Assistant Professor of Physics,
Room 312, McCullough Bldg.
476 Lomita Mall
Stanford, CA 94305-4045
- In the past year I have started to develop a new approach to holographic duality, which I named "exact holographic mapping". The goal of this approach is to construct the dual gravity theory and understand quantum space-time geometry starting from the non-gravity side of the duality. This approach is based on two simple principles: 1) The definition of "points" in a quantum many-body system is determined by locality of the physics. 2) Quantum entanglement determines distance between points. This proposal is discussed in http://arxiv.org/abs/1309.6282. Here is a lecture I gave on this topic: http://pirsa.org/14030107/
- I wrote a Perspective "Symmetry Meets Topology" on Science, which is a simple introduction for the article "Symmetry-Protected Topological Orders in Interacting Bosonic Systems" by X. Chen, Z.-C. Gu, Z.-X. Liu, X.-G. Wen, Science 338, 1604 (2012).
- Invited talk at Perimeter Institute, Synthetic non-Abelian anyons and beyond.
- Invited talk on APS March meeting 2012:
Generic Wavefunction Description of Fractional Quantum Anomalous Hall States and Fractional Topological Insulators
- One direction I am recently very interested in is the holographic duality, also known as AdS/CFT correspondence. Here is a talk I gave on the KITP workshop last Nov. An attempt to understand the holographic duality through a functional formalism
- I gave a "blackboard lunch" talk at KITP on topological states of matter, with the title of "To See A Knot In A Grain Of Sand -- The Story Of Topological States"
- I am at KITP, UCSB this fall (Sep to Dec), co-organizing the workshop on topological insulators and superconductors.
- I recently organized a tutorial session on Topological insulators on the 2011 APS March meeting. The speakers are Joel Moore, M. Zahid Hasan, Marcel Franz, Yulin Chen and myself.
- Topological Nematic States and Non-Abelian Lattice Dislocations, Maissam Barkeshli and Xiao-Liang Qi , Phys. Rev. X 2, 031013 (2012)
- Topological insulators and superconductors, Xiao-Liang Qi and Shou-Cheng Zhang, Rev. Mod. Phys. 83, 1057–1110 (2011).
- General Relationship between the Entanglement Spectrum and the Edge State Spectrum of Topological Quantum States, Xiao-Liang Qi, Hosho Katsura and Andreas W. W. Ludwig, Phys. Rev. Lett. 108, 196402 (2012).
- Generic Wavefunction Description of Fractional Quantum Anomalous Hall States and Fractional Topological Insulators, Xiao-Liang Qi, Phys. Rev. Lett. 107, 126803 (2011).
- Entanglement Entropy and Entanglement Spectrum of the Kitaev Model, Hong Yao and Xiao-Liang Qi, Phys. Rev. Lett. 105, 080501 (2010)
- The quantum spin Hall effect and topological insulators Xiao-Liang Qi and Shou-Cheng Zhang Physics Today 63, 33-38 (2010)
- Inducing a Magnetic Monopole with Topological Surface States, Xiao-Liang Qi, Rundong Li, Jiadong Zang and Shou-Cheng Zhang Science 323, 1184 (2009)
- Topological Insulators in Bi2Se3, Bi2Te3 and Sb2Te3 with single Dirac cone on the surface Haijun Zhang, Chao-Xing Liu, Xiao-Liang Qi, Xi Dai, Zhong Fang, Shou-Cheng Zhang Nature Physics 5, 438 (2009)
- Topological Field Theory of Time-Reversal Invariant Insulators, Xiao-Liang Qi, Taylor L. Hughes, and Shou-Cheng Zhang Phys. Rev. B 78, 195424 (2008)
- Fractional charge and quantized current in the quantum spin Hall state, Xiao-Liang Qi, Taylor L. Hughes, Shou-Cheng Zhang Nat. Phys. 4, 273 - 276 (2008)
- Spin-Charge Separation in the Quantum Spin Hall State, Xiao-Liang Qi and Shou-Cheng Zhang Phys. Rev. Lett. 101, 086802 (2008)
- 1999-2003, Bachelor, Tsinghua University
- 2003-2007, Ph.D., Institute for Advanced Study, Tsinghua University
- 2007-2009, Research Associate, SLAC, Stanford University
- 2009-2010, Postdoctoral researcher, Microsoft Station Q, UCSB
- 2009-present, Assistant Professor of Physics, Stanford University
At this moment I
am mainly interested in three related fields in condensed matter physics---topological phenomena, quantum entanglement and holographic duality.
Topological phenomena are the phenomena which are
determined by some topological structure in the physical system, which are thus
usually universal and robust against perturbations. For example, two famous topological
phenomena are the flux quantization in superconductors and Hall conductance
quantization in the Quantum Hall states. Recent discovery of topological
insulators and topological superconductors in different symmetry classes bring
the opportunity to study a large family of new topological phenomena. For
example the three-dimensional topological insulator provides a condensed matter
realization of the important theoretical concepts in high energy physics such
as ”\theta-vacuum” and “axion”. The interplay of topological insulators and
superconductors with conventional phases of matter such as ferromagnets and
superconductors lead to richer topological phenomena. For an intuitive
introduction to topological insulators, see Qi and Zhang, Physics Today Jan 2010.
Quantum entanglement is the unique feature of
quantum mechanics, which is essential for quantum information and quantum
computation. The understanding of quantum entanglement provides a new probe to
the physical properties of the many-body systems compared to the conventional
response properties such as conductivity, spin susceptibility, etc. On the
other hand, more systematical understanding of quantum entanglement in
many-body systems may also lead to breakthrough in building a quantum computer.
It is far more difficult to study entanglement properties in many-body systems
compared to few-body systems. There are a lot of open questions for which the
answer is not known or only known for specific systems. For example, what is
the general relation between entanglement properties and other physical
observables in a given system? What is the relation between quantum
entanglement and topological states of matter? Besides the known description of
entanglement such as von Neumann entropy, what other measure can be defined to
provide more refined characterization of entanglement? I am pursuing these
directions. For a recent work I did along this line, click here.
Holographic duality uncovers an intrinsic relationship
dimensional gravitational theories and
dimensional non-gravitational theories such as
CFT’s. This duality is often referred to as AdS/CFT correspondence when
the d-dimensional non-gravitational theory is a conformal field theory
(CFT). Each field
in the bulk gravity theory corresponds to a
in the boundary theory, in the sense that all correlation
functions in the large N limit are determined by the
classical action of the bulk theory as a functional of the boundary conditions. The extra dimension in the (d +
1) dimensional gravity theory can be interpreted as corresponding to energy
scale in the CFT. In a suitable coordinate choice, the scaling dimension of an
is determined by the mass of the corresponding
bulk field. I am interested in understanding holography starting from the boundary quantum field theory (a condensed matter system) rather than the string theory. I am interested in developing a new framework called
“functional holographic duality” which takes a generic boundary theory as the
starting point and exactly constructs the dual bulk theory. I gave a talk at KITP about this subject.