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Events on Thursday, April 6th, 2017

R. G. Herb Condensed Matter Seminar
Coherent coupling between a quantum dot and a donor in silicon
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Patrick Harvey-Collard, Sandia National Labs
Abstract: Individual donors and quantum dots in silicon chips are used as bits of quantum information with different but complementary advantages. In this work, we show that these two qubit systems can be combined by demonstrating the coherent interaction of a 31P donor electron with the electron of a metal-oxide-semiconductor quantum dot. We form a qubit from the spin singlet and triplet states of the two-electron system. We show that the donor nuclear spin drives coherent rotations between the electronic qubit states through the contact hyperfine interaction. This provides every key element for compact two-electron spin qubits requiring only a single dot and no additional magnetic field gradients, as well as a means to interact with the nuclear spin qubit. This system furthermore introduces an engineered path to couple donors together, alleviating the need for challenging atomic-precision fabrication and providing a scalable path to multi-donor qubit systems.

In this talk, I will also discuss our advances in engineering the valley splitting and the shell filling of QDs to overcome the system’s challenges. I will present a scheme for high fidelity spin readout that combines the advantages of the Pauli blockade and spin 1/2 readouts.

This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. DOE under contract DE-AC04-94AL85000.​

Host: Coppersmith
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Astronomy Colloquium
Turbulence and Dynamo Action in Accretion Flows
Time: 3:30 pm - 5:00 pm
Place: 4421 Sterling Hall, Coffee and cookies at 3:30 PM, Talk begins at 3:45 PM
Speaker: Fausto Cattaneo, University of Chicago
Abstract: Accretion is an important process in astrophysics: it allows the growth of compact objects and it powers some of the most energetic phenomena in the universe. Often the accreting material comes from a disk. In this case the accretion rate is controlled by the outward flux of angular momentum. Collisional process, like viscosity, are many orders of magnitude too small to provide the efficient angular momentum transport required to account for the observed accretion rates. Thus it is commonly assumed that the transport in an accretion disk is mediated by some form of turbulence. The nature of this turbulence is a matter of intense debate. In electrically conducting disks, its origin is most likely related to the Magneto Rotational Instability (MRI), which requires that the disk be threaded by a coherent weak magnetic field. This raises the interesting possibility that the disk turbulence, through dynamo action, may be able to generate the very magnetic filed that is necessary for the instability to develop. This process of self-sustaining magnetization has indeed been observed in numerical simulations. However many issues remain, the most notable of which are the ability of the MRI driven dynamo to operate in the limit of high electrical conductivity and the efficiency of the angular momentum transport. In this talk I shall describe some of the efforts to date to address these issues.
Host: UW Astronomy Department
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