Monthly Archives: September 2014

The experimentalist next door

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At 9:10 AM, the lab next door was blasting “Born to Be Wild.”

I was at Oxford, moonlighting as a visiting researcher during fall 2013. My hosts included quantum theorists in Townsend Laboratory, a craggy great-uncle of a building. Poke your head out of the theory office, and Experiment would flood your vision. Our neighbors included laser wielders, ion trappers, atom freezers, and yellow signs that warned, “DANGER OF DEATH.”

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Down the corridor in Townsend Laboratory.

Hardly the neighborhood Mr. Rogers had in mind.

The lab that shared a wall with our office blasted music. To clear my head of calculations and of Steppenwolf, I would roam the halls. Some of the halls, that is. Other halls had hazmat warnings instead of welcome mats. I ran into “RADIATION,” “FIRE HAZARD,” “STRONG MAGNETIC FIELDS,” “HIGH VOLTAGE,” and “KEEP THIS TOILET NEAT AND TIDY.” Repelled from half a dozen doors, I would retreat to the office. Kelly Clarkson would be cooing through the wall.

“We can hear them,” a theorist observed about the experimentalists, “but they can’t hear us.”

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Dangers lurked even in the bathroom.

Experiment should test, disprove, and motivate theories; and theory should galvanize and (according to some thinkers) explain experiments. But some theorists stray from experiment like North America from Pangaea.

The theoretical physics I’ve enjoyed is abstract. I rarely address platforms, particular physical systems in which theory might incarnate. Quantum-information platforms include electrons in magnetic fields, photons (particles of light), ion traps, quantum dots, and nuclei such as the ones that image internal organs in MRI machines.

Instead of addressing electrons and photons, I address mathematics and abstract physical concepts. Each of these concepts can incarnate in different forms in different platforms. Examples of such concepts include preparation procedures, evolutions, measurements, and memories. One preparation procedure defined by one piece of math can result from a constant magnetic field in one platform and from a laser in another. Abstractness has power, enabling one idea to describe diverse systems.

I’ve enjoyed wandering the hills and sampling the vistas of Theory Land. Yet the experimentalist next door cranked up the radio of reality in my mind. “We can hear them,” a theorist said. In Townsend Laboratory, I began listening. My Oxford collaborators and I interwove two theoretical frameworks that describe heat transferred and work performed on small scales. One framework, one-shot statistical mechanics, has guest-starred on this blog.

The other framework consists of fluctuation relations, which describe deviations from average behaviors by small physical systems. A quantum particle on one side of a wall has a tiny probability of tunneling through without boring any hole. Since the probability is tiny, the average particle doesn’t tunnel (during any reasonably short amount of time). When analyzing macroscopic systems—say, the roughly 1024 atoms that form your left thumbnail—we assume that every particle behaves like the average particle. We can’t when analyzing minuscule systems such as one short strand of DNA. Deviations from average behaviors appear in experimental data about small systems as they do not appear in data about large systems. Fluctuation relations help us understand those deviations.

My colleagues and I addressed “information,” “systems,” and “interactions.” We deployed abstract ideas, referencing platforms only when motivating our work. Then a collaborator challenged me to listen through the wall.

Experimentalists have tested fluctuation relations. Why not check whether their data supports our theory? At my friend’s urging, I contacted experimentalists who’d shown that DNA obeys a fluctuation relation. The experimentalists had unzipped and re-zipped single DNA molecules using optical tweezers, which resemble ordinary tweezers but involve lasers. Whenever the experimentalists pulled the DNA, they measured the force they applied. They concluded that their platform obeyed an abstract fluctuation theorem. The experimentalists generously shared their data, which supported our results.

http://www.europhysicsnews.org/articles/epn/abs/2010/02/epn20102p27/epn20102p27.html

Experimentalists unzipped and rezipped DNA to test fluctuation relations. This depiction of the set-up comes from this article.

My colleagues and I didn’t propose experiments. We didn’t explain why platforms had behaved in unexpected ways. We checked calculations with recycled data. But we ventured outside Theory Land. We learned that one-shot theory models systems modeled also by fluctuation relations, which govern experiments. This link from one-shot theory to experiment, like the forbidden corridors in Townsend Laboratory, invite exploration.

