Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Nature Communications

Cooper pair splitting in parallel quantum dot Josephson junctions

Russell Deacon, A. Oiwa, J. Sailer, S. Baba, Yasushi Kanai, Kenji Shibata, Kazuhiko Hirakawa, Seigo Tarucha

Published Jul 1, 2015• 82 citations
Publisher

Abstract

Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair.

DOI
10.1038/ncomms8446

Related papers

Dynamical current correlations in Cooper pair splitters based on proximized quantum dots

Grzegorz Michałek, Bogdan R. Bułka

Abstract Entanglement of electrons is studied by means of current–current correlations in two Cooper pair splitter devices: with one and two proximized quantum dots (1QD and 2QD), in presence of intra- and inter-dot Coulomb interactions, and weakly coupled with metallic electrodes. The 1QD system, where Cooper pairs can be transmitted to the same or split to different normal electrodes, is contrasted with the 2QD device, where double occupancy of a single quantum dot is forbidden and transport is only through an inter-dot singlet due to non-local crossed Andreev reflection processes deep in the superconducting energy gap. Separating the current correlation function into components for partial currents of electrons and holes through various Andreev bound states, one can see bunching and antibunching of split particles: inter-level components between electron and hole currents flowing to different electrodes are positive, while intra-level electron–electron or hole–hole components are negative, respectively. Spectral decomposition of the frequency-dependent current cross-correlation is performed to get better insight into mechanisms of entanglement and dynamics of split Cooper pairs, and to extract various charge fluctuation processes with different relaxation times, related to electron and hole currents flowing through the Andreev bound states. Only low frequency polarization fluctuations are seen in the current cross-correlations, while various negative and positive high frequency (charge fluctuations) components compensate each other in the symmetric system.

New Journal of Physics•Dec 12, 2020•4 citations

Cooper pair splitter realized in a two-quantum-dot Y-junction

L. Hofstetter, S. Csonka, Jesper Nygård +1 more

Electron entanglement: splitting pairs One of the most counterintuitive aspects of quantum mechanics is non-locality, manifesting as spatially separated objects influencing each other in a direct way. Experimental verifications of such concepts have been conducted successfully using entangled pairs of photons to test so-called Bell inequalities, but similar demonstrations using electrons have remained elusive owing to the inherent difficulty of creating and splitting pairs of entangled electrons. Lukas Hofstetter and colleagues now demonstrate that this is possible in a Y-shaped electron entangler consisting of a superconductor at its stem, coupled via tunnelling barriers to two separate quantum dots along the fork-like branches of the device. The entangled pairs of electrons are naturally formed in the superconductor, which in its ground state consists of Cooper pairs of electrons, and split by Coulomb interactions and careful tuning of the energy levels of the quantum dots. The study paves the way for the study of electronic entanglement and experimental tests of Bell inequalities in the solid state.

•Jan 1, 2009•0 citations

Finite-Bias Cooper Pair Splitting

L. Hofstetter, Szabolcs Csonka, Andreas Baumgartner +4 more

In a device with a superconductor coupled to two parallel quantum dots (QDs) the electrical tunability of the QD levels can be used to exploit nonclassical current correlations due to the splitting of Cooper pairs. We experimentally investigate the effect of a finite potential difference across one quantum dot on the conductance through the other completely grounded QD in a Cooper pair splitter fabricated on an InAs nanowire. We demonstrate that the nonlocal electrical transport through the device can be tuned by electrical means and that the energy dependence of the effective density of states in the QDs is relevant for the rates of Cooper pair splitting (CPS) and elastic cotunneling. Such experimental tools are necessary to understand and develop CPS-based sources of entangled electrons in solid-state devices.

arXiv:1105.2583•Physical Review Letters•Sep 19, 2011•166 citations

Interference and Switching of Josephson Current Carried by Nonlocal Spin-Entangled Electrons in a SQUID-Like System with Quantum Dots

Zhi Wang, Xiao Hu

The Josephson current of spin-entangled electrons through the two branches of a SQUID-like structure with two quantum dots exhibits a magnetic-flux response different from the conventional Josephson current. Because of their interference, the period of maximum Josephson current changes from h/2e to h/e, which can be used for detecting the Cooper-pair splitting efficiency. The nonlocal spin entanglement provides a quantum mechanical functionale for switching on and off this novel Josephson current, and explicitly a switch is formulated by including a pilot junction. It is shown that the device can be used to measure the magnitude of split-tunneling Josephson current.

arXiv:1009.6028•Physical Review Letters•Jan 19, 2011•16 citations

Entangling electrons by splitting Cooper pairs: Two-particle conductance resonance and time coincidence measurements

