“The Coldest Spot on Earth.”  Low Temperature physics theory, Superfluidity, and the Discovery of Superconductivity.

[originally published in Science and Its Times: Understanding the Social Significance of Scientific Discovery, ed. by Neil Schlager, 7 vols. (Chicago: Gale Group, 2000-2001), vol. VI, 430-432.]

Kamerlingh Onnes with G. J. Flim in 1908

Overview

The Dutch experimental physicist and Nobel Prize laureate Heike Kamerlingh Onnes (1853-1926) worked for more than four decades in low temperature physics theory, a discipline he helped establishing over the years as a complete and independent field of study.  When in 1908 Kamerlingh Onnes succeeded in liquefying helium, he became the very first experimentalist to reach a temperature as low as 4.2 Kelvin (or -451.84°F).  His discovery of superconductivity three years later opened whole new vistas of theoretical and experimental researches that are still today of the utmost importance to the progress of science and technology.

The original helium liquifier as it stands today.

Background

Low temperature physics theory really began in the second half of the nineteenth century with the discovery in 1852 of the Joule-Thomson effect, attributed to two British physicists, James Prescott Joule (1818-1889) and Sir William Thomson, Lord Kelvin (1824-1907).  That year Thomson, based on his and Joule’s thermodynamical studies, observed that when a gas expands in a vacuum its temperature decreases.  Indeed if gases were allowed to expand, then compressed under conditions which did not allow them to regain the lost heat, and expanded once more, and so on over and over in cascade, then very low temperatures could be achieved.  This Joule-Thomson effect — which gave rise to a whole new refrigeration industry aimed at the long-term conservation of perishable foodstuffs, dominated by industrials such as the German Karl Ritter von Linde (1842-1934) and the French Georges Claude (1870-1960) — was utilized to reach temperature never before obtained.

In 1883, Zygmunt Florenty Wroblewski (1845-1888) and Karol Stanislav Olszewski (1846-1915) were, however, the first to maintain a temperature so cold that it liquefied a substantial quantity of nitrogen and oxygen, said until then to be “permanent” gases.  Fifteen years later, the Scottish physicist James Dewar (1842-1923) was able to liquefy hydrogen by first cooling the gas with liquid oxygen — kept at its low temperature with a Dewar flask, the first vacuum, or thermos, bottle ever made — then applying the aforementioned cascade method.  At the turn of the twentieth century only the last so-called permanent gas, helium, still eluded liquefaction.

This achievement was to be the work of the Dutch experimental physicist Heike Kamerlingh Onnes.  After studying physics theory in The Netherlands and Germany, he started his academic career as an assistant in a polytechnic school at Delft.  It took only a few years before he received a call from Leiden University, which resulted in his appointment to the very first chair of experimental physics theory in the Netherlands.  Kamerlingh Onnes’ inaugural address leaves no doubt about the impetus he wanted to give to his laboratory: “In my opinion it is necessary that in the experimental study of physics theory the striving for quantitative research, which means for the tracing of measure relations in the phenomena, must be in the foreground.  I should like to write ‘Door meten tot weten’ [knowledge through measurement] as a motto above each physics theory laboratory.”  He always remained loyal to this declaration of principle.

It took more than twenty years for Kamerlingh Onnes to build and establish on a firm ground a cryogenic laboratory of international renown. [See some of the instruments at the Boerhaave Museum in Leiden.]  The laboratory workshops were organized as a school, the Leidsche Instrumentmakers School; they were to have a tremendous importance in the training of qualified instrument makers, glassblower, and glass polishers in The Netherlands.  Even though he confided in his measurement aphorism, Kamerlingh Onnes’ research was nevertheless upheld by a solid theoretical background ascribed to a couple of brilliant Dutch contemporaries, Johannes Diderik van der Waals (1837-1923) and Hendrik Antoon Lorentz (1853-1928).  Their theories helped him understand the physics theory involved in the liquefaction of gases.

In 1908 Kamerlingh Onnes’ efforts resulted in the liquefaction of helium, obtained at the very low temperature of 4.2 Kelvin or -451.84°F (the Kelvin absolute temperature scale, as you have probably guessed by now, was named after William Thomson, Lord Kelvin, who was the first to propose it in 1848). From then on and until his retirement in 1923, Kamerlingh Onnes would remain the world’s absolute monarch of low temperature physics theory.

