawa Institute for Theoretical Physics, Kyoto University): “Elucidation of topological origin of non-Hermitian skin effects and its extension”

• Yuya Shimazaki (RIKEN Center for Emergent Matter Science): “Exploration of physical properties in electrically controlled two-dimensional semiconductor heterostructures”

4.11 Optical properties of condensed matter

• Yuta Murakami (RIKEN Center for Emergent Matter Science): “Theoretical exploration of high harmonic generation in strongly correlated systems”

• Naotaka Yoshikawa (Department of Physics, Graduate School of Science, The University of Tokyo): “Investigation of light-driven electron systems by using intense mid-infrared and terahertz pulses”

4.12 Metal physics (liquid metals, quasicrystals), low-temperature physics (ultralow temperatures, superconductivity, density waves)

• Takanobu Hiroto (Materials Analysis Station, National Institute for Materials Science (NIMS)): “Discovery of ferromagnetic long-range order and non-coplanar spin order in quasicrystal approximants”

• Takahiko Makiuchi (Department of Applied Physics, School of Engineering, The University of Tokyo): “Study of elastic anomaly in absorbed molecular films as a probe of quantum phase transition”

4.13 Molecular solids

• Mari Einaga (KYOKUGEN, Graduate School of Engineering Science, Osaka University): “Experimental Study of Sulfur Hydride Exhibiting Superconductivity above 200 Kelvin”

• Daichi Kozawa (RIKEN): “Study of exciton photophysics in low-dimensional nanomaterials”

4.14 Strongly correlated electron systems

• Takuya Aoyama (Department of Physics, Graduate School of Science, Tohoku University): “Study on Spatial Inversion Symmetry Breaking Induced by Spin and Orbital Degrees of Freedom in Strongly Correlated Electron System”

• Hisashi Inoue (National Institute of Advanced Industrial Science and Technology, Research Institute for Advanced Electronics and Photonics, Correlated Electronics Group): “Synthesis and characterization of thin film magnetic topological materials”

• Yusei Shimizu (International Research Center for Nuclear Materials Science, Institute for Materials Research, Tohoku University): “Study on superconducting symmetry, magnetic properties, and non-Fermi-liquid metallic state of uranium heavy-fermion superconductors”

• Hakuto Suzuki (Frontier Research Institute for Interdisciplinary Sciences, Tohoku University): “Resonant inelastic x-ray scattering study of elementary excitations in strongly correlated materials”

4.15 Surfaces and interfaces and crystal growth

• Kazuki Sumida (Japan Atomic Energy Agency): “Electronic structure of chalcogenide compounds studied by time-resolved photoemission spectroscopy and magnetic circular dichroism”.

• Kotaro Takeyasu (Faculty of Pure and Applied Sciences, University of Tsukuba): “Studies on flow and controlling factor of energies in surface reactions”.

4.16 Dielectrics, ferroelectricity, lattice defects and nanostructures, phononic properties, and X-ray and particle beams

• Izumi Umegaki (High-Energy Accelerator Research Organization): “Establishment of techniques using muon beam to detect Li diffusion and metallic Li deposition in a Li-ion battery”

• Shota Ono (Department of Electrical, Electronic and Computer Engineering, Gifu University): “Dynamical stability of two- and three-dimensional metallic systems from first-principle calculations”

4.17 Fundamental theory of condensed matter physics, statistical mechanics, fluid dynamics, applied mathematics, and socio- and econophysics

• Norihiro Oyama (TOYOTA CENTRAL R&D LABS): “Unraveling the origin of universal properties of amorphous solids under shear”

• Ryo Nagai (Department of Physics, The University of Tokyo): “Development of machine-learning-based exchange correlation functional”

• Ryo Hanai (Asia Pacific Center for Theoretical Physics): “Study of non-reciprocal phase transitions in non-equilibrium systems”

• Vu Van Tan (Faculty of Science and Technology, Keio University): “Theoretical studies on the irreversibility in non-equilibrium thermodynamics”

4.18 Soft matter physics, chemical physics, and biophysics

• Harukuni Ikeda (Faculty of Science, Gakushuin University): “Numerical and theoretical study of glass and jamming transition”

• Yuki Uematsu (Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology): “Chemical physics and hydrodynamics of solution interfaces”

• Naoyuki Sakumichi (Department of Bioengineering, School of Engineering, The University of Tokyo): “Discovery and elucidation of fundamental physical laws of rubbers and gels”