Bulletin of the American Physical Society
Fall 2009 Meeting of the Four Corners Section of the APS
Volume 54, Number 14
Friday–Saturday, October 23–24, 2009; Golden, Colorado
Session C4: Spintronics and Quantum Computing |
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Chair: Mark Coffey, Colorado School of Mines Room: Green Center 211 |
Friday, October 23, 2009 3:40PM - 4:04PM |
C4.00001: Observing coherent spin motion with electrical currents Invited Speaker: The spin degree of freedom of electrons and nuclei is important for many materials properties of condensed matter. Spins have also been proposed as information carriers for quantum information and spin-electronic applications. The investigation of spin states for materials research and technological applications therefore requires very sensitive spin measurement (readout) techniques. Our research is aimed at the investigation of such spin readout mechanisms for electron and nuclear spins in semiconductor materials. The focus of this work is on spin-selection rules which allow control of electronic transitions such as charge carrier recombination, transport, trapping or scattering. I will present two spin-dependent mechanisms which allow the extremely sensitive observation of coherent spin nutation of electron spins in crystalline silicon and a conducting pi-conjugated polymer, respectively. It will be shown that using these mechanisms, it is possible to observe spin effects such as spin-Rabi nutation, spin-echo, spin inversion recovery and spin polarization by technologically simple transient current measurements. [Preview Abstract] |
Friday, October 23, 2009 4:04PM - 4:16PM |
C4.00002: Spin incoherence of donor electrons near c-Si(111)/SiO2 interface defects Seoyoung Paik, Sang -Yun Lee, William J. Baker, Dane R. McCamey, Christoph Boehme Electron and nuclear spins of phosphorous ($^{31}$P) donors in crystalline silicon have been investigated extensively in recent years as they both have extremely long quantum mechanical coherence times which makes them extremely interesting candidates for quantum information and spin-electronics applications [1]. Existing silicon quantum computer concepts [2] propose to use $^{31}$P qubits close to the silicon surface. We present here a study of how microscopic defects at the oxide layer of the silicon surface influence the spin coherence times (T$_{1}$ and T$_{2}$ times) of the $^{31}$P qubits. Using pulsed electrically detected magnetic resonance spectroscopy [3], we show that due to the interaction of the $^{31}$P qubits with the interface states, the previously known, extremely long bulk coherence times are drastically shortened [4]. \\[4pt] [1] J. J. L.Morton, et al., Nature \textbf{455}, 1085 (2008). \\[0pt] [2] B. E. Kane, Nature 393, 133 (1998). \\[0pt] [3] A. R. Stegner, et al., \textit{Nature Physics} 2, 835 (2006). \\[0pt] [4] S.-Y. Paik, et al., arXiv:cond-mat/0905.0416 (2009). [Preview Abstract] |
Friday, October 23, 2009 4:16PM - 4:28PM |
C4.00003: Enhanced estimation of quantum evolution parameters with entangled states David Collins, Mike Frey Quantum estimation considers the issue of estimating parameters associated with the description of a quantum state or of the evolution of a quantum state when only a finite number of copies of the quantum system are available. The accuracy of any estimation scheme is limited by both standard statistical sampling issues as well as the inherent statistical nature of measurement outcomes for quantum systems. We consider rotations of a spin-1/2 particle about a fixed axis and which are parametrized by a rotation angle, which is to be estimated. We use the quantum Fisher information to establish optimal bounds on the variance in any estimator of this parameter in scenarios involving one use of the rotation upon each of a collection of spin-1/2 particles. We show that optimal estimation occurs when all spin-1/2 particles are entangled and present exact analytical results for the bound that is generated and the required input state. We show that this offers a significant advantage over the use of unentangled states. [Preview Abstract] |
Friday, October 23, 2009 4:28PM - 4:40PM |
C4.00004: Fidelity of Arbitrary Single-Qubit Gates Nathan Steiger, Peter Pemberton-Ross Recent work suggests that conservation laws limit the inherent accuracy of gate operations in quantum computing. One way to quantify these limitations is through a gate operation's fidelity. We extend and clarify previous work by Karasawa et al. (J. Phys. A \textbf{42}, 225303, (2009)) for an arbitrary single-qubit gate operation by incorporating the Schr\"{o}dinger form of the uncertainty relation and arrive at a Bloch sphere representation of the gate fidelity. We find that these modifications are non-trivial and could have important ramifications for quantum computing. [Preview Abstract] |
Friday, October 23, 2009 4:40PM - 4:52PM |
C4.00005: Consensus and Frustration in the Heisenberg Model Wesley Krueger, Manuel Berrondo In the creation of a model for flocking behavior, we have developed a set of two rules, termed consensus and frustration, which consist of a topologically unique non-symmetric alignment tendency among individual particles, coupled with an antagonistic, generally external influence opposing full particle alignment. These rules act to produce a spectacular range of deterministic, complex motion. Placing the particles in a lattice structure and allowing the velocity to go to zero produces a modified Heisenberg spin model. We discuss the development and exploration of such a model; in particular the compatibility of common numerical integration methods with our consensus and frustration rules and quantification of the results using thermodynamic techniques. [Preview Abstract] |
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