Multiplexed charge-locking device for large arrays of quantum devices

Abstract

We present a method of forming and controlling large arrays of gate-defined quantum devices. The method uses a novel, on-chip, multiplexed charge-locking system and helps to overcome the restraints imposed by the number of wires available in cryostat measurement systems. Two device innovations are introduced. Firstly, a multiplexer design which utilises split gates to allow the multiplexer to divide three or more ways at each branch. Secondly we describe a device architecture that utilises a multiplexer-type scheme to lock charge onto gate electrodes. The design allows access to and control of gates whose total number exceeds that of the available electrical contacts and enables the formation, modulation and measurement of large arrays of quantum devices. We fabricate devices utilising these innovations on n-type GaAs/AlGaAs substrates and investigate the stability of the charge locked on to the gates. Proof-of-concept is shown by measurement of the Coulomb blockade peaks of a single quantum dot formed by a floating gate in the device. The floating gate is seen to drift by approximately one Coulomb oscillation per hour.Motivation for the measurement of large numbers of quantum devices arises both from interest in the associated physical properties such as the formation of minibands [1] and from the drive to up-scale and integrate quantum phenomenon, such as spin physics[2], into future technology and quantum information processing [3]. Much of the physics of interest is only observable using cryogenic systems and the number of coupled devices is limited by the number of available contacts. Recent work has shown the use of multiplexing to greatly increase the number of isolated quantum devices available for measurement on a single chip and single cool-down [4,5] and frequency multiplexing, for the readout of spin qubits [6], has been demonstrated as a potential up-scaling route. The significant challenges presented by the need to upscale however are far from surmounted.The measurement of many individually addressable quantum devices has led to initial studies on yield[4], reproducibility [7] and statistical analysis of complex quantum phenomena [8]. The split gate[9-11] can be considered as the building block for more complex gatedefined devices, such as quantum dots [12]. Tuneable quantum dots require stable charge on several surface gates simultaneously in order to function. The multiplexing architecture presented in [4] doesn't allow the simultaneous use of multiple gates. We therefore present two innovations that facilitate the fabrication and measurement of large interacting quantum device arrays.We firstly show how a split gate can be used within a multiplexer-type addressing system, to enable the multiplexer to divide three or more ways at each node rather than two. Figure 1 shows a schematic of a single node of a 3-way multiplexer. A semiconducting two dimensional electron gas (2DEG), shown in blue, divides into three

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