Abstract

Dielectric loss is suspected to be a major contributor limiting state-of-the-art superconducting qubit lifetimes. Recent experiments imply upper bounds on bulk dielectric loss tangents on the order of 1e-7, but because these inferences are drawn from fully fabricated devices with many loss channels, it is difficult to know the actual dielectric loss tangents with a high degree of certainty. We have devised a method capable of separating and resolving dielectric loss with a sensitivity on the order of 1e-8. We call our method the Dielectric Dipper, as the method involves the in-situ insertion of a dielectric sample into a high-quality superconducting cavity mode. Continuous variation of the sample’s participation in the cavity mode enables a highly selective differential measurement of dielectric loss. Our method probes the low-power behavior of dielectrics at cryogenic temperatures without the need for lithographic processes. This enables controlled comparison of isolated substrates and processing techniques. Such comparisons will inform designs and practices to better minimize dielectric loss. We present experimental comparisons of common dielectric substrates measured using this method.

Abstract

Developing large-scale quantum information processors has become a major industrial goal over the last few years. Of the many quantum systems available to tackle this difficult task, superconducting circuits have shown impressive results thus far and appear to be posed to scale up rapidly. In this presentation, I will provide a basic introduction to superconducting qubits, their fabrication, measurement, and coupled operations. Then, I will focus on some of the difficulties associated with developing superconducting circuits for large scale quantum information processors. Specifically, I will highlight the materials science challenges that are present in fabricating superconducting quantum bits and provide a historical overview of the field that shows the enormous progress that has be made thus far, but also highlights the major obstacles still faced.

Abstract

Superconducting circuits are a promising platform for quantum computing, communication, and sensing. Through many years of development these quantum circuits have achieved quality factors of several million even at single photon powers. Most of this work has been based around aluminum circuits operating at 10mK and in the band of 4-8 GHz. Leveraging insights from niobium-based superconducting radio frequency accelerators we have developed superconducting cavities adapted to interact with superconducting qubits with quality factors exceeding 1 billion. Further we have begun to develop cavities and non-linear circuits at mm-wave frequencies near 100GHz. These developments can enable long lived quantum memories, quantum accelerated searches for dark matter, operation of quantum computers at high temperatures with integrated control, and higher speed operation.

Abstract

Recent quantum computing experiments based on Josephson qubits have demonstrated primordial versions of error detection. A demonstration of full fault requires simultaneous increases in device scale (10’s -> 100’s of qubits) and performance. In particular, the speed and accuracy of qubit readout must be improved through design of the superconducting chip, while the size of the off-chip microwave receiver (amplifiers, circulators) must be reduced. In this talk, we give an overview of these requirements. We show how theory predicts experimentally observed speed and accuracy of multiplexed qubit readout at the level of 1% errors, and we use this theory to provide guidelines for the design of a qubit readout system suitable for a demonstration of fault tolerance with ~1000 qubits. Focus is given to frequency crowding, amplifier saturation, impedance matching (between the chip, package, and receiver), and loss between the chip and receiver. We also comment on the thermal and space requirements of circulators and 4 Kelvin amplifiers that follow the quantum limited paramps.

More information provided here.

Abstract

Superconducting circuits have emerged as one of the most promising platforms for quantum computation as a result of rapid advances in coherence and control over the past few decades. Most modern superconducting processors are based on the transmon circuit, and rely on nearest-neighbor interactions for gate operations and entanglement. In this talk, I will present an alternative architecture for superconducting quantum information and simulation, involving many harmonic modes of a multimode cavity coupled and controlled by a single quantum circuit. This multimode circuit-QED system leverages the long coherence times and restricted decoherence channels of superconducting microwave cavities. Additionally, the architecture has a high degree of connectivity while being hardware efficient, with gate operations performed between arbitrary pairs of cavity modes using only a few control lines that drive the transmon. Our implementation of such a processor uses - the quantum flute, a novel rectangular 3D multimode cavity with a tailored mode dispersion, that is protected from seam loss and possesses O(10) distinct modes with photon lifetimes approaching a millisecond. I will present various schemes for universal control of the multimode Hilbert space using the dispersively coupled transmon, and discuss schemes for engineering designer photon-photon interactions.

More information provided here.

