I greatly enjoy the comedy series The Big Bang Theory. Last night, Jim Parsons - the actor who portrays a brilliant yet quirky physicist - won an Emmy for his role.
The Washington Post said it best,
"When Parsons won for his role as uber-serious physicist Sheldon Cooper on "The Big Bang Theory," voice-over man John Hodgman joked that nerds were "taking the streets" in fits of joy. He was half-right; they actually took to Twitter to celebrate this victory for geeks everywhere."
Monday, August 30, 2010
Sunday, August 29, 2010
Preparing for class
I am spending large chunks of time preparing for a new class that I am teaching this fall. I never found classical mechanics particularly difficult; but, writing lectures and solving problems is still a challenge.
I devote each Saturday and Tuesday to course development. Though I took a couple of breaks to eat and surf the web, I remained true to my schedule. After grading last week's homework assignment and a quiz on Saturday, I continued to plow through the textbook and organize the material for my lectures.
My serious teaching career (excluding my work as a teaching assistant in grad school and an instructor at a community college) started 20 years ago at Washington State University. Those years have not jaded my enthusiasm for teaching. I continue to make adjustments based on my past successes failures.
But how are improvements possible when good teaching is difficult to define? While there is mounting research on pedagogy, in my mind, many of these studies are inherently flawed. For example, while courses that are based on peer instruction and conceptual problem solving certainly lead to better understanding, it makes it difficult to cover the same amount material. Admittedly, it is wasteful to teach lots of stuff that everyone forgets; but, coverage is also important - especially if a course is a prerequisite in a sequence courses. Such trade-offs must be carefully weighed in an undergraduate curriculum, especially for the student who will take one or two physics classes in a lifetime.
Graduate programs, on the other hand, are populated by motivated students who have both an interest in and an aptitude for physics. PhD programs like ours are based on coursework and research. All students take a set of core classes in their first two years. To become a PhD candidate, they must pass the PhD qualifying exam, which is given at the end of the forth semester.
The qualifier exam committee solicits two problems from each faculty member. A list of topic areas is used as the basis of the solicitation to ensure that the test is well-balanced. Thus, the qualifier exam reflects what the faculty as a whole believe is the core competency of a PhD in physics, and is not necessarily limited to the material covered in class. However, past exams are made available to the students as a study aid.
I find this system to be the ideal game-theoretic approach to ensure buy-in by all parties. It reflects poorly on me as a professor if the students were to do poorly on the part of the exam that is associated with my course. This makes me think very carefully about how to most effectively cover the material to get the optimal balance between breadth and depth. The looming qualifier exam motivates the students to learn the material for long-term understanding, not just for a particular test. Everyone works harder as a result.
My approach is to stress the fundamentals and give lots of examples. I gloss over topics that the students can learn on their own. When preparing a lecture, I first read the material, sometimes many times, until I feel I have a good understanding of the concepts. I then identify what I think are the important points, and use them as anchors in my lectures. I post readings and homework assignments on the web well ahead of the lecture dates so that the students are well prepared for class.
In crafting my lectures, I select problems from the end of the chapter on the basis of how well they complement my notes and whether or not they challenge the student to think more deeply. To select appropriate problems requires me to first suffer through the calculations. This time-consuming task give me ideas on how to fine tune my notes to address potential misunderstandings.
The night before my class, I go over my notes to make sure that I stress the important issues. The morning before my class, I copy my notes to scrap paper, going over in my mind the flow of my presentation. I pay particular attention to the anchor points.
Finally, I reproduce my lecture on scrap paper without looking at my notes. My preparation is complete when I am able to navigate from one anchor point to the next based on general principles of physics and logic.
So to finally get back to my diary entry after this long-winded diversion, I spent most of Saturday reading the textbook, writing notes, and working physics problems. This reminded me of how learning physics requires an intense and prolonged effort. I am thankful to my employer that my teaching responsibilities force me to spend time thinking very deeply about the subject that I love so dearly. And then, I get to share my enjoyment with a group acolytes who share my enthusiasm for learning.
I devote each Saturday and Tuesday to course development. Though I took a couple of breaks to eat and surf the web, I remained true to my schedule. After grading last week's homework assignment and a quiz on Saturday, I continued to plow through the textbook and organize the material for my lectures.
My serious teaching career (excluding my work as a teaching assistant in grad school and an instructor at a community college) started 20 years ago at Washington State University. Those years have not jaded my enthusiasm for teaching. I continue to make adjustments based on my past successes failures.
But how are improvements possible when good teaching is difficult to define? While there is mounting research on pedagogy, in my mind, many of these studies are inherently flawed. For example, while courses that are based on peer instruction and conceptual problem solving certainly lead to better understanding, it makes it difficult to cover the same amount material. Admittedly, it is wasteful to teach lots of stuff that everyone forgets; but, coverage is also important - especially if a course is a prerequisite in a sequence courses. Such trade-offs must be carefully weighed in an undergraduate curriculum, especially for the student who will take one or two physics classes in a lifetime.
Graduate programs, on the other hand, are populated by motivated students who have both an interest in and an aptitude for physics. PhD programs like ours are based on coursework and research. All students take a set of core classes in their first two years. To become a PhD candidate, they must pass the PhD qualifying exam, which is given at the end of the forth semester.
The qualifier exam committee solicits two problems from each faculty member. A list of topic areas is used as the basis of the solicitation to ensure that the test is well-balanced. Thus, the qualifier exam reflects what the faculty as a whole believe is the core competency of a PhD in physics, and is not necessarily limited to the material covered in class. However, past exams are made available to the students as a study aid.
I find this system to be the ideal game-theoretic approach to ensure buy-in by all parties. It reflects poorly on me as a professor if the students were to do poorly on the part of the exam that is associated with my course. This makes me think very carefully about how to most effectively cover the material to get the optimal balance between breadth and depth. The looming qualifier exam motivates the students to learn the material for long-term understanding, not just for a particular test. Everyone works harder as a result.
My approach is to stress the fundamentals and give lots of examples. I gloss over topics that the students can learn on their own. When preparing a lecture, I first read the material, sometimes many times, until I feel I have a good understanding of the concepts. I then identify what I think are the important points, and use them as anchors in my lectures. I post readings and homework assignments on the web well ahead of the lecture dates so that the students are well prepared for class.
In crafting my lectures, I select problems from the end of the chapter on the basis of how well they complement my notes and whether or not they challenge the student to think more deeply. To select appropriate problems requires me to first suffer through the calculations. This time-consuming task give me ideas on how to fine tune my notes to address potential misunderstandings.
The night before my class, I go over my notes to make sure that I stress the important issues. The morning before my class, I copy my notes to scrap paper, going over in my mind the flow of my presentation. I pay particular attention to the anchor points.
Finally, I reproduce my lecture on scrap paper without looking at my notes. My preparation is complete when I am able to navigate from one anchor point to the next based on general principles of physics and logic.
