| 1. |
- Battista, Francesca, et al.
(författare)
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Proposal for nonlocal electron-hole turnstile in the quantum Hall regime
- 2011
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 83:12
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Tidskriftsartikel (refereegranskat)abstract
- We present a theory for a mesoscopic turnstile that produces spatially separated streams of electrons and holes along edge states in the quantum Hall regime. For a broad range of frequencies in the nonadiabatic regime the turnstile operation is found to be ideal, producing one electron and one hole per cycle. The accuracy of the turnstile operation is characterized by the fluctuations of the transferred charge per cycle. The fluctuations are found to be negligibly small in the ideal regime.
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| 2. |
- Battista, Francesca, et al.
(författare)
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Spectral distribution and wave function of electrons emitted from a single-particle source in the quantum Hall regime
- 2012
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 85:7
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Tidskriftsartikel (refereegranskat)abstract
- We investigate theoretically a scheme for spectroscopy of electrons emitted by an on-demand single-particle source. The total system, with an electron turnstile source and a single-level quantum dot spectrometer, is implemented with edge states in a conductor in the quantum Hall regime. Employing a Floquet scattering approach, the source and the spectrometer are analyzed within a single theoretical framework. The nonequilibrium distribution of the emitted electrons is analyzed via the direct current at the dot spectrometer. In the adiabatic and intermediate source frequency regimes, the distribution is found to be strongly peaked around the active resonant level of the turnstile. At high frequencies the distribution is split up into a set of fringes, resulting from the interplay of resonant transport through the turnstile and absorption or emission of individual Floquet quanta. For ideal source operation, with exactly one electron emitted per cycle, an expression for the single-electron wave function is derived.
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| 3. |
- Bergenfeldt, Christian, et al.
(författare)
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Microwave quantum optics and electron transport through a metallic dot strongly coupled to a transmission line cavity
- 2012
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 85:4
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Tidskriftsartikel (refereegranskat)abstract
- We investigate theoretically the properties of the photon state and the electronic transport in a system consisting of a metallic quantum dot strongly coupled to a superconducting microwave transmission line cavity. Within the framework of circuit quantum electrodynamics, we derive a Hamiltonian for arbitrary strong capacitive coupling between the dot and the cavity. The dynamics of the system is described by a quantum master equation, accounting for the electronic transport as well as the coherent, nonequilibrium properties of the photon state. The photon state is investigated, focusing on, for a single active mode, signatures of microwave polaron formation and the effects of a nonequilibrium photon distribution. For two active photon modes, the intermode conversion and polaron coherences are investigated. For the electronic transport, electrical current and noise through the dot and the influence of the photon state on the transport properties are at the focus. We identify clear transport signatures due to the nonequilibrium photon population, in particular the emergence of superpoissonian shot noise at ultrastrong dot-cavity couplings.
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| 4. |
- Bergenfeldt, Christian, et al.
(författare)
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Nonlocal transport properties of nanoscale conductor-microwave cavity systems
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:19
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Tidskriftsartikel (refereegranskat)abstract
- Recent experimental progress in coupling nanoscale conductors to superconducting microwave cavities has opened up for transport investigations of the deep quantum limit of light-matter interactions, with tunneling electrons strongly coupled to individual cavity photons. We have investigated theoretically the most basic cavity-conductor system with strong, single photon induced nonlocal transport effects: two spatially separated double quantum dots (DQDs) resonantly coupled to the fundamental cavity mode. The system, described by a generalized Tavis-Cummings model, is investigated within a quantum master equation formalism, allowing us to account for both the electronic transport properties through the DQDs as well as the coherent, nonequilibrium cavity photon state. We find sizable nonlocally induced current and current cross-correlations mediated by individual photons. From a full statistical description of the electron transport we further reveal a dynamical channel blockade in one DQD lifted by photon emission due to tunneling through the other DQD. Moreover, large entanglement between the orbital states of electrons in the two DQDs is found for small DQD-lead temperatures.
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| 5. |
- Chung, S. -W. V., et al.
(författare)
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Quantum pump driven fermionic Mach-Zehnder interferometer
- 2007
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 75:11
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the characteristics of the currents in a pump driven fermionic Mach-Zehnder interferometer. The system is implemented in a conductor in the quantum Hall regime, with the two interferometer arms enclosing an Aharonov-Bohm flux Phi. Two quantum point contacts with transparency modulated periodically in time drive the current and act as beam splitters. The current has a flux-dependent part I-(Phi) as well as a flux-independent part I-(0). Both current parts show oscillations as a function of frequency on the two scales determined by the lengths of the interferometer arms. In the nonadiabatic, high-frequency regime I-(Phi) oscillates with a constant amplitude while the amplitude of the oscillations of I-(0) increases linearly with frequency. The flux-independent part I-(0) is insensitive to temperature while the flux-dependent part I-(Phi) is exponentially suppressed with increasing temperature. We also find that for low amplitude, adiabatic pumping rectification effects are absent for semitransparent beam splitters. Inelastic dephasing is introduced by coupling one of the interferometer arms to a voltage probe. For a long charge relaxation time of the voltage probe, giving a constant probe potential, I-(Phi) and the part of I-(0) flowing in the arm connected to the probe are suppressed with increased coupling to the probe. For a short relaxation time, with the potential of the probe adjusting instantaneously to give zero time-dependent current at the probe, only I-(Phi) is suppressed by the coupling to the probe.
