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 !