Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session L2: Correlated States for Topological Quantum Computing |
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Sponsoring Units: DCMP Chair: Chetan Nayack, Station Q, University of California, Santa Barbara Room: Oregon Ballroom 202 |
Tuesday, March 16, 2010 2:30PM - 3:06PM |
L2.00001: Interferometric schemes for the detection of non-abelian statistics Invited Speaker: Kirill Shtengel States of matter are conventionally classified according to broken symmetries. Topologically ordered phases fall outside of this paradigm: with no local order parameter, they nevertheless have many peculiar properties setting them apart from disordered phases. In 2D, such phases may support anyons - quasiparticles that are neither bosons nor fermions. Moreover, anyons with \emph{non-Abelian} statistics can occur, particularly in the fractional quantum Hall regime.\\ In this talk, I will focus on solid state interferometers designed to detect such exotic statistics. I will discuss recent experiments in the $\nu=5/2$ quantum Hall state where the evidence for the existence of non-Abelian quasiparticles may have in fact been observed for the first time [1]. Potential applications of such interferometeric schemes for topological quantum computation will also be addressed.\\ {[1]} R.~L.~Willett, L.~N.~Pfeiffer and K.~W.~West, PNAS \textbf{106}, 8853 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 3:06PM - 3:42PM |
L2.00002: Half-quantum vortices in $p_{x}$\textit{+ ip}$_{y}$ superconductors Invited Speaker: Suk Bum Chung Half-quantum vortices, each with flux of h/4e, are needed to realize topological quantum computation in a p+ip superconductor. However, until recently, there had not been any clear experimental observation of such vortices. We point out, although the magnetic energy is reduced by breaking full vortices into half-quantum vortices, there is an energy cost (which diverges with system size) due to the unscreened spin current and the spin state locking. The recent observation of half-quantum vortices by the Budakian group can be best explained by the fact that the magnetic energy savings can dominate over the spin energy cost in a mesoscopic setting. A finite density vortex lattice may have similar energetics, leading to a lattice of half-quantum vortices. Lastly we show that there can be entropy driven dissociation of a full vortex into two half-quantum vortices. [Preview Abstract] |
Tuesday, March 16, 2010 3:42PM - 4:18PM |
L2.00003: Observation of Fractional Fluxoid States in Mesoscopic Rings of Sr$_{2}$RuO$_{4}$ by Ultrasensitive Cantilever Magnetometry Invited Speaker: Raffi Budakian In the past decade, there has emerged strong evidence to support spin-triplet superconductivity in the layered-perovskite Sr$_{2}$RuO$_{4}$, whose ground state is thought to be analogous to the A-phase of $^{3}$He. It is believed that the spin and orbital degrees of freedom of the superconducting order parameter can give rise to states with remarkable properties, such as chiral domains and half-quantum vortices (HQV) that may obey non-Abelian statistics. With regards to the latter, recent theoretical work suggests that the HQV state could be made energetically favorable in mesoscopic samples [1]. In this talk, I will present a new method for ultrasensitive cantilever magnetometry that allows us to probe the magnetic response of mesoscopic samples of Sr$_{2}$RuO$_{4}$. Using this technique, we have detected the entry of individual vortices into micron-size rings of Sr$_{2}$RuO$_{4}$. Our most intriguing observation is the appearance of fractional fluxoid states that have half the magnetic moment of the full (integer) fluxoid. We find that the stability region of the fractional fluxoid state grows linearly with the magnitude of the in-plane magnetic field applied to the crystal. While the physical origin of the fractional state is yet unknown, I will present a recent theoretical proposal that predicts spontaneous spin polarization in the HQV state [2] which could explain the observed field dependence.\\[4pt] [1] S. B. Chung, H. Bluhm, and E. A. Kim, Phys. Rev. Lett. \textbf{99}, 197002 (2007). \\[0pt] [2] V. Vakaryuk, and A. J. Leggett, Phys. Rev. Lett. \textbf{103}, 057003 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 4:18PM - 4:54PM |
L2.00004: Transport and thermodynamic signatures of non-abelian quantum Hall states Invited Speaker: Ady Stern In this talk I will review several proposed experiments aimed at identifying non-abelian quantum Hall states, particularly the nu=5/2. These proposed experiments will include the temperature dependence of the compressibility and the magnetization of macroscopic samples, interference in mesoscopic samples and Coulomb blockade in quantum dots. In particular, I will discuss the conditions needed for the compressibility and magnetization to reflect non-abelian quasi- particles, the inter-relations between interference and Coulomb blockade, and the subtleties associated with each of them. I will also comment on existing experimental data. [Preview Abstract] |
Tuesday, March 16, 2010 4:54PM - 5:30PM |
L2.00005: The role of MBE in observing coherence in a quantum Hall interferometer Invited Speaker: Loren Pfeiffer The integer Quantum Hall Effect was discovered in 1980 in Silicon MOSFETs. Two years later the Fractional Quantum Hall Effect was discovered in GaAs-AlGaAs heterostructures. Now, recent experiments\footnote{R. L. Willett, L. N. Pfeiffer, and K. W. West, ``Alternating e/4 and e/2 period interference oscillations consistent with filling factor 5/2 non-abelian quasiparticles,'' arXiv:0911.0345.} suggest the existence of a third Quantum Hall variety, the Quantum Hall Effect of Quasiparticles obeying Non-abelian Statistics. This apparent discovery of non-abelian quasiparticles makes possible a potential application of the Quantum Hall Effect, that may lead to an elegant topological lock against decoherence of entangled quantum states, and thus would point the way toward building a quantum computer with built-in error correction. We will review how the sequential discoveries of the various levels of the Quantum Hall effect have depended on the gradually improving quality of the semiconductor samples, and how semiconductor perfection still limits current experiments that are exploring the properties of non-abelian quasiparticles. [Preview Abstract] |
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