演讲人： 罗乐
时间： 2011-04-07 15:00-2011-04-07 16:45
地点：FIT 1-222
内容：

In Tsinghua-IIIS-CQI, we are targeting the cutting edge researches in quantum information based on atomic, molecular and optical physics. We are planning to implement several research projects that are able to win international reputation and train top postdoc and graduate students in several years. In Chinese words, that is a “Big Movement Fast Growing (da kan kuai shang)” strategy. At the technical level, we are extremely cautious to pick up our road map.  In this talk, I will present two research directions that have substantial potentials. These two directions are complementary: One is to use laser cooled and trapped neutral atoms for a top-down study of quantum physics; the other is to use trapped ions for a bottom-up study. Specifically I will use ultracold Fermionic atoms and ion-photon network as examples.

Ultracold Fermi atoms provide a paradigm system to explore intriguing many-body physics in a wide range of exotic systems, including high-temperature superconductors, neutron stars, the quark-gluon plasma, and black holes in string theory.  All those systems have universal thermodynamics and hydrodynamics governed by the nature of unitary strong interactions. In such sense, a table-top experiment with laser-cooled and trapped Fermionic atoms is an ideal ultracold quantum simulator for the condensed matter and nuclear physics. I will review my experimental work including all-optical method for producing degenerate and strongly interacting Fermi gases, probing the universal thermodynamics by implementing the first model-independent thermodynamic measurement, obtaining the thermometry of strongly interacting Fermi gases experimentally and thus determining the critical temperature of Fermi condensation, and the first study of the quantum viscosity behavior in the unitary regime. My focus is in search of a so-called perfect fluid that has exceedingly low shear viscosity and possible existed in strongly interacting systems. Unlike a superfluid, such perfect fluid is not in a single quantum state but a many-body quantum phenomenon which could connect to string theory. Our results from both thermodynamic and hydrodynamic measurements confirm that a strongly interacting Fermi gas enters into the perfect fluidity regime and is very close to the estimation data from the quark-gluon plasma.

Quantum networks based on trapped atomic ions and scattered photons provide a promising way to build a large scale quantum information processor. Such systems promise storing and processing information in a way that could eclipse the performance of conventional computers. Previous work has demonstrated generating entanglement and operating gates between two distant trapped ion qubits. Recently we also realize several quantum algorithms including the first quantum random number generator by using remote entangled ions. In particular, enhancing the collection of spontaneous emitted photons from trapped ions is likely to help scaling up atom–photon quantum networks in the next several years. By integrating a micro-fabricated ion trap with a cavity QED system in the intermediate coupling regime, we recently observe an enhancement of the spontaneous emission from a single trapped ytterbium ion into a cavity mode by a factor of hundreds comparing with the free-space emission. Such ion cavity systems provide a platform to realize a large scale atom-photon quantum network that could possibly close both locality and detection holes in a Bell test experiment. Furthermore, trapped charged particles inside an optical cavity open the door for the potential applications in other fields such as trapping mesoscopic material and biomolecule for optical study.

个人简介:

美国联合量子研究所 (Joint Quantum Institute, University of Maryland and the National Institute of Standards and Technology) JQI Postdoc Fellow and Research Scientist。 杜克大学物理学博士硕士, 北京大学光学硕士, 中山大学物理学学士。多年来在实验原子分子光物理领域有着活跃的学术研究，涉及冷原子物理，囚禁离子量子计算，原子光子量子网络，空腔电子电动力学，超快光学等多个前沿领域。

   费米原子凝聚是继冷原子实验技术和玻色爱因斯坦凝在1997年和2001年分别获得诺贝尔物理学奖之后冷原子物理领域又一里程碑。我在这一领域的贡献包括首次从实验上得到了强相互作用费米气体的温标并确定了费米凝聚的相变温度，实施了第一个不依赖理论模型的热力学测量从而在实验上验证了强相互作用量子体系中的普适热力学预言，首次在强相互作用的量子流体中观测到接近弦理论所预言的量子极限的流体性，以及在实验中首次观测到费米气体的自旋分离。囚禁离子是目前最有希望实现量子计算和量子网络的物理体系。我最近在这一领域的工作包括通过远距离间两个离子的纠缠实现第一个量子随机数产生器，提出可拓展的原子光子量子网络实验方案，结合囚禁离子阱与空腔电子电动力学技术实施增强的量子界面，以及在半导体芯片离子阱上实施量子逻辑门。获得的学术奖励，包括获得美国联合量子研究所第一个实验物理方向上的JQI Postdoc Fellowship, Fritz London 博士研究生奖，中国政府海外优秀自费留学生奖，王大珩光学奖学生奖。在重要期刊上发表过超过二十篇论文，其中多篇发表在Nature和Physics Review Letters，并以"费米气体热力学"和"原子光子量子网络"为主题发表过两个长篇综述。

   目前的学术兴趣包括两个方面，一方面以超冷量子气体为实验工具探索在多体和少体量子物理领域具有普适性的问题，实现凝聚态与核物理领域一些基础问题的冷原子量子模拟，并探索进行拓扑量子计算的可能性。另一方面以囚禁离子为工具，实现大规模的量子纠缠和量子逻辑，实现大空间尺度可拓展的原子光子量子网络，为最终实现量子信息处理奠定物理的基础。