Quantum Physics in Biological World

Does quantum physics come into play in photosynthesis? 

Quantum phase slip

A superfluid shows several strange behaviors which are absent in a classical fluid. One such phenomenon that can be observed in superfluids is the nucleation of quantized vortices.  Consider the flow of a superfluid through a narrow channel. A vortex may nucleate in the fluid near its one edge due to thermal or quantum fluctuations, and it may roll across the channel. When this happens, the superfluid loses its phase and hence the velocity because the vortex carries energy with it and finally it dissipates as thermal energy. The loss in phase in such an event is 2pi. Such an event is called a quantum phase slip event or a velocity slip event. A quantum phase slip event can be utilized to detect rotation by using a toroidal supefluid in a superfliud gyroscope.

Eigenstates, eigenvectors, and eigenvalues

The eigenstates of  a system are its characteristic states, the eigenvectors are the characteristic vectors describing the states,  and the eigenvalues are the characteristic values representing the states of the system. For example, if we consider a one dimensional quantum harmonic oscillator, its ground state is one of its eigenstates which is represented by the eigenvector |g> and the eigenvalue is (one-half *hbar*omega), where (omega) is the frequency of the oscillator. The other eigenstates of the oscillator are the excited states |e> with the increase of energy by (hbar*omega) while climbing up from the ground state.

Quantum World

'The World of Small' has been given a new title 'Quantum World' to make its purpose obvious to the readers !

Happy reading !

Condensed Matter via Atomic Physics

Condensed matter systems are complicated systems  because they are ensemble of atoms and molecules held  tight by inter-atomic and inter-molecular forces. The forces arise as a result of various interactions - interactions between electrons in neighboring atoms, dipole interactions, overlap of the wave functions, etc. A condensed matter system may also have defects  and dislocations of various kinds. Therefore, studying the properties of  condensed matter systems like a chunk of gold or  a cup of water is not an easy subject. 

Because of  the discovery of new ideas and a rapid development of technology, there are a lot of new methods developed to study condensed matter systems. One such way is simulating condensed matter using an optical lattice. An optical lattice is a 'light crystal' formed by interfering laser light waves traveling in opposite directions. A pair of counter-propagating laser light waves form a standing wave - a wave with intensity maxima and minima at regular spatial intervals. This is a one dimensional optical lattice. Two orthogonal pairs of lasers form a sheet of optical lattice - a two dimensional structure. If three pairs of counter-propagating lasers along X-, Y- , and Z- directions interfere each other, they form a structure which is called a three dimensional optical lattice. 

An optical lattice can be controlled as you wish, by varying the wavelength of the component lasers. What is an optical lattice good for? An optical lattice is a clean system - free of defects. It is tunable, controllable and easily manipulated as desired and required. An optical lattice can simulate a condensed matter system. How? In an optical lattice, there are arrays of regularly spaced sites of low potential which can be filled with atom(s). One can fill with similar or dissimilar atoms in the sites. Therefore,  the optical lattice with atoms sitting in the potential minima simulates condensed matter systems. 

A condensed matter system as it stands is 'GOD-MADE', and so it can not be manipulated easily. For example, you can not change the lattice constant or the coupling strength in a block of silver. Therefore, a system which may represent widely distributed condensed matter systems - ranging from a water molecule to the complex structure like a human brain is extremely important to understand the properties of the condensed matter, and ultimately the Universe !

Note: This posting is in progress. Your comments are highly appreciated !

BOSE-EINSTEIN CONDENSATE vs EXAM

Read for fun !


A Bose-Einstein condensate(BEC) is like an Exam ! It seems funny, but please keep on reading, I'll prove it. A BEC is created out of atoms or molecules at low temperatures so that all atoms in an ensemble reach the ground state of the potential or a trap. A commonly used trap is a Magneto-Optical Trap (MOT). This is like an exam room with physical walls, exam questions, proctors, professors, and the career in a long term. They bind the test-takers in the exam room tightly.

