Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C28: Topological Quantum Information with Majorana Nanowires |
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Sponsoring Units: DQI Chair: Angela Kou, Yale Univ Room: BCEC 161 |
Monday, March 4, 2019 2:30PM - 2:42PM |
C28.00001: Probing coherent coupling of Majorana modes via single-electron photon assisted tunneling: Part 1 Deividas Sabonis, David Van Zanten, Judith Tabea Suter, Dmitry Pikulin, Jukka Vayrynen, Torsten Karzig, Eoin C O'Farrell, Davydas Razmadze, Karl D Petersson, Peter Krogstrup, Charles M Marcus The coherent coupling between Majorana zero modes localized in distinct topological islands mixes the 1e charge states of islands. This coherent superposition of even and odd parity states is a necessary condition for the operation of topological qubits. We demonstrate the coherent coupling of zero modes in a superconducting double island created in a InAs/Al nanowire. This is achieved by tracking microwave induced charge transitions between the islands. The dispersion of photon assisted tunneling features is 1e periodic and shows the presence of an anti-crossing between even and odd parity charge states. |
Monday, March 4, 2019 2:42PM - 2:54PM |
C28.00002: Probing coherent coupling of Majorana modes via single-electron photon assisted tunneling: Part 2 David Van Zanten, Deividas Sabonis, Judith Tabea Suter, Dmitry Pikulin, Jukka Vayrynen, Torsten Karzig, Eoin C O'Farrell, Davydas Razmadze, Karl D Petersson, Peter Krogstrup, Charles M Marcus The coherent coupling between Majorana zero modes localized in distinct topological islands mixes the 1e charge states of islands. This coherent superposition of even and odd parity states is a necessary condition for the operation of topological qubits. We demonstrate the coherent coupling of zero modes in a superconducting double island created in a InAs/Al nanowire. This is achieved by tracking microwave induced charge transitions between the islands. The dispersion of photon assisted tunneling features is 1e periodic and shows the presence of an anti-crossing between even and odd parity charge states. |
Monday, March 4, 2019 2:54PM - 3:06PM |
C28.00003: Single-shot readout of spin-orbit-split Andreev doublets: motivation and setup Valla Fatemi, Max Hays, Kyle Serniak, Daniël Bouman, Gijs De Lange, Spencer Diamond, Peter Krogstrup, Jesper Nygård, Attila Geresdi, Michel H. Devoret Modern efforts towards constructing exotic superconducting qubits such as Andreev spin qubits and Majorana bound states hinges on spin-orbit coupling. The physics of these unique quantum systems may be explored using the well-developed microwave techniques of circuit QED, which can yield sharp spectral resolution and time-domain information. Here we report on measurements of long InAs-nanowire Josephson junctions embedded in a circuit QED architecture. The Andreev bound state spectrum includes transitions which correspond to the transfer of a single quasiparticle between two spin-orbit-split Andreev doublets. Some of these transitions exhibit large coupling to the on-chip resonator. Thus, fast, time-domain measurement of the many-body state of the junction can be achieved through dispersive readout. In this first part of a joint presentation, we will present the background and motivation, as well as the experimental setup and a theoretical model for our system. |
Monday, March 4, 2019 3:06PM - 3:18PM |
C28.00004: Single-shot readout of spin-orbit-split Andreev doublets: experimental data Max Hays, Valla Fatemi, Kyle Serniak, Daniël Bouman, Gijs De Lange, Spencer Diamond, Peter Krogstrup, Jesper Nygård, Attila Geresdi, Michel H. Devoret Modern efforts towards constructing exotic superconducting qubits such as Andreev spin qubits and Majorana bound states hinges on spin-orbit coupling. The physics of these unique quantum systems may be explored using the well-developed microwave techniques of circuit QED, which can yield sharp spectral resolution and time-domain information. Here we report on measurements of long InAs-nanowire Josephson junctions embedded in a circuit QED architecture. The Andreev bound state spectrum includes transitions which correspond to the transfer of a single quasiparticle between two spin-orbit-split Andreev doublets. Some of these transitions exhibit large coupling to the on-chip resonator. Thus, fast, time-domain measurement of the many-body state of the junction can be achieved through dispersive readout. In this second part of a joint presentation, we will describe the experimental data and discuss the outlook. |
Monday, March 4, 2019 3:18PM - 3:30PM |
