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  1. Article ; Online: Josephson Junction π-0 Transition Induced by Orbital Hybridization in a Double Quantum Dot.

    Debbarma, Rousan / Tsintzis, Athanasios / Aspegren, Markus / Souto, Rubén Seoane / Lehmann, Sebastian / Dick, Kimberly / Leijnse, Martin / Thelander, Claes

    Physical review letters

    2024  Volume 131, Issue 25, Page(s) 256001

    Abstract: In this Letter, we manipulate the phase shift of a Josephson junction using a parallel double quantum dot (QD). By employing a superconducting quantum interference device, we determine how orbital hybridization and detuning affect the current-phase ... ...

    Abstract In this Letter, we manipulate the phase shift of a Josephson junction using a parallel double quantum dot (QD). By employing a superconducting quantum interference device, we determine how orbital hybridization and detuning affect the current-phase relation in the Coulomb blockade regime. For weak hybridization between the QDs, we find π junction characteristics if at least one QD has an unpaired electron. Notably the critical current is higher when both QDs have an odd electron occupation. By increasing the inter-QD hybridization the critical current is reduced, until eventually a π-0 transition occurs. A similar transition appears when detuning the QD levels at finite hybridization. Based on a zero-bandwidth model, we argue that both cases of phase-shift transitions can be understood considering an increased weight of states with a double occupancy in the ground state and with the Cooper pair transport dominated by local Andreev reflection.
    Language English
    Publishing date 2024-01-05
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.131.256001
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Quantum Confinement Suppressing Electronic Heat Flow below the Wiedemann-Franz Law.

    Majidi, Danial / Josefsson, Martin / Kumar, Mukesh / Leijnse, Martin / Samuelson, Lars / Courtois, Hervé / Winkelmann, Clemens B / Maisi, Ville F

    Nano letters

    2022  Volume 22, Issue 2, Page(s) 630–635

    Abstract: The Wiedemann-Franz law states that the charge conductance and the electronic contribution to the heat conductance are proportional. This sets stringent constraints on efficiency bounds for thermoelectric applications, which seek a large charge ... ...

    Abstract The Wiedemann-Franz law states that the charge conductance and the electronic contribution to the heat conductance are proportional. This sets stringent constraints on efficiency bounds for thermoelectric applications, which seek a large charge conduction in response to a small heat flow. We present experiments based on a quantum dot formed inside a semiconducting InAs nanowire transistor, in which the heat conduction can be tuned significantly below the Wiedemann-Franz prediction. Comparison with scattering theory shows that this is caused by quantum confinement and the resulting energy-selective transport properties of the quantum dot. Our results open up perspectives for tailoring independently the heat and electrical conduction properties in semiconductor nanostructures.
    Language English
    Publishing date 2022-01-14
    Publishing country United States
    Document type Journal Article
    ISSN 1530-6992
    ISSN (online) 1530-6992
    DOI 10.1021/acs.nanolett.1c03437
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Parity-conserving Cooper-pair transport and ideal superconducting diode in planar germanium.

    Valentini, Marco / Sagi, Oliver / Baghumyan, Levon / de Gijsel, Thijs / Jung, Jason / Calcaterra, Stefano / Ballabio, Andrea / Aguilera Servin, Juan / Aggarwal, Kushagra / Janik, Marian / Adletzberger, Thomas / Seoane Souto, Rubén / Leijnse, Martin / Danon, Jeroen / Schrade, Constantin / Bakkers, Erik / Chrastina, Daniel / Isella, Giovanni / Katsaros, Georgios

    Nature communications

    2024  Volume 15, Issue 1, Page(s) 169

    Abstract: Superconductor/semiconductor hybrid devices have attracted increasing interest in the past years. Superconducting electronics aims to complement semiconductor technology, while hybrid architectures are at the forefront of new ideas such as topological ... ...

