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arXiv:1808.10204 · Advanced Quantum Technologies

Time‐Domain Spectroscopy of Mesoscopic Conductors Using Voltage Pulses

Pablo Burset, Janne Kotilahti, Michael Moskalets, Christian Flindt

Published Feb 27, 2019• 15 citations
arXivHTMLPDF

Abstract

Abstract The development of single‐electron sources is paving the way for a novel type of experiment in which individual electrons are emitted into a quantum‐coherent circuit. However, to facilitate further progress toward fully coherent on‐chip experiments with electrons, a detailed understanding of the quantum circuits is needed. Here, it is proposed to perform time‐domain spectroscopy of mesoscopic conductors by applying Lorentzian‐shaped voltage pulses to an input contact. Specifically, it is shown how characteristic timescales of a quantum‐coherent conductor can be extracted from the distribution of waiting times between charge pulses propagating through the circuit. To illustrate the idea, Floquet scattering theory is employed to evaluate the electron waiting times for an electronic Fabry–Pérot cavity and a Mach–Zehnder interferometer. The perspectives for an experimental realization of the proposal are discussed and possible avenues for further developments are identified.

DOI
10.1002/qute.201900014

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Abstract The development of single‐electron sources is paving the way for a novel type of experiment in which individual electrons are emitted into a quantum‐coherent circuit. However, to facilitate further progress toward fully coherent on‐chip experiments with electrons, a detailed understanding of the quantum circuits is needed. Here, it is proposed to perform time‐domain spectroscopy of mesoscopic conductors by applying Lorentzian‐shaped voltage pulses to an input contact. Specifically, it is shown how characteristic timescales of a quantum‐coherent conductor can be extracted from the distribution of waiting times between charge pulses propagating through the circuit. To illustrate the idea, Floquet scattering theory is employed to evaluate the electron waiting times for an electronic Fabry–Pérot cavity and a Mach–Zehnder interferometer. The perspectives for an experimental realization of the proposal are discussed and possible avenues for further developments are identified.
The distribution of electron waiting times is useful to characterize quantum transport in mesoscopic structures. Here we consider a generic quantum-coherent conductor consisting of a mesoscopic scatterer in a two-terminal setup. We extend earlier results for single-channel conductors to setups with several (possibly spin degenerate) conduction channels and we discuss the effect of a finite electronic temperature. We present detailed investigations of the electron waiting times in a quantum point contact as well as in two mesoscopic interferometers with energy-dependent transmissions: a Fabry--P\'erot interferometer and a Mach--Zehnder interferometer. We show that the waiting time distributions allow us to determine characteristic features of the scatterers, for instance, the number of resonant levels in the Fabry--P\'erot interferometer that contribute to the electronic transport.
We propose to generate heat pulses in mesoscopic conductors using light fields. In contrast to single-electron excitations such as levitons, which are created by accurate voltage drives, our approach relies on modulating the temperature of an electronic reservoir. To this end, we show that the interactions with a light field can induce a controllable time-dependent temperature in an electrode. The temperature modulations generate charge-neutral heat pulses that can be emitted into a mesoscopic conductor and detected in the outputs. We illustrate our approach by evaluating the time-dependent currents and their fluctuations using a tight-binding model of two electronic reservoirs connected by a quantum point contact. Our work establishes a route towards on-demand caloritronics, where energy rather than charge carries quantum information, and it paves the way for probing time-resolved heat transport and quantum coherence in thermally driven conductors.
In this study, we investigate the potential of electronic interferometers for probing the quantum state of electromagnetic radiation on a chip at subnanosecond timescales. We propose to use single-electron excitations propagating within an electronic Mach-Zehnder interferometer in the Aharonov-Bohm-dominated regime. We discuss how information about the quantum state of the electromagnetic radiation is encoded into the interference contribution to the average outgoing electrical current. By investigating squeezed radiation and single-edge magnetoplasmons probed by leviton pulses in a realistic setup, we show that single-electron interferometers have the potential to probe quantum radiation in the time domain with subnanosecond to picosecond time resolution. Our research could have significant implications for probing the fundamental properties of light in the microwave to terahertz domains at extremely short timescales.
Abstract The recent developments of electron quantum optics in quantum Hall edge channels have given us new ways to probe the behavior of electrons in quantum conductors. It has brought new quantities called electronic coherences under the spotlight. In this paper, we explore the relations between electron quantum optics and signal processing through a global review of the various methods for accessing single‐ and two‐electron coherences in electron quantum optics. We interpret electron quantum optics interference experiments as analog signal processing, converting quantum signals into experimentally observable quantities such as current averages and correlations. This point of view also gives us a procedure to obtain quantum information quantities from electron quantum optics coherences. We illustrate these ideas by discussing two‐mode entanglement in electron quantum optics. We also sketch how signal processing ideas may open new perspectives for representing electronic coherences in quantum conductors and understand the properties of the underlying many‐body electronic state.
Abstract We review our recent proposals for the on‐demand generation of entangled few‐electron states using dynamic single‐electron sources. The generation of entanglement can be traced back to the single‐electron entanglement produced by quantum point contacts (QPCs) acting as electronic beam splitters. The coherent partitioning of a single electron leads to entanglement between the two outgoing arms of the QPC. We describe our various approaches for generating and certifying entanglement in dynamic electronic conductors and we quantify the influence of detrimental effects such as finite electronic temperatures and other dephasing mechanisms. The prospects for future experiments are discussed and possible avenues for further developments are identified. (a) The coherent partitioning of a single electron on a QPC leads to entanglement between the outgoing arms. The entanglement can be detected using two copies of the state. (b) A time‐bin entangled state is generated by partitioning two electrons on a QPC followed by projection onto the subspace with one electron in each arm. The two‐electron entanglement is due to the entanglement of the individual single‐electron states. In both panels, circles represent single‐electron sources and squares represent detectors.
Electron quantum optics explores coherent single-electron charge pulse propagation in electronic nanoscale circuits akin to tabletop photon setups. While past experiments focused on normal-state conductors, incorporating superconductors holds promise for exploiting the electron-hole degree of freedom in quantum sensing applications and quantum information processing. Here, we propose and analyze an on-demand and tunable mechanism for converting single-electron pulses into holes through Andreev processes on a superconductor. We develop a Floquet-Nambu scattering formalism to demonstrate the dynamic conversion of charge pulses and the controllable generation of coherent electron-hole superpositions through interferometric magnetic flux control based on the chiral edge states of a quantum Hall sample. Our discussion covers optimal conditions in realistic scenarios, affirming the feasibility of our proposal with current technology.