So to finally get back to my diary entry after this long-winded diversion, I spent most of Saturday reading the textbook, writing notes, and working physics problems. This reminded me of how learning physics requires an intense and prolonged effort. I am thankful to my employer that my teaching responsibilities force me to spend time thinking very deeply about the subject that I love so dearly. And then, I get to share my enjoyment with a group acolytes who share my enthusiasm for learning.
Thursday, August 26, 2010
August 26th, 2010
This day was, for the most part, a non-physics day. I got up at 7:00am and went through my daily routine of responding to emails. I also managed to get a bit of work done, responding to the reviewers' comments on our two-electron optimization paper - before having breakfast.
At 9:15am I attended a meeting with a prospective candidate who was interviewing for the position of dean in the college of sciences. Much of the discussions centered on the doom and gloom of the next round of budget cuts that could be as high as 10%. This is on top of a 30% cut from last year, which was on top of smaller cuts in the previous years.
It's all a mater of simple math. The cost of educating a student is X. Let's say that the state pays 50% and the tuition paid by the student (or scholarships) pays the remaining 50%. Because of the bad economy, the state can now afford to pay only 35%. If we were to cut 15% of the faculty we would be able to teach fewer courses so the students would have less choice and more students would be packed into larger classes. If we bring in fewer students, revenue drops. If faculty teach more courses, research productivity and funding drops. The only real solution is to raise tuition to cover the difference; but, in this bad economy, increased tuition would shift the burden to the families of students, many of whom are also in a financial bind. These are tough times and there are no clear solutions.
After the meeting, I spent a couple hours working on our paper and going over my lecture notes. Subsequently, I had a quick lunch and attended a practice talk by a postdoc. After that, I spent a couple of hours in my office answering questions about a homework assignment that is due tomorrow in the graduate classical mechanics class that I am teaching.
In addition, Shoresh reported on progress he is making in testing the sum rules in quantum wires and Shiva showed me some interesting data using his new temperature controlled chamber. We also talked about some new ideas for designing a better experiment for simultaneously measuring the linear absorption spectrum and the ASE signal.
When I got home, I worked some more on my class notes and wrote up solutions to one of the homework problems. Before we ate dinner, our son Skyped us to show off his cool new digs - an ultramodern house with a movie theater. He will be house-sitting for one of his professors for the academic year.
After dinner, I played floor hockey. I felt unusually fatigued and could do nothing right. I got home at 9:15pm, took a shower, and worked on my notes a bit. I really did not feel like working, so I decided to make an entry on my blog.
This post is incredibly boring; but, it captures my mood. To be happy, I need to spend more time thinking about physics. If I do not exceed a minimum threshold, I feel that my day has been wasted. I plan to do lots of work this weekend, and look forward to the enjoyment associated with the rush of firing neurons.
At 9:15am I attended a meeting with a prospective candidate who was interviewing for the position of dean in the college of sciences. Much of the discussions centered on the doom and gloom of the next round of budget cuts that could be as high as 10%. This is on top of a 30% cut from last year, which was on top of smaller cuts in the previous years.
It's all a mater of simple math. The cost of educating a student is X. Let's say that the state pays 50% and the tuition paid by the student (or scholarships) pays the remaining 50%. Because of the bad economy, the state can now afford to pay only 35%. If we were to cut 15% of the faculty we would be able to teach fewer courses so the students would have less choice and more students would be packed into larger classes. If we bring in fewer students, revenue drops. If faculty teach more courses, research productivity and funding drops. The only real solution is to raise tuition to cover the difference; but, in this bad economy, increased tuition would shift the burden to the families of students, many of whom are also in a financial bind. These are tough times and there are no clear solutions.
After the meeting, I spent a couple hours working on our paper and going over my lecture notes. Subsequently, I had a quick lunch and attended a practice talk by a postdoc. After that, I spent a couple of hours in my office answering questions about a homework assignment that is due tomorrow in the graduate classical mechanics class that I am teaching.
In addition, Shoresh reported on progress he is making in testing the sum rules in quantum wires and Shiva showed me some interesting data using his new temperature controlled chamber. We also talked about some new ideas for designing a better experiment for simultaneously measuring the linear absorption spectrum and the ASE signal.
When I got home, I worked some more on my class notes and wrote up solutions to one of the homework problems. Before we ate dinner, our son Skyped us to show off his cool new digs - an ultramodern house with a movie theater. He will be house-sitting for one of his professors for the academic year.
After dinner, I played floor hockey. I felt unusually fatigued and could do nothing right. I got home at 9:15pm, took a shower, and worked on my notes a bit. I really did not feel like working, so I decided to make an entry on my blog.
This post is incredibly boring; but, it captures my mood. To be happy, I need to spend more time thinking about physics. If I do not exceed a minimum threshold, I feel that my day has been wasted. I plan to do lots of work this weekend, and look forward to the enjoyment associated with the rush of firing neurons.
Monday, August 23, 2010
Note on ideology
In reading my last post, it occurred to me that I am offended when accused of being a liberal and embarrassed by being called a conservative. However, I take it as the highest complement when members of each group accuse me of siding with the other one.
It is wiser to treat each issue on its own merits rather than parrot the party line, and to change one's mind as new evidence accumulates - qualities lacking in ideologues.
It is wiser to treat each issue on its own merits rather than parrot the party line, and to change one's mind as new evidence accumulates - qualities lacking in ideologues.
Sunday, August 22, 2010
Uncritical thinking and ideology
Nothing annoys me more than the absence of reason, especially when an individual intentionally chooses to be ignorant for the purpose of championing an ideology. I usually ignore debates between ideologies, as espoused by conservatives versus liberals, because ideologues - by definition - don't care about the truth. I normally would have ignored Paul Krugman's writings in The Conscience of a Liberal had my wife not directed me to one of his pieces that pointed out a ludicrous attack on a subject I understand.
Apparently, some conservatives believe that the theory of relativity is a liberal plot. An entry on conservapedia.com states that,
"The theory of relativity is a mathematical system that allows no exceptions. It is heavily promoted by liberals who like its encouragement of relativism and its tendency to mislead people in how they view the world.[1]
"[1] See, e.g., historian Paul Johnson's book about the 20th century, and the article written by liberal law professor Laurence Tribe as allegedly assisted by Barack Obama. Virtually no one who is taught and believes relativity continues to read the Bible, a book that outsells New York Times bestsellers by a hundred-fold."
Ideologue Andy Schlafly has a problem with relativity because it contradicts the Bible. In particular, he believes that the miracles by Jesus described in John 4:46-54 imply that they occurred instantaneously using action-at-a-distance.
conservapedia.com lists 30 counterexamples to the theory of relativity. Each one of them can be debunked. For illustration, I focus on the conservapedia entry on Quantum Entanglement, which states,
"The implications of this phenomenon are enormous, and form the basis for the new field of quantum computing. For example, there seems to be an instantaneous communication between the participles at the moment of observation of one of them. Some physicists resist that notion and claim that no information is actually communicated."