    Abstract Superconductor/semiconductor hybrid devices have attracted increasing interest in the past years. Superconducting electronics aims to complement semiconductor technology, while hybrid architectures are at the forefront of new ideas such as topological superconductivity and protected qubits. In this work, we engineer the induced superconductivity in two-dimensional germanium hole gas by varying the distance between the quantum well and the aluminum. We demonstrate a hard superconducting gap and realize an electrically and flux tunable superconducting diode using a superconducting quantum interference device (SQUID). This allows to tune the current phase relation (CPR), to a regime where single Cooper pair tunneling is suppressed, creating a [Formula: see text] CPR. Shapiro experiments complement this interpretation and the microwave drive allows to create a diode with ≈ 100% efficiency. The reported results open up the path towards integration of spin qubit devices, microwave resonators and (protected) superconducting qubits on  the same silicon technology compatible platform.
    Language English
    Publishing date 2024-01-02
    Publishing country England
    Document type Journal Article
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-023-44114-0
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Book ; Online ; Thesis: Transport spectroscopy and control of molecular quantum dots

    Leijnse, Martin

    2010  

    Abstract: Zusammenfassung in dt. und engl. ... ...

    Author's details vorgelegt von Martin Leijnse
    Abstract Zusammenfassung in dt. und engl. Sprache
    Language English
    Size Online-Ressource
    Document type Book ; Online ; Thesis
    Thesis / German Habilitation thesis Techn. Hochsch., Diss.--Aachen, 2009
    Database Library catalogue of the German National Library of Science and Technology (TIB), Hannover

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  5. Book ; Online ; Thesis: Transport spectroscopy and control of molecular quantum dots

    Leijnse, Martin

    2010  

    Abstract: Zusammenfassung in dt. und engl. ... ...

    Author's details vorgelegt von Martin Leijnse
    Abstract Zusammenfassung in dt. und engl. Sprache
    Language English
    Size Online-Ressource
    Document type Book ; Online ; Thesis
    Thesis / German Habilitation thesis Techn. Hochsch., Diss.--Aachen, 2009
    Database Former special subject collection: coastal and deep sea fishing

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  6. Article ; Online: Two-Dimensional Platform for Networks of Majorana Bound States.

    Hell, Michael / Leijnse, Martin / Flensberg, Karsten

    Physical review letters

    2017  Volume 118, Issue 10, Page(s) 107701

    Abstract: We model theoretically a two-dimensional electron gas (2DEG) covered by a superconductor and demonstrate that topological superconducting channels are formed when stripes of the superconducting layer are removed. As a consequence, Majorana bound states ( ... ...

    Abstract We model theoretically a two-dimensional electron gas (2DEG) covered by a superconductor and demonstrate that topological superconducting channels are formed when stripes of the superconducting layer are removed. As a consequence, Majorana bound states (MBSs) are created at the ends of the stripes. We calculate the topological invariant and energy gap of a single stripe, using realistic values for an InAs 2DEG proximitized by an epitaxial Al layer. We show that the topological gap is enhanced when the structure is made asymmetric. This can be achieved either by imposing a phase difference (by driving a supercurrent or using a magnetic-flux loop) over the strip or by replacing one superconductor by a metallic gate. Both strategies also enable control over the MBS splitting, thereby facilitating braiding and readout schemes based on controlled fusion of MBSs. Finally, we outline how a network of Majorana stripes can be designed.
    Language English
    Publishing date 2017-03-10
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.118.107701
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Book ; Online: Optimal power and efficiency of single quantum dot heat engines

    Josefsson, Martin / Svilans, Artis / Linke, Heiner / Leijnse, Martin

    theory and experiment

    2019  

    Abstract: Quantum dots (QDs) can serve as near perfect energy filters and are therefore of significant interest for the study of thermoelectric energy conversion close to thermodynamic efficiency limits. Indeed, recent experiments in [Nat. Nano. 13, 920 (2018)] ... ...

    Abstract Quantum dots (QDs) can serve as near perfect energy filters and are therefore of significant interest for the study of thermoelectric energy conversion close to thermodynamic efficiency limits. Indeed, recent experiments in [Nat. Nano. 13, 920 (2018)] realized a QD heat engine with performance near these limits and in excellent agreement with theoretical predictions. However, these experiments also highlighted a need for more theory to help guide and understand the practical optimization of QD heat engines, in particular regarding the role of tunnel couplings on the performance at maximum power and efficiency for QDs that couple seemingly weakly to electronic reservoirs. Furthermore, these experiments also highlighted the critical role of the external load when optimizing the performance of a QD heat engine in practice. To provide further insight into the operation of these engines we use the Anderson impurity model together with a Master equation approach to perform power and efficiency calculations up to co-tunneling order. This is combined with additional thermoelectric experiments on a QD embedded in a nanowire where the power is measured using two methods. We use the measurements to present an experimental procedure for efficiently finding the external load $R_P$ which should be connected to the engine to optimize power output. Our theoretical estimates of $R_P$ show a good agreement with the experimental results, and we show that second order tunneling processes and non-linear effects have little impact close to maximum power, allowing us to derive a simple analytic expression for $R_P$. In contrast, we find that the electron contribution to the thermoelectric efficiency is significantly reduced by second order tunneling processes, even for rather weak tunnel couplings.
    Keywords Condensed Matter - Mesoscale and Nanoscale Physics
    Subject code 621 ; 612
    Publishing date 2019-03-29
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  8. Article ; Online: Effects of Parity and Symmetry on the Aharonov-Bohm Phase of a Quantum Ring.

