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Application in Adiabatic Quantum Annealing
Published in Edward Wolf, Gerald Arnold, Michael Gurvitch, John Zasadzinski, Josephson Junctions, 2017
One of the critical problems of developing scalable quantum annealers is to read out the states of all qubits truthfully. The state of a flux qubit is represented by the direction of superconducting circulation current in the RF-SQUID ring. The usual way of measuring small magnetic signal using DC-SQUID running in either the flux-locked loop mode or small signal mode would not work, because for both methods the DC-SQUID is operated in the finite voltage branch of the current-voltage characteristics (IVC), which not only generate on-chip heat but also microwaves with frequency in the range of 10-102 GHz, enough to excite the qubits out of the ground state, due to the AC Josephson effect (Eq. 1.2). An alternative way is to measure the state of the qubit using an underdamped hysteretic DC-SQUID inductively coupled to the qubit. Because the critical current of the DC-SQUID depends on the magnetic flux threading its loop, the state of the qubit can be inferred by measuring the critical current of the DC-SQUID. However, the sudden jump from the zero voltage to the finite voltage state generates a large transient pulse. The jolt is so severe that it can randomly flip the states of other qubits, thus destroying the ground state of the ISG system reached at the end of adiabatic quantum evolution. To solve this so-called readout destruction problem, Berkley et al. developed a scalable XY-addressable readout system for superconducting adiabatic quantum annealer [42]. The readout system is designed specifically for reading out the states of the superconducting flux qubits in an adiabatic quantum annealer. For an N-qubit adiabatic quantum annealer, this readout system uses N hysteretic DC-SQUIDs and N hysteretic (Lj/L ^1) RF-SQUIDs operated as quantum flux parametrons (QFPs). The qubits are coupled to QFPs, which then couple to the DC-SQUIDs. This readout architecture not only solves the problem of readout destruction but also has significantly higher flux sensitivity than DC-SQUIDs directly coupled to flux qubits. The readout system has been tested and demonstrated successfully and was subsequently deployed in D-Wave 1 (128-qubit), 2 (512-qubit), and 2X (1024-qubit) quantum annealers [24,43].
Diamond with nitrogen: states, control, and applications
Published in Functional Diamond, 2022
Yuting Zheng, Chengming Li, Jinlong Liu, Junjun Wei, Haitao Ye
Furthermore, scaling a quantum computer to the large number of qubits required to outperform classical algorithms is a grand challenge, which requires the ability to correct the inevitable errors due to the delicate, analogue nature of quantum states. The utilization of the Quantum Experience quantum computing system to simulate different scenarios involving common hybrid quantum system components, the NV center, and the flux qubit was proposed [153]. By readout the NV signal using multicolor optical microscopy, one can read, write, and reset arbitrary data sets with two-dimensional (2D) binary bit density comparable to present digital-video-disk (DVD) technology for long-term data storage (Figure 13) [154].