To understand why entanglement does not imply action at a distance, consider two spin 1/2 particles that are entangled and reside on opposite ends of the universe. A measurement of the spin of one particle along a fixed axis can yield a result of up or down. A measurement of up in this part of the universe immediately places the entangled particle in a state of spin down. The key point is that the result of the measurement is random. Half the time, the measurement gives spin up, and the other half of the time the result is spin down. There is no way to control the spin of the particle when doing the measurement. As a result, the receiver at the other end of the universe would detect random bits - thus no information is transmitted.*
One may argue that it's just a matter of time that someone will determine how to control the spin of a particle when doing the measurement, making instantaneous communication possible. However, if this were possible, the implications would be profound. All the other predictions made by quantum mechanics would fail. But, since quantum mechanics makes many accurate predictions for a broad range of phenomena, it is highly unlikely that information will ever be transmitted using quantum entanglement.
Having too often used the excuse that I am overly busy to do anything about such nonsense, I have decided that the time is ripe for action. This morning, I opened an account on conservapedia and plan to correct the article. Let's see how long the correction will stand...
*Interestingly, the distant observer, after measuring the state of the local particle, would not have any way of knowing whether or not the transmitter was making a measurement. The observed random bit pattern would be the same with and without a measurement being performed by the transmitter.
***UPDATE***
When I tried to make a change on conservapedia, I was blocked by TK, an administrator of the site. Apparently, a new user must first convince TK that (s)he is a conservative. To quote TK:
"All voices should be represented on the Net. But if their intentions are merely to argue and dispute Conservative or Christian points of view, that becomes a form of vandalism, inasmuch as it is a great time waster and distraction for those who genuinely want to contribute, and build this encyclopedia."
Interesting that disagreement is tantamount to vandalism. In closing, below is a quote from TK's page. I think it's a joke, but I am not sure.
"Sometimes you can only look for answers from God and failing that...Fox News" -- Denny Crane
Apparently, some conservatives believe that the theory of relativity is a liberal plot. An entry on conservapedia.com states that,
"The theory of relativity is a mathematical system that allows no exceptions. It is heavily promoted by liberals who like its encouragement of relativism and its tendency to mislead people in how they view the world.[1]
"[1] See, e.g., historian Paul Johnson's book about the 20th century, and the article written by liberal law professor Laurence Tribe as allegedly assisted by Barack Obama. Virtually no one who is taught and believes relativity continues to read the Bible, a book that outsells New York Times bestsellers by a hundred-fold."
Ideologue Andy Schlafly has a problem with relativity because it contradicts the Bible. In particular, he believes that the miracles by Jesus described in John 4:46-54 imply that they occurred instantaneously using action-at-a-distance.
conservapedia.com lists 30 counterexamples to the theory of relativity. Each one of them can be debunked. For illustration, I focus on the conservapedia entry on Quantum Entanglement, which states,
"The implications of this phenomenon are enormous, and form the basis for the new field of quantum computing. For example, there seems to be an instantaneous communication between the participles at the moment of observation of one of them. Some physicists resist that notion and claim that no information is actually communicated."
To understand why entanglement does not imply action at a distance, consider two spin 1/2 particles that are entangled and reside on opposite ends of the universe. A measurement of the spin of one particle along a fixed axis can yield a result of up or down. A measurement of up in this part of the universe immediately places the entangled particle in a state of spin down. The key point is that the result of the measurement is random. Half the time, the measurement gives spin up, and the other half of the time the result is spin down. There is no way to control the spin of the particle when doing the measurement. As a result, the receiver at the other end of the universe would detect random bits - thus no information is transmitted.*
One may argue that it's just a matter of time that someone will determine how to control the spin of a particle when doing the measurement, making instantaneous communication possible. However, if this were possible, the implications would be profound. All the other predictions made by quantum mechanics would fail. But, since quantum mechanics makes many accurate predictions for a broad range of phenomena, it is highly unlikely that information will ever be transmitted using quantum entanglement.
Having too often used the excuse that I am overly busy to do anything about such nonsense, I have decided that the time is ripe for action. This morning, I opened an account on conservapedia and plan to correct the article. Let's see how long the correction will stand...
*Interestingly, the distant observer, after measuring the state of the local particle, would not have any way of knowing whether or not the transmitter was making a measurement. The observed random bit pattern would be the same with and without a measurement being performed by the transmitter.
***UPDATE***
When I tried to make a change on conservapedia, I was blocked by TK, an administrator of the site. Apparently, a new user must first convince TK that (s)he is a conservative. To quote TK:
"All voices should be represented on the Net. But if their intentions are merely to argue and dispute Conservative or Christian points of view, that becomes a form of vandalism, inasmuch as it is a great time waster and distraction for those who genuinely want to contribute, and build this encyclopedia."
Interesting that disagreement is tantamount to vandalism. In closing, below is a quote from TK's page. I think it's a joke, but I am not sure.
"Sometimes you can only look for answers from God and failing that...Fox News" -- Denny Crane
Friday, August 20, 2010
We finally got it right (we hope)
It's been three years since Juefei Zhou finished his Ph.D. research that culminated in a nice piece of collaborative work with the group of Koen Clays of the University of Leuven in Belgium. The research used a combination of theory and experiments to determine all the parameters needed to predict the full wavelength dependence of the two-photon absorption cross section. The beauty of the approach is that the theory uses the Thomas Kuhn sum rules to significantly reduce the number of parameters required to describe a molecule. This reduced set of parameters was determined from two experiments - a linear absorption spectrum and the measurement of the hyperpolarizability at just one wavelength.
Given that nonlinear-optical quantum calculations are notoriously inaccurate; and, independent measurements (such as first and second hyperpolarizability measurements) often disagree, we were elated that our approach led to a global agreement between all quantities using just one small set of parameters. The only problem was that our theory was wrong. We had made a false assumption. Thus, our manuscript was placed on the back burner.
A year later, in 2009, I spent a summer in Belgium, and used a combination of symmetry arguments and sum rules to show that our equations turned out to be correct, but for very different reasons. As we were applying the final touches to the manuscript when I returned back to Pullman, Xavi found an error. After days of intense debate, we found a way to correct the mistake and submitted a revised manuscript to Physical Review A.
A very sharp reviewer caught what appeared to be a fatal error. Our symmetry arguments were correct, but they implied an additional condition that rendered our approach untenable. For the next 12 months, we were haunted by a model that was wrong yet seemed to fit the data perfectly well.
