🔬 mesoscale physics

Scalable Multiple Electron Transport Architectures for Feedback Traceable Current Sources

This paper presents a scalable, floating-gate-based Multiple Electron Transport (MET) architecture that utilizes controlled charge injection and non-destructive readout to generate stable, programmable, and electron-traceable current sources with noise reduction scaling to the square root of parallel measurements.

Original authors: Agustin Javier Lapi, Guillermo Fernandez Moroni, Fernando Chierchie, Fabricio Alcalde Bessia, Miqueas Ezequiel Gamero, Brenda Aurea Cervantes Vergara, Blas Junior Irigoyen Gimenez, Eduardo Paolini, Cl

Published 2026-09-22

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Agustin Javier Lapi, Guillermo Fernandez Moroni, Fernando Chierchie, Fabricio Alcalde Bessia, Miqueas Ezequiel Gamero, Brenda Aurea Cervantes Vergara, Blas Junior Irigoyen Gimenez, Eduardo Paolini, Claudio Rodrigo Chavez Blanco, Juan Estrada, Javier Tiffenberg

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

In the world of precision measurement, the definition of the ampere, the unit we use to measure electric current, has undergone a profound shift. For decades, the standard relied on physical artifacts and complex setups, but a new era has begun where the ampere is defined by the fundamental building blocks of electricity itself: the electron. To realize this definition in practice, scientists need a way to count individual electrons moving over time, creating a current that is traceable directly to the number of particles flowing. This is not merely an academic exercise; it is the foundation for a new kind of metrology that could redefine how we measure electricity with absolute certainty. However, achieving this has been difficult. Traditional methods often require extreme cold, complex nanofabrication, and the ability to move single electrons at incredibly high speeds, making them impractical for many applications. The challenge has been to find a way to generate and count these tiny packets of charge reliably, without needing the most extreme conditions or the most intricate machinery.

A team of researchers has now demonstrated a new approach that sidesteps many of these hurdles by repurposing a type of image sensor known as a Skipper-CCD. These sensors, originally designed to capture light in astronomy and other fields, have a unique ability: they can measure the same packet of electric charge over and over again without destroying it. By taking many measurements of the same charge and averaging the results, the sensor can reduce its internal noise to a level where it can distinguish a single electron from nothing at all. The researchers took this existing technology and turned it into a current source. Instead of waiting for light to create charge, as these sensors usually do, they used a controlled electronic method to inject specific amounts of charge directly into the sensor's memory. They then measured these injected packets with single-electron precision and drained them out at a steady rate. This process creates a current that is defined entirely by the number of electrons moved per second, making it directly traceable to the fundamental charge of an electron.

The work involved testing several different ways to arrange these sensors to make them more useful. The researchers explored building a single, compact unit that could generate a small, precise current, and then looked at how to scale this up. They simulated what would happen if they placed multiple sensors side-by-side or stacked them in a line to increase the total current output. Their computer models showed that by combining these units, they could generate larger currents while maintaining high precision. Crucially, they found that by using a digital counting method to round their measurements to whole numbers of electrons, they could actually improve the accuracy of the current measurement, turning a potential source of error into a tool for better precision. This technique allows the system to operate with improved stability, though the experimental setup required cooling the sensor to 140K using a cryocooler to ensure reliable operation, a temperature significantly higher than the near-absolute zero required by some other quantum current standards.

To prove this concept worked in the real world, the team set up a physical experiment using a Skipper-CCD inside a vacuum chamber, cooled to a stable temperature to ensure reliable operation. They configured the sensor so that one end acted as a pump, injecting charge packets into a serial register, while the other end read them out. By adjusting the voltage applied to the injection point, they could control exactly how many electrons entered the system. They successfully generated and measured charge packets ranging from a single electron up to 2,500 electrons. In a significant achievement, they were able to create a calibration curve that mapped the sensor's output directly to the number of electrons with high accuracy across this entire range. This demonstrated that the device could generate a current that is absolutely known, without relying on light or external references.

The team also tested the stability of this current over time. By running the system for an extended period, they observed that the flow of electrons remained remarkably steady. Statistical analysis of the data showed that the current fluctuated very little, staying well within expected limits of stability. This confirmed that the method is not just a one-time trick but a robust way to generate a reliable electrical signal. The researchers also showed that they could combine two of these current-generating units to double the output, proving that the design can be scaled up to produce stronger currents if needed. The entire setup was compact, using a single sensor chip to perform both the injection and the measurement, suggesting that this could be built into a small, self-contained device.

