News

• [December 2020] I defended my dissertation successfully on December 28, 2020! Ph.Done.

Selected Publications

• 

  Teaching Quantum Computing with an Interactive Textbook

  James R. Wootton, Francis Harkins, Nicholas T. Bronn, Almudena Carrera Vazquez, Anna Phan, Abraham T. Asfaw

  Read Abstract

  Quantum computing is a technology that promises to offer significant advantages during the coming decades. Though the technology is still in a prototype stage, the last few years have seen many of these prototype devices become accessible to the public. This has been accompanied by the open-source development of the software required to use and test quantum hardware in increasingly sophisticated ways. Such tools provide new education opportunities, not just for quantum computing specifically, but also more broadly for quantum information science and even quantum physics as a whole. In this paper we present a case study of one education resource which aims to take advantage of the opportunities: the open-source online textbook 'Learn Quantum Computation using Qiskit'. An overview of the topics covered is given, as well as an explanation of the approach taken for each.

  [arXiv]

• 

  Learn Quantum Computation Using Qiskit

  Abraham T. Asfaw, Luciano Bello, Yael Ben-Haim, Sergey Bravyi, Nicholas Bronn, Lauren Capelluto, Almudena Carrera Vazquez, Jack Ceroni, Richard Chen, Albert Frisch, Jay Gambetta, et al.

  qiskit.org/textbook (2019).

  Read Abstract

  This is the first digital open-source textbook on quantum computation, demonstrating how to implement quantum algorithms on real quantum computers. The textbook is designed as a supplement to traditional quantum computing textbooks for university courses. It covers the mathematics behind quantum algorithms, details about today's non-fault-tolerant quantum devices, and shows how to write code in Qiskit to implement quantum algorithms on IBM's cloud quantum systems.

  [Textbook] [GitHub]

• 

  Narrow Optical Line Widths in Erbium Implanted in TiO2

  Christopher M Phenicie, Paul Stevenson, Sacha Welinski, Brendon C Rose, Abraham T Asfaw, Robert J Cava, Stephen A Lyon, Nathalie P De Leon and Jeff D Thompson

  Nano Letters 19, 12, 8928-8933 (2019).

  Read Abstract

  Atomic and atom-like defects in the solid-state are widely explored for quantum computers, networks and sensors. Rare earth ions are an attractive class of atomic defects that feature narrow spin and optical transitions that are isolated from the host crystal, allowing incorporation into a wide range of materials. However, the realization of long electronic spin coherence times is hampered by magnetic noise from abundant nuclear spins in the most widely studied host crystals. Here, we demonstrate that Er\(^{3+}\) ions can be introduced via ion implantation into TiO\(_2\), a host crystal that has not been studied extensively for rare earth ions and has a low natural abundance of nuclear spins. We observe efficient incorporation of the implanted Er\(^{3+}\) into the Ti\(^{4+}\) site (40% yield), and measure narrow inhomogeneous spin and optical linewidths (20 and 460 MHz, respectively) that are comparable to bulk-doped crystalline hosts for Er\(^{3+}\). This work demonstrates that ion implantation is a viable path to studying rare earth ions in new hosts, and is a significant step towards realizing individually addressed rare earth ions with long spin coherence times for quantum technologies.

  [Journal] [arXiv] doi:10.1021/acs.nanolett.9b03831

• 

  Nanowire Superinductance Fluxonium Qubit

  T. M. Hazard, A. Gyenis, A. Di Paolo, A. T. Asfaw, S. A. Lyon, A. Blais and A. A. Houck

  Phys. Rev. Lett. 122, 010504 (2019).

  Read Abstract

  Disordered superconducting materials provide a new capability to implement novel circuit designs due to their high kinetic inductance.Here, we realize a fluxonium qubit in which a long NbTiN nanowire shunts a single Josephson junction. We explain the measured fluxonium energy spectrum with a nonperturbative theory accounting for the multimode structure of the device in a large frequency range. Making use of multiphoton Raman spectroscopy, we address forbidden fluxonium transitions and observe multilevel Autler-Townes splitting. Finally, we measure lifetimes of several excited states ranging from \(T_1=620\) ns to \(T_1=20~\mu\)s, by applying consecutive \(\pi\)-pulses between multiple fluxonium levels. Our measurements demonstrate that NbTiN is a suitable material for novel superconducting qubit designs.