The most energetic atoms leave an MOT quickly, the same way as a smart test-taker does. The low energy atoms go towards the lower and lower state of the trap and they are bound to form a BEC. Similarly, a less smart test-taker remains in the exam room for the whole time assigned to the exam or even more if the proctors or professors allow to do so ! If the trap is stronger or tighter, the atoms are more firmly trapped than in a weaker trap and the coherence is also maintained for a longer time. Analogously, if the questions in the exam are tougher, it makes a test-taker to remain in the exam room for a longer time; but if the questions are easier, the test takers escape right away ! A good exam will help making a good career of a test taker; it is a similar situation to a good BEC, which can be used for various purposes ranging from the study of its properties to the applications in inertial navigation systems and precision measurements. Oh, most importantly, all atoms in a BEC are in the same quantum state like all the test takers in an exam room; all of them are solving the problems the same way, with a goal of succeeding in the test; they are supposedly in the same state of their minds!

I hope I convinced you that a BOSE-EINSTEIN CONDENSATE is NOT different from an EXAM !

Spin-1/2 system is bizarre object !

Consider a spin-1/2 particle. Rotate it about an axis by a 2 pi angle. You are not getting it back into the same state but with sign flipped. If you rotate it further by another 2 pi angle, you will see the particle in the original state. This is a bizarre object, which is beyond our intuition !

If you ask physicists, why is this? The answer is simple : it is an SU(2) physics, not an SO(3) ! If you want to visualize it, please look at Feynman's description of the rotation of a coffee cup in the following links:

(1) WIKI: http://en.wikipedia.org/wiki/Orientation_entanglement

(2) DEMO: http://www.youtube.com/watch?v=Rzt_byhgujg

Your views on this matter are highly welcome !

Quantum Biology

If there is something very complex and mysterious in nature, that should be the creation of 'life' from 'non-living' atoms and molecules. How is life created out of these atoms and molecules? Keeping the identity from generation to generation with slight modifications in each generation is a real mystery. No two individuals are exactly identical ! 'Thinking ability' or 'intelligence' is a superior quality that humans have; how does this work? Will classical thoughts and laws be enough to solve this mystery or should quantum physics come into play to address this problem ? Erwin Schrodinger, a pioneer of Quantum Physics wrote 'What is life?' in the 1930s and has expressed his thoughts about this in this book. What is BEYOND there than what we think about life?

Let's consider the living beings around us. There are lives of all kinds in nature and they are going this way from millions of years in the past. What forms of life were there in the start of life? It might be an assembly of some materials in a little microscopic pouch which showed some signs - movement, being two or more from the single existing one in the course of time, absorbing some water or air, etc, etc. At first what stimulated the formation of this pouch out of the those non-living atoms? There is another mystery there of atoms and its constituents but for now lets assume that the atoms were already there for some reason. Why did that pouch need to proliferate? Why did it start moving?

Note: This posting is in progress.

BEC and spontaneous symmetry breaking

When we consider a non interacting or a weakly interacting dilute thermal gas containing in a vessel, there is a symmetry in the system. That means for an atom, there is not a preferred direction, all directions look the same and it has a random phase. Once the gas is cooled to some low temperature in a trap, it enters in a new phase called a condensate, in which all atoms lie in the same quantum state and have the same macroscopic quantum phase, which is a completely different situation in comparison to the thermal gas. Therefore, the phenomenon of Bose-Einstein condensation is a spontaneous symmetry breaking !

Note: This posting is in progress !

Optically synthesized magnetic field

When charged particles move in a magnetic field, gauge potentials arise and the effective Hamiltonian has a term containing the vector potential, A. Neutral atoms can also behave like charged particles if the container in rotated in a trapping magnetic fields. But recently, an optically synthesized magnetic field has been created where the neutral atoms experience an effective gauge potential without any rotation, similar to the case of charged particles in an electromagnetic field.

Please look at the following reference for details:

(1) http://www.nature.com/nature/journal/v462/n7273/full/nature08609.html

(2) http://prl.aps.org/abstract/PRL/v102/i13/e130401

Note: This post is in progress.

30th CNLS Annual conference at SANTA FE, NM

The 30th CNLS Annual Conference, http://cnls.lanl.gov/ultralow/, was organized on 'COMPLEXITY and DISORDER at ULTRA-LOW TEMPERATURES' in La Fonda Hotel, Santa Fe, NM from June 21-25, 2010. A lot of strange and impossible-looking things happen at ultra-low temperatures, including the phenomenon of Bose-Einstein Condensation (BEC). There were a lot of nice oral and poster presentations in the program by the physicists from all around the world. I also presented a poster in the program.