At the beginning of the summer of 2010, Shengting was getting frustrated with a laser that refused to work properly, and asked for a theoretical project as a diversion. I suggested that he learn group theory and apply it to fixing the model. While Shengting was making good progress in both learning group theory and developing a plan of attack to address our problems, Xavi arrived from Belgium for a six-week stay. During my trip to Budapest, they had found a solution, albeit with a few holes.
A day before I returned, Koen Clays arrived in Pullman, and spent some time discussing the problem with Xavi and Shengting. As a result, they got closer to a solution. When I got back to Pullman (a day late because of a missed connection in Amsterdam), the four of us met to discus the problem and the proposed fix. Xavi acted as the spokesperson and very animatedly described the approach on the blackboard. Within an hour, everything fell into place. Not only did the original mathematical form of the theory turn out to be true, the underlying physics was even more beautiful than we had imagined. This project has led to new ideas that will take us into novel areas of research that we hope will make a closer connection between our theory, which is a bit esoteric, and real molecules.
It was worth the wait. This paper will add a significant new paradigm to the body of knowledge that seeks to more deeply understand the nonlinear-optical response of complex molecules. The path of our research took us through exhilarating highs and unbearable lows. Hopefully, our models are finally right. If not, the self-correcting process of the scientific method will eventually lead us, or someone else, closer to the truth.
Given that nonlinear-optical quantum calculations are notoriously inaccurate; and, independent measurements (such as first and second hyperpolarizability measurements) often disagree, we were elated that our approach led to a global agreement between all quantities using just one small set of parameters. The only problem was that our theory was wrong. We had made a false assumption. Thus, our manuscript was placed on the back burner.
A year later, in 2009, I spent a summer in Belgium, and used a combination of symmetry arguments and sum rules to show that our equations turned out to be correct, but for very different reasons. As we were applying the final touches to the manuscript when I returned back to Pullman, Xavi found an error. After days of intense debate, we found a way to correct the mistake and submitted a revised manuscript to Physical Review A.
A very sharp reviewer caught what appeared to be a fatal error. Our symmetry arguments were correct, but they implied an additional condition that rendered our approach untenable. For the next 12 months, we were haunted by a model that was wrong yet seemed to fit the data perfectly well.
At the beginning of the summer of 2010, Shengting was getting frustrated with a laser that refused to work properly, and asked for a theoretical project as a diversion. I suggested that he learn group theory and apply it to fixing the model. While Shengting was making good progress in both learning group theory and developing a plan of attack to address our problems, Xavi arrived from Belgium for a six-week stay. During my trip to Budapest, they had found a solution, albeit with a few holes.
A day before I returned, Koen Clays arrived in Pullman, and spent some time discussing the problem with Xavi and Shengting. As a result, they got closer to a solution. When I got back to Pullman (a day late because of a missed connection in Amsterdam), the four of us met to discus the problem and the proposed fix. Xavi acted as the spokesperson and very animatedly described the approach on the blackboard. Within an hour, everything fell into place. Not only did the original mathematical form of the theory turn out to be true, the underlying physics was even more beautiful than we had imagined. This project has led to new ideas that will take us into novel areas of research that we hope will make a closer connection between our theory, which is a bit esoteric, and real molecules.
It was worth the wait. This paper will add a significant new paradigm to the body of knowledge that seeks to more deeply understand the nonlinear-optical response of complex molecules. The path of our research took us through exhilarating highs and unbearable lows. Hopefully, our models are finally right. If not, the self-correcting process of the scientific method will eventually lead us, or someone else, closer to the truth.
Monte Carlo simulation appears on the Spotlight on Optics section of OpticsInfoBase.org
Our paper on Monte Carlo simulations of the second hyperpolarizability has just appeared in the Journal of the Optical Society of America B. The paper was selected to be highlighted on Spotlight on Optics. An excerpt from the summary follows:
Spotlight summary: The paper of Shafei et al. belongs to a series of papers initiated a decade ago by M.G. Kuzyk, oriented toward a theoretical analysis of fundamental limits and the optimization of attainable first- and second-order off-resonant electronic nonlinear hyperpolarizabilities, which describe a molecule’s response—its nonlinear polarization—to optical fields. Nonlinear hyperpolarizabilities are expressed in terms of infinite series. In the absence of a small parameter, the optimization of hyperpolarizabilities and the search for universal features constitute a challenge, which requires, first of all, a deep physical intuition.
In earlier papers, Kuzyk et al. calculated the fundamental limits for nonlinear hyperpolarizabilities using the three-state ansatz, which states that when a hyperpolarizability is near the fundamental limit, the system can be described by a three-level model. To this end they have used sum rules—one of standard approaches in quantum theories—that put constraints on infinite sets of energy levels and transition moments.
Surprisingly, experimental studies and earlier theoretical approaches have revealed a large gap between attainable values of the first and second hyperpolarizabilities and predicted fundamental limits. This casted doubt on the validity of the three-state ansatz...see more
Spotlight summary: The paper of Shafei et al. belongs to a series of papers initiated a decade ago by M.G. Kuzyk, oriented toward a theoretical analysis of fundamental limits and the optimization of attainable first- and second-order off-resonant electronic nonlinear hyperpolarizabilities, which describe a molecule’s response—its nonlinear polarization—to optical fields. Nonlinear hyperpolarizabilities are expressed in terms of infinite series. In the absence of a small parameter, the optimization of hyperpolarizabilities and the search for universal features constitute a challenge, which requires, first of all, a deep physical intuition.
In earlier papers, Kuzyk et al. calculated the fundamental limits for nonlinear hyperpolarizabilities using the three-state ansatz, which states that when a hyperpolarizability is near the fundamental limit, the system can be described by a three-level model. To this end they have used sum rules—one of standard approaches in quantum theories—that put constraints on infinite sets of energy levels and transition moments.
Surprisingly, experimental studies and earlier theoretical approaches have revealed a large gap between attainable values of the first and second hyperpolarizabilities and predicted fundamental limits. This casted doubt on the validity of the three-state ansatz...see more
Wednesday, August 18, 2010
When the lights go out in Budapest
After a kind introduction by one of the conference organizers, I presented the Monday afternoon plenary lecture at ICOOPMA 2010, an international meeting on optical materials and technologies. Budapest is a beautiful city rich in history and culture, but also the host to the horrors of World War II. The lecture hall, which was a large room in the lower level adjacent to a pool and reception area, could have been anywhere.
The gentle hum of the air conditioning system was barely perceptible, as it toiled to protect the room from the hot and muggy air that blanketed the city. My wife and I had traveled almost a full day to get to Budapest from Pullman, albeit in the relative comfort of business class, courtesy of a complimentary upgrade from Delta Airlines. The five star Intercontinental Continental Hotel provided a tad of luxury at a bargain price of $49 per night, thanks to Hotwire.com. But the purpose of my trip was to attend the meeting and to give my talk.
