arXiv subjects

Clément Geffroy

Publications and source records attributed to Clément Geffroy.

5 recordsLinked to original sources

arXiv2026

Active control of THz plasmon propagation in a one-dimensional electronic waveguide

Quantum nanoelectronics is pushing towards ever higher operating frequencies in order to realise quantum technologies capable of processing information at unprecedented speeds. A particularly promising direction is the development of flying electron qubits, which offer the prospect of quantum operations on picosecond timescales. Achieving in-flight quantum control in this regime would establish a fundamentally new paradigm for studying quantum entanglement and enable a novel form of quantum information processing based on propagating electronic wavepackets. Here we report a first step towards this goal by injecting ultrashort electron wavepackets into an engineered quantum nanoelectronic device. We demonstrate active control over the propagation speed of an electron wavepacket with a temporal duration as short as 4 ps in a quasi-one-dimensional electron waveguide with a length ranging from 10 $\mathrmμ$m to 40 $\mathrmμ$m. This advance provides a key building block for ultrafast quantum operations using flying electrons. Beyond its technological implications, our approach offers a platform for exploring the intrinsic dynamical processes that govern quantum transport and coherence in nanoscale electronic systems.

cond-mat.mes-hall↗

arXiv2025

Evidence of Coulomb liquid phase in few-electron droplets

Emergence of universal collective behaviour from interactions within a sufficiently large group of elementary constituents is a fundamental scientific paradigm. In physics, correlations in fluctuating microscopic observables can provide key information about collective states of matter such as deconfined quark-gluon plasma in heavy-ion collisions or expanding quantum degenerate gases. Mesoscopic colliders, through shot-noise measurements, have provided smoking-gun evidence on the nature of exotic electronic excitations such as fractional charges, levitons and anyon statistics. Yet, bridging the gap between two-particle collisions and the emergence of collectivity as the number of interacting particles increases remains a challenging task at the microscopic level. Here we demonstrate all-body correlations in the partitioning of electron droplets containing up to N = 5 electrons, driven by a moving potential well through a Y-junction in a semiconductor device. Analyzing the partitioning data using high-order multivariate cumulants and finite-size scaling towards the thermodynamic limit reveals distinctive fingerprints of a strongly-correlated Coulomb liquid. These fingerprints agree well with a universal limit where the partitioning of a droplet is predicted by a single collective variable. Our electron-droplet collider provides critical insight into the interplay of confinement and interaction effects in small electron systems and highlights a new way to study engineered states of matter.

cond-mat.mes-hall↗

arXiv2023

Ultrashort electron wavepackets via frequency-comb synthesis

Single-electron sources are an essential component of modern quantum nanoelectronic devices. Owing to their high accuracy and stability, they have been successfully employed for metrology applications, studying fundamental matter interactions and more recently for electron quantum optics. They are traditionally driven by state-of-the-art arbitrary waveform generators that are capable of producing single-electron pulses in the sub-100 ps timescale. In this work, we use an alternative approach for generating ultrashort electron wavepackets. By combining several harmonics provided by a frequency comb, we synthesise Lorentzian voltage pulses and then use them to generate electron wavepackets. Through this technique, we report on the generation and detection of an electron wavepacket with temporal duration of 27 ps generated on top of the Fermi sea of a 2-dimensional electron gas - the shortest reported to date. Electron pulses this short enable studies on elusive, ultrafast fundamental quantum dynamics in nanoelectronic systems and pave the way to implement flying electron qubits by means of Levitons.

cond-mat.mes-hall↗

arXiv2022

Semiconductor-based electron flying qubits: Review on recent progress accelerated by numerical modelling

The progress of charge manipulation in semiconductor-based nanoscale devices opened up a novel route to realise a flying qubit with a single electron. In the present review, we introduce the concept of these electron flying qubits, discuss their most promising realisations and show how numerical simulations are applicable to accelerate experimental development cycles. Addressing the technological challenges of flying qubits that are currently faced by academia and quantum enterprises, we underline the relevance of interdisciplinary cooperation to move emerging quantum industry forward. The review consists of two main sections: Pathways towards the electron flying qubit: We address three routes of single-electron transport in GaAs-based devices focusing on surface acoustic waves, hot-electron emission from quantum dot pumps and Levitons. For each approach, we discuss latest experimental results and point out how numerical simulations facilitate engineering the electron flying qubit. Numerical modelling of quantum devices: We review the full stack of numerical simulations needed for fabrication of the flying qubits. Choosing appropriate models, examples of basic quantum mechanical simulations are explained in detail. We discuss applications of open-source (KWANT) and the commercial (nextnano) platforms for modelling the flying qubits. The discussion points out the large relevance of software tools to design quantum devices tailored for efficient operation.

cond-mat.mes-hall↗

arXiv2020

Efficient 3-dimensional photonic-plasmonic photo-conductive switches for picosecond THz pulses

The efficiency of photo-conductive switches, which continue to be used for the generation and detection of THz waves, has been overlooked for a long time. The so far 'optics-dominated' devices are making their way through to new and emerging fields of research that require ultrafast picosecond voltage pulses, as well as to new applications where power efficiency is of uttermost importance. To address the efficiency problems, in this article we present a novel photo-conductive switch that is based on a 3-dimensional design. In contrast to conventional planar designs, our photo-conductive switch drastically enhances the overall efficiency by maximising the laser absorption within the device, while at the same time optimising the carrier collection efficiency at the electrodes. To maximise the optical absorption we take advantage of photonic and plasmonic modes that are excited in our device due to a periodic array of nanopillars, whereas the collection efficiency is optimised by converting each nanopillar into a single nano-photo-conductive switch. Our numerical calculations show a 50-fold increase in the overall generated current and a 5-fold bandwidth increase compared to traditional interdigitated planar photo-conductive switches. This opens up a wealth of new possibilities in quantum science and technology where efficient low power devices are indispensable.

physics.app-ph↗