Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R18: Quantum Dots and Artificial Molecules: Electronic properties |
Hide Abstracts |
Sponsoring Units: DCMP DMP Chair: Anthony Sigillito, Princeton Univ Room: LACC 306B |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R18.00001: Design of a Two Channel Kondo Interferometer Winston Pouse, Lucas Peeters, Shintaro Takada, Yuval Oreg, David Goldhaber-Gordon The transmission phase of electrons passing through a quantum dot gives insight into the many-body state of the mesoscopic system the dot is a part of. When coupled to a reservoir, the impurity spin is screened and a Kondo singlet is formed. This Kondo state scatters electrons, inducing a π/2 transmission phase shift, which was recently measured [1,2]. When an impurity is equally coupled to two reservoirs, the over-screening of the impurity leads to non-Fermi liquid behavior [3]. This two-channel Kondo state does not scatter electrons into one single particle state, but into an infinite number of such states, each with zero amplitude. Thus, a well-defined transmission phase might not be expected. However, it has been suggested that coherent transport of a new type of low-energy excitations can still produce a measurable phase shift [4]. We discuss design and preliminary implementation of a quantum dot device to measure the phase signature across a two-channel Kondo state. |
Thursday, March 8, 2018 8:12AM - 8:24AM |
R18.00002: Long-range quantum coherence in electronic dot–cavity systems Michael Ferguson, David Oehri, Clemens Rössler, Giorgio Nicolì, Thomas Ihn, Klaus Ensslin, Johann Blatter, Oded Zilberberg We present a theoretical analysis of coherent electronic transport across a mesoscopic dot--cavity system and extensions thereof. Such coherent transport has been recently demonstrated in an experiment with a dot--cavity hybrid implemented in a high-mobility two-dimensional electron gas [PRL 115, 166603 (2015)] and its spectroscopic signatures have been interpreted in terms of a competition between Kondo-type dot-lead and molecular-type dot--cavity singlet-formation. We analyze the system in a progressive fashion, starting with a single particle numerical investigation of the 2D geometry which allows us to postulate an effective 1D model with a local impurity. We then address this model using many body techniques, from exact diagonalisation to Fermi liquid theory through an equation of motion approach for Green's functions, to predict the system's transport properties. Our analysis brings forward all the transport features observed in the experiments and supports the claim that a spin-coherent molecular singlet forms across the full extent of the dot--cavity device. We then propose a new experimental setup which paves the way for an all electronic, long range entangling gate and could be used to study a delocalised impurity in a Kondo system, the Kondo cat. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R18.00003: Orbital effects of an in-plane field in a 2DEG quantum dot Peter Stano, Chen-Hsuan Hsu, Liuqi Yu, Leon Camenzind, Dominik Zumbuhl, Daniel Loss We report on the orbital effects of an in-plane magnetic field on the spectrum of a quantum dot based on two dimensional electron gas (2DEG). We present an effective two dimensional Hamiltonian where these effects enter in proportion to the flux penetrating the 2DEG. We show how the orbital effects allow to extract a wealth of information, e.g., on the heterostructure interface, the quantum dot size and orientation, or the spin-orbit fields. We present experimental data illustrating this new spectroscopic method for quantum dots. |
Thursday, March 8, 2018 8:36AM - 8:48AM |
R18.00004: Effects of an In-plane Magnetic Field on the Electron g-factor in a 2DEG Quantum Dot Chen-Hsuan Hsu, Peter Stano, Daniel Loss We investigate the interplay between an in-plane external magnetic field and the spin-orbit interaction in a quasi-two-dimensional electron gas (2DEG) quantum dot formed in the GaAs/AlGaAs heterostructure. In the presence of the applied in-plane magnetic field and out-of-plane electric field, the spin-orbit interaction can alter the spin states of the electron in the 2DEG quantum dot. We quantify such effect by computing the corrections to the electron g-factor in the lowest subband of the dot confinement potential. Using the third-order Lowdin perturbation theory, we find that the spin-orbit interaction can lead to significant corrections to the g-factor in a finite magnetic field, with the triangular confinement potential perpendicular to the 2DEG and bi-harmonic confinement potential in the 2DEG plane. We present the anisotropic g-factor corrections up to third order in the magnetic flux, as a function of the magnitude and direction of the magnetic field, as well as the dot orientation with respect to the crystallographic axes. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R18.00005: Removal of Accidental Degeneracy in Semiconductor Quantum Dots Siddhant Pandey, Sathwik Bharadwaj, L Ram-Mohan We present a quantitative analysis of the energy levels and wavefunctions of carriers in a cubic quantum dot of GaAs embedded in GaAlAs with finite confining potential barriers at their interfaces. The energy spectrum has substantially reduced degeneracies compared to the analytically determined energy levels of the infinite-barrier quantum box of the same dimensions. The level degeneracy of states has been explained by group representations of the octahedral point group. Projection operators for the irreducible representations provide a unique way of obtaining the linear combinations of the degenerate wavefunctions which form a basis set for the representations. Energy level splittings in the presence of externally applied electric and magnetic fields are also studied. |
