# Shih-I Chu

**Primary office**:

Room 1033

### Academic Degrees

- B.S., 1965, M.S., 1968, National Taiwan University
- D.Sc., 1971, National Tsing Hua University
- Ph.D., 1974, Harvard University
- Research Associate, JILA (Joint Institute for Laboratory Astrophysics), University of Colorado 1974-76

### Areas of Specialization

Theoretical and Computational Chemistry, Ultrafast Science and Quantum Control

### Research Interests

*Theoretical and Computational Quantum Chemistry, Atomic, Molecular, and Optical Physics*: Structure and dynamics of atomic and molecular systems in intense and ultrashort laser fields, time-dependent density functional theory, quantum chaos and fractals, scattering theory and reaction dynamics, many-body resonances, coherent control of quantum dynamics, SQUID quantum computing and information, attosecond science and technology.

The general research direction of Professor Chu's group is to develop new theoretical formalisms and accurate and efficient large-scale computational techniques for in-depth ab initio investigation of chemical, physical and astronomical problems of current significance in science and technology. Specific research problems now being undertaken fall into several areas:

#### 1) Atomic and Molecular Physics and Chemistry in Strong Fields.

Multiphoton and very-high-order (100th–300th order) nonlinear optical processes driven by intense laser fields. The study of high-order nonlinear optical response and dynamic behavior of atoms and molecules in the presence of intense laser fields is a subject of much current interest in science and technology. The recent advancement of intense ultrashort laser pulse technology has led to the discovery of a number of novel high-intensity phenomena which cannot be understood and treated by means of traditional perturbation theories. Professor Chu's group has undertaken a series of pioneering developments of generalized Floquet formalisms as well as new time-dependent computational methods for nonperturbative treatment of a broad range of strong field chemical and physical processes and phenomena. Among them are: multiphoton and above-threshold ionization of atoms, multiphoton and above-threshold dissociation of molecules, the nature of chemical bonds in intense laser fields (bond softening and hardening), very high-order harmonic generation, table-top x-ray laser generation, comb laser, coherent control of atomic and molecular motion, and the creation and control of attosecond (10^{–18} sec) laser technology.

#### 2) New Development of Time-Dependent (TD) Density functional Theory (*DFT)*.

The Kohn-Sham DFT has been widely used for the study of the ground-state properties of atoms, molecules, and condensed matter in the last decades. Due to the approximation of the energy functionals, the existence of the spurious self-interaction term, and the improper long-range potential, the conventional DFT does not provide an adequate description for the excited, resonance, and continuum states. Professor Chu and his group have recently initiated a series of new development of self-interaction-free DFT, including relativistic generalization, for overcoming some of these fundamental problems. The group is also developing new self-interaction-free TDDFT, allowing nonperturbative treatment of the multiphoton dynamics and strong-field phenomena of many-electron atomic and molecular systems for the first time. These new DFT/TDDFT developments open a host of potential new applications in the exploration of the electronic structure and quantum dynamics of complex atomic, molecular, cluster, quantum dot, and nano-material systems in the future.

#### 3) Quantum Computing and Information.

Recently increasing worldwide effort has been directed toward exploring submicron or even molecular level devices operating in the quantum regime. Quantum computer, if it is realized, for example, can perform tasks exponentially faster than any classical supercomputer, leading to revolution in science and technology. In quantum computing, information is manipulated not discretely, in the classical way, as a series of zeros and ones (bits), but as continuous superpositions (qubits) where the number of possibilities is vastly greater. Professor Chu's group is currently interacting with other experimental groups in the exploration of the feasibility of sold-state quantum computing. Of particular interest is the SQUID (Superconducting Quantum Interference Device), which can be designed and scaled up, much easier than other quantum computing systems (such as NMR and trapped ions). Of fundamental significance is to explore the nature and control of decoherence and the study of multiple-qubit entangled states and associated quantum logics in SQUID driven by microwaves.

#### 4) Classical and Quantum Chaos and Fractals.

The discovery of the universality of chaotic phenomena in a wide range of scientific and other disciplines is considered to be one of the major breakthroughs in the late twentieth century. The main interest of Professor Chu in this direction is to explore the quantum dynamics of microscopic systems whose classical correspondence is chaotic. Also of relevant interest is the exploration of "quantum" fractal behavior in microscopic and mesoscopic systems discovered at KU.

#### 5) Attosecond Science and Technology.

One of the most recent scientific breakthroughs is the realization of attosecond laser pulse technology. The attosecond pulse will allow the direct exploration of the electron wave packet dynamics in chemical and biologoical systems in the future, leading to revolutionary advancement beyond the well-established femtosecond technology. Professor Chu's group is currently exploring the highly nonlinear interaction of attosecond laser pulse with atomic and molecular systems and the methodology for the optimal control of the attosecond pulse generation.

### Selected publications

- Y. Yu, S. Han, X. Chu, S. I. Chu, and Z. Wang, Coherent temporal oscillations of macroscopic quantum states in a Josephson junction,
*Science***296**, 889–892 (2002). - S. I. Chu and D. A. Telnov, Beyond the Floquet theorem: generalized Floquet formalisms and quasienergy methods for atomic and molecular multiphoton processes in intense laser,
*Phys. Rep.***390**, 1-131 (2004). - Z. Y. Zhou, S. I. Chu, and S. Y. Han, Rapid optimization of working parameters of microwave-driven multilevel qubits for minimal gate leakage,
*Phys. Rev. Lett*.**95**, 120501 (2005). - S. I. Chu, Recent development of self-interaction-free time-dependent density functional theory for nonperturbative treatment of atomic and molecular multiphoton processes in intense laser fields,
*J. Chem. Phys.***123**, 062207 (2005). - J. J. Carrera, X. M. Tong, and S. I. Chu, Creation and control of single attosecond XUV pulse by few-cycle laser pulses,
*Phys. Rev. A***74**, 023404 (2006). - J. Heslar, J. J. Carrera, D. A. Telnov, and S. I. Chu, High-order harmonic generation of heteronuclear diatomic molecules in intense ultrashort laser fields: An all-electron TDDFT study,
*Int. J. Quantum Chem*.**107**, 3159–3168 (2007). - J. J. Carrera, S.-K. Son, and S. I. Chu, Ab initio theoretical investigation of the frequency comb structure and coherence in the vuv-xuv regimes via high-order harmonic generation,
*Phys. Rev. A***77**, 031401(R) (2008). - S.-K. Son, S. Han, and S. I. Chu, Floquet formulation for the investigation of multiphoton quantum interference in a superconducting qubit driven by a strong ac field, P
*hys. Rev. A***79**, 032301 (2009). - S.-K. Son and S. I. Chu, Multielectron effects on the orientation dependence and photoelectron angular distribution of multiphoton ionization of CO2 in strong laser fields,
*Phys. Rev. A***80**, 011403(R) (2009). - S.-K. Son, D. A. Telnov, and S. I. Chu, Probing the origin of elliptical high-order harmonic generation from aligned molecules in linearly polarized laser fields,
*Phys. Rev. A***82**, 043829 (2010). - T. S. Ho, H. Rabitz, and S. I. Chu, A general formulation of monotonically convergent algorithms in the control of quantum dynamics beyond the linear dipole interaction,
*Comput. Phys. Comm.***182**, 14 (2011).