DAMOP2010 at Houston, Texas

DAMOP2010, http://damop2010.rice.edu/, was organized in Hyatt Regency Hotel, Houston, Texas from May 25-29, 2010. There were a lot of interesting presentations - oral and poster both, several exciting activities, including some activities to celebrate the 50th anniversary of the invention of LASER. In fact, the discovery of LASER has drastically changed the science and technology and the world as a whole. The LASER has found its applications in diverse fields. In fact, one can rarely find a field of science and technology where there is no presence/use of a LASER in one form or another. Atomic, molecular and optical physics is one of the major fields which has gotten a tremendous advantage from the discovery of LASER. In fact, the first observation of a BOSE-Einstein Condensate (BEC) became possible in 1995, after about 70 years of its prediction by Einstein, because of the development of the technique of cooling atoms using a laser.

There were thousands of atomic, molecular and optical physicists, including several Nobel Laureates in the fields.

I also presented by current research in the meeting http://meetings.aps.org/Meeting/DAMOP10/Event/126565.

Third Annual Greater Boston Area Quantum Matter Meeting

The Third Annual Greater Boston Area Quantum Matter Meeting took place on Saturday, April 3, 2010 at the University of Massachusetts Boston, Campus Center, 3rd floor, 100 William T. Morrissey Blvd., Boston. There were four invited talks and more than 30 contributed talks. Here is a link for more information:

http://cmt.harvard.edu/bahbar/

Here is a group photo taken on the conference site:

http://www.physics.umb.edu/news.htm

How does a Cs-fountain clock work?

A clock is a timekeeping device. In the past, people used the shadow of a building, the position of some fixed stars, the sun, the moon and some other heavenly bodies to keep track of time. As the human civilization progressed, they developed some devices like a water clock and a sand clock to know time. In the early seventeenth century, Galileo discovered that a swinging pendulum can be used as a time keeping device. Inspired by this discovery, Christian Huygens invented a pendulum clock in the mid seventeenth century. These clocks can still be seen used in several places. In the mid twentieth century, it was discovered that atoms can be used to keep time. The 1955 Cesium Atomic Clock with a Cesium beam tube developed at the National Physical Laboratory, UK, kept time to a second in 300 years. To increase the accuracy of the clocks, the interrogation time had to be increased. This could be done by decreasing the speed of the atomic beam or by increasing the length of the the tube. But the problem with the increasing the length of the tube was that the atoms would form a sag in travelling through the tube due to gravitational potential. A new idea was developed where the tube could be rotated so that it would be in a vertical position and the atomic beam could be projected vertically upward. This new configuration along with the development of the laser cooling techniques developed in early nineties made the modern, highly accurate Cesium fountain clocks possible. The modern Cesium clocks developed at NIST, Boulder, Colorado, USA would neither gain nor lose a second in more than 60 million years.

Note: This posting is in progress.

Physics Journals

The following links contain a number of physics and astrophysics journals published all around the world:

(1) http://www.slac.stanford.edu/spires/coden/list.shtml

(2) http://www-library.desy.de/eljnl.html#physics

(3) http://www.ifpan.edu.pl/journal.html

(4) http://journals.aip.org/

Bosons or Fermions?

A class of particles which have an integer spin are called bosons. Example - photon, etc. Any number of bosons can go to the same quantum state. Thus they are friendly to each other ! They obey Bose-Einstein statistics. The wave function associated with bosons is symmetric.

A class of particles which have a half- integer spin are called fermions. Example - proton, neutron, electron, etc. Unlike bosons, only two fermions (at maximum) can go to the same quantum state, as dictated by the Pauli Exclusion Principle. They obey Fermi-Dirac statistics. The wave function associated with fermions is anti-symmetric.

An atom can also be classified as a composite boson or a composite fermion.  To find whether an atom is a composite boson or a composite fermion, you need to look at the net spin of the atom due to its constituent particles that make it. For example, consider the simplest of the atoms - Hydrogen. Hydrogen has a proton and an electron. A proton is a half-integer particle and so is an electron. Therefore, the net spin of a normal hydrogen atom is one, which is an integer. Therefore, hydrogen is a composite boson. If we consider a helium-4 atom, there are two protons, two neutrons and two electrons. Each of these particles has a half integer spin. Therefore, the net spin of a normal helium atom is an integer. Hence, helium is a composite boson. What's about lithium-7 ? A lithium-7 atom has three protons, four neutrons and three electrons. Therefore, the net spin of a lithium-7 atom is an integer and hence it is a composite boson. On the other hand, by the same way of reasoning, lithium-6 is a composite fermion.

