Tsinghua-NTU Joint Workshop on Quantum Materials

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1 Department of Physics Institute of Advanced Studies Tsinghua-NTU Joint Workshop on Quantum Materials September 19-20, 2016 Beijing, China

2 Tsinghua-NTU Joint Workshop on Quantum Materials Contact Information Mr. Tao Wang( 王涛 ), Prof. Guilu Long( 龙桂鲁 Useful Information For your convenience, here are Some Important Tips: 1. Department of Physics Address: Science Building, Tsinghua University, Haidian District, Beijing , China. 北京市海淀区清华大学 - 理科楼内 2. Workshop Venue: C rd Floor ( 三楼会议室 ) 3. Lunch & Dinner Venue: JIN CHUN YUAN Restaurant( 近春园餐厅 ) 4. Shuttle Bus Pick-up arrangement (page 2) 5. Liaoning International Hotel Address ( 锦江集团北京辽宁大厦 ) No.2 West Road of the North 4th Ring Road, Haidian District, Beijing P.R.China 北京海淀区北四环西路甲二号邮编 : , 保福寺桥东南角 6. Recommended Route From International Airport to Liaoning International Hotel (page 3) 7. Free Wi-Fi: DIVI, DIVI-2 (no password) 1

Shuttle Bus Pick-up arrangement (Useful Information 4) We have prepared Daily Shuttle Buses from Liaoning International Hotel to Physics Department, Tsinghua University everyday.

3 Shuttle Bus Pick-up arrangement (Useful Information 4) We have prepared Daily Shuttle Buses from Liaoning International Hotel to Physics Department, Tsinghua University everyday. Please put the Nametag on when getting on the bus. The bus will set out exactly at the leaving time, please don t be late. Shuttle Bus time-table September 19 September 20 07:45 Pickup from Liaoning International Hotel 08:00 Pickup from Liaoning International Hotel 19:30 Pickup to Liaoning International Hotel 19:30 Pickup to Liaoning International Hotel Map of Hotel 2

Recommended Route to Hotel (Useful Information 6) Taxi: From Capital International Airport( 首都国际机场 ) to Liaoning International Hotel ( 辽宁大厦 ): The cost is about 100 RMB (45min) Airport Shuttle Bus:

4 Recommended Route to Hotel (Useful Information 6) Taxi: From Capital International Airport( 首都国际机场 ) to Liaoning International Hotel ( 辽宁大厦 ): The cost is about 100 RMB (45min) Airport Shuttle Bus: Take the Airport Shuttle Bus-ZHONG GUAN CUN Line ( 机场大巴 - 中关村专线 ), get off at the final station West BAO FU SI Bridge. Then walk about 800m to the Liaoning International Hotel The cost is about 24 RMB per person (1h40min) 3

5 Program 19 September Registration Chairman: Guilu Long Welcome address by Xi Chen, Chair, Department of Physics, Tsinghua Welcome address by Kok Khoo Phua, Director, IAS NTU Rainer Dumke (NTU) Qikun Xue Superconducting Atom Chips Is the high temperature superconductivity an interface problem? Coffee Break Chairman: Rainer Dumke (NTU) Pinaki Sengupta (NTU) Hui Zhai Leong Chuan Kwek (NTU) Strange correlations as a probe for Symmetry Protected Topological phases Universal Efimovian Expansion of Scale Invariant Quantum Matters Quantum simulators with hollow fibers Lunch Chairman: Li You Shuyun Zhou Jun Ni Experimental realization of type-ii Weyl semimetal in MoTe2 from electron and vibrational spectroscopies Electronic structure and superconductivity in 2D B based system 4

6 15.30 Tomasz Paterek (NTU) To be advised Coffee Break Chairman: Jun Ni Li You Qihua Xiong (NTU) Hong Yao Squeezed atomic state beyond the standard limit Fluorescence and Resolved-sideband Raman Cooling of Semiconductors Emergent edge supersymmetry in 2D topological superconductors: a sign-problem-free Majorana quantum Monte Carlo study Short Discussion End of Session Dinner 5

7 20 September 2016 Chairman: Shau-Yu Lan (NTU) Guilu Long Ke He Duality quantum algorithms for efficient simulation of quantum systems Recent experimental progresses on the quantum anomalous Hall effect Group Photo & Coffee Break Chairman: Ke He Shau-Yu Lan (NTU) Yayu Wang Bei Zeng A velocity sensor and large Fizeau s light dragging effect based on the collective state of atoms Electronic structure of lightly doped cuprated studied by STM Geometry of reduced density matrices Lunch Chairman: Leong Chuan Kwek (NTU) Yong Xu Weibo Gao (NTU) Topological quantum states: from electrons to phonons Coherent spectroscopy of a strongly driven silicon vacancy in diamond Coffee Break Lab Tour End of Session Dinner 6

8 Tsinghua-NTU Joint Workshop on Quantum Materials Abstract 7

9 Superconducting Atom Chips Rainer Helmut Dumke In recent years, microtraps for neutral atoms based on superconductors, i.e. superconducting atom chips have become a subject of intensive research. Motivated by the prediction of extremely low magnetic and thermal noise compared to normal conductors, superconducting atom chips have first been implemented in the expectation of improving the coherence of atomic quantum states close to surfaces by several orders of magnitude. This boost in coherence time holds promising expectations for quantum information processing applications. In particular, superconducting atom chips are ideal candidates for the realization of hybrid quantum systems between atomic and superconducting solid state qubits, merging the fast gate operation times for superconducting qubits with the long coherence times of atomic qubits. In this talk I will discuss our work towards realizing this hybrid quantum system via coupling ultra cold atoms and superconducting circuits. 8