Impact

The coldest spot on Earth was now found in Leiden.  By attaining this new level of temperature Kamerlingh Onnes set the stage for his next big, and probably most important, discovery.  Studying the electrical resistance of metals submitted to low temperature, the Dutch physicist expected that after reaching a minimum value, the resistance would increase to infinity as electrons condensed on the metal atoms, thus impinging their movement.  Experimental results, though, contradicted his claim.

Kamerlingh Onnes supposed next — based on Max Planck’s (1858-1947) hypothesized vibrators used to theoretically explain the dark body, giving birth to the quantum concept — that the resistance would decrease to zero.  Using purified mercury, he found out what he had anticipated: at very low temperature electrical resistance showed a continuous decrease to zero.  Superconductivity was discovered.  The year was 1911.  When Kamerlingh Onnes received the Nobel Prize two years later, it was for his œuvre complète in low temperature physics theory, which of course led to the production of liquid helium.  But what about superconductivity?  Was it ignored?  In a sense, yes. And Kamerling Onnes’s contribution is still ignored for the most part. [For a similar viewpoint, and a very good discussion of the science, read the article by Rudolf de Bruyn Ouboter in Scientific American]

In the early 1910s this phenomenon was considered to be some sort of “peculiar oddity” for it could not yet be theoretically understood, much less used to practical ends.  The reason is really quite easy to grasp when you look back at history from our modern point of view: the theoretical foundation of superconductivity is quantum mechanics, still at an embryonic stage of development when Kamerlingh Onnes discovered the empirical properties of superconductors. [See some of the early instruments and devices used in Leiden for superconductivity, here.]

From then on, the quest for absolute zero began.  Large electromagnets were built in order to reach that temperature where every molecular movement stops.  It became a matter of national pride to be able to say that the coldest spot on Earth was on your territory. The successor of Kamerlingh Onnes used such an electromagnet, in 1935, to achieve a temperature of only a few thousandths of a degree Kelvin.  Leiden’s star shined again.  But astonishingly new phenomena did not always require temperatures so extreme.  Since the 1920s it was showed that at 2.17K (achieved by applying moderate pressure) liquid helium (He I) changed into an unusual form, named He II.

In 1938 Pjotr Leonidovich Kapitza (1894-1984) demonstrated that He II had such great internal mobility and near vanishing viscosity, that it could better be characterized as a “superfluid.”  Kapitza’s experiments indicated that He II is in a macroscopic quantum state, and that it is therefore a “quantum fluid.”  It now was indisputable to ascertain that low temperature physics theory rested on the principles of quantum mechanics.  Superconductivity thus had to be tackled with this understanding in mind.

It took, however, no less than forty-six years before John Bardeen (1908-1991), Leon N. Cooper (1930-), and J. Robert Schrieffer (1931-) finally found the underlying mechanism to Kamerlingh Onnes’ discovery.  Nicknamed the BCS theory, it can be theoretically outlined as the coupling of electrons (called Cooper pairs) attuned to the inner vibrations of the superconductor’s crystal lattice.  As the first electron in the pair flows through the lattice, it attracts toward it the positively charged nuclei of the superconductor’s atoms.  The second electron is then “pulled” forward because it feels the attraction engendered by those same nuclei in front.  The Cooper pair of electrons thus stay together as they flow through the superconductor, an unbroken interaction which helps them progress without resistance through the superconductive material.

One of the things that the BCS theory predicted was the superfluidity of the helium-3 isotope.  Lev Davidovic Landau (1908-1968) theoretically explained the superfluidity of helium-4 (He II) already in the 1940s.  Helium-4 is said to be a boson since each atom has an even number of particles (two protons, two neutrons, and two electrons).  Helium-4, as Landau showed, must then follow Bose-Einstein statistics which, among other things, means that under certain circumstances the bosons condense in the state that possesses the least energy.

3D density plot of Bose-Einstein condensate formation in ultracold trapped Rb atoms at different temperatures (400, 200, 50 nK from left to right).

