The CAT group studies quantum optics and atomic physics within the Department of Physics and Astronomy and The Institute of Optics, and is part of the Rochester Center for Coherence and Quantum Optics (CCQO). Our recent work has focused on the creation and study of ultracold quantum gasses, the manipulation and control of atomic motion using light, the laser cooling and trapping of neutral atoms and molecules (NaCs), topological structures in Bose-Einstein condensates (87-Rb), the quantum nature of the fundamental atom-photon interaction, and the application of these ideas to quantum information and technologies.
Right now we have two labs: the Bose-Einstein condensate lab, and the ultracold polar molecule lab. Prof. Bigelow is involved in studying the nanoscience of daguerreotypes, and we are involved in building a magneto-optical trap for UR's undergraduate teaching lab.
Our experimental research activities center around the creation and manipulation of ultracold atomic vapors which are mixtures of atoms of distinct atomic species. Current projects include the realization of a spinor Bose-Einstein condensate, and the application of quantum control and ultra-fast spectroscopy to the creation and manipulation of ultracold molecules, including heteronculear molecular species (NaCs - sodium cesium) and in the cooperative behavior of ultracold molecular vapors. Our group is also engaged in theoretical research and current projects include the investigation of Bose-Einstein condensation of atomic vapors with internal degrees of freedom such as spinor condensates, vortices, atom lasers, atom-atom interactions, cold collisions, and self-organization of dense, ultracold polar molecular vapors.
1997 and 2001. PBS NOVA's 'Absolute Zero - The Conquest of Cold' is a documentary on the history of the understanding and control of cold, including ultracold atoms. The magneto-optical trap (MOT) is central to our experimental work. Michaela Kleinart, a graduate of our group, has an excellent explanation of how MOTs work on her website. Additionally, Dallin Durfree wrote an introduction to a BEC lab while he was in Wolfgang Ketterle's group.
The University of Rochester has both the coldest stuff in the universe (Bose-Einstein condensates in our group) and the hottest (Laboratory for Laser Energetics) -- read about these extremes on the LaserFest site.
Watch a brief video by Prof. Bigelow about lasers and how our labs use them:
A Basic Introduction
The concept of a single entity as the building block of matter dates back to the Ancient Greece. The philosopher Democritus thought the world was made of an unbreakable and incredibly small entity, the atom.
The contemporary view of the world (as seen by the scientists - or by most of them) also relies on the idea that there are building blocks that make up everything that surround us, including ourselves. However, our notion of the world is a little more complex than what Democritus had originally envisaged. We now believe the atoms are themselves made out of other particles: the electrons, protons and neutrons. In fact, the neutrons and protons are also believed to be made out of even tinier particles, the quarks. But, for our purposes, we don't need to worry about them, since their properties can only be studied in very peculiar environments, such as inside large accelerators.
The electrons carry a negative charge and surround the atomic nucleus, formed by the neutrons and protons (with positive charge). To describe the atom, we can not simply use the familiar laws of classical physics. Instead, we rely on a new set of rules, called quantum physics. It tells us, for instance, that the atoms can not have an arbitrary energy. Instead, they have discrete energy levels, each one corresponding to a certain atomic configuration. The atoms can go to different energy levels by absorbing or emitting light.
In the year of 1905, Albert Einstein proposed the idea that light was also composed of basic blocks, the photons. He showed that each photon carried a certain amount of energy, proportional to its frequency. So, if the light had the correct frequency, it could be absorbed by an atom, such that the energy carried by the photon would be responsible to make it go to a higher energy level. By the same token, an excited atom (one that is in a high energy level) can loose energy by emitting a photon.
Albert Einstein was responsible for the concept of photons. Later, he did not accept quantum physics. In his view, the Universe had to be governed by more deterministic laws, such as the ones found in classical physics. In a famous statement, he said that he could not believe that God "played dice" with the universe, a reference to the probabilistic interpretation of quantum physics.
Well, you may now ask yourself: if light is really made out of particles (the photons) how can it show interference effects like water waves do? Well, it turns out that light is not only a particle, it is also a wave. This apparent contradiction is an example of how quantum physics can differ from the familiar case of classical physics of our daily life.
Manipulating Atoms with Photons
To understand how we control the atoms with light, you have to know one more thing about light: it can exert a force! Another way to say that is: light (or photons) carries momentum. When an atoms absorbs light, it will bounce back (it will gain momentum). Analogously, when it emits light, the photon carries away momentum, while the atoms recoils on the opposite direction.
With the advent of tunable lasers, it became possible to have a source of light with the proper frequencies and intensities to enable light manipulation of atoms. By correctly aligning and tuning laser beams, along with the help of magnetic fields, we can trap and cool neutral atoms. These techniques allow us to make atomic measurements with unprecedented precision, to study numerous quantum effects, some of them extremely puzzling, to cool the atoms to the lowest temperatures ever achieved. In fact, in the same way as it is possible to control light with the use of matter (we can reflect light from a mirror, or focus it with a lens), nowadays it is possible to control both the external and internal degrees of freedom of atoms by light. This field of research is called Atom Optics and is also one of the topics of investigation of the CAT group.
This work has been supported by The National Science Foundation (NSF), The Army Research Office (ARO) of the United States Army Research Laboratory (ARL), The Defense Advanced Research Projects Agency (DARPA) of The United States Department of Defense (DOD), and the NASA-JPL Physical Science Research Program Cold Atom Laboratory (CAL).