Abstract

Parametric driving has long been used in weakly nonlinear superconducting circuits to create nearly quantum-limited ‘parametric’ amplifiers, which are in wide use for the readout of superconducting qubits. However, our and others’ recent work show that we can extend parametric pumping schemes to create a variety of other vital components of quantum computers. These parametric controls are extremely flexible, coupling both linear cavities and qubits, and are currently in use in our laboratory for a variety of applications including qubit bath engineering, single- and two-qubit gates as well as controlled, coherent links between qubits in multiple quantum modules. In each experiment the key source of nonlinearity is a so-called SNAIL device whose three-wave couplings we exploit to controllably couple quantum modes. More, by applying multiple, simultaneous drives we can drive both parallel operations between multiple pairs of modes and three or more body interactions and gates. In this talk I will review our recent experimental efforts, especially our realization of four transmon all-to-all quantum modules and a quantum state router [1] which can link four modules with highly coherent operations, as well as the prospects for scaling to larger modular quantum processors.
[1] A modular quantum computer based on a quantum state router C. Zhou, P. Lu, M. Praquin, T.-C. Chien, R. Kaufman, X. Cao, M. Xia, R. Mong, W. Pfaff, D. Pekker, M. Hatridge. arXiv:2109.06848 (2021).

Abstract

Recent experiments show that quantum enhanced sensing methods can benefit searches for hypothetical dark matter particles such as axions and dark photons. These quantum enhanced experiments use superconducting circuits to measure and manipulate the quantum state of the microwave cavities that couple to the hypothetical dark matter. In this talk, I’ll describe several concepts that make use of entanglement and squeezing to speed up the search for dark matter. These concepts already double the quantum-limited search rate in an axion search, but with the fragile nature of squeezed states precluding much larger speed-ups. To go beyond the modest speed-ups already demonstrated, future experiments should consider quantum enhanced methods during the initial design, rather than adding them to existing experiments. Indeed, learning to use these quantum enhanced measurement concepts most effectively in dark matter searches is a new frontier of experiment design.

Abstract

Readout for superconducting transmon qubits involves the dispersive coupling of their energy levels to a detuned resonator, which is then probed with a resonant microwave tone. To extract qubit information from this microwave field, the field is amplified and demodulated to yield a pair of heterodyne signals that must be inverted to infer the corresponding measurement-conditioned qubit evolution in the form of stochastic quantum trajectories. This talk details the hardware implementation of multi-transmon chips and discusses several theoretical subtleties about the state trajectory inversion process from measured data. The talk also highlights recent experimental progress in using modern machine learning methods for automated calibration and tracking of the conditioned qubit evolution.

Abstract

This talk will give an overview of some of the collider options and the required superconducting magnet technologies followed by a brief review of current world-wide activities. A comprehensive long-term roadmap, taking into consideration future potential challenges, is proposed.

Abstract

What will be the next large science facility to require thousands of tons of superconducting wire? When will it begin construction? Since requirements of existing science facilities already exceed the performance limits of the Nb-Ti conductor technology shared by the multi-billion-dollar medical imaging market, and since there is no other billion-dollar market requiring performance beyond that of Nb-Ti at present, how can conductor manufacturing supply what is needed for the next billion-dollar facility, let alone other construction episodes beyond it?The applied superconductivity community has contemplated the questions above for some time, reflecting on the episodic nature of large projects and the wide gap between project requirements and products in the marketplace. In this plenary presentation, I will draw upon experiences with public-private partnerships established by the US Dept. of Energy (DOE) in the late 1990s to sustain “warm” manufacturing over decades and support innovation. 

Abstract

The Google Quantum AI team develops chip-based circuitry that one can interact with, which behaves reliably according to a simple quantum model. Such quantum hardware holds promise as a platform for tackling problems intractable to classical computing hardware. While the demonstration of a universal, fault-tolerant, quantum computer remains a goal for the future, it has informed the design of a prototype with which we can control quantum systems of unprecedented scale. This talk introduces Google’s quantum computing effort from both hardware and quantum-information perspectives, including an overview of some technological developments and results.

Abstract

After theoretical discovery of magnetic vortices by Abrikosov, which received 2003 Nobel Prize in Physics, vortex pinning in type II superconductors has been an important topic of research for high critical current densities in applied magnetic fields desired for a variety of applications in electric and electronic devices and systems. The small vortex core size of a few nanometer comparable to the coherence length in high temperature superconductors (HTSs) has prompted an intensive research in development of nanoscale artificial pinning centers (APCs) in so-called HTS nanocomposites. Exciting results of much enhanced in-field critical current densities and pinning force densities have been achieved. This talk intends to highlight the progress made recently in HTS nanocomposites towards controllable generation of APCs with desired morphologies, dimension, concentration, and pinning efficiency for targeted applications. The future research in HTS nanocomposites to meet the need of practical applications will also be discussed.

