Nonlocal quantum state engineering with the Cooper pair splitter beyond the Coulomb blockade regime

We consider the sub-gap physics of a hybrid double-quantum dot Cooper-pair splitter with large single-level spacings, in the presence of tunnelling between the dots and finite Coulomb intra-and inter-dot Coulomb repulsion. In the limit of a large superconducting gap, we treat the coupling of the dots to the superconductor exactly. We employ a generalized master-equation method which easily yields currents, noise and cross-correlators. In particular, for finite inter-and intra-dot Coulomb interaction, we investigate how the transport properties are determined by the interplay between local and nonlocal tunneling processes between the superconductor and the dots. We examine the effect of inter-dot tunneling on the particle-hole symmetry of the currents with and without spinorbit interaction. We show that spin-orbit interaction in combination with finite Coulomb energy opens the possibility to control the nonlocal entanglement and its symmetry (singlet/triplet). We demonstrate that the generation of nonlocal entanglement can be achieved even without any direct nonlocal coupling to the superconducting lead.

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“…Lowest order corrections in 1/∆ can be also included in the system Hamiltonian according to Ref. 61.…”

Section: Model and Master-equationmentioning

confidence: 99%

Double quantum dot Cooper-pair splitter at finite couplings

et al. 2016

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“…For noninteracting (14) 205422-1 ©2020 American Physical Society systems, tight-binding models [25,26] or scattering theory [27] provide a convenient theoretical framework. Interactions can be included using Green function techniques [28][29][30][31][32], quantum master equations [5,[33][34][35][36][37][38], or the real-time diagrammatic approach to quantum transport [39][40][41][42][43]. In most cases, these methods enable numerical calculations of the average currents and the low-frequency noise in the output leads.…”

Section: Introductionmentioning

confidence: 99%

Noise and full counting statistics of a Cooper pair splitter

et al. 2020

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We investigate theoretically the noise and the full counting statistics of electrons that are emitted from a superconductor into two spatially separated quantum dots by the splitting of Cooper pairs and further on collected in two normal-state electrodes. With negatively biased drain electrodes and a large superconducting gap, the dynamics of the Cooper pair splitter can be described by a Markovian quantum master equation. Using techniques from full counting statistics, we evaluate the electrical currents, their noise power spectra, and the power-power correlations in the output leads. The current fluctuations can be attributed to the competition between Cooper pair splitting and elastic cotunneling between the quantum dots via the superconductor. In one regime, these processes can be clearly distinguished in the cross-correlation spectrum with peaks and dips appearing at characteristic frequencies associated with elastic cotunneling and Cooper pair splitting, respectively. We corroborate this interpretation by analyzing the charge transport fluctuations in the time domain, specifically by investigating the g (2) function of the output currents. Our work identifies several experimental signatures of the fundamental transport processes involved in Cooper pair splitting and provides specific means to quantify their relative strengths. As such, our results may help guide and interpret future experiments on current fluctuations in Cooper pair splitters.

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“…Several previous works on similar systems completely neglect the possibility of EC processes [7,52–54 71–72]. In other works EC coupling is taken into account [44,61,64–65 67–68 73], but in most of the cases it is defined as a constant coupling term that is equivalent to the IT coupling used here, therefore they can be incorporated to the same term. However, as we demonstrate below, in certain models the EC term is not constant, but it can depend on the on-site energies of the QDs.…”

Section: Introductionmentioning

confidence: 99%

Transport signatures of an Andreev molecule in a quantum dot–superconductor–quantum dot setup

Scherübl¹,

Pályi²,

Csonka³

2019

Beilstein J. Nanotechnol.

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Hybrid devices combining quantum dots with superconductors are important building blocks of conventional and topological quantum-information experiments. A requirement for the success of such experiments is to understand the various tunneling-induced non-local interaction mechanisms that are present in the devices, namely crossed Andreev reflection, elastic co-tunneling, and direct interdot tunneling. Here, we provide a theoretical study of a simple device that consists of two quantum dots and a superconductor tunnel-coupled to the dots, often called a Cooper-pair splitter. We study the three special cases where one of the three non-local mechanisms dominates, and calculate measurable ground-state properties, as well as the zero-bias and finite-bias differential conductance characterizing electron transport through this device. We describe how each non-local mechanism controls the measurable quantities, and thereby find experimental fingerprints that allow one to identify and quantify the dominant non-local mechanism using experimental data. Finally, we study the triplet blockade effect and the associated negative differential conductance in the Cooper-pair splitter, and show that they can arise regardless of the nature of the dominant non-local coupling mechanism. Our results should facilitate the characterization of hybrid devices, and their optimization for various quantum-information-related experiments and applications.

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Nonlocal quantum state engineering with the Cooper pair splitter beyond the Coulomb blockade regime

Cited by 11 publications

References 38 publications

Double quantum dot Cooper-pair splitter at finite couplings

Double quantum dot Cooper-pair splitter at finite couplings

Noise and full counting statistics of a Cooper pair splitter

Transport signatures of an Andreev molecule in a quantum dot–superconductor–quantum dot setup

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