Thursday, March 8, 2018 9:00AM - 9:12AM |
R18.00006: Coupling between Majorana bound state and quantum dot mediated by continuum Juan Ramos Andrade, Pedro Orellana, Edson Vernek Systems which include Majorana-like zero-energy excitations are gaining great deal of attention because their interesting properties. For instance, because of their non-Abelian statistics they are potentially useful for quantum computation implementations. Among other systems, they are predicted to be found bound to the end of a topological superconductor nanowire. When the MBS is connected to a quantum dot (QD), unique features are observed at zero-energy due to the leakage of the MBS into the QD. In this work we consider a single level QD and an MBS placed at the end of a topological nanowire. Both are coupled to the continuum and does not have a direct connection between them. We addressed the behavior of Coulomb blockade and Kondo effect in the QD due to the presence of MBS in the continuum. By employing a Green's function formalism via equation of motion procedure we are able to calculate the relevant physical quantities. Our results show that the leakage of the MBS into continuum state can alter the either the Kondo physics of the system. We believe that our findings could be useful to establish new measurables features in MBS-QD systems. |
Thursday, March 8, 2018 9:12AM - 9:24AM |
R18.00007: Majorana Bound States in Chains of Superconducting Islands John Stenger The differential conductance is calculated for charge tunneling into a semiconductor wire proximity coupled to several superconducting islands. Alone the islands are too small to host well separated Majorana bound states, however, together strong topological protection can arise. The topological phase boundary is studied with respect to the magnetic field, chemical potential, and coupling between the islands. It is shown that the onset of the topological phase has a non-trivial dependence on the island coupling. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R18.00008: A 2x2 quantum dot analogue simulator Juan Pablo Dehollain, Uditendu Mukhopadhyay, Christian Reichl, Werner Wegscheider, Lieven Vandersypen The interaction between electrons in arrays of electrostatically defined quantum dots is naturally described by a Fermi-Hubbard Hamiltonian. Moreover, the high-degree of tunability of these systems make them a perfect platform to simulate different regimes of the Hubbard model. We present an array of 2x2 gate-defined quantum dots in a AlGaAs/GaAs heterostructure. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R18.00009: Environment-Induced Suppression of the Landau-Zener Transition Probability in a Driven Two-Level System Mikhail Raikh, Eugene Mishchenko, Rajesh Malla When the drive that causes the level crossing of a qubit is slow, the probability, PLZ, of the Landau-Zener transition is close to 1. We show that, in this regime, which is most promising for applications, the noise due to coupling to the environment, reduces the average PLZ. At the same time, the survival probability, 1-PLZ, which is exponentially small for a slow drive, can be completely dominated by the noise-induced correction. On the physical level, the enhancement of the survival probability is due to the absorption of the “noise quanta”. This absorption can be calculated analytically by treating coupling to the environment perturbatively. The absorption is most efficient for the frequency components of noise of the order of the level repulsion, J. Thus, the survival probability is the function of the product, Jτ, where τ is the noise correlation function. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R18.00010: Dephasing effects on a driven triple quantum dot system Jorge Villavicencio, Irene Maldonado, L. D. Contreras-Pulido, E. Cota, J. A. Maytorena We analyze the effect of environmental dephasing on the electronic current in an ac-driven triple quantum dot system in a symmetric Λ-configuration characterized by an interdot energy. The electronic current is explored by solving the time evolution equation of the density matrix as a function of the frequency and amplitude of the driving field. Depending on the field amplitude, we observe two characteristic spectra, a Fano-type profile or a more symmetric structure. At resonance, the former shows a prominent peak, while the latter exhibits a strong suppression due to dynamic localization. In the first the case, we observe the maximum is reduced due to dephasing, while in the second it is shown that dephasing lifts the localization. In both cases, off resonance, we find that dephasing increases the current systematically at the current minima. This dephasing assisted tunneling phenomenon is found to persist for a large range of values of the coupling to the drain, in contrast to the known undriven case. The effect of dephasing is also discussed using Floquet theory, and by analytical expressions for the electronic current within the rotating wave approximation. |
Thursday, March 8, 2018 10:00AM - 10:12AM |
