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arXiv:cond-mat/0608652 · Applied Physics Letters

Multiplexing single electron transistors for application in scalable solid-state quantum computing

Vincent I. Conrad, Andrew D. Greentree, Lloyd C. L. Hollenberg

Published Jan 22, 2007• 7 citations
arXivHTMLPDF

Abstract

Single electron transistors (SETs) are nanoscale electrometers of unprecedented sensitivity, and as such have been proposed as readout devices in a number of quantum computer architectures. The authors show that the functionality of a standard SET can be multiplexed so as to operate as both readout device and control gate for solid-state qubit systems based on charge localization and spin-charge transduction. Such multiplexing offers new possibilities for gate density reduction in nanoscale devices, and may therefore play a role in scalable quantum computer architectures.

DOI
10.1063/1.2435335

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Single electron transistors (SETs) are nanoscale electrometers of unprecedented sensitivity, and as such have been proposed as readout devices in a number of quantum computer architectures. The authors show that the functionality of a standard SET can be multiplexed so as to operate as both readout device and control gate for solid-state qubit systems based on charge localization and spin-charge transduction. Such multiplexing offers new possibilities for gate density reduction in nanoscale devices, and may therefore play a role in scalable quantum computer architectures.
Single-spin detection will be crucial for solid-state quantum computer architectures in which information is encoded in the spin-state of single nuclear or electron spins. The formidable problem of single-spin detection in a solid can be mapped to a more tractable problem of single-charge detection through spin-dependent electron transfer which may be observed using ultra-sensitive solid-state nanostructure electrometers. Here we describe a readout architecture using single electron transistors (SETs) that can detect the charge-state of two coupled metal dots, which simulates charge transfer in a two-quantum bit (qubit) spin system. This twin-SET architecture allows significant reduction of random charge noise by correlating two detector outputs, reducing the probability of readout errors in the quantum computer.
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Single-spin detection will be crucial for solid-state quantum computer (QC) architectures in which information is encoded in the spin state of single nuclear or electron spins. The formidable problem of single-spin detection in a solid can be mapped to a more tractable problem of single-charge detection through spin-dependent electron transfer which may be observed using ultrasensitive solid-state nanostructure electrometers. Here we describe a read-out architecture using single-electron transistors (SETs) that can detect the charge state of two coupled metal dots, which simulates charge transfer in a two-quantum-bit (qubit) spin system. This twin-SET architecture allows significant reduction of random charge noise by correlating two detector outputs, reducing the probability of read-out errors in the QC.
There is currently a worldwide effort towards the realisation of large-scale quantum computers that exploit quantum phenomena for information processing. While these computing systems could potentially redefine the technological landscape, harnessing quantum effects is challenging due to their inherently fragile nature and the experimentally demanding environments in which they arise. In order for quantum computation to be viable it is first necessary to demonstrate the operation of two-level quantum systems (qubits) which have long coherence times, can be quickly read out, and can be controlled with high fidelity. Focusing on these key requirements, this thesis presents four experiments towards scalable solid state quantum computing using gate-defined quantum dot devices based on gallium arsenide (GaAs) heterostructures. The first experiment investigates a phonon emission process that limits the charge coherence in GaAs and potentially complicates the microwave control of multi-qubit devices. We show that this microwave analogy to Raman spectroscopy can provide a means of detecting the unique phonon spectral density created by a nanoscale device. Experimental results are compared to a theoretical model based on a non-Markovian master equation and approaches to suppressing electron-phonon coupling are discussed. The second experiment demonstrates a technique involving in-situ gate electrodes coupled to lumped-element resonators to provide high-bandwidth dispersive read-out of the state of a double quantum dot. We characterise the charge sensitivity of this method in the few-electron regime and benchmark its performance against quantum point contact charge sensors. The third experiment implements a low-loss, chip-level frequency multiplexing scheme for the readout of scaled-up spin qubit arrays. Dispersive gate-sensing is realised in combination with charge detection based on two radio frequency quantum point contacts to perform multiplexed readout of a double quantum dot in the few-electron regime. Demonstration of a 10-channel multiplexing device is achieved and limitations in scaling spin qubit readout to large numbers using multiplexed channels discussed. The final experiment ties previously presented results together by realising a micro-architecture for controlling and reading out qubits during the execution of a quantum algorithm. The basic principles of this architecture are demonstrated via the manipulation of a semiconductor qubit using control pulses that are cryogenically routed using a high-electron mobility transistor switching matrix controlled by a field programmable gate array. Finally, several technical results are also presented including the development of printed circuit board solutions to allow the high-frequency measurement of nanoscale devices at cryogenic temperatures and the design of on-chip interconnects used to suppress electromagnetic crosstalk in high-density spin qubit device architectures.
Semiconductor quantum dot arrays are a promising platform to perform spin-based error-corrected quantum computation with large numbers of qubits. However, due to the diverging number of possible charge configurations combined with the limited sensitivity of large-footprint charge sensors, achieving single-spin occupancy in each dot in a growing quantum dot array is exceedingly complex. Therefore, to scale-up a spin-based architecture we must change how individual charges are readout and controlled. Here, we demonstrate single-spin occupancy of each dot in a foundry-fabricated array by combining two methods. 1/ Loading a finite number of electrons into the quantum dot array; simplifying electrostatic tuning by isolating the array from the reservoirs. 2/ Deploying multiplex gate-based reflectometry to dispersively probe charge tunneling and spin states without charge sensors or reservoirs. Our isolated arrays probed by embedded multiplex readout can be readily electrostatically tuned. They are thus a viable, scalable approach for spin-based quantum architectures. Large-footprint, low-sensitivity charge sensors hinder scaling semiconductor quantum dot arrays for quantum computation. Here the authors present a potentially scalable approach using multiplexed gate-based readout and operation in a foundry-fabricated quantum dot array, demonstrating single-electron occupancy.
Large-scale, fault-tolerant quantum computing requires the integration of a substantial number of quantum bits (qubits). Efficient readout of these qubits depends on the underlying technology but invariably calls for scalable multiplexed schemes. This paper introduces a novel digital code multiplexing approach for charge readout in quantum computing. Operating entirely at digital levels, the proposed scheme eliminates the need for complex waveform or sinusoidal signal generation. Unlike conventional reflectometry, where the number of qubits dictates the number of physical resonant circuits, our method only influences the digital clock frequency, enabling a more compact and scalable implementation. We demonstrate this scheme by modulating two industrial single-electron transistors (SETs) through a transimpedance amplifier (TIA)-based readout chain operating at 4.2~K. Experimental results show that the proposed method reliably distinguishes SET conductivity states under multiplexing, achieving a bit-error rate (BER) below 10−310^{-3}10−3 within an integration time of 4.55 μ4.55~\mu4.55 μs.