A scalable control system for a superconducting adiabatic quantum optimization processor

Johnson, Mark W.; Bunyk, P.; Maibaum, F.; Tolkacheva, E.; Berkley, A. J.; Chapple, E. M.; Harris, Richard E.; Johansson, J.; Lanting, T.; Perminov, I.; Ladizinsky, E.; Oh, T.; Rose, Geordie

doi:10.1088/0953-2048/23/6/065004

Cited by 153 publications

(155 citation statements)

References 29 publications

(63 reference statements)

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“…The devices studied in this experiment are from a QA processor made of 128 superconducting flux qubits, all controlled by on-chip Single Flux Quantum superconducting digital circuitry as well as filtered analog signal input lines. The qubits are briefly discussed in this section and in detail in Harris et al 33 The on-chip control circuitry is described in detail in Johnson et al 39 The qubits are numbered 0-127 starting from the top-left corner of the chip, and the 16-qubit subset used in this experiment is depicted in Supplementary Fig. S2.…”

Section: Methodsmentioning

confidence: 99%

Thermally assisted quantum annealing of a 16-qubit problem

et al. 2013

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Efforts to develop useful quantum computers have been blocked primarily by environmental noise. Quantum annealing is a scheme of quantum computation that is predicted to be more robust against noise, because despite the thermal environment mixing the system's state in the energy basis, the system partially retains coherence in the computational basis, and hence is able to establish well-defined eigenstates. Here we examine the environment's effect on quantum annealing using 16 qubits of a superconducting quantum processor. For a problem instance with an isolated small-gap anticrossing between the lowest two energy levels, we experimentally demonstrate that, even with annealing times eight orders of magnitude longer than the predicted single-qubit decoherence time, the probabilities of performing a successful computation are similar to those expected for a fully coherent system. Moreover, for the problem studied, we show that quantum annealing can take advantage of a thermal environment to achieve a speedup factor of up to 1,000 over a closed system.

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Section: Methodsmentioning

confidence: 99%

Thermally assisted quantum annealing of a 16-qubit problem

et al. 2013

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“…These devices and the underlying technology have been described before in detail in various publications (e.g., Refs. [37][38][39]44]). …”

Section: Benchmarking Using Antiferromagnetic Chainsmentioning

confidence: 99%

Performance of two different quantum annealing correction codes

Mishra

Albash

Lidar

2015

Quantum Inf Process

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Quantum annealing is a promising approach for solving optimization problems, but like all other quantum information processing methods, it requires error correction to ensure scalability. In this work we experimentally compare two quantum annealing correction codes in the setting of antiferromagnetic chains, using two different quantum annealing processors. The lower temperature processor gives rise to higher success probabilities. The two codes differ in a number of interesting and important ways, but both require four physical qubits per encoded qubit. We find significant performance differences, which we explain in terms of the effective energy boost provided by the respective redundantly encoded logical operators of the two codes. The code with the higher energy boost results in improved performance, at the expense of a lower degree encoded graph. Therefore, we find that there exists an important tradeoff between encoded connectivity and performance for quantum annealing correction codes.

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“…Such static offsets can readily be calibrated and compensated for in situ using either analog control lines or on-chip programmable flux sources. 44 For typical device parameters and junction variability on the order of a few percent, these offsets will be ϳ1 → 10 m⌽ 0 . Equations ͑5a͒-͑5d͒ with ⌽ q 0 = ⌽ ccjj 0 = 0 will be referred to hereafter as the ideal CCJJ rf-SQUID model.…”

Section: A Compound-compound Josephson-junction Structurementioning

confidence: 99%

“…The PMM has been described in detail in Ref. 44. Note that the extrema of the CCJJ rf-SQUID qubits in Fig.…”

Section: Device Architecture Fabrication and Readout Operationmentioning

confidence: 99%

“…Further details concerning cryogenics, magnetic shielding, and signal filtering have been discussed in previous publications. [44][45][46][47] We have calibrated the relevant mutual inductances between devices in situ and have attempted to measure a significant portion of the parasitic cross couplings between bias controls ͑both analog lines and PMM elements͒ into unintended devices. These cross couplings were typically below our measurement threshold Շ0.1 fH while designed mutual inductances between bias controls and intended devices were typically O͑1 pH͒.…”

Section: Device Architecture Fabrication and Readout Operationmentioning

confidence: 99%

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Experimental demonstration of a robust and scalable flux qubit

et al. 2010

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A rf-superconducting quantum interference device ͑SQUID͒ flux qubit that is robust against fabrication variations in Josephson-junction critical currents and device inductance has been implemented. Measurements of the persistent current and of the tunneling energy between the two lowest-lying states, both in the coherent and incoherent regimes, are presented. These experimental results are shown to be in agreement with predictions of a quantum-mechanical Hamiltonian whose parameters were independently calibrated, thus justifying the identification of this device as a flux qubit. In addition, measurements of the flux and critical current noise spectral densities are presented that indicate that these devices with Nb wiring are comparable to the best Al wiring rf SQUIDs reported in the literature thus far, with a 1 / f flux noise spectral density at 1 Hz of 1.3 −0.5 +0.7 ⌽ 0 / ͱ Hz. An explicit formula for converting the observed flux noise spectral density into a freeinduction-decay time for a flux qubit biased to its optimal point and operated in the energy eigenbasis is presented. I. MOTIVATIONExperimental efforts to develop useful solid-state quantum information processors have encountered a host of practical problems that have substantially limited progress. While the desire to reduce noise in solid-state qubits appears to be the key factor that drives much of the recent work in this field, it must be acknowledged that there are formidable challenges related to architecture, circuit density, fabrication variation, calibration, and control that also deserve attention. For example, a qubit that is inherently exponentially sensitive to fabrication variations with no recourse for in situ correction holds little promise in any large-scale architecture, even with the best of modern fabrication facilities. Likewise, a qubit that requires an inordinate number of custom-tuned time-dependent control signals to be launched onto the chip, in order to correct for fabrication variations or to compensate for unintended on-chip crosstalk, would also not be useful in a large-scale processor. Thus, a qubit designed in the absence of information concerning its ultimate use in a larger-scale system may prove to be of little utility in the future. In what follows, we present an experimental demonstration of a superconducting flux qubit 1 that has been specifically designed to address several issues that pertain to the implementation of a large-scale quantum information processor. While noise is not the central focus of this paper, we nonetheless present experimental evidence that, despite its physical size and relative complexity, the observed flux noise in this flux qubit is comparable to the quietest such devices reported on in the literature to date.It has been well established that rf superconducting quantum interference devices ͑SQUIDs͒ can be used as qubits given an appropriate choice of device parameters. Such devices can be operated as a flux-biased phase qubit using two intrawell energy levels 2 or as a flux qubit using...

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A scalable control system for a superconducting adiabatic quantum optimization processor

Cited by 153 publications

References 29 publications

Thermally assisted quantum annealing of a 16-qubit problem

Thermally assisted quantum annealing of a 16-qubit problem

Performance of two different quantum annealing correction codes

Experimental demonstration of a robust and scalable flux qubit

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