Abstract

Granular aluminum (grAl) is an intriguing superconducting material, which has been receiving increasing attention in the superconducting quantum bits (qubits) and detectors communities. Among its key features are a tunable kinetic inductance up to nH/sq, amenable nonlinearity, and low microwave frequency losses [1,2,3]. Furthermore, quasiparticle relaxation times on the order of ~s have been observed [1]. In elucidating the sources of excess quasiparticles, the role of ionizing radiation has recently come to the forefront, and abatement of quasiparticle bursts remains an open challenge [4]. Besides showcasing the key features of grAl, we will present our results on a fluxonium qubit, where granular aluminum strips realize a so-called superinductor with an inductance of 225 nH at an impedance > 6.6 kΩ [5]. We will also discuss a transmon-type qubit in which 

Abstract

Fluxonium consists of a superconducting loop interrupted by over 100 Josephson junctions, strips of insulating material AlOx a few nanometers thick sandwiched between superconducting Al layers. Consequently, the loop has an exceptionally large value inductance, which makes fluxonium distinct and useful. Having so many junctions per qubit has been generally viewed as a liability for establishing long coherence times. Yet, we observed coherence in excess of 1 millisecond and conclude that even longer coherence time should be possible by upgrading our fabrication procedures to the state of the art. We discuss how the exceptional combination of fluxonium's high coherence and strong anharmonicity can be utilized for improving the fidelity of logical gates and constructing analog simulators of strongly interacting quantum spin models.

Abstract

The field of superconducting qubits is currently dominated by the transmon qubit. Over the course of more than a decade, much effort has been devoted to enhancing this circuit's coherence times. Despite the remarkable success, we should ask: is the transmon the best we can do, and will it ultimately suffice for implementing quantum error correction and leaving the NISQ era behind? As I will show, there are interesting circuit alternatives with enhanced intrinsic protection from noise that may well play a decisive role in the future. I will give a tour of some of our recent work on noise-protected qubits, and illustrate how our open-source "scqubits" package has made it simpler than ever to explore the world of superconducting qubits.

Abstract

Superconducting electronic circuits are ideally suited for studying quantum physics and its applications. Since complex circuits containing hundreds or thousands of elements can be designed, fabricated, and operated with relative ease, they are one of the prime contenders for realizing quantum computers. Currently, both academic and industrial labs vigorously pursue the realization of universal fault-tolerant quantum computers. However, building systems which can address commercially relevant computational problems continues to require significant conceptual and technological progress. For fault-tolerant operation quantum computers must correct errors occurring due to unavoidable decoherence and limited control accuracy. Here, we demonstrate quantum error correction using the surface code, which is known for its exceptionally high tolerance to errors. Using 17 physical qubits in a superconducting circuit, we encode quantum information in a distance-three logical qubit building up on our recent distance-two error detection experiments [1]. In an error correction cycle taking only 1.1 µs, we demonstrate the preservation of four cardinal states of the logical qubit. Repeatedly executing the cycle, we measure and decode both bit- and phase-flip error syndromes using a minimum-weight perfect-matching algorithm in an error-model-free approach and apply corrections in postprocessing. We find a low logical error probability of 3% per cycle [2]. The measured characteristics of our device agree well with a numerical model. Our demonstration of repeated, fast, and high-performance quantum error correction cycles, together with recent advances in ion traps, support our understanding that fault-tolerant quantum computation will be practically realizable.
[1] C. Kraglund Andersen et al., Nature Physics 16, 875–880 (2020)
[2] S. Krinner, N. Lacroix et al., Nature 605, 669–674 (2022)

Abstract

Since 1966, the ASC has been the premier home for applied superconductivity conferences to report, discuss and contemplate important and timely technical advances in science and engineering from the broad fields of electronics, large scale, and materials. We warmly welcome everyone to this 2022 Applied Superconductivity Conference in Honolulu for a program of exciting plenary, special session and oral speakers, and engaging posters and workshops.

Abstract

May we find comfort in the treasured memories of those no longer with us. And let us not forget the lasting impact that they have had both personally and professionally in the field of applied superconductivity.