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 Y54: Materials for Quantum Information Science-2 (Superconducting and Semiconducting Materials)Focus Live
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Sponsoring Units: DMP DQI Chair: Jinkyoung Yoo, Los Alamos National Laboratory |
Friday, March 19, 2021 11:30AM - 12:06PM Live |
Y54.00001: New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds Invited Speaker: Andrew Houck The superconducting transmon qubit is a leading platform for quantum computing and quantum science. Building large, useful quantum systems based on transmon qubits will require significant improvements in qubit relaxation and coherence times, which are orders of magnitude shorter than limits imposed by bulk properties of the constituent materials. This indicates that relaxation likely originates from uncontrolled surfaces, interfaces, and contaminants. Previous efforts to improve qubit lifetimes have focused primarily on designs that minimize contributions from surfaces. However, significant improvements in the lifetime of two-dimensional transmon qubits have remained elusive for several years. We will present a materials-based approach to reliably reproduce long coherence times by using tantalum-based devices, and present detailed characterization of devices to understand remaining sources of decoherence. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y54.00002: A density-functional theory study of the Al/AlOx/Al tunnel junction Changeun Kim, Keith Ray, Vincenzo Lordi The aluminum oxide Josephson tunnel junction (JJ) is a key component of superconducting quantum devices. The coherence time of superconducting qubits has seen five orders of magnitude increase over the last twenty years, however, further improvements in JJ quality and uniformity are needed to realize a scalable quantum computer. We used ab-initio calculations to study the atomistic features limiting JJ performance. We created realistic models of Al/AlOx/Al JJs and compared to experimental observations. The true thickness of the insulating part of the JJ can be different from what is visible under electron microscopes. We compute the JJ critical current by solving the Schrödinger equation for tunneling over the Kohn-Sham effective potential. Comparison between amorphous and crystalline cases highlights what is possible with better control over the interface microstructure. Further analysis of the interfaces revealed the amorphous nature of the oxide leads to local dipole formation, fostering disruptive two-level-systems. Our ab-initio atomistic analysis presents an approach to predict the performance of superconducting quantum tunnel junction and assess novel materials. Prepared by LLNL under Contract DE-AC52-07NA27344. |
Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y54.00003: Cooperative Photon Emission from Indistinguishable Quantum Dots in Free Space ZheXian Koong, Eleanor Scerri, Ted Santana, Moritz Cygorek, Yong Ma, Suk-In Park, Jin Dong Song, Erik Gauger, Brian D Gerardot The ability to observe cooperative effects in light-matter coupling such as super-radiance is an important steppingstone towards realizing photon-mediated communication between matter qubits and a versatile quantum optics platform. Here, we experimentally demonstrate cooperative emission from a pair of individually tunable semiconductor quantum dots in a free-space (2D) geometry. By measuring photon correlations with Hanbury-Brown and Twiss and Hong-Ou-Mandel interferometers, we fully map the quantum optical signatures of super-radiant photon emission for resonant driving and incoherent pumping as a function of detuning. We find unambiguous evidence for collective emission, with particularly clear signatures of super-radiance from pulsed resonance fluorescence. This includes the observation of photon bunching and Poissonian photon statistics of the super-radiant state. Our data is well-described by a theoretical model which incorporates the sub-micron spacings between these emitters and the decoherence from the emitters’ solid-state environment. Our work represents an important step towards tailoring controllable cooperative behavior, enabling prospects for harnessing collective light-matter interaction effects. |
Friday, March 19, 2021 12:30PM - 12:42PM Not Participating |
