Quantum jumps: a bumpy road to light-matter interaction

This year marks the Centennial of Niels Bohr’s model of atoms and molecules by which he explained the observed discrete absorption and emission spectra of light.

The radiation energy is absorbed and emitted in quanta, proposed by Planck and Einstein in 1900 and 1905, and Bohr associated with each absorption and emission event a quantum jump: an electron jumps among a discrete set of allowed orbits of motion in the atom. Energy is conserved if the difference between motional energies in the different orbits equals the energy of the light quantum, ΔE=hf.

In 1926, the eigenfunctions and the discrete spectrum of the stationary Schrödinger equation replaced Bohr’s description in terms of electron orbits. Both the light quantum and the quantum jump hypotheses then became largely superfluous and, to a large extent, even in disagreement with the quantum mechanical description of optical processes in atoms and molecules.

In this talk, I shall review how the light quanta at first lost, but later regained their role as important ingredients in light-matter quantum interactions, and how the quantum jumps first disappeared completely from the formal quantum theory, but are now essential in the description and application of quantum phenomena.

The talk will include an opportunity to play an online "quantum computer game" if you bring along a laptop.
To get access to the quantum computer game, you must first register to obtain a login.

To register, you go to the site http://www.scienceathome.org/qgame/register_withgroup.php?schoolId=18
and you enter the information marked with a red star.
Note that we have prefilled the group “Heriot-Watt”, so that you will automatically be part of the Heriot-Watt score boards when we play on Wednesday.

After registering, you will receive an email, and you can then activate your account.

Normally, you will be able play the game by entering the site www.scienceathome.org, but to avoid network traffic problems on Wednesday, we will ask you to download the special package of games that will be featured at the seminar.

You download the package from the site: http://www.scienceathome.org/index.php?Heriot-Watt
(file may only be available for download from Tuesday).

The code uses Java script, and it may suggest that you upload to the latest version of Java on your computer.

It is much easier to play the game with a loose mouse than with the touch pad on a laptop computer.