  [Journal] [arXiv] doi:10.1103/PhysRevLett.122.010504

• 

  Transport Measurements of Surface Electrons in 200 nm Deep Helium-Filled Microchannels Above Amorphous Metallic Electrodes

  A. T. Asfaw, E. I. Kleinbaum and S. A. Lyon

  Journal of Low Temp. Phys. 195, 300–306 (2019).

  Read Abstract

  We report transport measurements of electrons on helium in a microchannel device where the channels are 200 nm deep and \(3~\mu\)m wide. The channels are fabricated above amorphous metallic Ta\(_{40}\)W\(_{40}\)Si\(_{20}\), which has surface roughness below 1 nm and minimal variations in work function across the surface due to the absence of polycrystalline grains. We are able to set the electron density in the channels using a ground plane. We estimate a mobility of 300 cm\(^2\)/V\(\cdot\)s and electron densities as high as 2.56\(\times10^{9}\text{ cm}^{-2}\). We demonstrate control of the transport using a barrier which enables pinchoff at a central microchannel connecting two reservoirs. The conductance through the central microchannel is measured to be 10 nS for an electron density of 1.58\(\times10^{9}\text{ cm}^{-2}\). Our work extends transport measurements of surface electrons to thin helium films in microchannel devices above metallic substrates.

  [Journal] [arXiv] doi:10.1007/s10909-018-02139-6

• 

  SKIFFS: Superconducting Kinetic Inductance Field-Frequency Sensors for Sensitive Magnetometry in Moderate Background Magnetic Fields

  A. T. Asfaw, E. I. Kleinbaum, T. M. Hazard, A. Gyenis, A. A. Houck and S. A. Lyon

  Appl. Phys. Lett. 113, 172601 (2018).

  Read Abstract

  We describe sensitive magnetometry using lumped-element resonators fabricated from a superconducting thin film of NbTiN. Taking advantage of the large kinetic inductance of the superconductor, we demonstrate a continuous resonance frequency shift of 27 MHz for a change in magnetic field of \(1.8~\mu\)T within a perpendicular background field of 60 mT. By using phase-sensitive readout of microwaves transmitted through the sensors, we measure phase shifts in real time with a sensitivity of 1 degree/nT. We present measurements of the noise spectral density of the sensors, and find their field sensitivity is at least within one to two orders of magnitude of superconducting quantum interference devices operating with zero background field. Our superconducting kinetic inductance field-frequency sensors enable real-time magnetometry in the presence of moderate perpendicular background fields up to at least 0.2 T. Applications for our sensors include the stabilization of magnetic fields in long coherence electron spin resonance measurements and quantum computation.

  [Journal] [arXiv] doi:10.1063/1.5049615

• 

  Multi-frequency spin manipulation using rapidly tunable superconducting coplanar waveguide microresonators

  A. T. Asfaw, A. J. Sigillito, A. M. Tyryshkin, T. Schenkel and S. A. Lyon

  Appl. Phys. Lett. 111, 032601 (2017). Selected as Editor's Pick

  Read Abstract

  In this work, we demonstrate the use of frequency-tunable superconducting NbTiN coplanar waveguide microresonators for multi-frequency pulsed electron spin resonance (ESR) experiments. By applying a bias current to the center pin, the resonance frequency (\(\sim\)7.6 GHz) can be continuously tuned by as much as 95 MHz in 270 ns without a change in the quality factor of 3000 at 2K. We demonstrate the ESR performance of our resonators by measuring donor spin ensembles in silicon and show that adiabatic pulses can be used to overcome magnetic field inhomogeneities and microwave power limitations due to the applied bias current. We take advantage of the rapid tunability of these resonators to manipulate both phosphorus and arsenic spins in a single pulse sequence, demonstrating pulsed double electron-electron resonance (DEER). Our NbTiN resonator design is useful for multi-frequency pulsed ESR and should also have applications in experiments where spin ensembles are used as quantum memories.

  [Journal] [arXiv] doi:10.1063/1.4993930

Presentations