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Analog coupled oscillator based weighted Ising machine

Summary

We report on an analog computing system with coupled non-linear oscillators which is capable of solving complex combinatorial optimization problems using the weighted Ising model. The circuit is composed of a fully-connected 4-node LC oscillator network with low-cost electronic components and compatible with traditional integrated circuit technologies. We present the theoretical modeling, experimental characterization, and statistical analysis our system, demonstrating single-run ground state accuracies of 98% on randomized MAX-CUT problem sets with binary weights and 84% with 5-bit weight resolutions. Solutions are obtained within 5 oscillator cycles, and the time-to-solution has been demonstrated to scale directly with oscillator frequency. We present scaling analysis which suggests that large coupled oscillator networks may be used to solve computationally intensive problems faster and more efficiently than conventional algorithms. The proof-of-concept system presented here provides the foundation for realizing such larger scale systems using existing hardware technologies and could pave the way towards an entirely novel computing paradigm.
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Summary

We report on an analog computing system with coupled non-linear oscillators which is capable of solving complex combinatorial optimization problems using the weighted Ising model. The circuit is composed of a fully-connected 4-node LC oscillator network with low-cost electronic components and compatible with traditional integrated circuit technologies. We present the...

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Suppressing relaxation in superconducting qubits by quasiparticle pumping

Summary

Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. We investigate a complementary, stochastic approach to reducting errors: instead of deterministically reversing the unwanted qubit evolution, we use control pulses to shape the noise environment dynamically. in the context of superconducting qubits, we implement a pumping sequence to reduce the number of unpaired electrons (quasiparticles) in close proximity to the device. A 70% reduction in the quasiparticle density reesults in a threefold enhancement in qubit relaxation times and a comparable reduction in coherence variablity.
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Summary

Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. We investigate a complementary, stochastic approach to...

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The role of master clock stability in quantum information processing

Published in:
npj Quantum Inf., Vol. 2, 8 November 2016, doi:10.1038/npjqi.2016.33.

Summary

Experimentalists seeking to improve the coherent lifetimes of quantum bits have generally focused on mitigating decoherence mechanisms through, for example, improvements to qubit designs and materials, and system isolation from environmental perturbations. In the case of the phase degree of freedom in a quantum superposition, however, the coherence that must be preserved is not solely internal to the qubit, but rather necessarily includes that of the qubit relative to the 'master clock' (e.g., a local oscillator) that governs its control system. In this manuscript, we articulate the impact of instabilities in the master clock on qubit phase coherence and provide tools to calculate the contributions to qubit error arising from these processes. We first connect standard oscillator phase-noise metrics to their corresponding qubit dephasing spectral densities. We then use representative lab-grade and performance-grade oscillator specifications to calculate operational fidelity bounds on trapped-ion and superconducting qubits with relatively slow and fast operation times. We discuss the relevance of these bounds for quantum error correction in contemporary experiments and future large-scale quantum information systems, and consider potential means to improve master clock stability.
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Summary

Experimentalists seeking to improve the coherent lifetimes of quantum bits have generally focused on mitigating decoherence mechanisms through, for example, improvements to qubit designs and materials, and system isolation from environmental perturbations. In the case of the phase degree of freedom in a quantum superposition, however, the coherence that must...

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The flux qubit revisited to enhance coherence and reproducibility

Summary

The scalable application of quantum information science will stand on reproducible and controllable high-coherence quantum bits (qubits). In this work, we revisit the design and fabrication of the superconducting flux qubit, achieving a planar device with broad frequency tunability, strong anharmonicity, high reproducibility, and relaxation times in excess of 40 us at its flux-insensitive point. Qubit relaxation times 1 T across 22 qubits of widely varying designs are consistently matched with a single model involving resonator loss, ohmic charge noise, and 1/f flux noise, a noise source previously considered primarily in the context of dephasing, with temporal variation in 1 T attributed to quasiparticles. We furthermore demonstrate that qubit dephasing at the flux-insensitive point is dominated by residual thermal photons in the readout resonator. The resulting photon shot noise is mitigated using a dynamical decoupling protocol, resulting in T2 ~ 85 us , approximately the 1 2T limit. In addition to realizing a dramatically improved flux qubit, our results uniquely identify photon shot noise as limiting 2 T in contemporary state-of-art qubits based on transverse qubit-resonator interaction.
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Summary

The scalable application of quantum information science will stand on reproducible and controllable high-coherence quantum bits (qubits). In this work, we revisit the design and fabrication of the superconducting flux qubit, achieving a planar device with broad frequency tunability, strong anharmonicity, high reproducibility, and relaxation times in excess of 40...

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Nonlinear equalization of microwave photonic links

Published in:
IEEE Int. Topical Meeting on Microwave Photonics, MWP 2016, 31 October - 3 November 2016.

Summary

High dynamic range is a key requirement in advanced microwave photonic systems. We demonstrate compensation of nonlinearities occurring in microwave photonic links using a novel digital nonlinear equalization technique and demonstrate suppression of distortion products by 33 dB with a small number of equalizer coefficients.
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Summary

High dynamic range is a key requirement in advanced microwave photonic systems. We demonstrate compensation of nonlinearities occurring in microwave photonic links using a novel digital nonlinear equalization technique and demonstrate suppression of distortion products by 33 dB with a small number of equalizer coefficients.