Y54.00004: Traveling Wave Parametric Amplification without Dispersion Engineering Chung Kow, Tristan Brown, Viktor A Podolskiy, Archana Kamal Josepshon Traveling Wave Parametric Amplifiers (J-TWPAs) are promising platforms for realizing quantum-limited broadband amplification of microwave signals. However, substantial gain in such systems is attainable only when strict constraints on phase matching the signal, idler and pump waves are satisfied -- this is rendered particularly challenging in the presence of nonlinear effects, such as self- and cross-phase modulation, which scale with the pump intensity. A recent notable approach to alleviate this problem involves introducing resonant elements into the transmission line and pumping near the stop band of the modified dispersion curve. Here we propose a new system that can realize large broadband gain without employing any dispersion engineering. The efficiency of the resultant four-wave mixing process allows achieving >20dB gain over few-GHz bandwidths with much shorter lines than previous implementations, making the proposed architecture particularly appealing from a fabrication perspective. Additional optimization, coupled with flexibility in pump engineering, can be used to modify the gain profile in view of targeted applications, such as optimizing maximum gain vs constant-gain bandwidth. |
Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y54.00005: Control of spin relaxation in GaAs nanowires with electric bias and nanowires aspect ratio ChanJu (Zoe) You, Stefania Castelletto, Abdel F. Isakovic Motivated by the importance of understanding spin relaxation in semiconductor nanostructures, such as quantum dots and quantum wells, we studied how electric field and contact geometry controls spin relaxation in 1D nanowires. We report spin relaxation time in 50-400 ns range for a range of sample geometries and nanowire aspect ratio. Further, the range of applied voltages, of the order of 1V, and electric fields is technologically relevant. In our experiments, we have relied on spin noise spectroscopy applied to substrate supported back-etched nanowires. One unusual feature of the spin noise spectrum in our nanowires is an appearance of a secondary, satellite peak, in addition to the expected peak. Both, the main and the secondary peak bear similarities to the single peak spin noise spectra in quantum dots and quantum wells. We modeled these spectra using a modified spectral response function, and we propose this secondary peak appears due to a transition between two modes of spin transport within nanowires. Namely, depending on biasing condition, temperature, and geometry, our analysis suggests that spin noise spectra show signs of both drift-diffusion transport and ballistic transport. |
Friday, March 19, 2021 12:54PM - 1:06PM Live |
Y54.00006: Modulation Doping of Template-Defined InGaAs Nanowires Kristopher Cerveny, Martin Friedl, Mohammad Samani, Didem Dede, Chunyi Huang, Lincoln J Lauhon, Dominik Zumbuhl, Anna Fontcuberta i Morral Templated semiconductor nanowires with strong spin-orbit interaction (SOI) are a scalable and versatile platform [1] to create and study novel quantum states of matter, such as helical states and spin helices, Majorana- and para-fermions. Modulation doping is a very well established technique to enhance mobility and control carrier concentration. Here, we report recent results on InGaAs nanowires with remote doping in the GaAs nanomembrane template grown via molecular beam epitaxy in a selective area growth approach [2]. By confining dopants near the top of the GaAs membrane and increasing the indium content, the process gives major improvements in mean free path and SOI. With a wrap-around top gate, the density was tuned down to full depletion. Using a split gate would make it possible to apply and tune an electric field, opening new avenues for investigating gate-controlled Rashba and Dresselhaus SOI. |
Friday, March 19, 2021 1:06PM - 1:18PM Live |
Y54.00007: The impact of using palladium gates for silicon quantum dot fabrication: defect densities and strain Ryan Stein, Michael David Stewart
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Friday, March 19, 2021 1:18PM - 1:30PM Live |
Y54.00008: Creation of dark exciton states in a semiconductor quantum dot by a light field with a strong longitudinal component Guillermo Quinteiro, Doris Reiter, Matthias Holtkemper, Tilmann Kuhn Depending on their spin configuration, excitons in quantum dots (QDs) are efficiently or poorly coupled to light, and so are called bright and dark, respectively. Ground-state dark excitons are long-lived states useful in quantum information technology. Here we predict the formation of ground-state dark excitons in QDs excited by light having a strong longitudinal component, e. g. a radially polarized beam. Our theoretical QD model includes asymmetry, light-matter interaction, Coulomb interaction between carriers, and valence-band mixing. Exciton states are calculated using Configuration Interaction and phonon relaxation processes are studied within a rate equation model. We find that the longitudinal field creates high-energy bright excitons with particular spin configurations that may relax with significant probability into ground-state dark excitons. For example, a possible optically excited bright-exciton is a mixture of non-interacting electron–hole (eh) pair states with one of its components being a dark eh pair state. Phonon-induced transitions do not alter the spin configuration, but cause this high-energy exciton to relax to a ground state in which the dominant non-interacting component is that dark eh pair, thus creating the desired dark exciton. |
