George Keefe

IBM (United States)

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Matthias Steffen

Technische Universität Berlin

Mary Beth Rothwell

IBM (United States)

Jerry M. Chow

IBM (United States)

Oliver Dial

IBM (United States)

M. B. Ketchen

IBM Research - Thomas J. Watson Research Center

Jay Gambetta

IBM (United States)

Antonio Córcoles

IBM (United States)

Santino D. Carnevale

IBM (United States)

Chad Rigetti

Rigetti Computing (United States)

R. H. Koch

Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo

Cooperative Institutions

IBM (United States)

IBM Research - Thomas J. Watson Research Center

Princeton University

IBM Research - Almaden

Yale University

Massachusetts Institute of Technology

University of Waterloo

University of Illinois Urbana-Champaign

Harvard University

RTX (United States)

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Demonstration of quantum volume 64 on a superconducting quantum computing system

Quantum Science and Technology (2021)

Petar Jurcevic Ali Javadi-Abhari Lev S. Bishop Isaac Lauer Daniela F. Bogorin

Abstract We improve the quality of quantum circuits on superconducting quantum computing systems, as measured by the quantum volume (QV), with a combination of dynamical decoupling, compiler optimizations, shorter two-qubit gates, and excited state promoted readout. This result shows that the path to larger QV systems requires the simultaneous increase of coherence, control gate fidelities, measurement fidelities, and smarter software which takes into account hardware details, thereby demonstrating the need to continue to co-design the software and hardware stack for the foreseeable future.

Decoupling (probability)

Dynamical decoupling

10.1088/2058-9565/abe519

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Citations (344)

Protecting superconducting qubits from radiation

Applied Physics Letters (2011)

Antonio Córcoles Jerry M. Chow Jay Gambetta Chad Rigetti John Rozen

We characterize a superconducting qubit before and after embedding it along with its package in an absorptive medium. We observe a drastic improvement in the effective qubit temperature and over a tenfold improvement in the relaxation time up to 5.7 $\mu$s. Our results suggest the presence of external radiation inside the cryogenic apparatus can be a limiting factor for both qubit initialization and coherence. We infer from simple calculations that relaxation is not limited by thermal photons in the sample prior to embedding, but by dissipation arising from quasiparticle generation.

Flux qubit

10.1063/1.3658630

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Citations (182)

Low-bandwidth control scheme for an oscillator-stabilized Josephson qubit

Physical Review B (2005)

R. H. Koch John Rozen George Keefe Frank Milliken C. C. Tsuei

We introduce a new Josephson junction circuit for which quantum operations are realized by low-bandwidth, nearly adiabatic magnetic-flux pulses. Coupling to the fundamental mode of a superconducting transmission line permits a stabilization of the rotation angle of the quantum operation against flux noise. A complete scheme for one-qubit rotations, and high-visibility Ramsey-fringe oscillations, is given. We show that high visibility depends on passing through a portal in the space of applied fluxes, where the width of the portal is proportional to the ramp-up rate of the flux pulse.

Flux qubit

10.1103/physrevb.72.092512

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Citations (22)

Demonstration of a High-Fidelity CNOT for Fixed-Frequency Transmons with Engineered ZZ Suppression.

arXiv (Cornell University) (2020)

Abhinav Kandala Ken Xuan Wei Srikanth Srinivasan Easwar Magesan Santino D. Carnevale

Improving two-qubit gate performance and suppressing crosstalk are major, but often competing, challenges to achieving scalable quantum computation. In particular, increasing the coupling to realize faster gates has been intrinsically linked to enhanced crosstalk due to unwanted two-qubit terms in the Hamiltonian. Here, we demonstrate a novel coupling architecture for transmon qubits that circumvents the standard relationship between desired and undesired interaction rates. Using two fixed frequency coupling elements to tune the dressed level spacings, we demonstrate an intrinsic suppression of the static $ZZ$, while maintaining large effective coupling rates. Our architecture reveals no observable degradation of qubit coherence ($T_1,T_2 > 100~\mu s$) and, over a factor of 6 improvement in the ratio of desired to undesired coupling. Using the cross-resonance interaction we demonstrate a 180~ns single-pulse CNOT gate, and measure a CNOT fidelity of 99.77(2)$\%$ from interleaved randomized benchmarking.

