1 Andrew Chi-Chih Yao Tsinghua University Quantum Computing: A Great Science in the Making

Make the case: Quantum Computing is Great Science What is quantum computing? Why many find it so exciting? 2

Paradigms for Great Science 3

1) X-Ray Crystallography  1895, Roentgen, discovered X-rays  1912, von Laue, confirmed X-ray diffraction 4 X-ray Crystal

5 1) X-Ray Crystallography  1913, W. Henry Bragg and W. Lawrence Bragg, derived math formula to determine crystal structures  1920s, structures of metals and inorganic molecules  , Hodgkin, biological molecules  1950s, Perutz & Kendrew, myoglobin structure  1950s, Crick, Watson, Wilkins, Franklin, Double Helix  1960 – present, many more molecules Paradigms for Great Science

Macro-Biological Molecules 6

7 2) Computers  1901, Hilbert, mechanization of proofs in math  1936, Turing, invented Turing machine model  1945, von Neumann, electronic computer design  s, Shockley, Bardeen & Brattain, invented transistors  1960 – present, developed enormous computing power & applied everywhere Paradigms for Great Science

8 Great science often happens when  A disruptive technology enables new explorations previously unimaginable Paradigms for Great Science

The Case for Quantum Computing 9

10 A disruptive computing technology: -- Computes f(n) by: 1. Grow a crystal C depending on f, n 2. Shine a quantum wave on C 3. Observe the diffraction pattern & figure out f(n) -- Software simulates Hardware exponentially more efficient The Case for Quantum Computing

11 Simon’s Problem: x: F(x):  2 to 1 mapping: There exists a secret s such that F(x+s) = F(x)  Problem: Determine s  Note: classical algorithms must make exponentially many queries F(x) = ? black box F Example : Simon’s Problem

12 light source x bright spots dark spots wallscreen

13 light source x wallscreen y z amp=

14 light source x wallscreen y z amp= x + s

15 light source x wallscreen y z amp= x + s

16  Light patterns on the wall determines s  Quantum computing: -- don’t need 2 N holes on screen or 2 N X 2 N dots on the wall -- can be implemented with N X 2N bits -- each bright spot location 1 bit of information on s Example : Simon’s Problem

17 An important result: Shor developed an efficient quantum algorithm for factoring large integers. His method uses an approach similar to Simon’s algorithm. N = p * q secret Example : Simon’s Problem

Sooner Than You Think 18

Major Quantum Information Centers  US NIST/U. Maryland – Joint Quantum Institute (JQI), with 29 professors including 1997 Nobel Laureate W.D. Phillips ， supported by NIST ， NSF ， DOD.  Harvard/MIT - Center for UltraCold Atoms (CUA) ， with 15 professors including 2001 Nobel Laureate W. Ketterle ， supported by NSF ， DOD.  Caltech/Microsoft Q-station ， with 17 professors including Fields Medalist M. Freedman ， supported by NSF, DOD, and Microsoft.  In Canada, Perimeter Institute/Waterloo - Institute for Quantum Computing (IQC) ， started with 100 million US dollars  In Singapore, National U of Singapore – Center for Quantum Technologies (CQT), 5 years 100 million US dollars  Centers in Europe, Japan, China,... 19

Quantum Network Project at Tsinghua  Internet is an indispensible part of modern society: Is a quantum network a remote goal? 20

Motivation  Quantum network is needed for practical realization of both quantum communication and computation  For Quantum Communication: 21  Quantum repeater network: Increase communication distance Distance limited by channel attention length! ~ 15km Sending single-photon pulses

Motivation Quantum network is needed for practical realization of both quantum communication and computation 22 For Quantum Computation: Expandable quantum computational network: To increase computational size and complexity David Wineland

Vision for Quantum Network/Computer 23

rf dc Ion Trap Quantum Register & Computation Node 24

| = ||V + ||H H V Quantization Axis  (m=0)   (m=1) Experimental entanglement between 1 ion and 1 photon S 1/2 P 3/2 pulsed excitation Blinov, Moehing, Duan, Monroe Nature 428, 153 (2004). |  |  25

D. L. Moehring, P. Maunz, S. Olmschenk, K. C. Younge, D. N. Matsukevich, L.-M. Duan, and C. Monroe, Nature 449, 68 (2007). Entanglement of remote ions: Entanglement fidelity: 87(2)% 26

Conclusions 27

28 Conclusions (1) Great science often happens when:  Scientific theories interact; scientific disciplines interact  New technology becomes available Quantum computing is in this happy situation!

Conclusions (2) What is Great Science?  It must have deep impact  Quantum Simulation can help design new materials, test physics theories  It must uplift the human spirit  Learns the language of the atomic worlds and asks the atoms to dance elegantly for computation 29

Thank You! 30