Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session Y29: Semiconducting Qubits: Automation of Tune-up |
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Sponsoring Units: DQI Chair: Natalia Ares Room: BCEC 162A |
Friday, March 8, 2019 11:15AM - 11:27AM |
Y29.00001: Silicon MOSFET quantum dots with simplified metal-gate geometry Eduardo Barrera, Francois Sfigakis, Ferhat Aydinoglu, Jonathan D Baugh Silicon (Si) CMOS spin qubits have become a promising platform for a future quantum information processor due to recent demonstrations of high fidelity single and two qubit gates [Veldhorst et. al., Nature 526.7573 (2015)], compatibility with industrial CMOS process and promising prospects for scalability. Typical Si spin qubits devices consist of gate-defined quantum dots, each defined by several metal gates, which pose a challenge to scaling the technology up. Hence, future designs of Si spin qubits will need to reduce the fabrication complexity and adopt a scalable design. |
Friday, March 8, 2019 11:27AM - 11:39AM |
Y29.00002: Single electron charge shuttling in a linear quantum dot array Adam Mills, David Zajac, Michael Gullans, Felix Schupp, Thomas Hazard, Jason R Petta Recent advances in silicon spin qubits have pushed single qubit fidelities beyond 99.9% [1,2] and have lead to the realization of two-qubit gates based on exchange coupling [3-6]. In order to advance spin qubits to the next level of technological complexity, it is important to start investigating how to scale up to larger multi-component architectures. These architectures must allow for arbitrary coupling of spatially separated qubits, demanding the development of inter-qubit quantum state transfer procedures. Here we demonstrate shuttling of a single electron across a linear array of 9 series-coupled Si quantum dots in ~50 ns with an approach that is extendable to larger quantum dot arrays. |
Friday, March 8, 2019 11:39AM - 11:51AM |
Y29.00003: Electron shuttling based error-correction architectures using quantum dot qubits Veit Langrock, David Peter DiVincenzo Spin-qubits based on electrons in gate-defined quantum dots [1] are currently one of the major candidates for quantum computers realized in semiconductor hosts. |
Friday, March 8, 2019 11:51AM - 12:03PM |
Y29.00004: Simulating coherent electron shuttling in quantum dots Brandon Buonacorsi, Benjamin D Shaw, Jonathan D Baugh Coherent transport of electron spins is required for several proposed large-scale architectures based on quantum dot spin qubits [1,2]. In [1], spin singlets are distributed across neighboring computational nodes by sequential single-electron tunneling through a linear array of quantum dots. We adopt a simplified metal-gate geometry for silicon MOS dots and use the Nextnano software to determine the potential landscape as a function of varying gate voltages, subsequently solving the time-dependent Schrodinger equation in 1D to simulate coherent shuttling. An algorithm is presented that calculates time-dependent voltages that maintain a desired fidelity with the ground state orbital wavefunction. These tools are used to vary the geometrical device parameters to maximize the electron shuttling velocity. We further show that the essential physics can be captured in an effective Hamiltonian model, which allows us to explore how spin-orbit and valley states affect the shuttling fidelity and maximum velocity. |
Friday, March 8, 2019 12:03PM - 12:15PM |
Y29.00005: Algorithm for automated tuning of a quantum dot to the single electron regime. Maxime Lapointe-Major, Julien Camirand Lemyre, Dany Lachance-Quirion, Sophie Rochette, Michel Pioro-Ladriere Tuning quantum dot devices to an operational target is a time-consuming process. In this work, we have developed an algorithm adapted to quantum dots measured by charge detection with a single electron transistor (SET). The program uses a computer-controlled visual approach, where the tuning of the quantum dot is performed with an intuitive heuristic approach. Small size stability diagrams of the dot and reservoir gates are measured in an adaptive sequence until the last electronic transition of the quantum dot is found. For each stability diagram, the charge detector background is removed and the electron occupancy transitions are identified. From these transition points, lines are reconstructed using a modified Hough transform and other image detection tools. Preliminary tests on previously measured stability diagrams show reliable performances of the algorithm for different samples. This work is a step towards fast automatized initialization of quantum dots arrays. |
Friday, March 8, 2019 12:15PM - 12:27PM |
Y29.00006: Control of a GaAs “QuByte” in the single electron regime – adding dots one-by-one Christian Volk, Anne-Marije Zwerver, Pieter Eendebak, Sjaak van Diepen, Floor van Riggelen, Uditendu Mukhopadhyay, Juan Pablo Dehollain, Toivo Hensgens, Christian Reichl, Werner Wegscheider, Lieven Vandersypen Spin qubits based on semiconductor quantum dots (QDs) are promising building blocks for quantum computation. So far, research mainly focused on devices with up to four QDs. However, quantum algorithms, quantum simulations and mediators to exchange quantum information require larger and scalable systems. Though, controlled filling becomes challenging with an increasing number of QDs due to cross-capacitances and electron latching effects. |