10 Strange correlations as a probe for Symmetry Protected Topological phases Pinaki Sengupta Recently, a strange correlator has been proposed as a direct probe for the topological character of interacting Symmetry Protected Topological (SPT) phases. Using projective quantum Monte Carlo, we are able to directly access the strange correlator in a variety of phases, as well as to examine its critical behavior at the quantum phase transition between trivial and non-trivial symmetry protected topological phases. After finding the expected long-range behavior in these two symmetry conserving phases, we go on to verify the topological nature of two-leg and three-leg spin-1 Heisenberg antiferromagnetic ladders. This demonstrates the power of the strange correlator in distinguishing between trivial and non-trivial symmetry protected topological phases. 9

11 Quantum simulators with hollow fibers Leong Chuan Kwek To circumvent the limitations of conventional computers in tackling complex physical pro-cesses, Richard Feynman proposed nearly thirty years ago a means of using well-understood quantum systems called quantum simulators (or quantum emulators) to emulate similar, but otherwise poorly understood, quantum systems. Among the various physical systems that could be used to build a quantum simulator, one possibility is the use of regular arrays of atoms or ions that are held in place by laser fields. In this talk, we describe how a quantum simulator is also possible through photons propagating through a nonlinear optical waveguide and interacting with cold atomic ensemble placed inside the fiber. 10

12 Fluorescence and Resolved-sideband Raman Cooling of Semiconductors Qihua Xiong Optical irradiation accompanied by spontaneous anti-stokes emission can lead to cooling of matter, a phenomenon known as laser cooling or optical refrigeration proposed in 1929 by Peter Pringsheim. In solid state materials, the cooling is achieved by annihilation of lattice vibrations (i.e., phonons). Since the first experimental demonstration in rare-earth doped glasses, considerable progress has been made particularly in ytterbium-doped glasses or crystals with a recent record of ~110 K cooling from ambient, surpassing the thermoelectric Peltier cooler. On the other hand, attempts of laser cooling of semiconductors based on III-V quantum wells have led to very minimum progress. In this talk, I will present the background of laser cooling of solids, and our recent breakthrough of 40 Kelvin laser cooling of semiconductors in II-VI semiconductors in nanoribbon morphology. The laser cooling is achieved by longitudinal optical phonon assisted photoluminescence upconversion. Recent results on semiconductor bulk crystals and organic-inorganic perovskite thin films for laser cooling towards the next generation optical refrigeration applications will also be discussed, which exhibit great promises in the field of cryogenics with the advantage of compactness, vibration- and cryogen-free, high reliability and direct integrability into nanoscale electronic and photonic devices. Finally, we will introduce our latest results on resolved-sideband Raman cooling of optical phonons in II-VI semiconductors. 11

13 A velocity sensor and large Fizeau s light dragging effect based on the collective state of atoms Shau-Yu Lan Atoms based velocimeter typically relies on measuring the first order Doppler shift of individual atoms. To detect the center-of-mass motion of an atomic cloud, one usually needs to map out the velocity distribution of the cloud. Here, I will describe the light dragging effect in a moving electromagnetically induced transparent (EIT) medium and use it to sense the center-of-mass motion of an atomic cloud directly. The light dragging effect or the deviation from the speed of light c in a moving medium was first observed by Fizeau in a flowing water experiment for the study of ether in the pre Einstein s special theory of relativity era. It was later explained by the Lorentz velocity addition to the first order. The phase shift of light through a moving medium is proportional to the duration travelling in the medium. We enhance the dragging effect in a cold atomic medium under EIT condition and demonstrate a velocity sensor at a sensitivity two orders of magnitude smaller than the velocity width of the atomic medium used. This new type of sensor depends on the collective motion of the atomic cloud and only single shot measurement, and could lead to a new design of motional sensor beyond the limitation of Doppler broadening of atoms. 12

14 Coherent spectroscopy of a strongly driven silicon vacancy in diamond Weibo Gao The ability to prepare, optically read out and coherently control single quantum states is a key requirement for quantum information processing. Optically active solid state qubits have emerged as promising candidates with their prospects for spin-photon interface and chip-level integration. To realize true quantum register, a system must be coherently driven and exhibit Rabi oscillations. Under strongly driving resonant laser field, such quantum emitter can exhibit quantum behavior such as Autler-Townes splitting and Mollow triplet spectrum. Here we demonstrate coherent manipulation of a strongly driven optical transition in silicon vacancy (SiV) center in diamond. Rapid optical detection of photons enabled the observation of time resolved coherent Rabi oscillations and the Mollow triplet from an optical transition of a single SiV defect. Detection with a probing transition further confirmed Autler-Townes splitting generated by strong laser field. Coherence time of the emitted photons is shown to be comparable to its lifetime and more importantly, robust even under very strong driving laser field. These results indicate the feasibility of the SiV as a promising solid state qubit for quantum information processing, including quantum networks and quantum logic gates. 13

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