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| 6. |
- Chung, VSW, et al.
(författare)
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Visibility of current and shot noise in electrical Mach-Zehnder and Hanbury Brown Twiss interferometers
- 2005
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:12
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the visibility of the current and shot-noise correlations of electrical analogs of the optical Mach-Zehnder interferometer and the Hanbury Brown Twiss interferometer. The electrical analogs are discussed in conductors subject to high magnetic fields where electron motion is along edge states. The transport quantities are modulated with the help of an Aharonov-Bohm flux. We discuss the conductance (current) visibility and shot noise visibility as a function of temperature and applied voltage. Dephasing is introduced with the help of fictitious voltage probes. Comparison of these two interferometers is of interest since the Mach-Zehnder interferometer is an amplitude (single-particle) interferometer, whereas the Hanbury Brown Twiss interferometer is an intensity (two-particle) interferometer. A direct comparison is only possible for the shot noise of the two interferometers. We find that the visibility of shot noise correlations of the Hanbury Brown Twiss interferometer as a function of temperature, voltage or dephasing, is qualitatively similar to the visibility of the first harmonic of the shot noise correlation of the Mach-Zehnder interferometer. In contrast, the second harmonic of the shot noise visibility of the Mach-Zehnder interferometer decreases much more rapidly with increasing temperature, voltage or dephasing rate.
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| 7. |
- Foerster, Heidi, et al.
(författare)
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Voltage and dephasing probes in mesoscopic conductors: A study of full-counting statistics
- 2007
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 75:3
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Tidskriftsartikel (refereegranskat)abstract
- Voltage and dephasing probes introduce incoherent inelastic and incoherent quasielastic scattering into a coherent mesoscopic conductor. We discuss in detail the concepts of voltage and dephasing probes and develop a full-counting statistics approach to investigate their effect on the transport statistics. The formalism is applied to several experimentally relevant examples. A comparison of different probe models and with procedures like phase averaging over an appropriate phase distribution shows that there is a perfect equivalence between the models for the case of one single-channel probe. Interestingly, the appropriate phase-distribution function is found to be uniform. A uniform distribution is provided by a chaotic cavity with a long dwell time. The dwell time of a chaotic cavity plays a role similar to the charge response time of a voltage or dephasing probe. For multichannel or multiple probes the transport statistics of voltage and dephasing probes differs and the equivalence with phase averaging is similarly lost.
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| 8. |
- Houzet, M., et al.
(författare)
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Multiple Andreev reflections in hybrid multiterminal junctions
- 2010
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 82:6
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Tidskriftsartikel (refereegranskat)abstract
- We investigate theoretically charge transport in hybrid multiterminal junctions with superconducting leads kept at different voltages. It is found that multiple Andreev reflections involving several superconducting leads give rise to rich subharmonic gap structures in the current-voltage characteristics. The structures are evidenced numerically in junctions in the incoherent regime.
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| 9. |
- Karlström, Olov, et al.
(författare)
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Canyon of current suppression in an interacting two-level quantum dot
- 2011
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 83:20
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the recent discovery of a canyon of conductance suppression in a two-level equal-spin quantum dot system [Phys. Rev. Lett. 104, 186804 (2010)], the transport through this system is studied in detail. At low bias and low temperature a strong current suppression is found around the electron-hole symmetry point independent of the couplings, in agreement with previous results. By means of a Schrieffer-Wolff transformation we are able to give an intuitive explanation to this suppression in the low-energy regime. In the general situation, numerical simulations are carried out using quantum rate equations. The simulations allow for the prediction of how the suppression is affected by the couplings, the charging energy, the position of the energy levels, the applied bias, and the temperature. We find that, away from electron-hole symmetry, the parity of the couplings is essential for the current suppression. It is also shown how broadening, interference, and a finite interaction energy cause a shift of the current minimum away from degeneracy. Finally we see how an increased population of the upper level leads to current peaks on each side of the suppression line. At sufficiently high bias we discover a coherence-induced population inversion.
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| 10. |
- Kiesslich, G, et al.
(författare)
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Counting statistics and decoherence in coupled quantum dots
- 2006
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 73:3, s. 1-033312
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically consider charge transport through two quantum dots coupled in series. The corresponding full counting statistics for noninteracting electrons is investigated in the limits of sequential and coherent tunneling by means of a master equation approach and a density matrix formalism, respectively. We clearly demonstrate the effect of quantum coherence on the zero-frequency cumulants of the transport process, focusing on noise and skewness. Moreover, we establish the continuous transition from the coherent to the incoherent tunneling limit in all cumulants of the transport process and compare this with decoherence described by a dephasing voltage probe model.
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