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arXiv:1703.04795 · Physical Review Applied

Thermal-Error Regime in High-Accuracy Gigahertz Single-Electron Pumping

Ruichen Zhao, Alessandro Rossi, S. P. Giblin, J. D. Fletcher, Fay E. Hudson, Mikko Möttönen, M. Kataoka, Andrew S. Dzurak

Published Oct 30, 2017• 47 citations
arXivHTMLPDF

Abstract

Single-electron pumps based on quantum dots (QDs) with tunable barriers are promising candidates for the emerging quantum standard of electrical current, but accuracy at elevated reservoir temperatures can be challenging. In this study, a planar silicon QD achieves accurate, high-speed single-electron pumping in the thermal regime, where reservoir temperature could rise to a few kelvin. This device operates without the demanding conditions of previous experiments, indicating that it could deliver a cost-effective and easily distributed standard of current---and, furthermore, could be useful for long-range transfer of quantum information.

DOI
10.1103/physrevapplied.8.044021

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Single-electron pumps based on quantum dots (QDs) with tunable barriers are promising candidates for the emerging quantum standard of electrical current, but accuracy at elevated reservoir temperatures can be challenging. In this study, a planar silicon QD achieves accurate, high-speed single-electron pumping in the thermal regime, where reservoir temperature could rise to a few kelvin. This device operates without the demanding conditions of previous experiments, indicating that it could deliver a cost-effective and easily distributed standard of current---and, furthermore, could be useful for long-range transfer of quantum information.
In quantum metrology, semiconductor single-electron pumps are used to generate accurate electric currents with the ultimate goal of implementing the emerging quantum standard of the ampere. Pumps based on electrostatically defined tunable quantum dots (QDs) have thus far shown the most promising performance in combining fast and accurate charge transfer. However, at frequencies exceeding approximately 1 GHz the accuracy typically decreases. Recently, hybrid pumps based on QDs coupled to trap states have led to increased transfer rates due to tighter electrostatic confinement. Here, we operate a hybrid electron pump in silicon obtained by coupling a QD to multiple parasitic states and achieve robust current quantization up to a few gigahertz. We show that the fidelity of the electron capture depends on the sequence in which the parasitic states become available for loading, resulting in distinctive frequency-dependent features in the pumped current.
We report high-speed single-hole (SH) transfer using Si tunable-barrier pumps comprising p-type metal-oxide-semiconductor field-effect transistors. A clear SH-transfer-current plateau with the current level of about 160 pA was observed when a clock signal having a frequency of 1 GHz was applied to one of the gates. Temperature dependence measurements of the transfer current reveal that the transfer probability is dominated by non-equilibrium SH escape by thermal hopping from the electrically formed charge island. The lower bound of the relative error rate for the 1-GHz transfer is about 10−3 at a temperature of about 17 K. In addition, we investigate the frequency dependence of the transfer, where we discuss possible sources causing the change in the error rate. These results pave the way for accurate manipulation of SHs and its application to metrological current standards.
Semiconductor-based quantum dot single-electron pumps are currently the most promising candidates for the direct realization of the emerging quantum standard of the ampere in the International System of Units. Here, we discuss a silicon quantum dot single-electron pump with radio frequency control over the transparencies of entrance and exit barriers as well as the dot potential. We show that our driving protocol leads to robust bidirectional pumping: one can conveniently reverse the direction of the quantized current by changing only the phase shift of one driving waveform with respect to the others. We anticipate that this pumping technique may be used in the future to perform error counting experiments by pumping the electrons into and out of a reservoir island monitored by a charge sensor.
A gigahertz single-electron (SE) pump with a semiconductor charge island is promising for a future quantum current standard. However, high-accuracy current in the nanoampere regime is still difficult to achieve because the performance of SE pumps tends to degrade significantly at frequencies exceeding 1 GHz. Here, we demonstrate robust SE pumping via a single-trap level in silicon up to 7.4 GHz, at which the pumping current exceeds 1 nA. An accuracy test with an uncertainty of about one part per million (ppm) reveals that the pumping current deviates from the ideal value by only about 20 ppm at the flattest part of the current plateau. This value is two orders of magnitude better than the best one reported in the nanoampere regime. In addition, the pumping accuracy is almost unchanged up to 7.4 GHz, probably due to strong electron confinement in the trap. These results indicate that trap-mediated SE pumping is promising for achieving the practical operation of the quantum current standard.
Recent studies of silicon spin qubits at temperatures above 1 K are encouraging demonstrations that the cooling requirements for solid-state quantum computing can be considerably relaxed. However, qubit readout mechanisms that rely on charge sensing with a single-island single-electron transistor (SISET) quickly lose sensitivity due to thermal broadening of the electron distribution in the reservoirs. Here we exploit the tunneling between two quantized states in a double-island single-electron transistor (SET) to demonstrate a charge sensor with an improvement in the signal-to-noise ratio by an order of magnitude compared to a standard SISET, and a single-shot charge readout fidelity above 99% up to 8 K at a bandwidth greater than 100 kHz. These improvements are consistent with our theoretical modeling of the temperature-dependent current transport for both types of SETs. With minor additional hardware overhead, these sensors can be integrated into existing qubit architectures for a high-fidelity charge readout at few-kelvin temperatures.
We measure the average number of electrons loaded into an electrostatically-defined quantum dot (QD) operated as a tunable-barrier electron pump, using a point-contact (PC) charge sensor 1 micron away from the QD. The measurement of the electron number probes the QD loading dynamics even in the limit of slow gate voltage rise-times, when the pumped current is too small to measure. Using simulations we show that, with optimised QD-PC coupling, the experiment can make single-shot measurements of the number of electrons in the QD with sufficiently high fidelity to test the error rate of the electron pump with metrological precision.