With 25 years of public speaking experience, I am pretty calm in front of crowd, but only when talking about physics. Ask me to say a few words at a wedding or a family event, and I am barely able to stammer out a few words before feeling sick. Physics provides the ultimate comfort. The enjoyment of presenting my work is akin to a parent bragging about the accomplishments of a child. But pride is not an accurate characterization of the feeling. It's more of a mutual admiration for the beauty and depth of how mother nature has written her story in the fabric of our universe. I am merely the story teller.
I derive great satisfaction in sharing insights with a couple hundred scientists, many of them strangers, but all having in common an appreciation of the beauty of the physical world, and the potential for new wonders that it offers.
``So as you can see, the Photomechanical Optical Device represents the 5 device classes, but using only optics rather than electronics..." My trance-like state was briefly interrupted by the rumble of distant thunder. I continued to present my talk with great excitement. A second bolt shook the building, the lights faltered, then the room went dark for an instant until the emergency backup power kicked in. The main transformer for one region of the city was fried, leaving a nonfunctional projector for the second half of my Power Point presentation.
I continued to speak, waving my hands, and making air drawings to get though the remaining part of my talk. While the lack of visuals undoubtedly detracted from the information that I tried to convey, it made my talk more memorable than if all had gone smoothly.
At the end, I fielded many questions and comments - a sign that people were listening and were interested in the topic. After the Q&A, the conference organizers presented me with a bottle of Chardonnay with a special label sporting my name and the conference's name and coordinates. I was also given a Rubik's cube, which I believe was invented by a Hungarian. After the event was over, several more people hung around to ask questions and make comments.
We hailed a cab back to the hotel, and prepared for our return trip, which commenced with a 3:00am wake-up call and a 4:00am shuttle to the airport. We ended up missing a connection that prolonged our travels over eight hours. In the end, I was satisfied with the trip - not because I could add another destination to my list of travels, but for the opportunity to share with others the work that I love. We will be landing in Seattle in an hour, and will make the 5-hour drive to Pullman, getting us home by about 3:00am. The stresses associated with the start of an academic year will be upon us when we awaken, but I am also looking forward to all the new results awaiting me in the minds and notebooks of my students and collaborators.
I can't wait to get home!
The gentle hum of the air conditioning system was barely perceptible, as it toiled to protect the room from the hot and muggy air that blanketed the city. My wife and I had traveled almost a full day to get to Budapest from Pullman, albeit in the relative comfort of business class, courtesy of a complimentary upgrade from Delta Airlines. The five star Intercontinental Continental Hotel provided a tad of luxury at a bargain price of $49 per night, thanks to Hotwire.com. But the purpose of my trip was to attend the meeting and to give my talk.
With 25 years of public speaking experience, I am pretty calm in front of crowd, but only when talking about physics. Ask me to say a few words at a wedding or a family event, and I am barely able to stammer out a few words before feeling sick. Physics provides the ultimate comfort. The enjoyment of presenting my work is akin to a parent bragging about the accomplishments of a child. But pride is not an accurate characterization of the feeling. It's more of a mutual admiration for the beauty and depth of how mother nature has written her story in the fabric of our universe. I am merely the story teller.
I derive great satisfaction in sharing insights with a couple hundred scientists, many of them strangers, but all having in common an appreciation of the beauty of the physical world, and the potential for new wonders that it offers.
``So as you can see, the Photomechanical Optical Device represents the 5 device classes, but using only optics rather than electronics..." My trance-like state was briefly interrupted by the rumble of distant thunder. I continued to present my talk with great excitement. A second bolt shook the building, the lights faltered, then the room went dark for an instant until the emergency backup power kicked in. The main transformer for one region of the city was fried, leaving a nonfunctional projector for the second half of my Power Point presentation.
I continued to speak, waving my hands, and making air drawings to get though the remaining part of my talk. While the lack of visuals undoubtedly detracted from the information that I tried to convey, it made my talk more memorable than if all had gone smoothly.
At the end, I fielded many questions and comments - a sign that people were listening and were interested in the topic. After the Q&A, the conference organizers presented me with a bottle of Chardonnay with a special label sporting my name and the conference's name and coordinates. I was also given a Rubik's cube, which I believe was invented by a Hungarian. After the event was over, several more people hung around to ask questions and make comments.
We hailed a cab back to the hotel, and prepared for our return trip, which commenced with a 3:00am wake-up call and a 4:00am shuttle to the airport. We ended up missing a connection that prolonged our travels over eight hours. In the end, I was satisfied with the trip - not because I could add another destination to my list of travels, but for the opportunity to share with others the work that I love. We will be landing in Seattle in an hour, and will make the 5-hour drive to Pullman, getting us home by about 3:00am. The stresses associated with the start of an academic year will be upon us when we awaken, but I am also looking forward to all the new results awaiting me in the minds and notebooks of my students and collaborators.
I can't wait to get home!
Thursday, August 12, 2010
Kicking Around New Ideas
For a couple months now, we have been struggling with calculations of the nonlinear-optical response of quantum wires. Our idea is to build up complex structures by connecting together pieces of straight wire segments. The problem is that the sum rules appear to have pathologies. But in reality, the problems lie in the way that we idealize the wire.
As I discussed in a previous post, the case of the quantum rotor is a specific example that had been treated rigorously by Stavros Fallieros. I had an idea of how to apply a similar argument to a straight section of wire. The upshot is that along a wire, the sum rules hold. The problem with an idealized one-dimensional wire is that the wave function is by definition confined to the wire, and therefore vanishes outside. By the Heisenberg uncertainty principle, a particle that is confined in that way must have an infinite transverse momentum, implying an infinite energy state.
If these infinite energy states are included, the sum rules are obeyed. I came up with a simple textbook approach that models transverse confinement with a Dirac delta function potential in the limit when the strength of the delta function is infinite. While I had not solved the full problem, I wrote up the concept in a file LaTeX where I wrote out the form of the solutions. Then, I passed the document along to my students for them to do the hard part: evaluating infinite sums of complicated expressions in the limit when various parameters are large and small. Since there are no loopholes in the way the sum rules are derived, I am confident that this approach will work.
The other day, after I emailed this file to the students, we had a spirited debate. They disagreed with my approach and gave all sorts of counterarguments to prove me wring. They constructed special cases that seemed airtight arguments against my approach. But slowly, they became convinced; not because I am the expert, but because my argument is sound. This is one of the most satisfying aspects of the community of science. In the end, reason wins. This time, I may have been vindicated, but I have made enough mistakes in the past to not be overly dejected when I am proven wrong. Being scientists requires us to admit error.
As an update to one of our papers that was initially rejected, in the process of responding to a substantive comment made by one of the reviewers, David Watkins found an intrinsic hyperpolarizability that exceeds unity - an impossibility, according to my theory. Though my theory has been tested over an over again using different computational techniques under a broad range of conditions, I panic when it appears that I might have missed something. David and I sent many emails back and forth on the topic, trying to understand if somehow the sum rules were being violated by the new case under study. To my delight, David found and fixed a couple of bugs in his code, which solved the problem. The results for this new case is now consistent with all our other calculations.
