| 1. |
- Acciai, Matteo, 1992, et al.
(author)
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Constraints between entropy production and its fluctuations in nonthermal engines
- 2024
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 109:7
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Journal article (peer-reviewed)abstract
- We analyze a mesoscopic conductor autonomously performing a thermodynamically useful task, such as cooling or producing electrical power, in a part of the system - the working substance - by exploiting another terminal or set of terminals - the resource - that contains a stationary nonthermal (nonequilibrium) distribution. Thanks to the nonthermal properties of the resource, on average no exchange of particles or energy with the working substance is required to fulfill the task. This resembles the action of a demon, as long as only average quantities are considered. Here, we go beyond a description based on average currents and investigate the role of fluctuations in such a system. We show that a minimum level of entropy fluctuations in the system is necessary, whenever one is exploiting a certain entropy production in the resource terminal to perform a useful task in the working substance. For concrete implementations of the demonic nonthermal engine in three- and four-terminal electronic conductors in the quantum Hall regime, we compare the resource fluctuations to the entropy production in the resource and to the useful engine output (produced power or cooling power).
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| 2. |
- Acciai, Matteo, 1992, et al.
(author)
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Influence of channel mixing in fermionic Hong-Ou-Mandel experiments
- 2022
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 105:12
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Journal article (peer-reviewed)abstract
- We consider an electronic Hong-Ou-Mandel interferometer in the integer quantum Hall regime, where the colliding electronic states are generated by applying voltage pulses (creating for instance levitons) to ohmic contacts. The aim of this work is to investigate possible mechanisms leading to a reduced visibility of the Pauli dip, i.e., the noise suppression expected for synchronized sources. It is known that electron-electron interactions cannot account for this effect and always lead to a full suppression of the Hong-Ou-Mandel noise. Focusing on the case of filling factor ?=2, we show instead that a reduced visibility of the Pauli dip can result from mixing of the copropagating edge channels, arising from tunneling events between them.
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| 3. |
- Acciai, Matteo, 1992, et al.
(author)
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Phase-coherent heat circulators with normal or superconducting contacts
- 2021
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 103:8
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Journal article (peer-reviewed)abstract
- We investigate heat circulators where a phase coherent region is contacted by three leads that are either normal- or superconducting. A magnetic field, and potentially the superconducting phases, allow to control the preferential direction of the heat flow between the three-different temperature-biased contacts. The main goal of this study is to analyze the requirements for heat circulation in nonideal devices, in particular focusing on sample-to-sample variations. Quite generally, we find that the circulation performance of the devices is good as long as only a few transport channels are involved. We compare the performance of circulators with normal conducting contacts to those with superconducting contacts and find that the circulation coefficients are essentially unchanged.
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| 4. |
- Dashti, Nastaran, 1988, et al.
(author)
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Readout of Quantum Screening Effects Using a Time-Dependent Probe
- 2021
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In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 127:24
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Journal article (peer-reviewed)abstract
- In voltage- and temperature-biased coherent conductors quantum screening effects occur if the conductor's transmission is energy dependent. Here, we show that an additional ac-driven terminal can act as a probe for a direct readout of such effects, hitherto unexplored. We find that screening of charges induced by the static biases impacts already their standard linear thermoelectric response coefficients due to nonlinear effects when accounting for the frequency of the time-dependent driving. Those effects should be observable under realistic experimental conditions and can literally be switched on and off with the ac driving.
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| 5. |
- Edlbauer, Hermann, et al.
(author)
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Semiconductor-based electron flying qubits: review on recent progress accelerated by numerical modelling
- 2022
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In: EPJ Quantum Technology. - : Springer Science and Business Media LLC. - 2196-0763 .- 2662-4400. ; 9:1
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Research review (peer-reviewed)abstract
- 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.
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| 6. |
- Eriksson, Jakob, 1996, et al.