In Townsend, I didn’t suffer the electric shocks or the explosions advertised on the doors (though the hot water in the bathroom nearly burned me). I turned out not to need those shocks. Blasting rock music at 9:10 AM can wake even a theorist up to reality.

Where are you, Dr. Frank Baxter?

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This year marks the 50th anniversary of my first publication. In 1964, when we were eleven-year-old fifth graders, my best friend Mace Rosenstein and I launched The Pres-stein Gazette, a not-for-profit monthly. Though the first issue sold well, the second issue never appeared.

Front page of the inaugural issue of the Pres-stein Gazette

Front page of the inaugural issue of the Pres-stein Gazette. Faded but still legible, it was produced using a mimeograph machine, a low-cost printing press which was popular in the pre-Xerox era.

One of my contributions to the inaugural  issue was a feature article on solar energy, which concluded that fossil fuel “isn’t of such terrific abundance and it cannot support the world for very long. We must come up with some other source of energy. Solar energy is that source …  when developed solar energy will be a cheap powerful “fuel” serving the entire world generously forever.”

This statement holds up reasonably well 50 years later. You might wonder how an eleven-year-old in 1964 would know something like that. I can explain …

In the 1950s and early 1960s, AT&T and the Bell Telephone System produced nine films about science, which were broadcast on prime-time network television and attracted a substantial audience. After broadcast, the films were distributed to schools as 16 mm prints and frequently shown to students for many years afterward. I don’t remember seeing any of the films on TV, but I eventually saw all nine in school. It was always a treat to watch one of the “Bell Telephone Movies” instead of hearing another boring lecture.

For educational films, the production values were uncommonly high. Remarkably, the first four were all written and directed by the legendary Frank Capra (a Caltech alum), in consultation with a scientific advisory board provided by Bell Labs.  Those four (Our Mr. Sun, Hemo the Magnificent, The Strange Case of the Cosmic Rays, and Unchained Goddess, originally broadcast in 1956-58) are the ones I remember most vividly. DVDs of these films exist, but I have not watched any of them since I was a kid.

The star of the first eight films was Dr. Frank Baxter, who played Dr. Research, the science expert. Baxter was actually an English professor at USC who had previous television experience as the popular host of a show about Shakespeare, but he made a convincing and pleasingly avuncular scientist. (The ninth film, Restless Sea, was produced by Disney, and Walt Disney himself served as host.) The other lead role was Mr. Writer, a skeptical and likeable Everyman who learned from Dr. Research’s clear explanations and sometimes translated them into vernacular.

The first film, Our Mr. Sun, debuted in 1956 (broadcast in color, a rarity at that time) and was seen by 24 million prime-time viewers. Mr. Writer was Eddie Albert, a well-known screen actor who later achieved greater fame as the lead on the 1960s TV situation comedy Green Acres. Lionel Barrymore appeared in a supporting role.

Dr. Frank Baxter and Eddie Albert in Our Mr. Sun.

Dr. Frank Baxter and Eddie Albert in Our Mr. Sun. (Source: Wikipedia)

Our Mr. Sun must have been the primary (unacknowledged) source for my article in the Pres-stein Gazette.  Though I learned from Wikipedia that Capra insisted (to the chagrin of some of his scientific advisers) on injecting some religious themes into the film, I don’t remember that aspect at all. The scientific content was remarkably sophisticated for a film that could be readily enjoyed by elementary school students, and I remember (or think I do) clever animations teaching me about the carbon cycle in stellar nuclear furnaces and photosynthesis as the ultimate source of all food sustaining life on earth. But I was especially struck by Dr. Baxter’s dire warning that, as the earth’s population grows, our planet will face shortages of food and fuel. On a more upbeat note he suggested that advanced technologies for harnessing the power of the sun would be the key to our survival, which inspired the optimistic conclusion of my article.

A lavishly produced prime-time show about science was a real novelty in 1956, many years before NOVA or the Discovery Channel. I wonder how many readers remember seeing the Dr. Frank Baxter movies when you were kids, either on TV or in school. Or was there another show that inspired you like Our Mr. Sun inspired me? I hope some of you will describe your experiences in the comments.

