Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session B1: Quantum Devices Based on Semiconductor Nanowires |
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Sponsoring Units: DCMP Chair: Sankar Das Sarma, University of Maryland Room: Ballroom A1 |
Monday, March 21, 2011 11:15AM - 11:51AM |
B1.00001: Cooper-pair splitter: towards an efficient source of spin-entangled EPR pairs Invited Speaker: In quantum mechanics the properties of two and more particles can be \textit{entangled}. In basic science pairs of entangled particles, so called Einstein-Podolsky-Rosen (EPR) pairs, play a special role as toy objects for fundamental studies. They provide such things as ``spooky interaction at distance,'' but they also enable secure encoding and teleportation and are thus important for applications in quantum information technology. Whereas EPR pairs of photons can be generated by parametric down conversion (PDC) in a crystal, a similar source for EPR pairs of electrons does not exists yet. In several theory papers, it has been suggested to use a superconductor for this purpose. The superconducting ground state is formed by a condensate of Cooper-pairs which are electron pairs in a spin-singlet state. Since there are many Cooper pairs in a metallic superconductor like Al, the main tasks are to extract Cooper pairs one by one and to split them into different arms. A controlled and efficient splitting is possible if one makes use of Coulomb interaction [1]. This has recently be demonstrated by two groups [2-4] using hybrid quantum-dot devices with both superconducting and normal metal contacts. In the present talk, I will discuss the Cooper-pair splitter results from the Basel-Budapest-Copenhagen team [3] and compare with the other experiments. As an outlook we discuss approaches that aim at entanglement detection. The Cooper pair splitter holds great promises because very large splitting efficiencies approaching 100{\%} and large pair current rates appear feasible. This work has been done by L. Hofstetter, S. Csonka, A. Geresdi, M. Aagesen, J. Nygard and C. Sch\"{o}nenberger \\[4pt] [1] P. Recher, E. V. Sukhorukov, and D. and Loss, Phys. Rev. B \textbf{63}, 165314 (2001). \\[0pt] [2] C. Strunk, \textit{Towards entangled electrons}, Nature Nanotechnology \textbf{5}, 11-12 (2009). \\[0pt] [3] L. Hofstetter, S. Csonka, J. Nygard, and C. Sch\"{o}nenberger, \textit{Cooper pair splitter realized in a two-quantum-dot Y-junction}, Nature \textbf{460}, 906 (2009). \\[0pt] [4] L.G. Herrmann, F. Portier, P. Roche, A. Levy Yeyati, T. Kontos, and C. Strunk, \textit{Carbon Nanotubes as Cooper Pair Beam Splitters}, Phys. Rev. Lett.\textbf{ 104}, 026801 (2010). [Preview Abstract] |
Monday, March 21, 2011 11:51AM - 12:27PM |
B1.00002: Spin-orbit qubit in a semiconductor nanowire Invited Speaker: Spin-orbit interaction in InAs nanowires is so strong that spin and motion cannot be separated. The eigenstates of a single electron confined to a quantum dot become a spin-orbital doublet. We perform coherent manipulation of spin-orbit states of a single electron, thereby demonstrating a spin-orbit qubit. Fast and universal qubit control is achieved using gigahertz electric fields, which couple to the orbital part of the wavefunction. Qubits in adjacent quantum dots are addressed separately due to a gate-tunable difference in g-factors. Dephasing due to interaction with nuclear spins is studied in a Ramsey experiment. Coherence is extended using Hahn echo as well as Carr-Purcell-Meiboom-Gill dynamical decoupling pulse sequences. The next step is the demonstration of entanglement between neighbor qubits which can be achieved using exchange interaction. [Preview Abstract] |
Monday, March 21, 2011 12:27PM - 1:03PM |
B1.00003: Prospecting for elusive Majorana particles in nanowires Invited Speaker: We propose and analyze theoretically an experimental setup for detecting the elusive Majorana particle in quasi-one dimensional semiconductor-superconductor heterostructures. The experimental system consists of a quasi one-dimensional semiconductor nanowire with strong spin-orbit Rashba interaction proximity coupled with an s-wave superconductor. Under appropriate conditions, such system can realize a non-trivial topological state supporting Majorana zero energy modes localized at the ends of the wire. These emerging Majorana quasiparticles, i.e. particles that are at the same time their own antiparticles, are effectively fractionalized objects (anyons) obeying non-Abelian statistics. We discuss several experiments for detecting Majorana fermions in nanowires. [Preview Abstract] |
Monday, March 21, 2011 1:03PM - 1:39PM |
B1.00004: Spin States, Spin Correlations, Supercurrent, and Multiple Andreev Reflections in InSb Nanowire Quantum Devices Invited Speaker: Bulk InSb is one of the most promising materials for applications in spintronics and quantum information processing, due to the fact that it has the highest electron mobility $\mu _{e}$ = 77000 cm2/Vs, the smallest electron effective mass m$_{e}$* = 0.015 me, and the largest electron magnetic moment $\vert $g*$\vert $ = 51 among all III-V semiconductors. Here, we report on realization and electrical measurements of InSb quantum dots and superconductor/InSb/superconductor hybrid quantum devices. The devices are made on a SiO2-capped Si substrate from InSb segments of InAs/InSb heterostructured nanowires grown by metal-organic vapor phase epitaxy. Spin states, effective g-factors, and spin-orbit interaction energy are measured for the fabricated InSb nanowire quantum dots [1]. We have also studied strong correlation phenomena and observed a new spin-correlation-induced phenomenon in the devices, namely the conductance blockade at the degeneracy of two orbital states with the same spin [2]. We attribute this conductance blockade to the effect of electron interference between two equivalent, strongly correlated, many-body states in the quantum dots. In superconductor/InSb nanowire/superconductor hybrid devices, we have observed supercurrent and multiple Andreev reflections, and have found that the fluctuations in the supercurrent are correlated to the conductance fluctuations of the corresponding InSb nanowires in the normal state. We have also observed multiple Andreev reflections and interplay between the Kondo correlation and proximity effect in the Coulomb blockade regime. \\[4pt] [1] H. A. Nilsson et al., Nano Lett. 9, 3151-3156 (2009). \\[0pt] [2] H. A. Nilsson et al., Phys. Rev. Lett. 104, 186804 (2010). [Preview Abstract] |
Monday, March 21, 2011 1:39PM - 2:15PM |
B1.00005: Measurement of Spin Relaxation in SiGe nanowire quantum dots Invited Speaker: This abstract not available. [Preview Abstract] |
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