(author)
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General Bounds on Electronic Shot Noise in the Absence of Currents
- 2021
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 127:13
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Journal article (peer-reviewed)abstract
- We investigate the charge and heat electronic noise in a generic two-terminal mesoscopic conductor in the absence of the corresponding charge and heat currents. Despite these currents being zero, shot noise is generated in the system. We show that, irrespective of the conductor's details and the specific nonequilibrium conditions, the charge shot noise never exceeds its thermal counterpart, thus establishing a general bound. Such a bound does not exist in the case of heat noise, which reveals a fundamental difference between charge and heat transport under zero-current conditions.
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| 7. |
- Rebora, Giacomo, et al.
(author)
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Collisional interferometry of levitons in quantum Hall edge channels at ν=2
- 2020
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 101:24
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Journal article (peer-reviewed)abstract
- We consider a Hong-Ou-Mandel interferometer for Lorentzian voltage pulses applied to quantum Hall edge channels at filling factor ν=2. Due to interedge interactions, the injected electronic wave packets fractionalize before partitioning at a quantum point contact. Remarkably enough, differently from what was theoretically predicted and experimentally observed by using other injection techniques, we demonstrate that when the injection occurs through time-dependent voltage pulses (arbitrarily shaped), the Hong-Ou-Mandel noise signal always vanishes for a symmetric device and that a mismatch in the distances between the injectors and the point of collision is needed to reduce the visibility of the dip. We also show that by properly tuning these distances or by applying different voltages on the two edge channels in each arm of the interferometer, it is possible to estimate the intensity of the interedge interaction. Lorentzian-type voltage pulses are chosen because of their experimental relevance.
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| 8. |
- Taktak, Imen, et al.
(author)
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Two-particle time-domain interferometry in the fractional quantum Hall effect regime
- 2022
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723 .- 2041-1723. ; 13:1, s. 5863-
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Journal article (peer-reviewed)abstract
- Quasi-particles are elementary excitations of condensed matter quantum phases. Demonstrating that they keep quantum coherence while propagating is a fundamental issue for their manipulation for quantum information tasks. Here, we consider anyons, the fractionally charged quasi-particles of the Fractional Quantum Hall Effect occurring in two-dimensional electronic conductors in high magnetic fields. They obey anyonic statistics, intermediate between fermionic and bosonic. Surprisingly, anyons show large quantum coherence when transmitted through the localized states of electronic Fabry-Pérot interferometers, but almost no quantum interference when transmitted via the propagating states of Mach-Zehnder interferometers. Here, using a novel interferometric approach, we demonstrate that anyons do keep quantum coherence while propagating. Performing two-particle time-domain interference measurements sensitive to the two-particle Hanbury Brown Twiss phase, we find 53 and 60% visibilities for anyons with charges e/5 and e/3. Our results give a positive message for the challenge of performing controlled quantum coherent braiding of anyons.
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| 9. |
- Tesser, Ludovico, 1996, et al.
(author)
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Charge, spin, and heat shot noises in the absence of average currents: Conditions on bounds at zero and finite frequencies
- 2023
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In: Physical Review B. - 2469-9969 .- 2469-9950. ; 107:7
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Journal article (peer-reviewed)abstract
- Nonequilibrium situations where selected currents are suppressed are of interest in fields like thermoelectrics and spintronics, raising the question of how the related noises behave. We study such zero-current charge, spin, and heat noises in a two-terminal mesoscopic conductor. In the presence of voltage, spin, and temperature biases, the nonequilibrium (shot) noises of charge, spin, and heat can be arbitrarily large, even if their average currents vanish. However, as soon as a temperature bias is present, additional equilibrium (thermal-like) noise necessarily occurs. We show that this equilibrium noise sets an upper bound on the zero-current charge and spin shot noises, even if additional voltage or spin biases are present. We demonstrate that these bounds can be overcome for heat transport by breaking the spin and electron-hole symmetries, respectively. By contrast, we show that the bound on the charge noise for strictly two-terminal conductors even extends into the finite-frequency regime.
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