Quantum Information Science

1. Putting Weirdness to Work: ??? Quantum Information Science John Preskill 30 Oct 2009

3. Caltech’s Information Science and Technology Initiative Murray Bruck “Within the next 10-20 years, information will be a unifying, core intellectual theme spanning physical sciences, biological sciences, social sciences, and engineering. IST will fundamentally transform the research and educational environment at Caltech and other universities around the world.” IST Planning Committee, 2002

4. Annenberg Center for Information Science and Technology Murray Bruck Gorilla Schröder

5. Caltech and Information Science Feynman Mead Nanotechnology: there’s plenty of room at the bottom. VLSI: New paradigm for the semiconductor industry. CNS: How does the brain compute? Hopfield

6. Feynman Mead Caltech and Information Science As we run out of “room at the bottom,” the world needs visionary ideas about how physical systems can store and process information. Providing those ideas, and training the people who will put them into practice, is part of the mission of IST. Hopfield

9. Turing Planck Shannon Quantum Information Science Quantum physics, information theory, and computer science are among the crowning intellectual achievements of the 20th century. Quantum information science is an emerging synthesis of these themes, which is providing important insights into fundamental issues at the interface of computation and physical science, and may guide the way to revolutionary technological advances.

10. Information is encoded in the state of a physical system.

11. Information is encoded in the state of a quantum system.

12. Put to work!

13. Quantum Entanglement classically correlated socks quantumly correlated photons • There is just one way to look at a classical bit (like the color of my sock), but there are complementary ways to observe a quantum bit (like the polarization of a single photon). Thus correlations among qubits are richer and much more interesting than correlations among classical bits. • A quantum system with two parts is entangled when its joint state is more definite and less random than the state of each part by itself. Looking at the parts one at a time, you can learn everything about a pair of socks, but not about a pair of qubits!

14. The quantum correlations of many entangled qubits cannot be easily described in terms of ordinary classical information. To give a complete classical description of one typical state of just a few hundred qubits would require more bits than the number of atoms in the visible universe! It will never be possible, even in principle to write down such a description.

15. We can’t even hope to describe the state of a few hundred qubits in terms of classical bits. As Feynman first suggested in 1981, a computer that operates on qubits rather than bits (a quantum computer) can perform tasks that are beyond the capability of any conceivable digital computer!

16. Finding Prime Factors 1807082088687 4048059516561 6440590556627 8102516769401 3491701270214 5005666254024 4048387341127 5908123033717 8188796656318 2013214880557 = ? ´ ? An example of a problem that is hard for today’s supercomputers: finding the factors of a large composite number. Factoring e.g. 500 digit numbers will be intractable for classical computers even far into the future.

17. 1807082088687 4048059516561 6440590556627 8102516769401 3491701270214 5005666254024 4048387341127 5908123033717 8188796656318 2013214880557 4553449864673 5972188403686 8972744088643 5630126320506 9600999044599 3968599945959 7454290161126 1628837860675 7644911281006 4832555157243 = ´ Finding Prime Factors But for a quantum computer, factoring is not much harder than multiplication! The boundary between the problems that are “hard” and the problems that are “easy” is different in a quantum world than a classical world. Shor

18. Alexei Kitaev Physics and Computer Science Gil Refael Physics Leonard Schulman Computer Science CENTER FOR THE PHYSICS OF INFORMATION John Preskill Physics Jeff Kimble Physics

19. Thanks!

20. IQI geography Annenberg (IST) Steele Jorgensen Lauritsen Sloan Annex

21. Annenberg Center for Information Science and Technology Murray Bruck Gorilla Schröder

22. Former IQI Postdocs now in faculty positions elsewhere Duan Vidal Hayden Shi Hallgren Terhal Bacon Nayak Doherty Geremia Raussendorf Bose Leung Bravyi Verstraete Wocjan Poulin Childs Ardonne Zhang Reichardt

23. Former IQI Postdocs now in faculty positions elsewhere McGill Penn State Waterloo Michigan Queensland UNM Michigan U. Wash. IBM Queensland UBC London Waterloo IBM Waterloo Vienna U. Central Fla Nordita Hong Kong Sherbrooke Waterloo

24. Quantum Information Challenges Cryptography Quantum Computer Privacy from physical principles Error correction Hardware Reliable quantum computers Toward scalable devices Algorithms What can quantum computers do? Noise And …what are the implications of these ideas for basic physics?

25. But .. what does it have to do with information? Perona

26. Since 1997: A physics course that includes … Complexity, algorithms, data compression, channel capacity, cryptography and security, error-correcting codes, fault tolerance, …

27. Fractional quantum Hall state High temp. superconductor Crystalline material Condensed matter physics In a nutshell: whole>(parts) Emergent phenomena: the collective behavior of many particles cannot be easily guessed, even if we have complete knowledge of how the particles interact with one another. Entangled quantum many-particle systems have an enormous capacity to surprise and delight us.

28. Efficient classical simulation of quantum systems with bounded entanglement Vidal In general, there is no succinct classical description of the quantum state of a system of n qubits. But suppose, e.g., for qubits arranged in one dimension, that for any way of dividing the line into two segments, the strength of the quantum correlation (the amount of entanglement) between the two parts is bounded above by a constant, independent of n. Vidal showed that in that case a succinct description is possible, with O(n) parameters rather than 2n, and that the description can be easily updated as the state evolves (if the interactions are local). This makes precise the idea that entanglement is the source of a quantum computer’s power: if the quantum computer does not become highly entangled, it can be efficiently simulated by a classical computer. Furthermore, in one-dimensional systems with local interactions, the entanglement increases no more rapidly than log n, and an efficient classical simulation of real time evolution is possible.