On another front, three students from my nonlinear optics class and I had finished a nice paper on cascading at the beginning of the summer. As I had reported in a previous post, just prior to submitting the paper, we had found a case where the fundamental limits were exceeded. Since then, we have tried all sorts of approaches to reconcile the problem, but to no avail. Nathan, the lead student on the project, believes that cascading is a way to beat the limits. However, based on general principles, I know the limits must hold. And it's not that I want my theory to be true, but, based on general arguments, the cascading results - which are a special case - must agree with the more general theory. If a specific case appears to violate the more general one, it is incumbent upon us to track down the source of the inconsistency. In other words, we have to specifically show how this case falls outside the realm of the theory. At this point, cascading seems to be formulated in a way that makes it a simple subset of the more general theory.
I have been writing much about theory, but our experimental work has been going well. Shiva has built a beautiful temperature-controlled chamber that will allow him to do experiments from temperatures well bellow ambient to over 100 C. Since the temperature-dependence of a measurement provides a window into the energetics of a process, we hope the new experiments will provide us with a clue as to the metastable species involved that usher self heal self healing of a molecule upon photodegradation. In parallel, I am trying to work out a general theory of self-healing based on our past observations. The real test of this theory will be its power to predict the behavior of new observations as better experiments push the envelope of our knowledge. As a sneak preview, the theory includes a recovery process that is akin to stimulated emission, but in the case of dye recovery, has to do with coupling between the guest molecules and phonons in the host polymer.
Prabodh, a new graduate student in our group is specializing in making a large variety of samples so that he can study how the dopant and polymer host affect the healing process. Ben is doing a a series of experiments to optically image the damaged areas to better pin down the population dynamics, and he is building a new experiment that will allow us to determine the absorption spectrum at each point in the damage region. The combination of new samples and new measurements will provide valuable complimentary data that will undoubtedly aid us in unraveling the puzzle of self healing.
Nathan is getting additional data on the photomechanical response that appears to be consistent with our models. While the results are giving us insights into the new class of liquid crystal elastomeric materials, our conclusions appear to be at odds with those of our collaborators, who supplied us with the samples. I am confident that we will eventually reach a consensus because the truth always bubbles to the top. Even if we are proven right, we most likely have only part of the answer. More interesting mysteries are undoubtedly lurking at the next layer of depth.
Xianjun is in the process of calculating the response of Photomechanical Optical Devices (PODs), with the goal of predicting how they will behave when acting in series. This is a highly nonlinear problem, with complex solutions. At this stage, we are still struggling with the relatively simple things, like the response of a single nonlinear etalon. More complex systems will require us to consider more subtle issues and to be clever in our approximations to solving the full problem. In parallel, Xianjun is starting experiments to burn Bgragg gratings in polymer optical fibers with the goal of making and characterizing PODs. Measurements will play an indispensable part in developing our numerical models.
I hve more to write, but our flight to Amsterdam is boarding. This long trip will eventually lead us to Budapest, where I am giving a plenary lecture on self healing and photo mechanical effects. I apologize for any typos that resulted from my haste, and will write about the meeting upon my return.
As I discussed in a previous post, the case of the quantum rotor is a specific example that had been treated rigorously by Stavros Fallieros. I had an idea of how to apply a similar argument to a straight section of wire. The upshot is that along a wire, the sum rules hold. The problem with an idealized one-dimensional wire is that the wave function is by definition confined to the wire, and therefore vanishes outside. By the Heisenberg uncertainty principle, a particle that is confined in that way must have an infinite transverse momentum, implying an infinite energy state.
If these infinite energy states are included, the sum rules are obeyed. I came up with a simple textbook approach that models transverse confinement with a Dirac delta function potential in the limit when the strength of the delta function is infinite. While I had not solved the full problem, I wrote up the concept in a file LaTeX where I wrote out the form of the solutions. Then, I passed the document along to my students for them to do the hard part: evaluating infinite sums of complicated expressions in the limit when various parameters are large and small. Since there are no loopholes in the way the sum rules are derived, I am confident that this approach will work.
The other day, after I emailed this file to the students, we had a spirited debate. They disagreed with my approach and gave all sorts of counterarguments to prove me wring. They constructed special cases that seemed airtight arguments against my approach. But slowly, they became convinced; not because I am the expert, but because my argument is sound. This is one of the most satisfying aspects of the community of science. In the end, reason wins. This time, I may have been vindicated, but I have made enough mistakes in the past to not be overly dejected when I am proven wrong. Being scientists requires us to admit error.
As an update to one of our papers that was initially rejected, in the process of responding to a substantive comment made by one of the reviewers, David Watkins found an intrinsic hyperpolarizability that exceeds unity - an impossibility, according to my theory. Though my theory has been tested over an over again using different computational techniques under a broad range of conditions, I panic when it appears that I might have missed something. David and I sent many emails back and forth on the topic, trying to understand if somehow the sum rules were being violated by the new case under study. To my delight, David found and fixed a couple of bugs in his code, which solved the problem. The results for this new case is now consistent with all our other calculations.
On another front, three students from my nonlinear optics class and I had finished a nice paper on cascading at the beginning of the summer. As I had reported in a previous post, just prior to submitting the paper, we had found a case where the fundamental limits were exceeded. Since then, we have tried all sorts of approaches to reconcile the problem, but to no avail. Nathan, the lead student on the project, believes that cascading is a way to beat the limits. However, based on general principles, I know the limits must hold. And it's not that I want my theory to be true, but, based on general arguments, the cascading results - which are a special case - must agree with the more general theory. If a specific case appears to violate the more general one, it is incumbent upon us to track down the source of the inconsistency. In other words, we have to specifically show how this case falls outside the realm of the theory. At this point, cascading seems to be formulated in a way that makes it a simple subset of the more general theory.
I have been writing much about theory, but our experimental work has been going well. Shiva has built a beautiful temperature-controlled chamber that will allow him to do experiments from temperatures well bellow ambient to over 100 C. Since the temperature-dependence of a measurement provides a window into the energetics of a process, we hope the new experiments will provide us with a clue as to the metastable species involved that usher self heal self healing of a molecule upon photodegradation. In parallel, I am trying to work out a general theory of self-healing based on our past observations. The real test of this theory will be its power to predict the behavior of new observations as better experiments push the envelope of our knowledge. As a sneak preview, the theory includes a recovery process that is akin to stimulated emission, but in the case of dye recovery, has to do with coupling between the guest molecules and phonons in the host polymer.