C28.00005: Entangling Spins in Double Quantum Dots and Majorana Bound States Marko Rancic, Silas Hoffman, Constantin Schrade, Jelena Klinovaja, Daniel Loss We theoretically investigate the coupling between a singlet-triplet (ST) spin qubit realized in a double quantum dot and a topological qubit composed of Majorana bound states. First, we derive an effective Hamiltonian which facilitates an entangling gate between the two individual qubits, thereby enabling a CNOT gate and, subsequently, a SWAP gate. Using standard readout and single qubit operations of the ST qubit, we show how the former gate can be used to readout the state of Majorana qubit while the latter gate enables universal quantum computation of the topological qubit. We estimate the fidelity of the entangling and SWAP gate operations to be 0.9997 and 0.993, respectively, using parameters that are consistent with realizing both of the qubits within a nanowire. Furthermore, we find that the coupling between the ST qubit and a single Majorana bound state induces an oscillation between the two singlet-triplet levels which has the utility to (1) perform single qubit operations on the singlet-triplet around the x axis without a need for a gradient of Zeeman fields and (2) provide a signature for the presence of zero energy bound states. Lastly, we propose a scheme to extend our setup to a scalable network using the ST-Marjorana bound state qubit as the atomic unit. |
Monday, March 4, 2019 3:30PM - 3:42PM |
C28.00006: Quasiparticle Poisoning in a Proximitized Semiconductor Nanowire Qubit Willemijntje Uilhoorn, Arno Bargerbos, James Kroll, Jasper Van Veen, Chung-Kai Yang, Jesper Nygård, Peter Krogstrup, Leo Kouwenhoven, Angela Kou, Gijs De Lange Topological qubits are predicted to have very long coherence times due to their inherent protection against local perturbations. However, non-parity preserving processes such as quasiparticle poisoning (QPP) set the bandwidth requirements for controlling topological qubits. Quasiparticle poisoning rates have been recorded in conventional superconducting transmon qubits [1, 2] and in hybrid proximitized semiconductor nanowire junctions [3] at zero magnetic field. |
Monday, March 4, 2019 3:42PM - 3:54PM |
C28.00007: Little-Parks effect in a semiconducting nanowire-based superconducting qubit with in-situ switching between transport and cQED Anders Kringhøj, Thorvald W Larsen, Oscar Erlandsson, Deividas Sabonis, Bernard Van Heck, Ivana Petkovic, Robert P. G. McNeil, Marina Hesselberg, Agnieszka Telecka, Sachin Yadav, Karolis Parfeniukas, Karthik Jambunathan, Peter Krogstrup, Lucas Casparis, Charles M Marcus, Karl D Petersson Proximitized semiconducting nanowires serve as a promising platform for both superconducting qubits [1] and topological qubits based on Majorana zero modes (MZM) [2,3]. Here we demonstrate in-situ switching between coherent cQED measurements and transport measurements based on a full-shell nanowire using a Josephson junction as a gate tuneable switch. These field-compatible devices show flux-dependent lobe spectra in both transport and cQED measurements associated with the Little-Parks effect. Coherent operations are performed both around zero applied field and around 90 mT, corresponding to one flux quantum being threaded through the wire, with a destructive regime in between. |
Monday, March 4, 2019 3:54PM - 4:06PM |
C28.00008: Cavity-based readout and control of Majorana qubits Thomas Smith, Arne Grimsmo, Stephen D Bartlett, Andrew C Doherty We discuss readout and control protocols based on coupling Majorana bound states to cavities. In particular, we consider hybrid superconductor-semiconductor nanowires where the Majorana-cavity coupling is mediated by a quantum dot. The resulting qubit-cavity interaction can be operated in the dispersive regime, familiar from circuit QED. Alternatively, a longitudinal interaction can be activated by parametric modulation of the qubit-cavity coupling strength [1]. We explore how these interactions can be used for readout of Majorana qubits, as well as their use for cavity-mediated entangling gates. |
Monday, March 4, 2019 4:06PM - 4:18PM |
C28.00009: Nonlinear quantum optics for the characterization of Majorana qubits Samuel Boutin, Anqi Mu, Pedro Lopes, Udson Mendes, Ion Garate Recent developments in the design of Majorana qubits have focused on devices with significant charging energy. In this parameter regime, methods from circuit QED can be used to study topological qubits. In particular, the toolbox of quantum optics opens new possible schemes for the characterization, measurement, and control of Majorana qubits. As a step in this direction, we investigate how the phenomenon of bifurcation in nonlinear cavities, commonly used for measuring qubits, is altered in the presence of Majorana bound states. Our preliminary results indicate that bifurcation could help characterize quasiparticle poisoning events in quantum wires-based Majorana qubits. |
Monday, March 4, 2019 4:18PM - 4:30PM |
C28.00010: On-chip microwave spectroscopy of an InAs nanowire Cooper-pair transistor Dominique Laroche, Alexander Proutski, Bas van 't Hooft, Jesper Nygård, Peter Krogstrup, Leo P Kouwenhoven, Attila Geresdi Controlling both the charging and the Josephson energies of superconducting islands is a crucial requirement for the operation and readout of prospective Majorana-based topological qubits. Here, we present the study of Cooper-pair transistors (CPTs) fabricated from InAs nanowires with superconducting Al shell, a promising platform for the physical realization of topological qubits. By utilizing on-chip microwave spectroscopy, we are able to induce excitations between energy levels of the CPT in a parity conserving manner. We map both the charge- and the photon-like excitations of the system, and show that it is possible to tune the CPT from a Coulomb-blockaded to a transmon-like regime by adjusting the system parameters. The quantum system is exhaustively modeled, allowing us to extract the effective charging and Josephson energies of the CPT. In addition, we study the ground state charge occupation of the CPT and attribute the observed temperature dependence of the even-odd parity structure to the presence of a sub-gap state on the superconducting island. |
