Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P45: Majorana Nanowire Based Topological DevicesFocus
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Sponsoring Units: DMP Room: 392 |
Wednesday, March 15, 2017 2:30PM - 3:06PM |
P45.00001: New theory insights and experimental opportunities in Majorana wires Invited Speaker: Jason Alicea Over the past decade, the quest for Majorana zero modes in exotic superconductors has undergone transformational advances on the design, fabrication, detection, and characterization fronts. The field now seems primed for a new era aimed at Majorana control and readout. This talk will survey intertwined theory and experimental developments that illuminate a practical path toward these higher-level goals. In particular, I will highlight near-term opportunities for testing fundamentals of topological quantum computing and longer-term strategies for building scalable hardware. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P45.00002: Scalable Designs for Topological Quantum Computation with Majorana Zero Modes: Part 1, Overview Torsten Karzig, Christina Knapp, Roman Lutchyn, Parsa Bonderson, Matthew Hastings, Chetan Nayak, Jason Alicea, Karsten Flensberg, Stephan Plugge, Yuval Oreg, Charles Marcus, Michael Freedman We present scalable designs for topological quantum computation using Majorana zero modes (MZMs). The topological qubits are encoded in aggregates of four or six MZMs assembled into superconducting islands with significant charging energy to protect against quasi particle poisoning. In such a scheme, quantum information can be manipulated according to a measurement-only protocol. In this talk, we will give an overview of different designs and the corresponding measurement-based protocols. [Preview Abstract] |
Wednesday, March 15, 2017 3:18PM - 3:30PM |
P45.00003: Scalable Designs for Topological Quantum Computation with Majorana Zero Modes: Part 2 Measurement Christina Knapp, Torsten Karzig, Roman Lutchyn, Parsa Bonderson, Matthew Hastings, Chetan Nayak, Jason Alicea, Karsten Flensberg, Stephan Plugge, Yuval Oreg, Charles Marcus, Michael Freedman Majorana zero modes (MZMs) provide an attractive platform for fault tolerant quantum computing by storing and manipulating quantum information non-locally. Qubits encoded in aggregates of four or more MZMs assembled into superconducting islands with significant charging energy are a promising avenue for scalable quantum computers. In such a design, quantum information can be manipulated according to a measurement-only protocol, which is facilitated by tunable couplings between MZMs and nearby semiconductor dots. In this talk, we discuss how to perform these projective MZM parity measurements and explain how these measurements allow for protected implementation of all Clifford gates. [Preview Abstract] |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P45.00004: Robust Schemes for Quantum Error Correction and Information Processing with Majorana Zero Modes Sagar Vijay, Liang Fu We present a measurement-based scheme for performing braiding operations on Majorana zero modes and for detecting their non-Abelian statistics. In our proposal, the topological qubit formed by well-separated Majoranas in a mesoscopic superconductor island is read out from the transmission phase shift in electron teleportation through the island in the Coulomb blockade regime, via a conductance measurement in an electron interferometer or persistent current measurement in a closed loop. Quasiparticle poisoning errors must be actively corrected in these systems in order for quantum information storage and longer computations to be feasible. To address this issue, we present families of error-correcting fermion codes that can correct for quasiparticle poisoning errors, and present a possible implementation of one such code. Certain codes may also be used to correct for de-phasing errors in systems with microscopic complex fermions. We discuss the important advantages for error-correction in Majorana platforms. [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P45.00005: Extended Majorana zero modes in a topological superconducting-normal T-junction Christian Spanslatt, Eddy Ardonne We investigate the sub gap properties of a three terminal Josephson T-junction composed of topologically superconducting wires connected by a normal metal region. This system naturally hosts zero energy Andreev bound states which are of self-conjugate Majorana nature and we show that they are, in contrast to ordinary Majorana zero modes, spatially extended in the normal metal region. If the T-junction respects time-reversal symmetry, we show that a zero mode is distributed only in two out of three arms in the junction and tuning the superconducting phases allows for transfer of the mode between the junction arms. We further provide tunneling conductance calculations showing that these features can be detected in experiments. Our findings suggest an experimental platform for studying the nature of spatially extended Majorana zero modes. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P45.00006: Optimal Diabatic Dynamics of Majoarana-based Topological Qubits Babak Seradjeh, Armin Rahmani, Marcel Franz In topological quantum computing, unitary operations on qubits are performed by adiabatic braiding of non-Abelian quasiparticles such as Majorana zero modes and are protected from local environmental perturbations. This scheme requires slow operations. By using the Pontryagin’s maximum principle, here we show the same quantum gates can be implemented in much shorter times through optimal diabatic pulses. While our fast diabatic gates no not enjoy topological protection, they provide significant practical advantages due to their optimal speed and remarkable robustness to calibration errors and noise. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P45.00007: Optimal control inspired algorithm for real-space optimization with application to Majorana fermion experiments Samuel Boutin, Julien Camirand Lemyre, Sara Turcotte, Michel Pioro-Ladrière, Ion Garate Inspired by the success of optimal control theory algorithms in the design of new, fast and accurate gates for quantum information processing, we import the mindset of these time-domain optimization strategies to static real-space functions in solid-state systems. Combining ideas from the GRAPE (Gradient Ascent Pulse Engineering) algorithm and transport calculations, we devise a new gradient-based algorithm for the optimization of transport-related quantities through the real-space variation of experimentally controllable parameters. This technique can be useful for the design of experiments in mesoscopic solid-state systems. As an example, we apply our algorithm to the optimization of the topological visibility of Majorana fermions in superconducting nanowires without spin-orbit coupling in a non-uniform magnetic field. