“Application”- “ Textbooks”-“Application”

Tan Lei （谭 磊）

July, 2012 广州 湛江

Institute of Theoretical Physics, Lanzhou University

2012 年高等学校热力学与统计物理学教学及学术研讨会

Introduction Motivation • So interesting-So many-So what ?• 60% (graduate):40% (work):• More is different• Interest• model Principle• Authoritative • Advanced • Colorful

outline• Why Is Ice Slippery

– Physics today 58, 50

• Photons in an optical microcavity

– Nuture 468, 545– Nature Photonics XXXX

• Geckos / water striders Macroscopic quantum phenomena

– Nature 464, 697 – Nature 405, 681/ Nature 443, 36

• Brownian Particle

– Science 328 1673

• Conclusions

outline

• Why Is Ice Slippery

– Physics today 58, 50

Why Is Ice Slippery ??

Can we skate over the glasses??

!! Explanation: pressure melting –in the textbooks for a very long time

The pressure exerted along the blade lowers the melting temperature of the top layer of ice, the ice melts and the blade glides on a thin layer of water that refreezes to ice as soon as the blade passes.

Textbooks are full of it

Correct Absolutely !!

This means that ice under pressure melts at a lower temperature or that we can melt ice by applying pressure.

Pressure Melting: ice skates

We can do a simple calculation to estimate the pressure exerted by the blades of a skate. Remember that we already learnt this on the first lecture: Pressure is force per unit area. P=F/A .

e.g. a150kG person and a typical blade edge, which is not razor sharp, is about one-eighth of an inch wide and about 12 inches long, yielding a surface area of 1.5 square inches each or 3 square inches for two blades

That amount of pressure lowers the meltingtemperature only a small amount, from 32 degrees to 31.97 degrees. Yet ice skaters can easily slip and fall at temperatures much colder.

For a flat-bottom shoes, a smaller amount temperature.

Explanation: Fails !! New idea are expected!

phenomilogically

Frictional melting ?? ------Beyond the textbooks

the rubbing of a skate blade or a shoe bottom over ice, heats the ice and melts it, creating a slippery layer.

Many of you might ask about the slipperiness of ice, that you can feel standing on ice without skates of skies. Pressure and friction do not explain it!

A liquid layer of water on the surface of ice ?? ----Beyond the textbooks

there are no molecules above them to help hold them in place, and they thus remain an unfrozen liquid even at temperatures far below freezing.

Michael Faraday

1. Pressure decreases the melting temperature of ice.2. However pressure is not the main reason why ice is so slippery.3. Pressure melting is only important down to -0.5 C .4. Frictional melting also contributes to the slipperiness of ice. At very low T's in order to gain speed it is necessary to ski faster!5. Independently of pressure or friction, there is always a liquid layer at the surface of ice. This layer is what makes ice slippery even without skies or skates.6. We can not skate over the glasses!

Conclusions: slippery when wet

It's amazing,“. "We're in 2012, and we're still talking about this thing."

The story is not completed yet.

continue to debate yet !!

The story is still far away from its end… where will we go?

The thin liquid layer

From Red Cells to Snowboarding: A New Concept for a Train Track, Phys. Rev. Lett., 93. 194501

Red Cells move quickly in the Vascular. Train runs on the Feather

….. Far away from the textbook

------Beyond the textbooksSo What ??

People flies on the grass ??

outline

• photons in an optical microcavity

– Nuture 468, 545– Nature Photonics XXXX

Photons

the electromagnetic field wave

the quantized harmonic oscillator Particle (bosonic)

Bosons Fermions

Laser cooling !!!

(Blackbody radiation)

(Bose-Einstein distribution)

Very lower temperatures are needed.

How to get there?