Friday, March 8, 2019 12:27PM - 12:39PM |
Y29.00007: Towards Autonomous Tuning of Double Quantum Dots Jana Darulova, Sebastian Pauka, Alice Mahoney, John Hornibrook, Nathan Wiebe, Christopher Granade, Maja C Cassidy, David Reilly, Matthias Troyer Defining quantum dots in semiconductor or semiconductor/superconductor heterostructures is an essential step in initializing solid-state qubits. To date, the majority of the repetitive procedure of finding suitable gate voltages defining a quantum dot is done manually. However, as the complexity of devices as well as the number of devices per chip grows, this approach becomes unfeasible. |
Friday, March 8, 2019 12:39PM - 12:51PM |
Y29.00008: A Machine Learning Approach for Automated Fine-Tuning of Semiconductor Spin Qubits Julian David Teske, Simon Humpohl, Rene Otten, Patrick Bethke, Pascal Cerfontaine, Hendrik Bluhm In the search for a technology best suited for quantum computation, spin qubits based on gate-defined quantum dots have demonstrated very favorable properties, one remaining challenge is their tuning into a suitable operating regime. Since this requires accurate tuning of the voltages applied to all electrostatic gates, this is a time-consuming procedure [1]. Thus, the automation of these tuning procedures is a necessary requirement for the operation of a quantum processor based on gate-defined quantum dots, which is yet to be fully addressed. |
Friday, March 8, 2019 12:51PM - 1:03PM |
Y29.00009: Image Analysis, Automation, and Machine Learning Techniques Applied to MOS Quantum Dot Tune-Up Andrew Mounce, Phillip J Lewis, Cara Monical, N. Tobias Jacobson, Albert Grine, Martin Rudolph, John Anderson, Joel R. Wendt, Tammy Pluym, Dan R Ward, Kurt W. Larson, Michael P Lilly, Malcolm S. Carroll Tune-up and analysis of quantum dots (QD) is an arduous manual task consisting of a sequence of steps that builds upon one another. The tuning and analysis complexity is increasing as designs extend from QDs to multi-objects (e.g., donor-QD coupling and multi-QDs). The process can be simplified by utilizing image recognition techniques and automation. In this talk, I will present image analysis techniques which extract information from transport and charge sensing stability plots. These analysis modules can determine parameters such as tunnel rates and charge configurations in the QD systems. We identify the necessary combination of tune-up steps and feedback from analysis modules (i.e., output parameters for the next scan) that can automate tuning to few-electron charge sensing. This talk presents some of the proof-of-concepts, details and key future challenges. |
Friday, March 8, 2019 1:03PM - 1:15PM |
Y29.00010: A Flexible Control System for Quantum Dot Qubits Nizar Messaoudi, Azfar Badaroudine, Larissa Njejimana, Gidget Heintz, Marc-Antoine Genest, Michel Pioro-Ladriere The advancement of Quantum Dot qubit technology is paving the way to fault-tolerant quantum computing systems. Although spin qubits are still at a relatively early stage, their strong robustness against noise makes them extremely attractive. However, quantum architectures still rely on classical electronics for control and readout. While traditional instrumentation has been used to manipulate and detect qubit spins, they lack the scalability necessary to move from single qubit to multi-qubit experiments. Even if the instruments can be synchronized for signal phase coherence, they lack the flexibility that is required for researchers to explore new control techniques and qubit architectures. This flexibility can be achieved through Digital Signal Processing (DSP) realized on Field Programmable Gate Arrays (FPGA). FPGAs allow the implementation of a range of DSP algorithms while also providing absolute time determinism. This paper discusses the use of commercial FPGA based instruments to implement a spin-qubit control system. A lock-in amplifier is implemented in the FPGA of the digitizer and quantum dot Coulomb blockade measurements are compared to when using a dedicated lock-in amplifier. |
Friday, March 8, 2019 1:15PM - 1:27PM |
Y29.00011: Scalable tuning of InAs quantum dots embedded in photonic structures Joel Grim, Allan S Bracker, Maxim Zalalutdinov, Samuel Carter, Alexander C. Kozen, Mijin Kim, Chul Soo Kim, Jerome Thomas Mlack, Michael K Yakes, Bumsu Lee, Daniel G Gammon The prospect of integrated quantum optics platforms based on semiconductor quantum dots (QDs) has driven quantum semiconductor research for decades. This has resulted in advanced demonstrations of single photon emission and switching, quantum transistors, and qubit-photon interfaces. However, the variation in QD emission energies – which prevents interfacing QDs with each other and photonic elements such as cavities and waveguides – has thus far limited these demonstrations to one or two QDs. We have developed an approach that addresses this challenge by laser-patterning strain via local phase transitions of a conformal thin film deposited on the surface of photonic architectures.1 Using this approach, InAs QDs can be tuned across the entire inhomogeneous distribution, with a spectral resolution down to the homogeneous linewidth, and sub-micron spatial resolution. We show that a scalable number of QDs embedded in the same bridge waveguide can be tuned into resonance. We also demonstrate that the emission energies of QDs embedded in photonic crystal cavities and waveguides can be tuned with this approach. |
