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This Week at Physics

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Events on Thursday, March 1st, 2012

R. G. Herb Condensed Matter Seminar
Challenges in Quantum Computer Architecture
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Ken Brown, Schools of Chemistry & Biochemistry; Computational Science & Engineering; and Physics, Georgia Institute of Technology
Abstract: The development of a large-scale quantum computer faces two challenges: faulty hardware components and the inability to copy quantum information. Despite the no-cloning theorem, it is possible to use fault-tolerant quantum error correction techniques to generate arbitrarily reliable logical components. In the context of an algorithm, the inability to copy quantum information requires that a block of data that needs to interact with two other data blocks must be transported first from one block and then to the other. Although it is widely appreciated that the bulk of resources in a scalable quantum computers will be devoted to error correction, the significant cost of communication during the computation is only now being understood [1]. This can have a dramatic effect on the utility of a quantum computer as a simulator of other quantum systems [2].

I will discuss methods for estimating the communication cost on two distinct hardware layouts for ion trap quantum computation in the context of concatenated error correcting codes. In the first hardware layout, the ions are held in multiple zones and communications is performed by physically shuttling ions between zones [3]. The second hardware layout uses photons to create entangled ions in distant traps by the process of heralded entanglement [4]. These entangled ions are then used as teleportation channels to transfer information. I will compare possible architectures for arranging these systems on the logical level. Finally, I will briefly describe how these same architectural ideas can be applied in the setting of topological error correction.

[1] M.G. Whitney, N. Isailovic, Y. Patel and J. Kubiatowicz, A fault tolerant, area efficient architecture for Shor's factoring algorithm, Proc. of the 39th Annual Intl. Symp. on Computer Architecture ( ISCA), 383 (2009).

[2]C. R. Clark, T. S. Metodi, S. D. Gasster, and K. R. Brown, Resource requirements for fault-tolerant quantum simulation: the transverse Ising model ground state, Phys. Rev. A 79, 062314 (2009).

[3] D. Kielpinski, C. Monroe & D. J. Wineland, Architecture for a large-scale ion-trap quantum computer, Nature 417, 709 (2002).

[4] L.-M. Duan and C. Monroe, Quantum networks with trapped ions ,Rev. Mod. Phys. 82, 1209 (2010).


Host: Saffman
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Plasma Physics (Physics/ECE/NE 922) Seminar
Rotation and turbulence in laboratory and astrophysical systems
Time: 12:00 pm
Place: 4274 Chamberlin
Speaker: Eric Edlund, Princeton Plasma Physics Laboratory
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Astronomy Colloquium
"Secular Chaos: Formation of Hot Jupiters and the organization of Planetary Systems"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Yoram Lithwick, Northwestern University
Abstract: In a planetary system with well-spaced planets, there is a nonlinear instability that can lead to chaotic behaviour. One of the planets can gradually become unstable, in which case its orbit becomes highly eccentric. This "secular chaos" is known to be responsible for the eventual destabilization of Mercury in our own Solar System. Here I focus on systems with multiple giant planets. I show that after an extended period of eccentricity diffusion, the inner planet's pericentre can approach the star to within a few stellar radii. Strong tidal interactions with the star then pull the planet inward, creating a hot Jupiter. In contrast to other proposed channels for the production of hot Jupiters, such a scenario (which I term "secular migration") explains a range of observations: the pile-up of hot Jupiters at 3-day orbital periods, the fact that hot Jupiters are in general less massive than other RV planets, that they may have misaligned inclinations with respect to stellar spin, and that they have few easily detectable companions (but may have giant companions in distant orbits). I will also show that if an unstable planet escapes the influence of the other planets, the remaining planetary system becomes increasingly stable. This may explain the stable architecture of observed systems.
Host: Professor Lazarian
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