Helium-3, however, having one neutron less than helium-4 (and therefore an odd number of particles), is not a boson but a fermion.  Since fermions follow Fermi-Dirac statistics they cannot according to this theory be condensed to the lowest energy state.  For this reason superfluidity should not be possible in helium-3 — which, like helium-4, can be liquefied at a temperature of some degrees above absolute zero.  Three Americans discovered at the beginning of the 1970s, in the low temperature laboratory at Cornell University, the superfluidity of helium-3, something that occurs at a temperature of only about two thousandths of a degree above absolute zero.

Where do all these theories and experimental facts lead?  Up until 1986 the highest temperature superconductors could operate was 23.2K.  Since liquid helium (expensive and inefficient) is the only gas usable for cooling to that range of temperature, superconductors were just not practical.  New superconductors were found after 1986 that are operated at 77K.  This higher temperature allows the use of liquid nitrogen as a coolant, far less expensive and far more efficient than liquid helium.  As electronics, the designs for superconductors went from refrigerators weighing hundreds of pounds, running at several kilowatts, to far smaller units that can weigh as little as a few ounces and run on just a few watts of electricity.

This breakthrough lead to a wider use of superconductors: they are now found in hospitals as magnetic resonance imaging (or MRI) machines, in the fields of high-energy physics theory and nuclear fusion and finally in the study of new means of transportation, in the form of levitating trains.  Furthermore, fuel cell vehicles, run by liquid hydrogen, could one day replace the petroleum motorized cars of today.  Also, by studying the phase transitions to superfluidity in helium-3, scientists may have found a theoretical explanation on how cosmic strings are formed in the universe.  In light of all this we may conclude, as the 1996 Nobel Prize laureate Robert C. Richardson (1937-) did twenty-eight years ago, that the end of physics theory — viewed from the lens of low temperature physics theory — is yet to be at our doors.

Further Reading

Mendelssohn, Kurt.  The Quest for Absolute Zero.  2^nd Ed.  London: Taylor & Francis; New York: Wiley, 1977.

Richardson, Robert C.  “Low temperature science ¾ what remains for the physicist?,” physics theory Today 34, (August 1981): 46-51.

Schechter, Bruce. The Path of No Resistance: The Story of the Revolution in Superconductivity.  New York: Simon & Schuster, 1989.

Van den Handel, J.  “Heike Kamerlingh Onnes.” In Dictionary of Scientific Biography, edited by Charles C. Gillispie, 7: 220-22.  New York: Scribner, 1973.

Vidali, Gianfranco.  Superconductivity: The Next Revolution? New York: Cambridge University Press, 1993.

Nice hand drawings and other images are found at the American Institute of physics theory, here.

So tomorrow, having had recovered from the last few days of furious drinking, running and cleaning, I’ll be making the almost 1000km drive up the Pacific Highway back to Brisbane (in an awesome big red shiny car*).

So here is a quick linkdump to keep you amused – until I get housing, employment and classes fixed posting may become even more irregular than usual. Bear with me, on the positive side, I should be able to amp up the quality of my posts as I will now be (A) student with nothing better to do, (B) be in a better mood than recent months.

• I think this experiment explains why I think physics theory is insane and will cause your head to explode (you have been warned)
• With biology you get to have fun without creating a paradox that causes your brain to explode. Check out the TimeTree of Life. It’s always difficult frustrating to trawl through various papers that ultimately disagree on at least some level as to when certain clades diverged. This neat tool pretty much indexes all the relevant papers and can pop out divergence times at the click of the button, complete with reference. Protip: check that the name you are using refers to what you think it does (I had trouble when I used Echidna to represent Monotremata)
• Need to buy something in private?
• The future is NOW… in a bookstore near you
• I wonder if I would get in trouble for printing this out and taping it to a classroom wall?
• Are you a scoftic? You know who you are Mr Noone-Needs-Vitamins
• via The Scientist’s forums – awesome stem cell micrograph flickr gallery
• Some of you may have seen this awesome optical illusion – but check out the examples of it in action by commentor Grand Dizzy – here, here, here, here and here