Friday, March 8, 2019 1:27PM - 1:39PM |
Y29.00012: Deep Reinforcement Learning Based Control of Coherent Transport by Adiabatic Passage of Spin Qubits Riccardo Porotti, Dario Tamascelli, Marcello Restelli, Enrico Prati Several tasks, involving the temporal evolution of a system of qubits, require stochastic methods to identify the best sequence of gates and the interaction time among qubits. The great success of deep reinforcement learning (DRL) methods to identify the best strategy in problems involving a competition between short and long-term rewards, has suggested its application to quantum information (QI) as well. |
Friday, March 8, 2019 1:39PM - 1:51PM |
Y29.00013: Controllable Approximations for Spin Qubit Design - Jacob's Ladder of Device Modelling Andre Saraiva, Christopher Escott, Anderson West, Ross Leon, Ruichen Zhao, Henry Yang, Andrew Steven Dzurak Some key quantities for spin qubits - tunnel rates, exchange coupling and electronic correlations in general - are hard to describe within the most commonly adopted approximations. Tunnel rates and the exchange coupling are small corrections to the total electronic energy, so that variational methods often fail to predict these quantities. Electronic correlations can be accurately calculated for few electrons through full CI, for example, but are difficult for many electrons. We discuss some of the limitations of these approaches and how to overcome these with state-of-the-art methods that are controllable. We review two methods to improve the accuracy of these quantities: the Path Integral Monte Carlo method for tunnel rates and exchange coupling; and the Density Functional Theory applied to the effective mass Hamiltonian for the many electron problem. Both methods have controllable approximations that may be systematically improved by enhancing the computational effort. |
Friday, March 8, 2019 1:51PM - 2:03PM |
Y29.00014: GPU-Accelerated Simulations of Single and Two Electron-Spin Qubit Operations in Semiconductor Devices. Hugo Lepage, Aleksander Lasek, David Arvidsson Shukur, Crispin Barnes Although experimental physicists can control the output of electron-spin setups in the lab, it is hard to know exactly what happened to the particles during the manipulation. We present GPU-accelerated simulations that provide valuable insights into how a particle behaves while in the metaphorical “black box” that is the experimental device. In particular, we show how the most general measurements can be implemented for dynamic qubits via a POVM protocol. We provide high fidelity simulations of entanglement distillation for electrons carried by surface acoustic waves. Furthermore, we compare two methods for generating entanglement between electron-spin qubits using the power-of-SWAP operation. By using realistic experimental parameters, we show that entanglement generation via electron-electron collisions in a harmonic channel cannot be implemented for multidimensional systems. We provide an alternative by demonstrating that a method based on the exchange energy across a tunnel barrier is more viable than previously thought. These findings pave the way to designing efficient entangling quantum logic gates. |
Friday, March 8, 2019 2:03PM - 2:15PM |
Y29.00015: Controlling spatial entanglement in interacting two electrons trapped in superlattices Dung Pham, Sathwik Bharadwaj, Yuchen Wang, L Ramdas Ram-Mohan Entanglement properties of two-electron systems have been the subject of considerable interest in recent years. Solutions to the Hamiltonian in few-electron systems require special techniques to evaluate computationally demanding Coulomb integrals. Here we develop a fully variational action integral formalism to obtain the coordinate space wavefunctions for two electrons trapped in semiconductor superlattices. The entanglement in such systems have contributions from not only the spin part but also from the spatial correlations of the confining potential. The latter contribution has been neglected in most considerations. We show that the probability distributions of electrons largely deviate from those of the widely-used slater-determinant representation. We demonstrate that the entanglement in such systems can be controlled by varying physical parameters, and by applying external fields. The entanglement resonances associated with anti-crossings of eigenstates are displayed for the first time, and these can be manipulated through geometric changes and by the applied electric field. |
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