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IEEE Transactions on Applied Superconductivity

Negative-Inductance Superconducting Quantum Interference Device With Energy Dissipation of 1.38 zJ/bit Measured by Inductively Coupled Coplanar Waveguide Resonator

Hao Li, Jianshe Liu, Han Cai, Qichun Liu, Yingshan Zhang, Gang Li, Wei Chen

Published Dec 20, 2016• 1 citation
Publisher

Abstract

High energy-efficient superconducting circuits are increasingly desirable for information technology. Negative-inductance superconducting quantum interference device (nSQUID) is considered to have the capability of approaching the physical limit of irreversible computing. Superconducting coplanar waveguide (CPW) resonator of high quality factor Q is widely used for detecting extremely small signals. To measure the energy dissipation in nSQUID, we have designed and fabricated an nSQUID with its common mode flux control inductively coupled to a superconducting CPW resonator. The energy dissipation can be obtained from the changes in transmission spectra of the coupled circuit at different input powers. Low temperature experimental results at 1.07 K show that the bit operation energy in nSQUID operating at 2.19 GHz is about 1.38 zJ.

DOI
10.1109/tasc.2016.2642047

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High energy-efficient superconducting circuits are increasingly desirable for information technology. Negative-inductance superconducting quantum interference device (nSQUID) is considered to have the capability of approaching the physical limit of irreversible computing. Superconducting coplanar waveguide (CPW) resonator of high quality factor Q is widely used for detecting extremely small signals. To measure the energy dissipation in nSQUID, we have designed and fabricated an nSQUID with its common mode flux control inductively coupled to a superconducting CPW resonator. The energy dissipation can be obtained from the changes in transmission spectra of the coupled circuit at different input powers. Low temperature experimental results at 1.07 K show that the bit operation energy in nSQUID operating at 2.19 GHz is about 1.38 zJ.
Abstract A negative-inductance superconducting quantum interference device (nSQUID) is an adiabatic superconducting logic device with high energy efficiency, and therefore a promising building block for large-scale low-power superconducting computing. However, the principle of the nSQUID is not that straightforward and an nSQUID driven by voltage is vulnerable to common mode noise. We investigate a single nSQUID driven by current instead of voltage, and clarify the principle of the adiabatic transition of the current-driven nSQUID between different states. The basic logic operations of the current-driven nSQUID with proper parameters are simulated by WRspice. The corresponding circuit is fabricated with a 100 A cm −2 Nb-based lift-off process, and the experimental results at low temperature confirm the basic logic operations as a gated buffer.
We successfully designed and fabricated an absorption-type of superconducting coplanar waveguide (CPW) resonators. The resonators are made from a niobium film (about 160 nm thick) on a high-resistance Si substrate, and each resonator is fabricated as a meandered quarter-wavelength transmission line (one end is short to the ground and another end is capacitively coupled to a through feedline). With a vector network analyzer we measured the transmissions of the applied microwave through the resonators at ultra-low temperature. The obtained loaded quality factors are significantly high, i.e. up to ∼10 6 . When the temperature increases slowly from the base temperature (20 mK), the resonance frequencies of the resonators are blue shifted and the quality factors are lowered slightly. In principle, this type of device can integrate a series of CPW resonators with a common feedline, making it a promising candidate as the data bus for coupling distant solid-state qubits and the sensitive detector of single photons.
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Quantum information processing (QIP) concerns communication between qubits in quantum computer. Coplanar waveguide (CPW) resonators which could easily be fabricated with the micro-techniques in integrated circuits started to show its potentiality in QIP in last few years. So far CPW resonators were used to arrange communication between Josephson q-bits which have relatively short decoherence time. The q-bits based on molecular spins mountain quantum coherence for much longer time, but they have too weak coupling to microwave field to allow effective spin manipulation. In this project we aimed to optimize CPW resonators in order to achieve strong coupling to molecular spins. \nWe present results for standard Coplanar Waveguide (CPW) Nb resonators fabricated on sapphire substrate. To achieve strong coupling between microwave field and molecular spins constrictions of the central conductor at the antinode of current were made to get local enhancement of magnetic field. We also present the simulation results for the key design elements: T-junctions and constrictions, which gave a good guideline for design and fabrication. Low temperature measurements of resonators with (and without) local constrictions were made and verified the accuracy of simulations. Finally, we discuss the temperature and power dependence of resonators transmission spectra.
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Abstract Two-junction SQUIDs with negative mutual inductance between their two arms, called nSQUIDs, have been proposed for significantly improving quantum information transfer but their quantum nature has not been experimentally demonstrated. We have designed, fabricated, and characterized superconducting nSQUID qubits. Our results provide clear evidence of the quantum coherence of the device, whose properties are well described by theoretical calculations using parameters determined from spectroscopic measurement. In addition to their future application for fast quantum information transfer, the nSQUID qubits exhibit rich characteristics in their tunable two-dimensional (2D) potentials, energy levels, wave function symmetries, and dipole matrix elements, which are essential to the study of a wide variety of macroscopic quantum phenomena such as tunneling in 2D potential landscapes.