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## Quantum Computing: A Great Science in the Making

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**Quantum Computing:A Great Science in the Making**Andrew Chi-Chih Yao Tsinghua University**Make the case:Quantum Computing is Great Science**What is quantum computing? Why many find it so exciting? 2**Paradigms for Great Science**1) X-Ray Crystallography • 1895, Roentgen, discovered X-rays • 1912, von Laue, confirmed X-ray diffraction Crystal X-ray**Paradigms for Great Science**• 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 • 1937-1954, Hodgkin, biological molecules • 1950s, Perutz & Kendrew, myoglobin structure • 1950s, Crick, Watson, Wilkins, Franklin, Double Helix • 1960 – present, many more molecules**Paradigms for Great Science**2) Computers • 1901, Hilbert, mechanization of proofs in math • 1936, Turing, invented Turing machine model • 1945, von Neumann, electronic computer design • 1940-50s, Shockley, Bardeen & Brattain, invented transistors • 1960 – present, developed enormous computing power & applied everywhere**Great science often happens when**A disruptive technology enables new explorations previously unimaginable Paradigms for Great Science 8**A disruptive computing technology:**-- Computes f(n) by: Grow a crystal C depending on f, n Shine a quantum wave on C Observe the diffraction pattern & figure out f(n) -- Software simulates Hardware exponentially more efficient The Case for Quantum Computing 10**black box**F Example : Simon’s Problem Simon’s Problem: x: 001011F(x): 100110 • 2 to 1 mapping: There exists a secrets such that F(x+s) = F(x) • Problem: Determine s • Note: classical algorithms must make exponentiallymany queries F(x) = ?**bright spots**dark spots light source x screen wall**z**light source amp= x screen wall y**z**x + s light source amp= x screen wall y**z**x + s light source amp= x screen wall y**Example : Simon’s Problem**• Light patternson the wall determiness • Quantum computing: --don’t need 2N holes on screen or 2NX 2N 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**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**Major Quantum Information Centers**• US NIST/U. Maryland– Joint Quantum Institute (JQI), with 29 professors including 1997Nobel 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: Sending single-photon pulses Distance limited by channel attention length! ~ 15km • Quantum repeater network: Increase communication distance**Motivation**Quantum network is needed for practical realization of both quantum communication and computation David Wineland For Quantum Computation: Expandable quantum computational network: To increase computational size and complexity**Ion Trap Quantum Register & Computation Node**rf dc dc rf 24**s (Dm=1)**p (Dm=0) pulsed excitation Quantization Axis V H | = ||V + ||H Experimental entanglement between 1 ion and 1 photon P3/2 S1/2 | | Blinov, Moehing, Duan, Monroe Nature 428, 153 (2004). 25**Entanglement of remote ions:**D. L. Moehring, P. Maunz, S. Olmschenk, K. C. Younge, D. N. Matsukevich, L.-M. Duan, and C. Monroe, Nature 449, 68 (2007). Entanglement fidelity: 87(2)% 26**Conclusions**27**Conclusions (1)**Great science often happens when: • Scientific theories interact; scientific disciplines interact • New technology becomes available Quantum computing is in this happy situation! 28**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