# News

• [December 2020] I defended my dissertation successfully on December 28, 2020! Ph.Done.
• [December 2020] Our paper describing the thought process behind the Qiskit textbook and some recent usage data is now on the arXiv! [arXiv:2012.09629]
• [October 2020] Qubit x Qubit, our partnership with The Coding School to teach quantum computing to 5000 high school students (and above) globally over 8 months and 2 semesters, begins! [IBM Research announcement]

It's the first of its kind, and offers high schoolers the opportunity to take a course on hands-on quantum computing with Qiskit and the IBM Quantum Experience in two semesters, with the potential to earn high school credit.

• [September 2020] @BlackInQuantum is now live on Twitter!

The goal of the project is to provide a welcoming and supportive environment for Black engineers and scientists across the world involved in the quantum sciences.

• [September 2020] The video lectures and labs from the Qiskit Global Summer School are now live on qiskit.org.
• [July 2020] Qiskit Global Summer School begins! [IBM Research announcement]

It's the world's largest quantum computing summer school, with 4000+ learners from 100+ countries.

• [June 2020] I hosted Real Scientists on Twitter! [Real Scientists announcement]
• [May 2020] The IBM Quantum Challenge launches! [IBM Research announcement] [IBM Research retrospective] [Exercises]

The Challenge celebrates 4 years of quantum computers on the cloud, and contains four exercises, starting with quantum gates and going through measurement error mitigation on real quantum systems, as well as quantum key distribution and unitary decomposition into quantum circuits.

• [January 2020] I am now leading a team at IBM Quantum focused on building a global mission for quantum education & open science. The goal of the team is to make quantum computing education & science open, accessible and inclusive for all.
• [September 2019] Learn Quantum Computation using Qiskit (the Qiskit Textbook) is live! [IBM Research announcement] [Qiskit Announcement]

It's the first open-source digital textbook in the field, showing how to program quantum computers and implement quantum algorithms in detail.

See more
• [August 2019] Coding With Qiskit, a 9-episode video series on YouTube explaining how to program quantum computers, launches.
• [March 2019] I joined the team at IBM Quantum, based at the T.J. Watson Research Center in Yorktown Heights, NY.

# Publications

For an up-to-date list of publications, please visit my Google Scholar page.
• ## Teaching Quantum Computing with an Interactive Textbook

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

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.

• ## 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).

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.

• ## 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).

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.

• ## 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).

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.

• ## 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).

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.

• ## 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).

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.

• ## 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

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.

# Presentations

For a list of presentations that I gave as part of my Ph.D., click this button to expand below.
• A Asfaw, E Kleinbaum and S.A. Lyon, Transport measurements of electrons above shallow helium-filled microchannels, March 2019, Contributed Talk, APS March Meeting (Boston, Massachusetts)
• A Asfaw, A.J. Sigillito, A.M. Tyryshkin, T. Schenkel and S.A. Lyon, Multi-Frequency Pulsed EPR and DEER Using Rapidly Tunable Superconducting Microresonators, July 2018, EPR Oral Session Talk, 59th Rocky Mountain Conference on Magnetic Resonance (Snowbird, Utah)
• A Asfaw and S.A. Lyon, Superconducting Kinetic Inductance Field-Frequency Sensors: High-Sensitivity Magnetic Field Sensing in Moderate Background Fields, March 2018, Contributed Talk, APS March Meeting (Los Angeles, California)
• A Asfaw and S.A. Lyon, Superconducting Kinetic Inductance Field-Frequency Sensors: High-Sensitivity Magnetometry in Moderate Background Fields, February 2018, Poster, Princeton Center for Complex Materials Annual Poster Night (Princeton, New Jersey)
• A Asfaw and S.A. Lyon, Superconducting Kinetic Inductance Devices for Electron Spin Resonance Applications, December 2017, Talk, Quantum Group Meeting (Princeton, New Jersey)
• A Asfaw, AJ Sigillito, AM Tyryshkin, and SA Lyon, Current-Tunable NbTiN Coplanar Photonic Bandgap Resonators, March 2017, Contributed Talk, APS March Meeting (New Orleans, Louisiana)
• A.T. Asfaw, A.M. Tyryshkin, and S.A. Lyon, Tracking Magnetic Field Fluctuations in Electron Spin Resonance, August 2016, Poster, Gordon Research Conference: Defects in Semiconductors, (New London, NH)
• A.T. Asfaw, A.M. Tyryshkin, and S.A. Lyon, Tracking Magnetic Field Fluctuations in Electron Spin Resonance, August 2016, Poster, Gordon Research Seminar: Defects in Semiconductors, (New London, NH)
• A.T. Asfaw, A.M. Tyryshkin, and S.A. Lyon, Tracking Field Fluctuations in Pulsed EPR, July 2016, EPR Oral Session Talk, 58th Rocky Mountain Conference on Magnetic Resonance, (Breckenridge, CO)
• A Asfaw, A Tyryshkin, and S Lyon, Dynamic field-frequency lock for tracking magnetic field fluctuations in electron spin resonance experiments, March 2016, Contributed Talk, APS March Meeting (Baltimore, Maryland)
• A. Asfaw, Introduction to Quantum Computation and Quantum Algorithms, 2-day workshop presented at 4-kilo campus, Addis Ababa University (2015).
• A Asfaw, G Wolfowicz, JJL Morton, A Tyryshkin, and S Lyon, Spin Ensembles as Sensitive Probes of Environmental Magnetic Field Noise, March 2015, Contributed Talk, APS March Meeting (San Antonio, Texas)
• A.T. Asfaw, A.M. Tyryshkin, and S.A. Lyon, Suppressing Effects of Magnetic Field Noise in Long Echo Decay Measurements, July 2014, EPR Oral Session Talk, 56th Rocky Mountain Conference on Magnetic Resonance, (Copper Mountain, CO)
• A. Asfaw and P. Boothe, Computing Backwards, 7th Annual Spuyten Duyvil Undergraduate Mathematics Conference (NSF Grant DMS-0846477) (2012)
• A. Asfaw, Computability and Turing Machines, Department of Mathematics and Computer Science, Manhattan College (2011)
• A. Asfaw, Mersenne Primes and the Global Internet Mersenne Prime Search (GIMPS), 6th Annual Spuyten Duyvil Undergraduate Mathematics Conference (NSF Grant DMS-0846477) (2011)
• A. Asfaw, Moments of Velocity in Arbitrary Dimension, 5th Annual Spuyten Duyvil Undergraduate Mathematics Conference (NSF Grant DMS-0846477) (2010)