High-resolution error detection in the capture process of a single-electron pump

Abstract

The dynamic capture of electrons in a semiconductor quantum dot (QD) by raising a potential barrier is a crucial stage in metrological quantized charge pumping. In this work, we use a quantum point contact (QPC) charge sensor to study errors in the electron capture process of a QD formed in a GaAs heterostructure. Using a two-step measurement protocol to compensate for 1/f noise in the QPC current, and repeating the protocol more than 10 6 times, we are able to resolve errors with probabilities of order 10 −6 . For the studied sample, one-electron capture is affected by errors in ∼ 30 out of every million cycles, while two-electron capture was performed more than 10 6 times with only one error. For errors in one-electron capture, we detect both failure to capture an electron, and capture of two electrons. Electron counting measurements are a valuable tool for investigating non-equilibrium charge capture dynamics, and necessary for validating the metrological accuracy of semiconductor electron pumps.

Single‐Electron Pumps and Quantum Current Metrology in the Revised SI

“…An alternative error‐counting scheme based on a GaAs quantum point contact (QPC) charge sensor was developed at the National Physical Laboratory (NPL, the national metrology institute of UK) and demonstrated the quantification of SEP transfer errors with levels of about 1 µA A −1 . Also, in the flourishing field of silicon‐based nano‐electronic devices for metrology, electron counting in tunable‐barrier SEPs was demonstrated, as for instance published in …”

“…Corresponding developments are currently pursued at several institutes from metrology and academia. Such schemes usually involve a charge detector that probes the charge state of a charge island in close vicinity of the SEP, that is, on‐chip . Given that, first, the detector senses the island charge with single‐electron resolution, and, second, the bandwidth of this detector is sufficiently large to detect practically all transfer errors (that is, much larger than the average rate of the random error events, which again in reasonable operation regimes is much smaller than the pumping frequency f SEP ), this allows access to full‐counting statistics of the error events.…”

Electron counting capacitance standard and quantum metrology triangle experiments at PTB

“…the repetition frequency of the voltage signals driving the pump, and 〈N〉 is the average number of electron transferred per pump cycle as quantified by erroraccounting using rf single-electron detectors. With an alternative in situ error-counting scheme developed at the National Physical Laboratory (NPL, UK), single-electron transfer errors with levels of one part per million were recently measured on a semiconductor SET pump [41]. The ultrastable low-noise current amplifier (ULCA), a new type of transimpedance amplifier developed at PTB, offers unparalleled measurement performance for small direct currents [42,43].…”

Superconducting charge sensor coupled to an electron layer in silicon

“…The accuracy of a pump is ultimately given by the mean number of electrons transferred per cycle of the periodic drive. Errors in the pumping protocol may lead to excess or missed transitions with respect to the ideal value of n. A number of experimental works have demonstrated the detection of such errors in real time with charge detectors capacitively coupled either to a counting island (CI) that collects pumped electrons [7][8][9] or to the QD directly [10].…”