Friday, March 19, 2021 1:30PM - 1:42PM Live |
Y54.00009: Closing the loop on valley splitting in 28Si/SiGe: atom probe tomography, tightbinding, and cryomultiplexing Brian Paquelet Wuetz, Merritt Losert, Sebastian Koelling, Anne-Marije Zwerver, Lucas Stehouwer, Nodar Samkharadze, Stephan Philips, Mateusz T Madzik, Guoji Zheng, Xiao Xue, Sergei Amitonov, Mario Lodari, Amir Sammak, Susan N Coppersmith, Lieven Vandersypen, Oussama Moutanabbir, Mark G Friesen, Giordano Scappucci 28Si/SiGe heterostructures provide a compelling host material for a scalable quantum computer, due to the long coherence times of spin qubits and compatibility with industry. Here we study 28Si/SiGe heterostructures with varying roughness of the critical Si/SiGe interfaces to understand the energy splitting of the lowest lying conduction valleys (valley splitting). To improve control of valley splitting in 28Si/SiGe, we implement a feedback cycle for materials stack engineering including several elements. |
Friday, March 19, 2021 1:42PM - 1:54PM Live |
Y54.00010: Gate-defined quantum dots in monolayer and bilayer WSe2: Part I, Fabrication Jeb Stacy, Shiva Davari Dolatabadi, Alejandro Mercado, Jeremy Tull, Rabindra Basnet, Krishna Pandey, Md Rafique Un Nabi, Kenji Watanabe, Takashi Taniguchi, Jin Hu, Hugh O. H. Churchill Gate-defined quantum dots in monolayer and bilayer WSe2 are a platform for novel quantum transport and quantum optoelectronic investigations of WSe2, as well as for potential applications in coherent valleytronics. In this presentation, we discuss design considerations and implementations for the fabrication of ~100 nm diameter gate-defined, p-type quantum dots in monolayer and bilayer WSe2. The devices were controlled using a combination of bottom confining gates and a top accumulation gate, with hBN used for gate insulation and encapsulation of the WSe2. Top hBN and WSe2 were transferred onto Pt for reliable p-type bottom contact. |
Friday, March 19, 2021 1:54PM - 2:06PM Live |
Y54.00011: Gate-defined quantum dots in monolayer and bilayer WSe2: Part II, Measurement Shiva Davari Dolatabadi, Jeb Stacy, Alejandro Mercado, Jeremy Tull, Rabindra Basnet, Krishna Pandey, Md Rafique Un Nabi, Kenji Watanabe, Takashi Taniguchi, Jin Hu, Hugh O. H. Churchill
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Friday, March 19, 2021 2:06PM - 2:18PM Live |
Y54.00012: Improvement in Superconducting Resonator Quality Factor Through Surface Passivation Cassidy Berk, Archan Banerjee, AHMED HAJR, John Mark Kreikebaum, Virginia Altoe, David Ivan Santiago, D. Frank Ogletree, Irfan Siddiqi High quality factor resonators are crucial components in photon detectors as well as many quantum computing architectures. There are two dominant mechanisms of loss in these devices. The first is due to two-level systems which mostly reside in the surface oxides. The second stems from a modification of the surface resistance due to quasiparticles within the superconductor. In this study, we characterize the effect of these loss mechanisms for Nb co-planar resonators with and without a TiN capping layer by correlating materials analysis (XPS,TEM) and low temperature electrical measurements. We find that the presence of the capping layer improves the quality factor relative to the standard resonator. |
Friday, March 19, 2021 2:18PM - 2:30PM Live |
Y54.00013: Robust Performance of Superconducting Nanowire Single Photon Detectors under High Magnetic Fields Claire Marvinney, Yun-Yi Pai, Brian Lerner, Matthew Feldman, Jie Zhang, Aaron Miller, Benjamin Lawrie Superconducting nanowire single photon detectors (SNSPDs) offer high-quantum-efficiency and low-dark-count single photon detection. For quantum applications, operation may require high magnetic fields if integrated with a spin-based device. Here, we explore the magnetic field dependence of amorphous SNSPDs, determining they are robust up to ±6T with a negligible dark count rate and unchanged quantum efficiency at operation bias currents. However, the maximum bias current is suppressed asymmetrically under opposing fields. The asymmetric dark count origins are under investigation, with additional experiments under perpendicular fields using a milliKelvin scanning confocal microscope. This enables near-diffraction limited resolution of the incident light on the SNSPD, allowing additional study of the position dependence of the SNSPD readout waveforms. Together, these measurements will provide a fundamental improvement in our understanding of the material constraints on SNSPDs. |
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