R18.00011: Charge Noise in InAs/GaAs Coupled Quantum Dot Devices Cameron Jennings, Parveen Kumar, Cyprian Czarnocki, Allan Bracker, Samuel Carter, Daniel Gammon, Michael Scheibner Exciton states in semiconductor quantum dots (QDs) shift their energy with electric field via the quantum-confined Stark effect, allowing detection of individual nearby charges using resonant optical excitation. Conversely, charge noise in QD devices broadens the optical transition linewidth above the lifetime-limited value. Tunnel-coupled QD pairs (CQDs) host interdot exciton states with a large electric dipole moment, resulting in higher electric field sensitivity and allowing for in-situ tuning of the transition energy over tens of meV within a charge stability plateau. We measure the photoluminescence and absorption spectra of diode-embedded InAs/GaAs CQDs at 20 K and observe interdot states with a significantly broader linewidth than the shorter-lived single-dot states, indicating spectral wandering from a noisy charge environment. We investigate defect charging mechanisms by monitoring the absorption linewidth while varying excitation conditions, including wavelength and power of the resonant laser and the effect of a second laser above the GaAs bandgap. Monte Carlo simulations of charged defects reproduce experimental observations, giving insight into their spatial distribution and dynamics. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R18.00012: Weak localization in variable-concentration embedded phosphorus delta layers in silicon produced by variable PH3 dosing Joseph Hagmann, Xiqiao Wang, Pradeep Namboodiri, Jonathan Wyrick, Roy Murray, M. Stewart Jr., Richard Silver, Curt Richter The key building block for devices based on the deterministic placement of dopants in Si is the formation of P dopant monolayers and the overgrowth of high quality crystalline Si. Lithographically defined dopant δ-layers can be formed with an STM, which can pattern device features on a H-terminated silicon surface by exposing Si dangling bonds at specific locations and placing P at these locations with atomic precision by exposing the surface to PH3. The motivation for this research is to advance the dopant formation and overgrowth processes necessary to produce prototypical few-atom devices in a controlled solid-state environment. Our earlier work has demonstrated that a careful magnetotransport study at low T, along with analysis of the weak localization (WL) feature, allows us to extract parameters associated with the electronic transport that offer a meaningful quantitative characterization of δ-layer quality and dopant diffusion, with better resolution than the more commonly used SIMS. We build on this work by examining the effect on the transport and WL behaviors in a set of samples with Si:P delta layers produced with different PH3 exposure procedures prior to a standard Si encapsulation. Here, we describe the overall methodology and the findings of this study. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R18.00013: Coupled quantum corrals Anthony Ruth, Laura Collins, David Green, Morten Eskildsen, Kenjiro Gomes, Boldizsar Janko We investigate the properties of electronic states in quantum corrals assembled by single molecule STM manipulation. In particular, we analyze theoretically corrals with geometries similar to various aromatic molecules, such as benzene. Furthermore, we couple the benzene-like structure to multiple rectangular corrals or resonators, and investigate the effect of the resonator-benzene corral interaction on the local density of states. We find that for a certain energy and coupling range the effect of the resonator on the trapped electron states of the corral is similar to that of a local electric field. This finding opens the possibility of using resonators as gates in studying the interaction between electronic states in the corral and external quantum systems. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R18.00014: Quantum Coherent Transport in a Synthetic Single Molecule Transistor Laura Collins, David Green, Anthony Ruth, Boldizsar Janko, Kenjiro Gomes The use of synthetic quantum systems makes it possible to study phenomena that cannot be probed by conventional experiments. We created synthetic molecules using atomic manipulation, and used a synthetic molecule to design and assemble a prototype synthetic single molecule transistor. We directly imaged the change in coherence using tunneling spectroscopy, and utilized quasiparticle scattering to visualize an electronic connection between the source and drain of our prototype single molecule transistor. |
Thursday, March 8, 2018 10:48AM - 11:00AM |
R18.00015: Tailoring Charge Modulation in Synthetic Molecules and Two-Dimensional Crystals David Green, Laura Collins, Anthony Ruth, Boldizsar Janko, Morten Eskildsen, Kenjiro Gomes We use atomic manipulation to explore methods to control charge modulation in synthetic systems. From synthetic molecules to two-dimensional systems, atomic manipulation allows us to engineer changes in the electronic behavior. We then visualize the resulting charge modulations within these synthetic systems with great detail through tunneling spectroscopy. For two-dimensional crystals this could also allow us to explore the formation of charge density waves. The control of charge modulation can create unique devices such as large bandwidth frequency sources and sub-Boltzmann switching transistors for ultra-low power digital operation. |
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