The concept of quantum simulations was proposed by physicist Richard Phillips Feynman in 1981, and quantum simulations become possible by manipulated ultracold atoms. In 1995, Bose-Einstein condensation was realized and degenerate fermi gas in 1999. The first BEC-BCS Crossover quantum simulation experiment was carried out in 2003 by using the Fermi Gas. In 1998, Austrian scientist Peter Zoller proposed that optical lattice could be used in quantum simulation.
Then in 2002, a German Research Group, Bloch, used three-dimensional optical lattice realized Bose-Hubbard simulation during the Superfluidity-Mott experiment. After that, the simulation of Fermi Hubbard model, Haldane model and KT phase transition was carried out by scientists. During the introduction of 2016 Nobel Prize Physics award, quantum simulations and optical lattices were mentioned, and three examples were used to illustrate the importance of ultracold atom simulations. There are many advantages by using the optical lattice in quantum simulation such as: changeable optical intensity, controllable parameters in quantum tunneling, system without impurities, accurate measurement on properties and so on. As optical lattice has the same Hamiltonian as condensed object, it is considered a powerful tool for simulating the novel quantum state (such as high temperature superconductor, topological insulating state, etc.). Therefore, the research has important scientific significance and potential application to carry out quantum simulation on ultracold atom optical lattice. The main contributions are included as follows.
1) Quantum simulation and Manipulation of ultracold atom in optical lattices.
As quantum topology and quantum magnetism are the frontier research fields for ultracold atom quantum simulation, we conduct the following research:
Study on topological superfluid in optical lattice. The topological superfluid state is considered to be our desire goal in the long term. In the experiment, the ultracold potassium atoms are loaded into the optical lattice and laser was applied to induce spin-orbit coupling. Using the Feshbach resonance s-wave spin pairing is realized and topological superfluid is obtained with measured non-Abel statistics.
Study on quantum magnetism in optical lattice. Quantum magnetism is based on spin exchange or super-exchange magnetism. By adjusting the tunneling between the lattice points of the spin-polarized atoms, the spin exchange or super-exchange is realized. By changing the J1/ J2 ratio of the tunneling, the quantum magnetic state and phase transition of the ferromagnetic state to the fringe state can be achieved.
Study on the high excited state in optical lattice. The phenomenon of the high excitation energy band of optical lattice is difficult to observe in condensed state physics. Therefore, we use the sequential control of laser pulses to manipulate the atoms into the excitation energy band, so that the phenomena of Bloch Oscillation, Senna tunneling and interference between bands can be observed.
Study on super-radiant scattering or Brag scattering in optical lattice. By controlling laser pulse width, incident angle and other parameters, the Bragg scattering and forward-backward ultra-radiation scattering of atoms in the Bose gas and optical lattice can be realized. Parameter of correlation, band energy in optical lattices can be detected with the super-radiant scattering or Brag scattering. In addition, the Superfluidity-Mott phase change can be observed.
2) Academic influence and value.
The space ultracold atomic experiment is a new opportunity base on four Nobel Physics Awards in 1997, 2001, 2005, 2012 in cold atom and precision spectroscopy. The classical phase transition is a universal property of nature, while the topological quantum phase transition and quantum magnetic phase transition has not yet been observed. Using two-dimensional optical field and ultra-cold atom in strongly correlated quantum system, it provides a new way to observe this new phase transition.
Its breakthrough will provide a new scheme for the design of high temperature superconducting materials. In addition, non-symmetry breaking phase change material is a very rare in nature today, the new design of optical lattice structures may likely to create such novel quantum substances to realize the dream of scientists. Extremely low temperature Fermi gas characteristics has always been a concerned to scientists, such as superconductivity, superfluidity and other phenomena. We use the magnetic levitation method to overcome the limitations of the Earth's gravity, which can obtain T=0.001TF's Fermi gas sample. This provides us a new way to understand the peculiar quantum phenomena.
Professor Chen Xuzong’s and Professor of Zhou Xiaoji’s research group from Department of Electronics, Peking University, has studied more than 10 years in the field of ultracold atom physics. They have accomplished a number of first places in China: China's first atom laser, China's first experimental ultracold atom papers published in the international Journals, China's first one-dimensional and three-dimensional optical lattice, China's first superfluid-Mott phase transition experiment. The group has published more than 50 articles in Nature Index journals in the last decade, and it is the research group in the China that has published the most papers in famous International Journal of ultracold atom physics experiment.
It has great significance to develop the ultracold atom quantum simulation in promoting scientific research and technological progress, strengthening national defense power and enhancing the prestige of the nation.
3) Industrial Transformation.
Prof. Chen Xuzong’s space ultra-cold atomic experimental team has achieved a series of breakthroughs in the basic research of quantum simulation and corresponding new technologies, including the ultra-cold atom vacuum system, ultra-high stability laser system, precision integrated optics system and related precision intelligent control system. Some of these technologies have been industrialized and used in the fields of atomic interferometer, precision measurement and accelerator experiment.