Monday, March 4, 2019 4:30PM - 4:42PM |
C28.00011: Rapid single-shot detection of coherent tunneling in an InAs nanowire double quantum dot through dispersive gate sensing Damaz De Jong, Jasper Van Veen, Luca Binci, Amrita Singh, Jesper Nygård, Peter Krogstrup, Leo P Kouwenhoven, Wolfgang Pfaff, John Watson Dispersive gate sensing can enable scalable and high-fidelity readout of solid-state quantum bits. In particular, it has been proposed for fast non-demolition readout of topological qubits that can be measured by single electrons tunneling through zero-energy modes [1, 2]. Such a readout requires resolving the coherent charge tunneling amplitude from a quantum dot in a Majorana zero-mode host system faithfully on short time scales. |
Monday, March 4, 2019 4:42PM - 4:54PM |
C28.00012: Dispersive gate-sensing of a quantum dot coupled to a superconducting island Jasper Van Veen, Damaz de Jong, Lin Han, Christian Prosko, Torsten Karzig, Peter Krogstrup, Jesper Nygård, Leo P Kouwenhoven, John Watson, Wolfgang Pfaff Combining superconductivity with quantum dots in proximitized, semiconducting nanowires has led to many novel phenomena ranging from π-junctions to Cooper-pair splitters. Currently, these hybrid systems are of interest in the context of Majorana-zero modes (MZMs). In particular, it has been proposed that a topological qubit can be made by coupling a superconducting island hosting MZMs to a dot. However, to date, even trivial superconducting island-dot systems are not yet fully understood. |
Monday, March 4, 2019 4:54PM - 5:06PM |
C28.00013: Observation of quantized conductance in quantum point contacts on near surface InAsSb quantum wells Mihir Pendharkar, Joon Sue Lee, Michael A Seas, Anthony McFadden, Taozhi Guo, Connor Dempsey, Sean Harrington, Daniel J Pennachio, Tobias Brown-Heft, Hadass Inbar, Chris Palmstrom Topological protection in Majorana Zero Mode (MZM) based quantum computation depends on the induced topological energy gap in the host superconductor-semiconductor hybrid system. Induced topological gap is in turn directly proportional to the spin-orbit coupling in the host system. Certain compositions of InAsSb are expected to have an enhanced spin-orbit coupling as compared to InAs and InSb, thus making InAsSb an ideal platform for robust and scalable topological networks. In this work, top gate control of electron density in near surface InAsSb 2DEGs has been demonstrated. Full depletion can be observed at relatively low top gate voltages, at 2K. Additionally, quantum point contacts on InAsSb 2DEGs show quantized conductance at zero-field at 2K. This work paves the way for coupling superconductivity and enabling the use of near surface InAsSb quantum wells as a host material system for MZM-based topological quantum computation. |
Monday, March 4, 2019 5:06PM - 5:18PM |
C28.00014: Majorana fermions in nanowire-superconductor systems in periodic magnetic fields and their resonant manipulation Viktoriia Kornich, Xiaoli Huang, Maxim Vavilov, Mark G Friesen, M. A. Eriksson, Susan Coppersmith, Y. V. Nazarov The nanowire-superconductor structures with a helical magnetic field are known to host Majorana fermions. We show that the structures built in Si can support Majorana fermions even for the field shapes that are very different from helical ones. We discuss various shapes and imperfections of the magnetic field, and present phase diagrams for a wide range of experimental parameters. |
Monday, March 4, 2019 5:18PM - 5:30PM |
C28.00015: Robust micro-magnet geometries for Majorana modes in low g-factor materials Sara Turcotte, Samuel Boutin, Julien Camirand Lemyre, Ion Garate, Michel Pioro-Ladriere Signatures of Majorana bound states (MBS) have been widely reported in semiconductor materials with large spin-orbit coupling and proximity-induced superconductivity [1]. In principle, MBS can also emerge in weakly spin-orbit coupled materials subjected to inhomogeneous magnetic fields [2]. However, in practice small g-factors make it difficult to reach the topological phase. In this work, we explore a versatile approach where spin-orbit coupling arises from a non-uniform magnetic field produced by a micro-magnet array [3]. Using the recently developed RGF-GRAPE algorithm [4], we optimize realistic micro-magnet geometries to find suitable conditions for the emergence of MBS in a one-dimensional wire without intrinsic spin-orbit coupling. In addition, we study robustness of MBS against possible micro-magnet nanofabrication errors. Finally, we identify suitable low g-factor materials commonly used in the microelectronic industry as promising candidates for experimental implementations. |
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