Prabodh, a new graduate student in our group is specializing in making a large variety of samples so that he can study how the dopant and polymer host affect the healing process. Ben is doing a a series of experiments to optically image the damaged areas to better pin down the population dynamics, and he is building a new experiment that will allow us to determine the absorption spectrum at each point in the damage region. The combination of new samples and new measurements will provide valuable complimentary data that will undoubtedly aid us in unraveling the puzzle of self healing.
Nathan is getting additional data on the photomechanical response that appears to be consistent with our models. While the results are giving us insights into the new class of liquid crystal elastomeric materials, our conclusions appear to be at odds with those of our collaborators, who supplied us with the samples. I am confident that we will eventually reach a consensus because the truth always bubbles to the top. Even if we are proven right, we most likely have only part of the answer. More interesting mysteries are undoubtedly lurking at the next layer of depth.
Xianjun is in the process of calculating the response of Photomechanical Optical Devices (PODs), with the goal of predicting how they will behave when acting in series. This is a highly nonlinear problem, with complex solutions. At this stage, we are still struggling with the relatively simple things, like the response of a single nonlinear etalon. More complex systems will require us to consider more subtle issues and to be clever in our approximations to solving the full problem. In parallel, Xianjun is starting experiments to burn Bgragg gratings in polymer optical fibers with the goal of making and characterizing PODs. Measurements will play an indispensable part in developing our numerical models.
I hve more to write, but our flight to Amsterdam is boarding. This long trip will eventually lead us to Budapest, where I am giving a plenary lecture on self healing and photo mechanical effects. I apologize for any typos that resulted from my haste, and will write about the meeting upon my return.
Tuesday, August 10, 2010
Authoring and reviewing manuscripts
Anyone who is accustomed to writing and reviewing manuscripts is familiar with the associated time burden. This morning, I reviewed a manuscript for Optics Letters, which brought to light some of my long-held pet peeves. I have been meaning to complain about the archaic formatting requirements of all scientific journals in which I publish, but, my high-level of morning testosterone nudged me into making my move. Below is a letter I sent to the optical society. I plan to write a similar email to other journals as I am asked to provide reviews.
The email, below, speaks for itself.
Dear Editors,
In the process of reviewing a manuscript for Optics Letters this morning, I was reminded of inefficiencies introduced simply by the formatting requirements. I am sharing these thoughts with you in hopes that you will change your submission guidelines.
When I prepare a manuscript, I use the two-column single-spaced format, placing the figures and captions near the referring text (in the same format used by OSA journals). I find this much easier to read when composing and editing a manuscript. Subsequently, when submitting the manuscript, I waste time reformatting it into a single-column double-spaced document with figures and captions at the end of the manuscript.
When reviewing a manuscript on my computer in the standard OSA format, I need to constantly jump around form the text to the captions to the figures. This is especially annoying on the small screen of a laptop and very difficult using a touch pad. For this reason, I always refuse to review when traveling - which I have been doing quite a bit lately. Even on my desktop, I estimate a 15% overhead in effort, not to mention the interruptions in the my thoughts.
I understand that this archaic system has its roots in the old days of paper manuscripts. I suggest that you consider accepting the two column format for submissions and using it in the review process. After acceptance, the authors could provide a manuscript that is suitable for editing. For manuscripts submitted in LaTeX, the OSA style file could have an option for "twocolumn" and one for "manuscript." Then, it would be a simple matter of changing one switch in the source file to reformat the whole thing in one single swoop.
I understand that such changes do not happen overnight. I therefore strongly urge you to consider the option of accepting submissions in two-column format. Given the heavy burdens placed on our time, an increase of efficiency in preparing a review may make it easier to find reviewers willing to make the effort. As I am becoming more of a curmudgeon, I have toyed with the idea of refusing to review manuscripts that are not reviewer friendly. I hope that OSA will be proactive in making the review process easier so that reviewers and authors remain loyal to what I believe is an excellent organization.
Sincerely,
Mark G. Kuzyk
The email, below, speaks for itself.
Dear Editors,
In the process of reviewing a manuscript for Optics Letters this morning, I was reminded of inefficiencies introduced simply by the formatting requirements. I am sharing these thoughts with you in hopes that you will change your submission guidelines.
When I prepare a manuscript, I use the two-column single-spaced format, placing the figures and captions near the referring text (in the same format used by OSA journals). I find this much easier to read when composing and editing a manuscript. Subsequently, when submitting the manuscript, I waste time reformatting it into a single-column double-spaced document with figures and captions at the end of the manuscript.
When reviewing a manuscript on my computer in the standard OSA format, I need to constantly jump around form the text to the captions to the figures. This is especially annoying on the small screen of a laptop and very difficult using a touch pad. For this reason, I always refuse to review when traveling - which I have been doing quite a bit lately. Even on my desktop, I estimate a 15% overhead in effort, not to mention the interruptions in the my thoughts.
I understand that this archaic system has its roots in the old days of paper manuscripts. I suggest that you consider accepting the two column format for submissions and using it in the review process. After acceptance, the authors could provide a manuscript that is suitable for editing. For manuscripts submitted in LaTeX, the OSA style file could have an option for "twocolumn" and one for "manuscript." Then, it would be a simple matter of changing one switch in the source file to reformat the whole thing in one single swoop.
I understand that such changes do not happen overnight. I therefore strongly urge you to consider the option of accepting submissions in two-column format. Given the heavy burdens placed on our time, an increase of efficiency in preparing a review may make it easier to find reviewers willing to make the effort. As I am becoming more of a curmudgeon, I have toyed with the idea of refusing to review manuscripts that are not reviewer friendly. I hope that OSA will be proactive in making the review process easier so that reviewers and authors remain loyal to what I believe is an excellent organization.
Sincerely,
Mark G. Kuzyk
--
Mark G. Kuzyk
Regents Professor of Physics
Washington State University
Pullman, WA 99164-2814
Phone: 509-335-4672
Fax: 509-335-7816
Web Page: www.NLOsource.com
Monday, August 2, 2010
Sophistication versus Understanding
I attended the SPIE meeting in San Diego over the weekend, where I gave an invited talk about work done in collaboration with David Watkins of the Math Department. The meeting was in a small room with perhaps a couple dozen attendees, all experts in organic nonlinear optics. We had a good time exchanging ideas and throwing about some new thoughts.
As I have mentioned in previous posts, I find travel physically draining. So, spending eight hours en route to San Diego on Saturday and eight hours on Sunday to return home took its toll. While I usually work on weekends, I find it much more relaxing than sitting on an airplane. So, I started the week in an uncharacteristically bad mood.
To add insult to injury, I learned on Sunday and Monday that two of my papers were outright rejected -- not something that I commonly experience. In addition, a paper submitted by my collaborators, to which my contribution was relatively minor, was also rejected. Thus, in a span of three days I had more rejection than in a typical decade. I think that my darker than usual mood was warranted given the extraordinary circumstances. In fact, I entertained the notion of quitting the professional life of physics altogether.
