The 2012 Nobel Prize in Physics

[DreamGypsy]

The Nobel Prize in Physics 2012 was awarded jointly to Serge Haroche and David J. Wineland "for ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems"

http://www.nobelprize.org/nobel_prizes/physics/laureates/2012/

The scientific background of their work and discoveries is available in the Scientific Background on the Nobel Prize in Physics: http://www.nobelprize.org/nobel_prizes/physics/laureates/2012/advanced-physicsprize2012.pdf

Here's the introduction from the Background paper:

The behaviour of the individual constituents that make up our world – atoms (matter) and photons (light) – is described by quantum mechanics. These particles are rarely isolated and usually interact strongly with their environment. The behaviour of an ensemble of particles generally differs from isolated ones and can often be described by classical physics. From the beginning of the field of quantum mechanics, physicists used thought experiments to simplify the situation and to predict single quantum particle behaviour.

During the 1980s and 1990s, methods were invented to cool individual ions captured in a trap and to control their state with the help of laser light. Individual ions can now be manipulated and observed in situ by using photons with only minimal interaction with the environment. In another type of experiment, photons can be trapped in a cavity and manipulated. They can be observed without being destroyed through interactions with atoms in cleverly designed experiments. These techniques have led to pioneering studies that test the basis of quantum mechanics and the transition between the microscopic and macroscopic worlds, not only in thought experiments but in reality. They have advanced the field of quantum computing, as well as led to a new generation of high-precision optical clocks.

This year’s Nobel Prize in Physics honours the experimental inventions and discoveries that have allowed the measurement and control of individual quantum systems. They belong to two separate but related technologies: ions in a harmonic trap and photons in a cavity (see Fig. 1).

There are several interesting similarities between the two. In both cases, the quantum states are observed through quantum non-demolition measurements where two-level systems are coupled to a quantized harmonic oscillator – a problem described by the so-called Jaynes-Cummings Hamiltonian. The two-level system consists of an ion (with two levels coupled by laser light) or a highly excited atom (with two Rydberg levels coupled by a microwave field). The quantized harmonic oscillator describes the ion’s motion in the trap or the microwave field in the cavity.

Lots of cool details and discussion follows in the referenced paper.



One concept with which I was embarrassingly not at all familiar is the Rydberg atom used in the photon trapping work.

From Wikipedia:

A Rydberg atom is an excited atom with one or more electrons that have a very high principal quantum number.[1] These atoms have a number of peculiar properties including an exaggerated response to electric and magnetic fields,[2] long decay periods and electron wavefunctions that approximate, under some conditions, classical orbits of electrons about the nuclei.

snip

It is now apparent why Rydberg atoms have such peculiar properties: the radius of the orbit scales as n2 (the n = 137 state of hydrogen has an atomic radius ~1 µm) and the geometric cross-section as n4. Thus Rydberg atoms are extremely large with loosely bound valence electrons, easily perturbed or ionized by collisions or external fields.

A Rydberg atom has a radius of about 125 nanometers which is roughly 1000 times larger than typical atoms.

The existence of the Rydberg series was first demonstrated in 1885 when Johann Balmer discovered a simple empirical formula for the wavelengths of light associated with transitions in atomic hydrogen. Three years later the Swedish physicist Johannes Rydberg presented a generalized and more intuitive version of Balmer's formula that came to be known as the Rydberg formula. This formula indicated the existence of an infinite series of ever more closely spaced discrete energy levels converging on a finite limit.[5]

This series was qualitatively explained in 1913 by Niels Bohr with his semiclassical model of the hydrogen atom in which quantized values of angular momentum lead to the observed discrete energy levels.[6] A full quantitative derivation of the observed spectrum was derived by Wolfgang Pauli in 1926 following development of quantum mechanics by Werner Heisenberg and others.

Always nice to learn new things, even if they were discovered 127 years ago!