This work represents a significant step forward in the field of quantum metrology. By showing that a Skipper-CCD can be used to generate a current that is traceable to the elementary charge without the need for complex single-electron pumps or the extreme cryogenic temperatures of single-electron pumps, the researchers have opened a new path for precision measurement. The ability to generate and count thousands of electrons with single-electron precision using a controlled electronic injection method offers a practical alternative to existing technologies. The results suggest that in the future, such devices could be used to calibrate other instruments or serve as the primary standard for electric current in a variety of settings, bringing the fundamental definition of the ampere into more accessible and versatile hardware. The study confirms that with the right architecture, the discrete nature of the electron can be harnessed to create a stable, measurable, and scalable source of electric current.

Technical Summary: Scalable Multiple Electron Transport Architectures for Feedback Traceable Current Sources

Problem Statement
The redefinition of the ampere in terms of the elementary charge has created a demand for ultra-low current sources with metrological accuracy and direct traceability to the electron. While existing quantum-based current sources, such as single-electron transistors (SETs) and pumps, offer high precision, they are limited by the need for complex nanofabrication, cryogenic operation, and high-frequency control (GHz order), which restricts their scalability and operational range. Conversely, room-temperature alternatives often lack direct electron-traceability. Recent approaches using Skipper-CCDs to generate current via optical illumination and charge draining offer a path toward traceability but are intrinsically limited by Poisson statistics, illumination stability, and the relationship between exposure time and charge magnitude.

Methodology
The authors propose a scalable architecture for an electron-counting current source based on a Multiple Electron Transport (MET) device. The core methodology involves repurposing the "fill-and-spill" charge injection technique, historically used in CCDs for memory writing and radiation damage characterization, to generate controlled, quantized charge packets directly within the sensor without optical illumination.

The paper explores three scalable architectures based on floating-gate amplifiers:

Basic Cell: A single charge pump (CP) injecting packets into a sequential memory, read out by a single Charge Measurement Module (CMM).
Series Architecture: Multiple CMMs (amplifiers) placed along a single serial register to perform independent, time-separated measurements of the same charge packet, averaging the results to reduce noise.
Parallel Architecture: Multiple basic cells connected in parallel to sum their output currents, increasing the total current magnitude while maintaining precision.

A key theoretical component is the incorporation of a quantizer block within the measurement chain. By mapping noisy charge measurements to the nearest integer (electron count), the system leverages the discrete nature of electron charge to suppress noise fluctuations below the single-electron level, provided the readout noise is sufficiently low.

Experimental validation was conducted using a Skipper-CCD with four output channels operated at 140K. The device was configured as two parallel current cells (using two halves of the sensor). Charge was injected via the fill-and-spill method by adjusting the voltage at the ohmic contact ( $V_{dr}$ ), and packets were shifted through the serial register. The output was read out using Skipper sampling (multiple non-destructive measurements) to achieve sub-electron noise resolution.

Key Results

Charge Injection and Calibration: The system successfully generated and measured charge packets ranging from the single-electron level up to 2,500 electrons. A linear calibration curve was established between Analog-to-Digital Units (ADU) and electron counts, demonstrating absolute traceability to the elementary charge. The authors note that achieving such a homogeneous, electrically generated single-electron spectrum up to the few-thousand-electron regime has not been previously demonstrated.
Noise Reduction: Experimental data confirmed that readout noise follows the expected $1/\sqrt{N_S}$ scaling, where $N_S$ is the number of non-destructive samples. With $N_S = 650$ , the readout noise was reduced to 0.18 electrons.
Quantizer Impact: Simulations and theoretical analysis indicate that while the quantizer block has negligible effect at high noise levels, it significantly improves measurement precision once the noise floor drops below the single-electron level, effectively discretizing the signal and eliminating noise-induced uncertainty in the integer count.
Current Stability: Long-term stability tests (approx. 15 minutes) showed that the generated current remained statistically stable. Using Chebyshev's inequality, the authors observed that only 0.27% of data points fell outside the $3\sigma$ bounds, significantly better than the theoretical upper bound of 11.1%, confirming the stability of the current source.
Scalability: Simulations of the proposed architectures demonstrate that increasing the number of parallel cells ( $N_C$ ) or series amplifiers ( $N_A$ ) improves the noise-to-signal ratio and output current, respectively, offering a pathway to generate larger current signals while maintaining quantum metrology standards.

Significance and Claims
The paper claims to present a compact, scalable, and self-calibrated platform for electron-counting current sources that operates at cryogenic temperatures (but not necessarily the extreme milli-Kelvin range required for SETs) and avoids the complexities of GHz-frequency control. By utilizing controlled electronic charge injection rather than optical generation, the method offers superior reproducibility and independence from optical source stability.

The authors emphasize that their approach enables the generation of quantized current units traceable to the elementary charge across an unprecedented dynamic range within a single device. The proposed architectures, particularly the parallel and series configurations, are presented as a viable path toward generating larger current signals suitable for precision quantum metrology applications, moving beyond the limitations of single-electron pumping. The work concludes with a proposed layout for a basic current cell, setting the stage for future experimental validation of the fully integrated, scalable architecture.

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