    Debbarma, Rousan / Potts, Heidi / Stenberg, Calle Janlén / Tsintzis, Athanasios / Lehmann, Sebastian / Dick, Kimberly / Leijnse, Martin / Thelander, Claes

    Nano letters

    2021  Volume 22, Issue 1, Page(s) 334–339

    Abstract: We experimentally investigate the properties of one-dimensional quantum rings that form near the surface of nanowire quantum dots. In agreement with theoretical predictions, we observe the appearance of forbidden gaps in the evolution of states in a ... ...

    Abstract We experimentally investigate the properties of one-dimensional quantum rings that form near the surface of nanowire quantum dots. In agreement with theoretical predictions, we observe the appearance of forbidden gaps in the evolution of states in a magnetic field as the symmetry of a quantum ring is reduced. For a twofold symmetry, our experiments confirm that orbital states are grouped pairwise. Here, a π-phase shift can be introduced in the Aharonov-Bohm relation by controlling the relative orbital parity using an electric field. Studying rings with higher symmetry, we note exceptionally large orbital contributions to the effective g-factor (up to 300), which are many times higher than those previously reported. These findings show that the properties of a phase-coherent system can be significantly altered by the nanostructure symmetry and its interplay with wave function parity.
    Language English
    Publishing date 2021-12-15
    Publishing country United States
    Document type Journal Article
    ISSN 1530-6992
    ISSN (online) 1530-6992
    DOI 10.1021/acs.nanolett.1c03882
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  9. Article ; Online: Coupling spin qubits via superconductors.

    Leijnse, Martin / Flensberg, Karsten

    Physical review letters

    2013  Volume 111, Issue 6, Page(s) 60501

    Abstract: We show how superconductors can be used to couple, initialize, and read out spatially separated spin qubits. When two single-electron quantum dots are tunnel coupled to the same superconductor, the singlet component of the two-electron state partially ... ...

    Abstract We show how superconductors can be used to couple, initialize, and read out spatially separated spin qubits. When two single-electron quantum dots are tunnel coupled to the same superconductor, the singlet component of the two-electron state partially leaks into the superconductor via crossed Andreev reflection. This induces a gate-controlled singlet-triplet splitting which, with an appropriate superconductor geometry, remains large for dot separations within the superconducting coherence length. Furthermore, we show that when two double-dot singlet-triplet qubits are tunnel coupled to a superconductor with finite charging energy, crossed Andreev reflection enables a strong two-qubit coupling over distances much larger than the coherence length.
    Language English
    Publishing date 2013-08-09
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.111.060501
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  10. Article ; Online: Quantum information transfer between topological and spin qubit systems.

    Leijnse, Martin / Flensberg, Karsten

    Physical review letters

    2011  Volume 107, Issue 21, Page(s) 210502

    Abstract: We propose a method to coherently transfer quantum information, and to create entanglement, between topological qubits and conventional spin qubits. Our suggestion uses gated control to transfer an electron (spin qubit) between a quantum dot and edge ... ...

    Abstract We propose a method to coherently transfer quantum information, and to create entanglement, between topological qubits and conventional spin qubits. Our suggestion uses gated control to transfer an electron (spin qubit) between a quantum dot and edge Majorana modes in adjacent topological superconductors. Because of the spin polarization of the Majorana modes, the electron transfer translates spin superposition states into superposition states of the Majorana system, and vice versa. Furthermore, we show how a topological superconductor can be used to facilitate long-distance quantum information transfer and entanglement between spatially separated spin qubits.
    Language English
    Publishing date 2011-11-18
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.107.210502
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