After a good-night's sleep, my mood dramatically improved so on Tuesday morning, I wrote a levelheaded email to the two editors who had rejected my papers. In the process of composing these letters, I realized that science has turned into a big efficient machine, with creativity a reluctant causality.
For more than three decades, lots of people have been expending a great deal of effort to make better molecules. In parallel, computational methods are getting more sophisticated so that theoretical chemists can calculate the properties of ever-larger molecules, taking into account more subtle effects and getting more accurate results. Similarly, chemists have made a huge number of very complex structures, many of which are pieces of art, such as the ever-branching dendrimers.
My own work, which uses sum rules to understand the nonlinear optical response of quantum systems (which I started ten years ago), illustrates how simple but powerful ideas can arise even in a mature field. The basic question that I asked was if there was a fundamental limit to the nonlinear optical response. The answer was a resounding "yes." This limit is not based on practical considerations, but on very fundamental quantum mechanical principles that span the basis of chemical reactions of life and govern the flow of electrons in electronic circuits. If the fundamental theory of quantum mechanics were to be wrong, then the world would be alien to us. In fact, we probably wouldn't exist. In short, I feel that my fundamental limits calculations stand on solid ground.
I expected great admiration for my theory when I first presented a talk on the topic a decade ago. Instead, I got some very nasty comments to the effect that my work was an insult to all the hard-working chemists who were trying to make better molecules. Who was I to say that it was not possible to do any better? Though that sentiment did not reflect my intentions, mother nature DOES place limits on what is possible.
To put this into perspective, my calculation does not imply a single numerical limit, but rather a limit in the presence of a contraint. For example, to investigate the largest possible area is nonsensical. It makes more sense to determine the largest possible area given a fixed perimeter. Similarly, when studying molecules, it is more appropriate to determine the largest nonlinear response for a given molecular size. Since size is not well defined in a quantum system, we used the more abstract concept of scaling.
The bottom line is that after three decades of research, the best molecules fall short of the fundamental limit by a factor of thirty. While people have been making bigger molecules with a larger nonlinear-optical response, the intrinsic nonlinearity has not changed since the birth of the field. That's why one of the reviewer's comments was particularly annoying. (S)he was critical of our simple fundamental approach as passe in light of all the sophisticated and precise methods available. Ironically, our simple approach has been the only one that has led to an improvement in the intrinsic hyperpolarizability.
Being a scientist, my priority is to understand, not to participate in the frenzy of doing the most sophisticated calculations. I prefer to study broad principles that apply to all systems rather than seeking higher precision in more complex calculations that apply to specific molecules. My long-term goal is to build an understanding of the fundamental issues that identify universal properties of systems that approach the fundamental limit. And in this quest, my small effort continues.
I end this post with good news. In response to my emails, both editors reversed their decisions and are giving us the opportunity to submit a revised manuscript. While I am concerned that the trend of sophistication worship is wasteful, I take comfort in the fact that our group is supported to continue our work. Perhaps a time will come when I will become one of the dinosaurs that was left behind, but for now; I take great satisfaction in my research and the potential it has for making a lasting contribution to the body of science.
As I have mentioned in previous posts, I find travel physically draining. So, spending eight hours en route to San Diego on Saturday and eight hours on Sunday to return home took its toll. While I usually work on weekends, I find it much more relaxing than sitting on an airplane. So, I started the week in an uncharacteristically bad mood.
To add insult to injury, I learned on Sunday and Monday that two of my papers were outright rejected -- not something that I commonly experience. In addition, a paper submitted by my collaborators, to which my contribution was relatively minor, was also rejected. Thus, in a span of three days I had more rejection than in a typical decade. I think that my darker than usual mood was warranted given the extraordinary circumstances. In fact, I entertained the notion of quitting the professional life of physics altogether.
After a good-night's sleep, my mood dramatically improved so on Tuesday morning, I wrote a levelheaded email to the two editors who had rejected my papers. In the process of composing these letters, I realized that science has turned into a big efficient machine, with creativity a reluctant causality.
For more than three decades, lots of people have been expending a great deal of effort to make better molecules. In parallel, computational methods are getting more sophisticated so that theoretical chemists can calculate the properties of ever-larger molecules, taking into account more subtle effects and getting more accurate results. Similarly, chemists have made a huge number of very complex structures, many of which are pieces of art, such as the ever-branching dendrimers.
My own work, which uses sum rules to understand the nonlinear optical response of quantum systems (which I started ten years ago), illustrates how simple but powerful ideas can arise even in a mature field. The basic question that I asked was if there was a fundamental limit to the nonlinear optical response. The answer was a resounding "yes." This limit is not based on practical considerations, but on very fundamental quantum mechanical principles that span the basis of chemical reactions of life and govern the flow of electrons in electronic circuits. If the fundamental theory of quantum mechanics were to be wrong, then the world would be alien to us. In fact, we probably wouldn't exist. In short, I feel that my fundamental limits calculations stand on solid ground.
I expected great admiration for my theory when I first presented a talk on the topic a decade ago. Instead, I got some very nasty comments to the effect that my work was an insult to all the hard-working chemists who were trying to make better molecules. Who was I to say that it was not possible to do any better? Though that sentiment did not reflect my intentions, mother nature DOES place limits on what is possible.
To put this into perspective, my calculation does not imply a single numerical limit, but rather a limit in the presence of a contraint. For example, to investigate the largest possible area is nonsensical. It makes more sense to determine the largest possible area given a fixed perimeter. Similarly, when studying molecules, it is more appropriate to determine the largest nonlinear response for a given molecular size. Since size is not well defined in a quantum system, we used the more abstract concept of scaling.
The bottom line is that after three decades of research, the best molecules fall short of the fundamental limit by a factor of thirty. While people have been making bigger molecules with a larger nonlinear-optical response, the intrinsic nonlinearity has not changed since the birth of the field. That's why one of the reviewer's comments was particularly annoying. (S)he was critical of our simple fundamental approach as passe in light of all the sophisticated and precise methods available. Ironically, our simple approach has been the only one that has led to an improvement in the intrinsic hyperpolarizability.
Being a scientist, my priority is to understand, not to participate in the frenzy of doing the most sophisticated calculations. I prefer to study broad principles that apply to all systems rather than seeking higher precision in more complex calculations that apply to specific molecules. My long-term goal is to build an understanding of the fundamental issues that identify universal properties of systems that approach the fundamental limit. And in this quest, my small effort continues.
I end this post with good news. In response to my emails, both editors reversed their decisions and are giving us the opportunity to submit a revised manuscript. While I am concerned that the trend of sophistication worship is wasteful, I take comfort in the fact that our group is supported to continue our work. Perhaps a time will come when I will become one of the dinosaurs that was left behind, but for now; I take great satisfaction in my research and the potential it has for making a lasting contribution to the body of science.
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