Two recent developments have revolutionized atomic physics: The observation of Bose-Einstein condensation (BEC), and a series of theoretical and experimental advances in quantum information. Atomic quantum fluids and quantum information theory are now among the most active and exciting areas of physics. Their common denominator is many-body quantum mechanics. Strongly correlated quantum systems realize some of the most fundamental states of matter, which are important for understanding phenomena in cosmology, condensed matter, nuclear and many other areas of physics. Ultracold atoms have become a test bed to tackle old and unresolved, and conceptually new questions in quantum systems of interacting particles.
The Center for Ultracold Atoms is building on the technical capabilities developed in its first phase and the advent of five new faculty members to focus on these areas. The deep questions that motivate this quest are the nature of high-temperature superconductivity, unresolved basic problems in quantum magnetism (e.g. antiferromagnetic frustration, spin liquids), and the desire to develop a deeper understanding and experimental control of entanglement. The quest is an exploration and control of the quantum world, uncovering and using unknown parts of the vast Hilbert space of possible wave functions. The ultimate pay-off could be the discovery of materials with novel properties, insight into how to increase the transition temperature of superconductors, and major advances towards the realization of quantum information systems.
To pursue this vision the Center is organizing its research program around two themes, strongly correlated states of ultracold atoms and quantum state control of atoms and photons. The first theme is centered on many-body physics and strongly overlaps with condensed matter physics. The second involves the interactions of a few or several atoms and photons, their entanglement and quantum state manipulation. These topics will be pursued by a team of eight Senior Investigators. Five of these are new to CUA, and their interests are a major driving force for the new research program. They have joined the vibrant CUA community that consists of approximately 65 graduate students, 15 undergraduates, and 15 postdocs. All the research will be performed on campus in CUA facilities, and will be fully integrated with the teaching and education programs at MIT and Harvard, through research opportunities for undergraduates, lab tours, and by being used in lectures as illustrations for basic concepts in physics. The Center reaches out to the community through the organization of a summer school, sponsorship of workshops, an annual program to recruit new science teachers, the creation of a virtual journal for ultracold atoms, a weekly seminar, and a visitor's program.
Funding for the CUA is provided by the Division of Physics through the Physics Frontiers Centers program and the Division of Materials Research through the Condensed Matter Physics program.
Massachusetts Institute of Technology Modern physics provides us with unprecedented insight into new materials, and gives us opportunities for further developments. Very often, the particles which determine the behavior of materials are the electrons. Materials with weakly interacting electrons, like metals and semiconductors, are well understood. A major challenge is posed by systems of strongly interacting and strongly correlated systems. They are much more difficult to describe, yet they offer the highest potential rewards since they may give rise to completely new phenomena and devices of superior performance. Advances on this frontier benefit from well-controlled and well-defined systems. In the Center for Ultracold Atoms, the "toolbox" for assembling such materials consists of ultracold atoms. Ensembles of atoms can be controlled and manipulated with the precision of atomic physics, and can be cooled to the lowest temperatures ever achieved, to the nanokelvin range, a billion times colder than interstellar space. The Center for Ultracold Atoms advances our understanding of quantum mattter by pursuing two themes: (1) Many-body systems and strongly correlated states, and (2) Quantum coherent control of few-body systems. Within the first theme, large clouds of ultracold atoms are exposed to various laser, radiofrequency and magnetic fields to realize systems with interesting properties for study, including conductors, superfluids, and quantum magnets. The second theme focuses on a small number of atoms and/or photons, which are prepared in novel quantum states. Of particular interest are entangled states due to their importance as building blocks in future quantum computers. One highlight of the funding period was the realization of a new quantum microscope. Using a specially designed microscope lens, it is now possible to observe individual atoms in a cloud of ultracold atoms. The new level of microscopic observation provides a powerful tool for studying ultracold atoms similar to what the tunneling microscope provided in the area of condensed matter physics. It allows connecting microscopic properties to macroscopic properties of the whole system. A second highlight has been the study of superfluidity with population imbalance. Superfluidity of fermionic particles requires that two kinds of particles form pairs. What happens when we have more particles of one kind than of the other kind? With ultracold atoms we could study in detail how this imbalance eventually suppressed superfluidity Those detailed studies of how superfluids work advances our understanding and quantitative description and may lead to improved superconducting materials in the future. A third highlight demonstrates the use of special quantum states for more precise measurements. Assume you want to measure the thickness of identical coins, and you can take measurements on N coins or perform N measurements on one coin. By averaging over N measurements, the precision of your result increases with the square root of N. However, there is a cleverer scheme. Stack up all the coins, and measure the height of the stack. In this case, the result is more precise - the precision increases proportionally to N. Frequency measurements of atoms are at the heart of the most precise atomic clocks and frequency standards. Using special quantum mechanical states (so-called squeezed states), we have been able to "stack up" atoms and perform a more precise frequency measurement on them. Such methods have the potential to improve the precision of atomic clocks, which are used for navigation (i.e., for the Global Positioning System) and communication. Finally, we extended our research from atoms to an atom-like system. CUA researchers showed that certain defects in diamond crystals can capture an electron and have properties similar to isolated atoms. These "artificial" atoms have the appeal that Nature prepares them for our use and localizes them without the technical effort of holding atoms in an atom trap in an ultrahigh vacuum chamber. Our key motivation for pursuing this new approach is to extend the atomic physics techniques to completely new parameter regimes not accessible with "real" atoms. At the same time, we will use these systems to explore new scientific directions and potential applications, such as very small sensors for magnetic fields in biological systems. The intellectual merit of this work is the quest to discover how natural and artificial materials work, to understand complex quantum systems, and to explore the basic physics and potential applications of engineered quantum systems. Research in the CUA lays the foundation for the development of new materials and sensors. As well as being a research center, the CUA focuses on education and outreach. A major impact of the CUA is through its education of graduate students and postdocs. A large number of young CUA researchers have advanced to leadership positions in academia and industry. Examples of successful outreach activities include our TOPS program for future high school teachers and the intensive summer course in atomic physics (open to students and other researchers worldwide).