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Side channel authenticity discriminant analysis for device class identification

Summary

Counterfeit microelectronics present a significant challenge to commercial and defense supply chains. Many modern anti-counterfeit strategies rely on manufacturer cooperation to include additional identification components. We instead propose Side Channel Authenticity Discriminant Analysis (SICADA) to leverage physical phenomena manifesting from device operation to match suspect parts to a class of authentic parts. This paper examines the extent that power dissipation information can be used to separate unique classes of devices. A methodology for distinguishing device types is presented and tested on both simulation data of a custom circuit and empirical measurements of Microchip dsPIC33F microcontrollers. Experimental results show that power side channels contain significant distinguishing information to identify parts as authentic or suspect counterfeit.
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Summary

Counterfeit microelectronics present a significant challenge to commercial and defense supply chains. Many modern anti-counterfeit strategies rely on manufacturer cooperation to include additional identification components. We instead propose Side Channel Authenticity Discriminant Analysis (SICADA) to leverage physical phenomena manifesting from device operation to match suspect parts to a class of...

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Resonance fluorescence from an artificial atom in squeezed vacuum

Published in:
Phys. Rev. X, Vol. 6, No. 3, July-September 2016, 031004.

Summary

We present an experimental realization of resonance fluorescence in squeezed vacuum. We strongly couple microwave-frequency squeezed light to a superconducting artificial atom and detect the resulting fluorescence with high resolution enabled by a broadband traveling-wave parametric amplifier. We investigate the fluorescence spectra in the weak and strong driving regimes, observing up to 3.1 dB of reduction of the fluorescence linewidth below the ordinary vacuum level and a dramatic dependence of the Mollow triplet spectrum on the relative phase of the driving and squeezed vacuum fields. Our results are in excellent agreement with predictions for spectra produced by a two-level atom in squeezed vacuum [Phys. Rev. Lett. 58, 2539 (1987)], demonstrating that resonance fluorescence offers a resource-efficient means to characterize squeezing in cryogenic environments.
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Summary

We present an experimental realization of resonance fluorescence in squeezed vacuum. We strongly couple microwave-frequency squeezed light to a superconducting artificial atom and detect the resulting fluorescence with high resolution enabled by a broadband traveling-wave parametric amplifier. We investigate the fluorescence spectra in the weak and strong driving regimes, observing...

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A near-quantum-limited Josephson traveling-wave parametric amplifier

Published in:
Sci., Vol. 350, No. 6258, 16 October 2015,pp. 307-10.

Summary

Detecting single photon level signals--carriers of both classical and quantum information--is particularly challenging for low-energy microwave frequency excitations. Here we introduce a superconducting amplifier based on a Josephson junction transmission line. Unlike current standing-wave parametric amplifiers, this traveling wave architecture robustly achieves high gain over a bandwidth of several gigahertz with sufficient dynamic range to read out 20 superconducting qubits. To achieve this performance, we introduce a sub-wavelength resonant phase matching technique that enables the creation of nonlinear microwave devices with unique dispersion relations. We benchmark the amplifier with weak measurements, obtaining a high quantum efficiency of 75% (70% including following amplifier noise). With a flexible design based on compact lumped elements, this Josephson amplifier has broad applicability to microwave metrology and quantum optics.
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Summary

Detecting single photon level signals--carriers of both classical and quantum information--is particularly challenging for low-energy microwave frequency excitations. Here we introduce a superconducting amplifier based on a Josephson junction transmission line. Unlike current standing-wave parametric amplifiers, this traveling wave architecture robustly achieves high gain over a bandwidth of several gigahertz...

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Reduction of trapped-ion anomalous heating by in situ surface plasma cleaning

Published in:
Phys. Rev. A, At. Mol. Opt. Phys., Vol. 92, No. 2, 2015, 020302.

Summary

Anomalous motional heating is a major obstacle to scalable quantum information processing with trapped ions. Although the source of this heating is not yet understood, several previous studies suggest that noise due to surface contaminants is the limiting heating mechanism in some instances. We demonstrate an improvement by a factor of 4 in the room-temperature heating rate of a niobium surface electrode trap by in situ plasma cleaning of the trap surface. This surface treatment was performed with a simple homebuilt coil assembly and commercially available matching network and is considerably gentler than other treatments, such as ion milling or laser cleaning, that have previously been shown to improve ion heating rates. We do not see an improvement in the heating rate when the trap is operated at cryogenic temperatures, pointing to a role of thermally activated surface contaminants in motional heating whose activity may freeze out at low temperatures.
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Summary

Anomalous motional heating is a major obstacle to scalable quantum information processing with trapped ions. Although the source of this heating is not yet understood, several previous studies suggest that noise due to surface contaminants is the limiting heating mechanism in some instances. We demonstrate an improvement by a factor...

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Comparison of gate dielectric plasma damage from plasma-enhanced atomic layer deposited and magnetron sputtered TiN metal gates

Published in:
J. Appl. Phys., Vol. 118, No. 4, 2015, 045307.

Summary

Fully depleted silicon-on-insulator transistors were fabricated using two different metal gate deposition mechanisms to compare plasma damage effects on gate oxide quality. Devices fabricated with both plasma-enhanced atomic-layer-deposited (PE-ALD) TiN gates and magnetron plasma sputtered TiN gates showed very good electrostatics and short-channel characteristics. However, the gate oxide quality was markedly better for PE-ALD TiN. A significant reduction in interface state density was inferred from capacitance-voltage measurements as well as a 1200 x reduction in gate leakage current. A high-power magnetron plasma source produces a much higher energetic ion and vacuum ultra-violet (VUV) photon flux to the wafer compared to a low-power inductively coupled PE-ALD source. The ion and VUV photons produce defect states in the bulk of the gate oxide as well as at the oxide-silicon interface, causing higher leakage and potential reliability degradation.
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Summary

Fully depleted silicon-on-insulator transistors were fabricated using two different metal gate deposition mechanisms to compare plasma damage effects on gate oxide quality. Devices fabricated with both plasma-enhanced atomic-layer-deposited (PE-ALD) TiN gates and magnetron plasma sputtered TiN gates showed very good electrostatics and short-channel characteristics. However, the gate oxide quality was...

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