In general,  an atom can be classified as a composite boson or a composite fermion on the basis of  the total number of constituent particles contained in it. If the total number of constituent particles  is even it is a composite boson where as if the total number of constituent particles is odd, it is a composite fermion !

Gordon Research Conferences - 2009 (Atomic Physics)

The gordon research conferences take place on a number of frontiers in research areas every years and the conference in the same area is organized every two years. They were started by Professor Neil E. Gordon in 1930s. Therefore, these confernces carry a long hostory with them. The GRC-2009 in Atomic Physics was organised from June 28-July 03 at Tilton Shcool, Tilton, New Hampshire.

More than 150 participants incuding twenty plus speakers were present in the conference. The speakers were the top researchers in the field from around the world. About a 100 posters were presented on current researches in two sessions. Most of the talks and posters were from the experimentalists on the subject but there were some atomic physics theorists too to give talks and present posters. The talks were on variety of disciplines of Atomic physics - Bose and Fermi gases, atomic reactions in ultra cold environments, formation of qubits using atomic ions, etc. A day started with breakfast at 7:30 A.M. and ended with a social from 10:00 P.M. - 12:00(midnight) or so. I was so surprised to see that the frontier research scientists work all the time no matter whether they are in a meeting hall or in a dining table or in a social or wherever they are !

There were a lot of indoor and outdoor extra activities too in the free time like hiking, rafting and kayaking. Unfortunately, because of the weather, we could not do outdoor activities. Most of the week was spent on campus, attending the conferences, presenting poster, chatting, working on computers and eating and drinking.

I can not stop myself writing on the quality and quantity of foods in the conference. It was the place where you could eat anything of your choice and any amount you would want. It was really great. The conference staffs in the kitchen and everywhere were so friendly and helpful. We spent a very good time in overall in the GRC-2009 in Atomic Physics at Tilton School !

Second Annual Greater Boston Area Quantum Matter Meeting

The Second Annual Greater Boston Area Quantum Matter Meeting took place in Metcalf Science Center, Physics Department, Boston University, on Saturday, May 9, 2009. The topics of presentation were mainly on quantum systems: strongly correlated systems, atomic and optical systems, and mesoscopics. There were four invited talks, each of about 30 minutes duration and more than thirty contributed talks, each of 4-5 minutes. The schedule is available here. This program was a continuation of the First Annual Greater Boston Area Quantum Matter Meeting, which took place in Jefferson Building, Physics department, on Saturday, May 10, 2008. The link of this meeting can be found in here.

How is the information extracted from cold atom interferometers?

The cold atoms (thermal atoms) or a BEC sitting at the bottom of a magnetic trap is split by a laser standing wave and the wave packets are allowed to evolve in time. At the end of the interferometric cycle, the wave-packets are recombined by a recombining pulse (identical to the splitting pulse). The trap is switched off and the wave packets are allowed to expand. Then the imaging of the wave packets is done by using laser light. One of the techniques is the absorption imaging technique. In this method, a resonant light is shone on the wave packets and the images obtained from this are fitted with some suitable known models. The useful information is then extracted by interpreting the fitting parameters.

Note: This post is in progress !

BEC in a triple well potential

This is a review of a paper by Rab et. al.

Consider a triple well potential with the wells 'L' , 'M' and 'R' for the left, middle and right wells respectively. A BEC sitting in the 'L' well can be transported to the 'R' well so that no atoms are left in the 'M' well. The researchers call this process as macroscopic matter-wave Transport Without Transit (TWT) and this can be done by Stimulated Raman Adiabatic Passage(STIRAP). In STIRAP, is a technique to transfer population between two atomic states - 1 and 3 via an intermediate excited state 2. The atomic population is adiabatically transferred from the state 1 to state 3 by coupling the states 1 to 2 and and 2 to 3 using electromagnetic pulses. The population transfer is achieved via a superposition of the states 1 and 3 with the occupation of the state 2 strongly suppressed. That's why is is called the TWT.

Note: This post is in progress.