29. Universal properties of entanglement Kitaev Preskill L For the ground state of a large two-dimensional quantum system, consider the entanglement of a disk (circumference L) with the rest of the system. For a system with a nonzero energy gap, the entanglement is: Term proportional to L, arising from short distance fluctuations near the boundary, is nonuniversal. Additive correction is universal (independent of geometry and microscopic details). The universal additive term, the topological entanglement entropy, is a global feature of the many-body quantum entanglement, characterizing the topological order of the gapped two-dimensional system. There is a simple formula for the universal constant , in terms of the properties of the particle excitations of the system.

30. black hole Bob decodes Bob radiation black hole Alice strongly mixing unitary radiation black hole maximal entanglement Alice’s qubits How fast does information escape from a black hole? Hayden Preskill Black holes are (we believe) efficient quantum information processors. How long do we have to wait for information absorbed by a black hole to be revealed in its emitted Hawking radiation? We have recently reconsidered this question using new tools from quantum information theory. Our (tentative) conclusion is that the retention time can be surprisingly short. The analysis uses the theory of quantum error-correcting codes and quantum circuits.

31. CPI is dedicated to the proposition that physical science and information science are interdependent and inseparable. Our research aims, on the one hand, to foster physical insights that can pave the way for revolutionary new information technologies, and, on the other hand, to stimulate new ideas about information that can illuminate fundamental issues in physics and chemistry. John Preskill (Ph) Jeff Kimble (Ph) Kerry Vahala (APh) Steering Committee Mike Cross (Ph) Jim Eisenstein (Ph/APh) Alexei Kitaev (Ph/CS) Oskar Painter (APh) Demetri Psaltis (EE) Gil Refael (Ph) Dave Rutledge (EE) Michael Roukes (Ph/APh) Erik Winfree (CS/CNS) Amnon Yariv (APh/EE) Etc.

32. CPI Postdoctoral Scholars Warwick Bowen (Kimble):Strong coupling in cavity quantum electrodynamics Younkyu Chung (Rutledge):High power 80 GHz amplifiers for wireless JM Geremia (Mabuchi):Stochastic feedback control & high precision measurement Tobias Kippenberg (Vahala):Optical driving of microcavity oscillators Paul Rothemund (Winfree):Complex patterns from DNA self-assembly Jacob Scheuer (Yariv):Ring resonators for all-optical nonlinear devices Frank Verstraete(Preskill):Efficient simulation of highly correlated quantum systems Tal Carmon (Vahala): Micron scale on-chip photonic devices Martin Centurion (Psaltis):Nonlinear optical processing via defocusing Barak Dayan (Kimble):Strong coupling of atoms to toroidal optical resonators Matt LaHaye (Roukes):Quantum limited measurements with nanoelectromechanics Sung Ha Park (Winfree):Algorithmic self-assembly with low error rate Mason Porter(Cross):Bose-Einstein condensates and nonlinear dynamics Eddy Ardonne(Kitaev):Braiding properties of two-dimensional quasiparticles Hui Deng (Kimble): Toward scalable quantum networks Ghislain Granger (Eisenstein):Nonabelian statistics in fractional quantum Hall states Mani Hossein-Zadeh (Vahala): Radiation pressure instability in toroidal resonators David Poulin(Preskill):Quantum belief propagation and many-body physics Kartik Srinivasan (Painter):Solid-state cavity quantum electrodynamics Scott Papp (Kimble): Information processing with cold atomic gases Avi Zadok (Yariv):Secure classical key distribution based on laser oscillations Darrick Chang(Preskill): Optical levitation of nanoscale mechanical systems Hansuek Lee(Vahala): Low loss waveguides and micro-resonators for optical integrated circuits

33. Coherent manipulation of encoded information CPB and NEMS Sample CPB and NEMS Sample 1m 1m CPB Gate CPB Gate SET SET CPB CPB SET Gate SET Gate l0 Resonator Gate Resonator Gate Resonator Resonator llaser Interacting optical and mechanical modes of silica microtoroids. Hossein-Zadeh (Vahala) Cavity QED with semiconductor quantum dots embedded in micro- disks. Srinivasan (Painter) =1 Mapping entangle- ment into and out of quantum memory. Deng (Kimble) Toward qubits in quantum Hall systems. Granger (Eisenstein) Coupling a GHz mechanical resonator to a Cooper-pair box. LaHaye (Roukes & Schwab)

34. Quantum Information Science Atomic-Molecular Optical Physics Condensed Matter Physics Exotic Quantum Systems!

35. Preskill Kitaev Schulman Eisenstein Roukes Schwab Kimble Painter Vahala Refael Motrunich Fisher Exotic Quantum Systems! All-Star All-Star

36. Caltech and quantum information – looking ahead • Quantum information science did not exist 30 years ago. There will be many more surprises in the next 30 years. • Caltech has a strong leadership position that should be nurtured. • The convergence of quantum information, condensed matter, and atomic-molecular-optical physics will continue, becoming one of Caltech’s great strengths. • PMA and EAS will share an increasing interest in quantum devices (broadly interpreted), e.g., coherent light, correlated electrons, quantized mechanical motion, control of quantum effects, etc. • As always, our future success • hinges on finding and recruiting • talented and visionary young • people.