And I also wonder what resource could have a comparable impact on an eleven-year-old in today’s very different media environment. The obvious comparison is with Neil deGrasse Tyson’s revival of Cosmos, which aired on Fox in 2014. The premiere episode of Cosmos drew 8.5 million viewers on the night it was broadcast, but that is a poor measure of impact nowadays. Each episode has been rebroadcast many times, not just in the US and Canada but internationally as well, and the whole series is now available in DVD and Blu-ray. Will lots of kids in the coming years own it and watch it? Is Cosmos likely to be shown in classrooms as well?

Science is accessible to the curious through many other avenues today, particularly on YouTube. One can watch TED talks, or Minute Physics, or Veritasium, or Khan Academy, or Lenny Susskind’s lectures, not to mention our own IQIM videos on PHD Comics. And there are many other options. Maybe too many?

But do kids watch this stuff? If not, what online sources inspire them? Do they get as excited as I did when I watched Dr. Frank Baxter at age 11?

I don’t know. What do you think?

The Graphene Effect

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Spyridon Michalakis, Eryn Walsh, Benjamin Fackrell, Jackie O'Sullivan

Lunch with Spiros, Eryn, and Jackie at the Athenaeum (left to right).

Sitting and eating lunch in the room where Einstein and many others of turbo charged, ultra-powered acumen sat and ate lunch excites me. So, I was thrilled when lunch was arranged for the teachers participating in IQIM’s Summer Research Internship at the famed Athenaeum on Caltech’s campus. Spyridon Michalakis (Spiros), Jackie O’Sullivan, Eryn Walsh and I were having lunch when I asked Spiros about one of the renowned “Millennium” problems in Mathematical Physics I heard he had solved. He told me about his 18 month epic journey (surely an extremely condensed version) to solve a problem pertaining to the Quantum Hall effect. Understandably, within this journey lied many trials and tribulations ranging from feelings of self loathing and pessimistic resignation to dealing with tragic disappointment that comes from the realization that a victory celebration was much ado about nothing because the solution wasn’t correct. An unveiling of your true humanity and the lengths one can push themselves to find a solution. Three points struck me from this conversation. First, there’s a necessity for a love of the pain that tends to accompany a dogged determinism for a solution. Secondly, the idea that a person’s humanity is exposed, at least to some degree, when accepting a challenge of this caliber and then refusing to accept failure with an almost supernatural steadfastness towards a solution. Lastly, the Quantum Hall effect. The first two on the list are ideas I often ponder as a teacher and student, and probably lends itself to more of a philosophical discussion, which I do find very interesting, however, will not be the focus of this posting.

The Yeh research group, which I gratefully have been allowed to join the last three summers, researches (among other things) different applications of graphene encompassing the growth of graphene, high efficiency graphene solar cells, graphene component fabrication and strain engineering of graphene where, coincidentally for the latter, the quantum Hall effect takes center stage. The quantum Hall effect now had my attention and I felt it necessary to learn something, anything, about this recently recurring topic. The quantum Hall effect is something I had put very little thought into and if you are like I was, you’ve heard about it, but surely couldn’t explain even the basics to someone. I now know something on the subject and, hopefully, after reading this post you too will know something about the very basics of both the classical and the quantum Hall effect, and maybe experience a spark of interest regarding graphene’s fascinating ability to display the quantum Hall effect in a magnetic field-free environment.

Let’s start at the beginning with the Hall effect. Edwin Herbert Hall discovered the appropriately named effect in 1879. The Hall element in the diagram is a flat piece of conducting metal with a longitudinal current running through. When a magnetic field is introduced normal to the Hall element the charge carriers moving through the Hall element experience a Lorentz force. If we think of the current as being conventionHallEffectal (direction flow of positively charged ions), then the electrons (negative charge carriers) are traveling in the opposite direction of the green arrow shown in the diagram. Referring to the diagram and using the right hand rule you can conclude a buildup of electrons at the long bottom edge of the Hall element running parallel to the longitudinal current, and an opposing positively charged edge at the long top edge of the Hall element. This separation of charge will produce a transverse potential difference and is labeled on the diagram as Hall voltage (VH). Once the electric force (acting towards the positively charged edge perpendicular to both current and magnetic field) from the charge build up balances with the Lorentz force (opposing the electric force), the result is a negative charge carrier with a straight line trajectory in the opposite direction of the green arrow. Essentially, Hall conductance is the longitudinal current divided by the Hall voltage.

