| 1. |
- Bergenfeldt, Christian, et al.
(författare)
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Hybrid Microwave-Cavity Heat Engine
- 2014
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Ingår i: Physical Review Letters. - 1079-7114. ; 112:7
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Tidskriftsartikel (refereegranskat)abstract
- We propose and analyze the use of hybrid microwave cavities as quantum heat engines. A possible realization consists of two macroscopically separated quantum-dot conductors coupled capacitively to the fundamental mode of a microwave cavity. We demonstrate that an electrical current can be induced in one conductor through cavity-mediated processes by heating up the other conductor. The heat engine can reach Carnot efficiency with optimal conversion of heat to work. When the system delivers the maximum power, the efficiency can be a large fraction of the Carnot efficiency. The heat engine functions even with moderate electronic relaxation and dephasing in the quantum dots. We provide detailed estimates for the electrical current and output power using realistic parameters.
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| 2. |
- Bergenfeldt, Christian, et al.
(författare)
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Cooling a micromechanical resonator to its ground state by measurement and feedback
- 2009
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 80:4
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Tidskriftsartikel (refereegranskat)abstract
- We present an analysis of the cooling of a micromechanical resonator by means of measurement and feedback. The measurements are performed via the coupling to a Cooper-pair box, and although the coupling does not lead to net cooling, the extraction of information and hence entropy from the system leads to a pure quantum state. Under suitable circumstances, the states become very close to coherent states, conditioned on the measurement record, and can hence be displaced to the oscillator ground state.
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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. |
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| 5. |
- 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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| 6. |
- Bergenfeldt, Christian
(författare)
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Transport effects in hybrid circuit QED structures
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation deals with the electron-photon interplay in hybrid circuit QED structures. The aim is to provide a framework in which this interplay can be understood and to predict experimentally measurable transport effects. In addition an application of this interplay is proposed. The thesis is based on four paper listed below: Article I comprises an investigation of the transport-induced photon state in a system with a metallic dot coupled to a transmission line cavity. Article II is an investigation of the non-local transport properties of a DQD-cavity system. Article III is a proposal for a DQD-cavity heat engine. Article IV is a proposal for a pump-probe scheme for investigating the electron-photon dynamics in a DQD-cavity system.
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| 7. |
- Blind, Per-Jonas, et al.
(författare)
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Fast-Track Program for Liver Resection - Factors Prolonging Length of Stay
- 2014
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Ingår i: Hepato-Gastroenterology. - 0172-6390. ; 61:136, s. 2340-2344
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Tidskriftsartikel (refereegranskat)abstract
- Background/Aims: Fast-track programs involving multi-modal measures to enhance recovery after surgery, reduce morbidity and decrease hospital length of stay (LOS) are used for different major surgical procedures. For liver resections, factors influencing LOS within a fast-track program have been studied only to a limited extent, which was the aim of the present study. Methodology: The present study comprises the first 64 patients included in a fast-track program for liver resections introduced in March 2012. Patient outcomes were compared to a historical cohort of patients (n=62) operated in 2009. Factors prolonging LOS was analyzed by uni- and multivariate analysis. Results: Median LOS was 6 days (range 3-42 days) within the fast-track program as compared with 8 days (range 5-47 days) in the historical cohort (P=0.004). On multivariate analysis, factors increasing LOS in the fast-track group were found to be the presence of complication (P=0.018), extent of resection (major as compared to minor) (P=0.001) and inability to drink > 1250 ml on the day after surgery (P=0.002). Conclusion: Patients who can only drink limited amounts of fluid the day after-liver resection represent a subset of patients that should be given special attention within a fast-track program.
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| 8. |
- Karlström, Olov, et al.
(författare)
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A diagrammatic description of the equations of motion, current and noise within the second-order von Neumann approach
- 2013
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Ingår i: Journal of Physics A: Mathematical and Theoretical. - : IOP Publishing. - 1751-8113 .- 1751-8121. ; 46:6
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the second-order von Neumann approach from a diagrammatic point of view and demonstrate its equivalence with the resonant tunneling approximation. The investigation of higher order diagrams shows that the method correctly reproduces the equation of motion for the single-particle reduced density matrix of an arbitrary non-interacting many-body system. This explains why the method reproduces the current exactly for such systems. We go on to show, however, that diagrams not included in the method are needed to calculate exactly higher cumulants of the charge transport. This thorough comparison sheds light on the validity of all these self-consistent second-order approaches. We analyze the discrepancy between the noise calculated by our method and the exact Levitov formula for a simple non-interacting quantum dot model. Furthermore, we study the noise of the canyon of current suppression in a two-level dot, a phenomenon that requires the inclusion of electron-electron interaction as well as higher order tunneling processes.
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| 9. |
- Malkoc, Ognjen, et al.
(författare)
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Full counting statistics of generic spin entangler with quantum dot-ferromagnet detectors
- 2014
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075. ; 105:4
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Tidskriftsartikel (refereegranskat)abstract
- Entanglement between spatially separated electrons in nanoscale transport is a fundamental property, yet to be demonstrated experimentally. Here we propose and analyse theoretically the transport statistics of a generic spin entangler coupled to a hybrid quantum dot-ferromagnet detector system. We show that the full distribution of charges arriving at the ferromagnetic terminals provides complete information on the spin state of the particles emitted by the entangler. This provides means for spin entanglement detection via electrical current correlations, with optimal measurement strategies depending on the a priori knowledge of ferromagnet polarization and spin-flip rates in the detector dots. The scheme is exemplified by applying it to Andreev and triple dot entanglers. Copyright (C) EPLA, 2014
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| 10. |
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