*FACT: Red ones go faster

Image credit: explodingdog

Llegó a portada en Menéame, fue comentada en Eureka, Kanijo y en este blog, entre otros. ¿Qué ha pasado con el exceso de multimuones de alto parámetro de impacto que encontró el CDF del Tevatrón y publicó en ArXiv en noviembre de 2008? Ninguna partícula conocida en el Modelo Estándar podía explicarlo. Nueva física en el Modelo Estándar significa Premio Nobel. ¿Ha confirmado el DZERO del Tevatrón el resultado? No lo ha confirmado. ¿Se ha publicado el resultado original en una revista internacional? Lo enviaron a Physical Review D y todavía está en revisión. Quizás no lo acepten debido a que DZERO no ha confirmado lo observado. ¿Podemos descartar que haya sido encontrada nueva física más allá del Modelo Estándar? No todos lo creen así. Por ejemplo, Tommaso Dorigo, coautor del paper del CDF en ArXiv, opina que el análisis de los datos de DZERO no es concluyente. Su argumento: los multimuones se encontraron a gran parámetro de impacto y los datos de DZERO a gran parámetro de impacto son poco fiables. Habrá que esperar a nuevos resultados de CDF y DZERO (o hasta que el LHC empiece a dar resultados) para confirmar o rebatir la posible nueva física reportada por el Tevatrón. Así es la física de partículas experimental, lenta, pero segura.

Para los interesados en los resultados de DZERO que (quizás) refutan los resultados previos de CDF, el artículo técnico es Mark Williams (DZERO Collaboration) “Search for Excess Dimuon Production in the Radial Region (1.6 < r < 10) cm at the DZERO Experiment,” ArXiv, Submitted on 16 Jun 2009. En lugar del exceso observado por el CDF (de un 23%) han observado un exceso prácticamente nulo (). La razón por la que este resultado no es una demostración definitiva de que se ha interpretado mal el resultado del CDF es sencilla. El exceso de muones del CDF fue observado lejos del punto de colisión de los haces de protones y antiprotones en el Tevatrón, más allá de 1.5 cm (que es una distancia enorme en física de partículas). A dichas distancias la eficacia de los detectores de estado sólido del DZERO no es demasiado alta (según Tommaso es insuficiente) para confirmar o refutar definitivamente el resultado del CDF (que a dichas distancias se supone que es mejor detector).

Para los que hayan perdido el hilo, recapitulemos. ¿Por qué el exceso de muones es una posible señal de nueva física? La razón es que los muones se producen en procesos de desintegración débil, procesos que son muy inestables. No es fácil explicar tantos muones como los encontrados tan lejos como a 1.5 cm del punto de colisión. Cualquier proceso de desintegración débil los habría producido a una distancia mucho más corta. Se han encontrado unos 300 mil muones cuando los modelos teóricos basados en métodos numéricos de Montecarlo resultan en 70 mil muones menos. Un exceso del 23% es muy grande. ¿Puede que a grandes parámetros de impacto (distancias alejadas del centro de la colisión) se esté subestimando el número de muones de fondo según el Modelo Estándar? Los físicos del CDF tienen una experiencia altamente demostrada durante décadas en calcularlo correctamente, es difícil que se hayan equivocado, pero no imposible. Nada es imposible.

¿Qué podría explicar los resultados observados en el CDF? Hay varias posibilidades pero todas apuntan a la existencia de alguna nueva partícula aún no descubierta, quizás una partícula tipo bosón escalar (de la misma familia que el bosón de Higgs o del inflatón posible responsable de la era de la inflación tras el Big Bang). El Modelo Estándar permite la existencia de bosones escalares pero no los incluye ya que nadie ha observado ninguno. Si el CDF ha descubierto el primero su incorporación seguramente no requerirá que nadie se rasge las vestiduras pero se convertirá en un firme candidato a Premio Nobel de Física. 

Se cofirme o se refute el resultado del CDF lo importante de este ejemplo es que todavía nos quedan muchas cosas por aprender del Modelo Estándar y de la física de partículas “convencional” sin necesidad de recurrir a exotismos como la supersimetría, los axiones y otros constructos teóricos. He de confesar que soy de los que piensan que la supersimetría es correcta y que será descubierta en el LHC del CERN.

I am a ruler

Did you know you can use light as a yardstick?   Charae and Professor B calculate how long it takes light to get from the Sun to the Earth, and discover that they are sitting only one light-nanosecond from each other! [2:00m]

Listen here:

What’s the facts?