BEC BCS

Wave-particle duality

Las

er

coo

ling

Doppler cooling

Ramam coolingVSCPT cooling

Cavity cooling

2B DK T

2 2

2B R

kK T

M

2BK T

Limit temperature Main processes

Spontaneous emission

spontaneous emission

Photon Escape

atom

certain atomic species

certain atomic species

Atom the ensemble of atoms Molecules

The order of nK temperatures can be achieved!

Laser cooling mechanism

Science 321, 232 (2008) Nat. Phys. 1, 122 (2005)

----Beyond the textbooks

Photons --?? Why not BEC

The reason is that the photon number is not constant when their temperature is changed, as the photons can be absorbed by atoms in the surrounding apparatus. In BECs comprised of cold atoms, the atoms reach thermal equilibrium by exchanging energy in collisions with other atoms. This is not possible with mass-less photons as they interact too weakly with each other.

Ultracold atomic gases

Mimicking condensed matter physics and beyond

Perfect models for a fundamental understanding of quantum many-body system

So What ??

Photons –Photons BEC: impossible or possible? which way on earth will be taken? where is the way?

An optical cavity formed between two curved mirrors was used to confine the photons, and a dye was placed in between the mirrors to fill the cavity. The large number of dye molecules acted as a heat sink and allowed the photon energy to rapidly reach thermal equilibrium with the dye. This process reduced the range of energy states the photons were in, until they all occupied the lowest state possible,and thereby producing a BEC.

Nuture 468, 545

----Beyond the textbooks

Photons BEC

So What ??

The applications of photon BECs are perhaps still some way off, but it is thought that they could be used as a novel light source, or for steps towards improving the efficiency of a laser. Nevertheless, the production of a BEC from photons is still an important experiment for our understanding of fundamental physical systems, and further blurs the distinctions we had previously made between atoms and light.

----Beyond the textbooks

----Beyond the textbooks

To the end? No

Photons -- wave-particle

1 2Photon C wave C particle

Fifty years of conscious thought still does not make me closer to the answer of light quantum.

Maybe, we just begin now or we are still on the way …

----Beyond the textbooks

outline

• Geckos / water striders Macroscopic quantum phenomena– Nature 464, 697 – Nature 405, 681/ Nature 443, 36

• Brownian Particle– Science 328 1673

quantum phenomena ?? Classical phenomena

Microscopic particles

quantum phenomena

Macroscopic objects ??

A quantum drum hasbecome the first visible object to be put into a superposition of quantum states.

Nature 464, 697

Optomechanical systemPhysics 2, 40

Largest ever object put into quantum state.

Which played a vital role in the conceptual exploration of theboundaries between classical and quantum mechanical systems

the surf is up

Milestones Nature and Science

Macroscopic quantum phenomena -BEC or BCS ? Or both not !

Geckos can easily walk on surfaces with any roughness, climb vertical walls, and even cling to the ceilings

Nature 448, 338

Spider-Man

water striders

So What ??

Who is the greatest “man” in qunatum world??

Maybe, there is a long way to go…

Brownian Particle

Modle: Langevin equation, …

Phenomena: Coastline, Zebra, Biological populations…

Picture

Quantum Brownian Particle --- the Second Law ?? ----decoherence??

?? the instantaneous velocity of a Brownian particle -----can we? How can ?

Still going on…

What we konw

Average speed, Fluctuation , Einstein relation….

Textbook …. Question-------Think deeply------Application

Conclusion

The knowledge in the textbook is the key to the Avenue of life and research !

The textbook is not only the textbook!

Correct: condition

The knowledge is limited!

Application

Conclusion

Acta Phys. Sin. 61, 140301 (2012)

arXiv: 0907.3795 (2009)

Acta Phys. Sin. 60, 024204(2011)

Mod. Phys. Lett. B 23, 1499 (2009)

Chin. Phys. Lett. 25, 48(2008)

Journal of Lanzhou University (Natural Sciences) 46, 119(2010)

Journal of Lanzhou University (Natural Sciences) 44, 131(2008)

Harvard University, Penn State University ……

Paper

University

Thank you for your attention!