Controlled NOT gate

Transmon

Crosstalk

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Citations (11)

High-T/sub c/ SQUID gradiometer for mobile magnetic anomaly detection

IEEE Transactions on Applied Superconductivity (2001)

T.R. Clem D. Overway J.W. Purpura J. Bono R. H. Koch

The prototype for a nitrogen-cooled high-T/sub c/ SQUID gradiometer has been developed and is being evaluated for magnetic anomaly detection of underwater targets in mobile surveys. The prototype's design is based on the concept of the Three-Sensor Gradiometer (TSG). In the TSG approach, balance of two independent SQUID magnetometers is more difficult to attain than for conventional low-T/sub c/ gradiometers in which signal subtraction occurs prior to a single SQUID stage. Experiments have been conducted using a platform-motion simulator to evaluate performance of this gradiometer for mobile operation. Sensor configuration, experimental procedures, approaches for improved performance, and empirical results are reported. Interesting results of predictions to estimate detection range obtained from matched-filter calculations are included. The paper concludes with description of current preparations for a sea test of this sensor and a perspective of future developments.

10.1109/77.919483

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Citations (30)

Bulk and surface loss in superconducting transmon qubits

Superconductor Science and Technology (2016)

Oliver Dial Douglas McClure Stefano Poletto George Keefe Mary Beth Rothwell

Decoherence of superconducting transmon qubits is purported to be consistent with surface loss from two-level systems on the substrate surface. Here, we present a study of surface loss in transmon devices, explicitly designed to have varying sensitivities to different surface loss contributors. Our experiments also encompass two particular different sapphire substrates, which reveal the onset of a yet unknown additional loss mechanism outside of surface loss for one of the substrates. Tests across different wafers and devices demonstrate substantial variation, and we emphasize the importance of testing large numbers of devices for disentangling different sources of decoherence.

Transmon

10.1088/0953-2048/29/4/044001

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Citations (79)

Scalable Superconducting Qubits

APS March Meeting Abstracts (2002)

R. H. Koch J. R. Kirtley Jie Sun John Rozen George Keefe

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Fast Tunable Coupler Architecture for Fixed Frequency Transmons

Bulletin of the American Physical Society (2021)

J. Stehlik D. M. Zajac Devin Underwood Timothy Phung Muir Kumph

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<title>Superconducting magnetic sensors for mine detection and classification</title>

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (1995)

T.R. Clem R. H. Koch George Keefe

Sensors incorporating Superconducting Quantum Interference Devices (SQUIDs) provide the greatest sensitivity for magnetic anomaly detection available with current technology. During the 1980's, the Naval Surface Warfare Center Coastal Systems Station (CSS) developed a superconducting magnetic sensor capable of operation outside of the laboratory environment. This sensor demonstrated rugged, reliable performance even onboard undersea towed platforms. With this sensor, the CSS was able to demonstrate buried mine detection for the US Navy. Subsequently the sensor was incorporated into a multisensor suite onboard an underwater towed vehicle to provide a robust mine hunting capability for the Magnetic and Acoustic Detection of Mines (MADOM) project. This sensor technology utilized niobium superconducting componentry cooled by liquid helium to temperatures on the order of 4 degrees Kelvin (K). In the late 1980's a new class of superconductors was discovered with critical temperatures above the boiling point of liquid nitrogen (77K). This advance has opened up new opportunities, especially for mine reconnaissance and hunting from small unmanned underwater vehicles (UUVs). This paper describes the magnetic sensor detection and classification concept developed for MADOM. In addition, opportunities for UUV operations made possible with high T_c technology and the Navy's current efforts in this area will be addressed.

10.1117/12.211333

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Citations (15)

Novel microwave readout for phase qubits

Bulletin of the American Physical Society (2010)

Shwetank Kumar Matthias Steffen Mary-Beth Rothwell J. R. Rozen George Keefe

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