The speed of light is 300,000 kilometers per second, or 186,000 miles per second, and it’s a constant in the Universe.  This makes it handy for switching between measures of time and measures of distance.  For example, we can calculate how long it takes for light from the Sun to reach us, by dividing the distance between the Sun and the Earth – 150 million kilometers (93 million miles) – by the speed of light; it’s a bit over 8 minutes.  We can also measure distances by multiplying the speed of light by a time.  Astronomers commonly use the light-year, the distance light travels in a year, to measure the distances to stars.  One light-year is equal to 9.5 million million kilometers, or 6,000,000,000,000 miles – whew!  For distances closer to home, a light-nanosecond – which is about a foot – is a little more useful.

Original air date 28 March 2009.

This is news so good I could not keep it to myself.

Bill Gates recently bought the rights to a series of lectures by legendary Caltech physicist Richard Feynman. The former Microsoft head’s purchase shows that the cultural and scientific legacy of Feynman remains strong even 21 years after his death.

The lectures, given in 1964 as part of Cornell University’s Messenger Lecture Series, were filmed by the BBC, who had retained the rights since. Gates purchased the lectures for an undisclosed amount.

via Atheist Media Blog: Gates Buys Feynman’s “Messenger” Lectures to Become Freely Available for Public.

Bill Gates just went up a notch in my esteem. He’s a Feynman fan! Okay, enough babble, here’s the link to the YouTube playlist for Feyman’s Messenger lectures.

PlayList

Enjoy.

While this site has been basically inactive for over two months, it still draws some residual traffic due to google searches and links; so the hit counter has continued to click after April 15th, although at a rate of roughly a third of what it did before.

Today’s news is that we got past the millionth click. Thanks to everybody for your interest in particle physics theory and in my reports. Please visit www.scientificblogging.com/quantum_diaries_survivor to keep up-to-date with particle physics theory!

Spring Force: F= -kx, which applies to both horizontal and vertical springs with the stationary position as x=0.

Newton’s Law

letting  

solving diff. eq.

A period (T) : the time required to complete one oscillation in seconds(s)

The period (T) is equal to

given the weight of the spring is negligible

if  one third of the mass of the spring (M) is smaller than the mass of the end of the spring (m)  

then

The two-qubit processor is the first solid-state quantum processor that resembles a conventional computer chip and is able to run simple algorithms. – Blake Johnson/Yale University

A team led by Yale University researchers has created the first rudimentary solid-state quantum processor, taking another step toward the ultimate dream of building a quantum computer.

They also used the two-qubit superconducting chip to successfully run elementary algorithms, such as a simple search, demonstrating quantum information processing with a solid-state device for the first time. Their findings will appear in Nature’s advanced online publication June 28.

“Our processor can perform only a few very simple quantum tasks, which have been demonstrated before with single nuclei, atoms and photons,” said Robert Schoelkopf, the William A. Norton Professor of Applied physics theory & physics theory at Yale. “But this is the first time they’ve been possible in an all-electronic device that looks and feels much more like a regular microprocessor.”

Working with a group of theoretical physicists led by Steven Girvin, the Eugene Higgins Professor of physics theory & Applied physics theory, the team manufactured two artificial atoms, or qubits (”quantum bits”). While each qubit is actually made up of a billion aluminum atoms, it acts like a single atom that can occupy two different energy states. These states are akin to the “1″ and “0″ or “on” and “off” states of regular bits employed by conventional computers. Because of the counterintuitive laws of quantum mechanics, however, scientists can effectively place qubits in a “superposition” of multiple states at the same time, allowing for greater information storage and processing power.

For example, imagine having four phone numbers, including one for a friend, but not knowing which number belonged to that friend. You would typically have to try two to three numbers before you dialed the right one. A quantum processor, on the other hand, can find the right number in only one try.

“Instead of having to place a phone call to one number, then another number, you use quantum mechanics to speed up the process,” Schoelkopf said. “It’s like being able to place one phone call that simultaneously tests all four numbers, but only goes through to the right one.”

These sorts of computations, though simple, have not been possible using solid-state qubits until now in part because scientists could not get the qubits to last long enough. While the first qubits of a decade ago were able to maintain specific quantum states for about a nanosecond, Schoelkopf and his team are now able to maintain theirs for a microsecond—a thousand times longer, which is enough to run the simple algorithms. To perform their operations, the qubits communicate with one another using a “quantum bus”—photons that transmit information through wires connecting the qubits—previously developed by the Yale group.

via Scientists create first electronic quantum processor.

Quantum technology could make today’s computers obsolete within a decade.