Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L46: Topological Superconductivity: Majorana ModesLive
|
Hide Abstracts |
Sponsoring Units: DCMP Chair: Jukka Vayrynen, Purdue University |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L46.00001: Transmission Amplitude through a Coulomb blockaded Majorana Wire Matthias Thamm, Bernd Rosenow We study electronic transport through a Coulomb blockaded superconducting Rashba wire in the co-tunneling regime between conductance resonances. Embedding such a wire into one arm of an electron interferometer allows to study the amplitude for coherent transmission. Varying an external Zeeman field allows to tune the wire into a topological regime, where localized Majorana zero modes are formed at both ends of the wire. In this topological phase, the nonlocal transport through Majorana zero modes is the dominant mechanism and gives rise to a maximum in the transmission amplitude as a function of Zeeman field, whose height is proportional to the wire length. On the other hand, for tunneling through a generic extended state or through a pair of Andreev bound states, the transmission amplitude is independent of wire length. Hence, the Zeeman field and length dependence of the transmission amplitude are unique signatures for the presence of Majorana zero modes. Our results allow an interpretation of the recent experimental results [1]. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L46.00002: Modeling transport in the Coulomb blockade regime in realistic Majorana nanowires Yi-Hua Lai, Jay Sau The ability to distinguish Andreev bound states and disorder-induced zero-bias peaks is a crucial step towards the demonstration of topological quantum computation using Majorana modes. Coulomb blockade (CB) transport that has been measured in Majorana nanowires is a probe that effectively probes both ends of the wire simultaneously. Here we theoretically study the Coulomb-blockaded Majorana nanowire with all the prominent realistic effects (self-energy, quantum dot, Zeeman-field-varying superconducting gap, SC states, metallic continuum states) included. Instead of using the computationally-demanding master equation approach due to its exponentially large space of many-body probabilities, we utilize a generalization of the Meir-Wingreen formalism to calculate the conductance. We will derive the generalized Meir-Wingreen formula from the rate equations in this work. Specifically, we will focus on the strong CB limit and discuss the transport from the few-electron process, two-level case, one-level case analytically. To explain the experimental phenomena from the past experimental works, we numerically demonstrate bright-dark-bright pattern, decreasing oscillations of conductance peak spacing, and suppressed normal CB peak relative to Andreev bound states/MBSs. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Live |
L46.00003: Double Majorana vortex zero modes in superconducting topological crystalline insulators with surface rotation anomaly Shingo Kobayashi, Akira Furusaki Multiple Majorana vortex zero modes can emerge when the parent material in proximity to an s-wave superconductor is a 3D topological crystalline insulator (TCI) with surface Dirac cones protected by crystal symmetry. Thus far a variety of TCIs have been predicted theoretically, while little has been known about Majorana vortex zero modes in superconducting TCIs, especially for newly-proposed TCIs having surface rotation anomaly, which realize a new class of topological surface states involving multiple Dirac cones. We show that the proximity-induced s-wave superconductivity on the surface of |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L46.00004: Majorana signatures in charge transport through a topological superconducting double-island system Jukka Vayrynen, Dmitry I. Pikulin, Roman Lutchyn We investigate the dynamics of a charge qubit consisting of two Coulomb-blockaded islands hosting Majorana zero modes. The frequency of the qubit is determined by coherent single-electron tunneling between two islands originating from the hybridization of two Majorana zero modes localized at the junction. We calculate the sequential tunneling current I through the double-island device coupled to normal metal leads. We demonstrate that the I−V characteristics in the large-bias regime can be used as a measurement of the coherent Majorana coupling EM. We propose dc and ac transport experiments for measuring EM, and discuss their limitations due to intrinsic dephasing mechanisms such as excited quasiparticles. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L46.00005: Quantum-critical dynamics of a Josephson junction at the topological transition Vladislav Kurilovich, Chaitanya Murthy, Pavel Kurilovich, Bernard Van Heck, Leonid Glazman, Chetan Nayak A semiconducting nanowire proximitized by a superconductor is emerging as a building block of a topological qubit. Magnetic field applied to a proximitized nanowire drives it through the critical point into a topological state. We investigate signatures of this quantum phase transition in the microwave response of a nanowire Josephson junction. To this end, we compute the finite-frequency admittance Y(ω) of the junction at the transition and in its vicinity. At the critical point, the dependence of the admittance on frequency and temperature is universal and determined by the symmetries of the system. We find that, despite the closing of the spectral gap at the transition, the dissipative response may remain weak: ReY(ω) ~ max(ω, T)2. This behavior is markedly different from the conventional transition between the superconducting and normal states. We also establish scaling functions for the frequency-dependence of the admittance near the transition. Our work paves the way towards the microwave detection of the topological phase transition in proximitized semiconducting nanowires. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L46.00006: Majorana fermions in p-wave superconducting wire Mehdi Zarea, James Sauls The mean-field model of a p-wave superconducting wire has localized zero energy Kitaev Majorana excitations [1]. We show that Majorana fermions appear only in the mean-field model in which the ground state is the superposition of states with different numbers of electrons. In a physical system with fixed number of particles the exact zero energy excitations are not Majorana but two delocalized Dirac fermions which adiabatically tunnel between even and odd condensates. We present a simple model of interacting electrons which in mean-field approximation reproduced Kitaev fermions but when it is solved exactly does not show them. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L46.00007: Braiding Floquet Majorana Modes in 1D Topological Superconductors Bill Truong, Tami Pereg-Barnea Recent work has established that Majorana zero modes can be braided in a single, clean Kitaev chain with a Floquet drive. Essential to this braiding protocol is the use of Majorana π modes, which are unique to Floquet systems, as an additional degree of freedom. In our work, we explore the consequences of introducing disorder and interactions into the braiding protocol developed by Ref. [1]. Furthermore, we investigate several methods of transporting Majorana modes across the chain with a focus towards their impact on the success of the braiding protocol. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L46.00008: Reducing Majorana Hybridization via Periodic Driving Brett Min, Ivar Martin, Tami Pereg-Barnea, Kartiek Agarwal It is an ongoing challenge to engineer setups in which Majorana zero modes at the ends of one-dimensional topological superconductor are well isolated which is the essence of topological protection. Recent developments have indicated that periodic deriving of a system can dynamically induce symmetries that its static counterpart does not possess [1]. We further develop the original protocol [2] where this idea [1] is applied to a system of quantum dot (QD) coupled to a Kitaev chain hosting an imperfect (overlapping) Majorana zero modes. We numerically simulate a protocol in which an electron periodically hops back and forth from the QD and the wire. We demonstrate that the current protocol reduces a non-zero hybridization energy that manifests from imperfect Majoranas by orders of magnitude. Furthermore, we examine the efficiency of the suppression and how robust it is to imperfections. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L46.00009: An architecture for "draiding" majoranas for quantum computing Kartiek Agarwal, Ivar Martin We propose and analyze a family of periodic braiding protocols in systems with multiple localized Majorana modes (majoranas) for the purposes of Hamiltonian engineering. The protocols rely on double braids – draids – which flip the signs of both majoranas, as one is taken all the way around the other. Rapid draiding can be used to dynamically suppresses some or all inter-majorana couplings, improving putative quantum memories, and realizing topological models. Remarkably, draids can be implemented without having to physically braid majoranas or performing projective measurements. For instance, we show that draids can be performed by periodically modulating the coupling between a quantum dot and a topological superconducting wire to dynamically suppress the hybridization of majoranas in the quantum wire. In current setups, this could lead to suppression of this coupling by a few orders of magnitude. The robustness of this protocol can be shown to parallel the topological robustness of physically braided majoranas. We propose an architecture that implements draids between distant majorana modes within quantum register using a setup with multiple quantum dots. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L46.00010: Topological superconductors with periodically modulated magnetic fields: Andreev vs Majorana bound states, and emergent supersymmetry Pasquale Marra, Daisuke Inotani, Muneto Nitta Majorana bound states can be realized in one-dimensional proximized superconductors in the presence of spatially-modulated magnetic fields. We will show that, if the field amplitude is not uniform, these systems can exhibit also topologically nontrivial Andreev bound states[1], which correspond to a topological invariant, the particle-hole Chern number, defined in a synthetic two-dimensional space in analogy to the spin Chern number of quantum spin Hall systems. Majorana and nontrivial Andreev states have similar spectroscopic signatures but are topologically inequivalent. Moreover, we will then show that emergent supersymmetry (SUSY) can be induced by spatially-modulated fields. The possible realization of SUSY in mesoscopic systems may lead to useful insights and unexpected analogies between high-energy and condensed matter physics. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L46.00011: Stability of topological superconducting qubits with number conservation Matthew Lapa, Michael Levin The study of topological superconductivity is largely based on the analysis of simple mean-field models that do not conserve particle number. A major open question is whether the properties of these mean-field models persist in more realistic models with a conserved particle number and long-range interactions. For quantum computing applications, two key properties that one would like to verify in more realistic models are (i) the existence of a set of low-energy states (the qubit states) that are separated from the rest of the spectrum by a finite energy gap, and (ii) an exponentially small (in system size) bound on the splitting of the energies of the qubit states. These |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L46.00012: Corner states in a second-order topological superconductor and their braiding Tudor E Pahomi, Manfred W Sigrist, Alexey A Soluyanov We model a second-order topological phase realized in a thin-film p-wave superconductor under the influence of an in-plane Zeeman field and proximity-induced spin-singlet pairing. This system exhibits two topologically-protected Majorana states localized at the corners of a square-shaped sample. By tuning certain Hamiltonian parameters, the centers of the two excitations can be shifted to various corners, while their energy is zero as long as particle-hole symmetry (PHS) is conserved. Within this degenerate ground-state manifold, we show there exists a closed path corresponding to the adiabatic braiding of the corner states. In one cycle, each Majorana accumulates a statistical phase π, which confirms their fractional statistics. This property, alongside the PHS-ensured Majorana operator algebra, suggests the proposed two-dimensional system might be a step toward topologically-protected non-Abelian braiding. The concept of a possible experimental realization of the proposed superconductor is presented. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L46.00013: Quantum doubles in one dimension Victor Albert, David Aasen, Wenqing Xu, Wenjie Ji, John P Preskill, Jason F. Alicea Non-Abelian defects that bind Majorana zero modes (or their parafermionic extensions) are central to intrinsically fault-tolerant quantum computation schemes. Underpinning their established understanding is the quantum Ising spin chain, which can be recast as a fermionic model or viewed as a standalone effective theory for the toric-code edge---both of which harbor non-Abelian defects. We generalize these notions by deriving an effective Ising-like spin chain describing the edge of quantum-double topological order. By relating Majorana and parafermion modes to anyonic strings, we develop quantum-double generalizations of non-Abelian defects. We also provide a continuum description of the spin chain that makes contact with strongly correlated systems via non-Abelian bosonization. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L46.00014: Volkov-Pankratov states and topological superconductivity in Pb monolayers David Alspaugh, Daniel E Sheehy, Mark Oliver Goerbig, Pascal Simon We study the in-gap states that appear at the boundaries of both one- and two-dimensional topological superconductors. While the massless Majorana quasiparticles are guaranteed to arise by the bulk-edge correspondence we find that they could be accompanied by massive Volkov-Pankratov (VP) states which are present only when the interface is sufficiently smooth. These predictions can be tested in an s-wave superconductor with Rashba spin-orbit coupling placed on top of a magnetic domain wall. We calculate the spin-resolved local density of states of the VP states about the band inversion generated by a magnetic domain wall and find that they are oppositely spin polarized on either side of the topological phase boundary. We also demonstrate that the spatial position energy-level spacing and spin polarization of the VP states can be modified by the introduction of in-plane electric fields. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700