ABOUT OUR PROJECT

Masahito Ueda
Rseearch Director

1. INTRODUCTION

The Macroscopic Quantum Control Project was launched in September 2005 as an Exploratory Research for Advanced Technology (ERATO) project funded by Japan Science and Technology Agency (JST). The goal of this project is to achieve quantum control over interatomic/ intermolecular interactions, atom-photon interactions and uncertainty relations. The methods employed in achieving this goal are to cool millions of atoms/molecules close to absolute zero and suspend them in an ultrahigh vacuum by applying shape-controllable electromagnetic potentials. We then aim to develop techniques for continuously controlling the material parameters (e.g., the atomic density, temperature, and the strength of the interaction), atomic quantum states, and external environmental parameters. We intend to systematically explore new phenomena in macroscopic quantum systems by developing these techniques

2. RESEARCH BACKGROND

The 2001 Nobel Prize in Physics was awarded to the researchers who had achieved Bose-Einstein condensation (BEC) in dilute gases of alkali atoms. The Nobel Prize Citation states, gcfor early fundamental studies of the properties of the condensatesh, indicating the high expectations that BEC study will continue to attain Nobel Prize-class achievements in the future. Indeed, to date, BEC has been achieved in more than 10 atomic species by over 40 research groups around the world. In 2004, superfluid phases of neutral atomic fermions were realized in the quantum gases of 40K and 6Li, these being the first cases of achieving neutral fermion superfluidity, except in 3He. The superfluid transition temperatures observed in these experiments were as high as 0.15 of the Fermi temperature (TF), which exceeded the 0.04 upper limit of the superconductivity transition temperature.

Meanwhile, research on applying laser-cooled atoms in the field of quantum information has been rapidly developing. Atoms trapped in the periodic potential of standing light waves are an ideal testing ground for quantum information theory since the decoherence induced by spontaneous emission can be substantially suppressed. The basic operation of quantum gates has been demonstrated by using these laser-cooled atoms.

Ultracold atoms represent the ultimate artificial quantum matter that enables us to continuously change almost every material parameter and external environmental parameter that determine system properties. These parameters include the temperature, atomic density, shape and/or dimensions of the trapping potential, and most importantly, the strength and sign of interatomic interactions.

Researchers in the field of ultracold atomic gases have come from different academic backgrounds: atomic physics, condensed matter physics, quantum optics, and quantum information. Active exchanges of ideas and techniques among these researchers have lead to significant research results such as observation of the BCS-BEC crossover and the invention of atom chips that can process quantum information by using cold atoms loaded on the surface of a microfabricated semiconductor substrate.

On the theoretical side, predicted new phenomena have been followed one after the other. These phenomena include new quantum condensate phases such as the cyclic phase, the fractional quantum Hall states in a rapidly rotating BEC, the dynamics of various symmetry breakings, and exotic quantum phases in spinor-dipolar systems, which are all compelling and thought-provoking topics for experimental physicists.

Accordingly, intensive research and development projects have been undertaken to achieve research goals that have needed considerable technical hurdles to be overcome. Our project team comprises of researchers from different academic backgrounds whose very diversity will be a key to achieve our goals, since sharing ideas and techniques, and collaborating on them will help us to reach new findings. We are aiming to achieve our goal of systematically exploring new research areas of macroscopic quantum systems by approaching the fields of physics, material science, and quantum information from a totally new research perspective: enabling continuous and independent control of the parameters that define systems.

3. CONCEPT

We are exploring a new area of research that involves quantum systems having a large number of degrees of freedom. In order to establish ultimate control over the material parameters of ultracold atoms and molecules, we need to overcome each material-specific parameter dependency by developing the technique for controlling the quantum states of matter and light as precisely as possible.

Our project has three particular research objectives: 1) establishing ultimate control over interatomic interactions, intermolecular interactions, atom-molecular interactions, and atom-photon interactions; 2) precisely controlling uncertainty relations in the translational/internal states of atoms and their measurement processes; and 3) applying the resulting techniques to strongly correlated ultracold atomic systems.

This research project will have a direct impact on material science and computational physics in terms of systematically controlling material parameters. Meanwhile, with respect to the ultimate control of quantum states and uncertainty relations, the result of the study will be applicable to such precise measurement as examining quantum information processing and testing the standard model of elementary particle physics.

The greatest challenge in the theory of high-temperature superconductivity is to elucidate its mechanism. What makes this so challenging is that, in order to examine the mechanism, it is desirable to systematically change the strength of interactions, spins, filling fraction of carriers, dimensions, and so forth. Although achieving these is considered to be a formidable task in the field of material science, our system can handle this just by tuning the strength of the laser light and magnetic field; we can even control each of these parameters with precise timing so that the ensuing nonequilibrium relaxation can be a target for research. Loading a cold Fermi gas into an optical lattice where we can continuously tune the parameters can result in the creation of a superfluid; studying this will offer new insight into the central issues of strongly correlated systems.

It is also expected that atomic/molecular laser research will result in innovations in science and technology that could contribute to the advancement of, for example, atomic-scale lithography of solid surfaces and isotope-dependent chemical reactions at ultracold temperatures.

In respect of research in the field of quantum information, we are now facing the challenge of extending the technology to build multiple-qubit systems. The manipulation techniques, which will have been developed in the research into interatomic interactions and uncertainty relations, will play a significant role in this endeavor.

Extremely precise measurement techniques using cold atoms will complement the experimental research into elementary particles. Again, precise control over quantum states and interactions is expected to play an essential role.

The project comprises four research groups with the following objectives and research foci:

1) Ultracold Molecules Group: cooling polar molecules down to a temperature of 1 millikelvin or lower and controlling the strength and sign of the intermolecular interactions can result in the creation of macroscopic artificial quantum matter with anisotropic, long-range interactions. The major objectives of this group are to create this quantum matter, and to explore new phenomena that will appear in it.

2) Quantum Information Group: this group aims to establish precise control over quantum uncertainty relations. In particular, by controlling the backreaction of quantum measurements, the group intends to project the post-measurement quantum states of atoms to the desired states, as well as to restore the quantum state that was disturbed through interactions with the external environment

3) Strongly Correlated Quantum Gases Group: Experiments in the field of solid state physics have identified several phenomena whose natures have not yet been fully elucidated due to an inability to assess the degree of influence that each of the following factors may have had on the observed phenomena: the strength of interactions, carrier density, effect/presence of impurities, and dimensional effects. The particular aim of this group is to explore the dynamics of the formation of long-range order. The use of artificial quantum matter involving ultracold atoms in optical lattices will play a key role.

4) Theory Group: this group will support to the three experimental groups by providing insight and obtaining feedback.

4. CONCLUDING REMARKS

Ultracold atomic gases, which can only exist at a temperature close to absolute zero, enable us to precisely control not only the temperature and number of atoms, but also the strength of the interatomic interactions. Moreover, these interactions could be tuned to be either attractive or repulsive. Ultracold atomic gases can therefore lose their individuality, which allows us to study a new state of matter.

Macroscopic quantum matter has a large number of degrees of freedom which makes it extremely difficult to probe new phenomena based only on first-principle calculations; experimental support is indispensable. However, such experiments often involve complex interlinking factors, which could require huge investment to systematically and experimentally explore what is essential to reproduce the phenomenon of interest.

We have nevertheless set an ambitious goal to methodically investigate hitherto unexplored combinations of parameters through comprehensive collaboration among the three experimental groups and the theory group. The support and understanding of those interested in this project is greatly appreciated.

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