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P45.00008: Andreev bound states in a semiconducting nanowire Josephson junction, Part I: Detection and manipulation of an Andreev qubit G. de Lange, M. Hays, K. Serniak, D.J. van Woerkom, J.I. V{\"a}yrynen, B. van Heck, U. Vool, P. Krogstrup, J. Nyg{\aa}rd, L. Frunzio, A. Geresdi, L.I. Glazman, M.H. Devoret Proximitized semiconducting nanowires subject to magnetic field should display topological superconductivity and support Majorana zero modes which exhibit non-Abelian braiding statistics. The conventional Andreev levels formed in such wires, in the absence of field, are a precursor to these exotic zero modes. In this talk, we report on the detection and coherent manipulation of an Andreev level qubit in a proximitized InAs nanowire non-topological Josephson junction, using circuit QED microwave techniques. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P45.00009: Andreev bound states in a semiconducting nanowire Josephson junction, Part II: Quantum jumps and Fermion parity switching M. Hays, G. de Lange, K. Serniak, D.J. van Woerkom, J.I. V{\"a}yrynen, B. van Heck, U. Vool, P. Krogstrup, J. NYG{\AA}RD, L. Frunzio, A. Geresdi, L.I. Glazman, M.H. Devoret Proximitized semiconducting nanowires subject to magnetic field should display topological superconductivity and support Majorana zero modes which have non-Abelian braiding statistics. The conventional Andreev levels formed in such wires in the absence of field are a precursor to these exotic zero modes. The fermion-parity switching time of Andreev levels sets a lower bound on the bandwidth required for experiments aimed at harnessing non-Abelian braiding statistics. We demonstrate the observation of quantum jumps between even and odd-parity states of an individual Andreev bound state in a non-topological junction, providing a direct measurement of the state populations and the parity lifetime. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P45.00010: Majorana zero modes in spintronics devices Chien-Te Wu, Brandon Anderson, Wei-Han Hsiao, K. Levin We show that topological phases should be realizable in readily available and well studied heterostructures. In particular we identify a new class of topological materials which are well known in spintronics: helical ferromagnet-superconducting junctions. We note that almost all previous work on topological heterostructures has focused on creating Majorana modes at the proximity interface in effectively two-dimensional or one-dimensional systems. The heterostructures we address exhibit finite range proximity effects leading to nodal superconductors with Majorana modes localized away from this interface. To show this, we implement a Bogoliubov-de Gennes (BdG) proximity numerical scheme, which importantly, involves two finite dimensions in a three dimensional junction. Incorporating this level of numerical complexity serves to distinguish ours from alternative numerical BdG approaches which are limited by assuming translational invariance along multiple directions. With this access to the edges, we are then able to illustrate in a concrete fashion the wavefunctions of Majorana zero modes, and, moreover, address finite size effects. In the process we establish consistency with a simple analytical model~[1]. \\[4pt] [1]C.-T. Wu, B. M. Anderson, W.-H. Hsiao, K. Levin, ArXiv:1609.0453 [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P45.00011: Detecting Majorana bound states coupling with an Aharonov-Bohm interferometer Pedro Orellana, Juan Pablo Ramos Andrade, Sergio Ulloa In this work we consider a quantum dot (QD) connected to current leads arranged to mediate the interaction between two topological nanowires, both hosting Majorana bound states (MBS) at their ends. In an interesting system geometry, one nanowire has both ends coupled with the QD, forming an Aharonov-Bohm (AB) interferometer, while the other is placed nearby such that two MBS belonging to different nanowires can interact. We model the system using an effective low energy Hamiltonian, considering that the QD is embedded between metallic leads. Using a Green’s function formalism via the equation of motion procedure, we find that the conductance across the leads can show MBS signatures, i.e. half-maximum conductance at zero-energy, when both topological nanowires are connected, independent of the AB flux phase. This system may be used as a detector of the effective connections between independent MBS by monitoring the conductance while tuning the AB phase. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P45.00012: Differential Conductance Strength in Majorana Devices John Stenger, Tudor Stanescu Recent differential conductance experiments on semiconductor nanowires proximity coupled to s-wave superconductors have shown several interesting features, including signatures of the induced and bulk gaps and zero-bias peaks. We describe theoretically these features using a tight binding model within a non-equilibrium Green function formalism. In particular, we study the dependence of the differential conductance on various model parameters and identify the low-energy states responsible for different experimentally-observed features. We find that the barrier height, as well as band mixing and the semiconductor-superconductor coupling can modify the strength of the conductance features. By changing these and other parameters we are able to distinguish between various features and suggest ways to strengthen certain features that might be too weak to recognize otherwise. [Preview Abstract] |
Wednesday, March 15, 2017 5:18PM - 5:30PM |
P45.00013: Optical coupling to atomic states in superconductors Matthias Le Dall, Igor Diniz, Rog\'{e}rio de Sousa Superconducting devices can act as sensitive detectors of optical excitations in many different quantum systems and are now being considered as a method to probe and manipulate neutral atoms in atomic clouds, as well as impurities and nanostructures with complex energy spectra. Here we present a theory for the optical excitations of hydrogenic atomic states hybridized with a superconductor, including the full orbital degeneracy. We derive a low energy effective Hamiltonian for the atom and show that the proximity effect leads to a rich spectrum of Yu-Shiba-Rusinov (YSR) bound states within the superconducting energy gap. The presence of superconducting correlations greatly affects the atomic electric dipole transitions, and the mixing with the superconducting vacuum opens up additional optical resonances. Furthermore, the strengths of the transitions are quantified through a modified optical sum rule. Our results demonstrate that the overlap between atomic states and the superconductor activates new optical transitions, and creates novel opportunities for detection and manipulation of YSR states. [Preview Abstract] |
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