Now, let’s take a look at the quantum Hall effect. On February 5th, 1980 Klaus von Klitzing was investigating the Hall effect, in particular, the Hall conductance of a two-dimensional electron gas plane (2DEG) at very low temperatures around 4 Kelvin (- 4520 Fahrenheit). von Klitzing found when a magnetic field is applied normal to the 2DEG, and Hall conductance is graphed as a function of magnetic field strength, a staircase looking graph emerges. The discovery that earned von Klitzing’s Nobel Prize in 1985 was as unexpected as it is intriguing. For each step in the staircase the value of the function was an integer multiple of e2/h, where e is the elementary charge and h is Planck’s constant. Since conductance is the reciprocal of resistance we can view this data as h/ie2. When i (integer that describes each plateau) equals one, h/ie2 is approximately 26,000 ohms and serves as a superior standard of electrical resistance used worldwide to maintain and compare the unit of resistance.

Before discussing where graphene and the quantum Hall effect cross paths, let’s examine some extraordinary characteristics of graphene. Graphene is truly an amazing material for many reasons. We’ll look at size and scale things up a bit for fun. Graphene is one carbon atom thick, that’s 0.345 nanometers (0.000000000345 meters). Envision a one square centimeter sized graphene sheet, which is now regularly grown. Imagine, somehow, we could thicken the monolayer graphene sheet equal to that of a piece of printer paper (≈ 0.1 mm) while appropriately scaling up the area coverage. The graphene sheet that originally covered only one square centimeter would now cover an area of about 2900 meters by 2900 meters or roughly 1.8 miles by 1.8 miles. A paper thin sheet covering about 4 square miles. The Royal Swedish Academy of Sciences at nobelprize.org has an interesting way of scaling the tiny up to every day experience. They want you to picture a one square meter hammock made of graphene suspending a 4 kg cat, which represents the maximum weight such a sheet of graphene could support. The hammock would be nearly invisible, would weigh as much as one of the cat’s whiskers, and incredibly, would possess the strength to keep the cat suspended. If it were possible to make the exact hammock out of steel, its maximum load would be less than 1/100 the weight of the cat. Graphene is more than 100 times stronger than the strongest steel!

Graphene sheets possess many fascinating characteristics certainly not limited to mere size and strength. Experiments are being conducted at Caltech to study the electrical properties of graphene when draped over a field of gold nanoparticles; a discipline appropriately termed “strain engineering.” The peaks and valleys that form create strain in the graphene sheet, changing its electrical properties. The greater the curvature of the graphene over the peaks, the greater the strain. The electrons in graphene in regions experiencing strain behave as if they are in a magnetic field despite the fact that they are not. The electrons in regions experiencing the greatest strain behave as they would in extremely strong magnetic fields exceeding 300 tesla. For some perspective, the largest magnetic field ever created has been near 100 tesla and it only lasted for a few milliseconds. Additionally, graphene sheets under strain experience conductance plateaus very similar to those observed in the quantum Hall effect. This allows for great control of electrical properties by simply deforming the graphene sheet, effectively changing the amount of strain. The pseudo-magnetic field generated at room temperature by mere deformation of graphene is an extremely promising and exotic property that is bound to make graphene a key component in a plethora of future technologies.

Graphene and its incredibly fascinating properties make it very difficult to think of an area of technology where it won’t have a huge impact once incorporated. Caltech is at the forefront in research and development for graphene component fabrication, as well as the many aspects involved in the growth of high quality graphene. This summer I was involved in the latter and contributed a bit in setting up an experimenKodak_Camera 1326t that will attempt to grow graphene in a unique way. My contribution included the set-up of the stepper motor (pictured to the right) and its controls, so that it would very slowly travel down the tube in an attempt to grow a long strip of graphene. If Caltech scientist David Boyd and graduate student Chen-Chih Hsu are able to grow the long strips of graphene, this will mark yet another landmark achievement for them and Caltech in graphene research, bringing all of us closer to technologies such as flexible electronics, synthetic nerve cells, 500-mile range Tesla cars and batteries that allow us to stream Netflix on smartphones for weeks on end.