Anindya Das, Yuval Ronen, Moty Heiblum +3 more

Entanglement, being at the heart of the Einstein-Podolsky-Rosen (EPR) paradox, is a necessary ingredient in processing quantum information. Cooper pairs in superconductors - being composites of two fully entangled electrons - can be split adiabatically, thus forming entangled electrons. We fabricated such electron splitter by contacting an aluminum superconductor strip at the center of a suspended InAs nanowire; terminated at both ends with two normal metallic drains. Intercepting each half of the nanowire by gate - induced Coulomb blockaded quantum dot strongly impeded the flow of Cooper pairs due to large charging energy, while still permitting passage of single electrons. Here, we provide conclusive evidence of extremely high efficiency Cooper pairs splitting via observing positive average (conductance) and time (shot noise) correlations of the split electrons in the two opposite drains of the nanowire. Moreover, The actual charge of the injected quasiparticles was verified by shot noise measurements.

arXiv:1205.2455•May 11, 2012•5 citations

Near-Unity Cooper Pair Splitting Efficiency

Jens Schindele, Andreas Baumgartner, Christian Schönenberger

The two electrons of a Cooper pair in a conventional superconductor form a spin singlet and therefore a maximally entangled state. Recently, it was demonstrated that the two particles can be extracted from the superconductor into two spatially separated contacts via two quantum dots in a process called Cooper pair splitting (CPS). Competing transport processes, however, limit the efficiency of this process. Here we demonstrate efficiencies up to 90%, significantly larger than required to demonstrate interaction-dominated CPS, and on the right order to test Bell's inequality with electrons. We compare the CPS currents through both quantum dots, for which large apparent discrepancies are possible. The latter we explain intuitively and in a semiclassical master equation model. Large efficiencies are required to detect electron entanglement and for prospective electronics-based quantum information technologies.

arXiv:1204.5777•Physical Review Letters•Oct 9, 2012•193 citations
Devices to generate on-demand non-local spin entangled electron pairs have potential application as solid-state analogues of the entangled photon sources used in quantum optics. Recently, Andreev entanglers that use two quantum dots as filters to adiabatically split and separate the quasi-particles of Cooper pairs have shown efficient splitting through measurements of the transport charge but the spin entanglement has not been directly confirmed. Here we report measurements on parallel quantum dot Josephson junction devices allowing a Josephson current to flow due to the adiabatic splitting and recombination of the Cooper pair between the dots. The evidence for this non-local transport is confirmed through study of the non-dissipative supercurrent while tuning independently the dots with local electrical gates. As the Josephson current arises only from processes that maintain the coherence, we can confirm that a current flows from the spatially separated entangled pair.
Abstract Entanglement of electrons is studied by means of current–current correlations in two Cooper pair splitter devices: with one and two proximized quantum dots (1QD and 2QD), in presence of intra- and inter-dot Coulomb interactions, and weakly coupled with metallic electrodes. The 1QD system, where Cooper pairs can be transmitted to the same or split to different normal electrodes, is contrasted with the 2QD device, where double occupancy of a single quantum dot is forbidden and transport is only through an inter-dot singlet due to non-local crossed Andreev reflection processes deep in the superconducting energy gap. Separating the current correlation function into components for partial currents of electrons and holes through various Andreev bound states, one can see bunching and antibunching of split particles: inter-level components between electron and hole currents flowing to different electrodes are positive, while intra-level electron–electron or hole–hole components are negative, respectively. Spectral decomposition of the frequency-dependent current cross-correlation is performed to get better insight into mechanisms of entanglement and dynamics of split Cooper pairs, and to extract various charge fluctuation processes with different relaxation times, related to electron and hole currents flowing through the Andreev bound states. Only low frequency polarization fluctuations are seen in the current cross-correlations, while various negative and positive high frequency (charge fluctuations) components compensate each other in the symmetric system.
Electron entanglement: splitting pairs One of the most counterintuitive aspects of quantum mechanics is non-locality, manifesting as spatially separated objects influencing each other in a direct way. Experimental verifications of such concepts have been conducted successfully using entangled pairs of photons to test so-called Bell inequalities, but similar demonstrations using electrons have remained elusive owing to the inherent difficulty of creating and splitting pairs of entangled electrons. Lukas Hofstetter and colleagues now demonstrate that this is possible in a Y-shaped electron entangler consisting of a superconductor at its stem, coupled via tunnelling barriers to two separate quantum dots along the fork-like branches of the device. The entangled pairs of electrons are naturally formed in the superconductor, which in its ground state consists of Cooper pairs of electrons, and split by Coulomb interactions and careful tuning of the energy levels of the quantum dots. The study paves the way for the study of electronic entanglement and experimental tests of Bell inequalities in the solid state.
In a device with a superconductor coupled to two parallel quantum dots (QDs) the electrical tunability of the QD levels can be used to exploit nonclassical current correlations due to the splitting of Cooper pairs. We experimentally investigate the effect of a finite potential difference across one quantum dot on the conductance through the other completely grounded QD in a Cooper pair splitter fabricated on an InAs nanowire. We demonstrate that the nonlocal electrical transport through the device can be tuned by electrical means and that the energy dependence of the effective density of states in the QDs is relevant for the rates of Cooper pair splitting (CPS) and elastic cotunneling. Such experimental tools are necessary to understand and develop CPS-based sources of entangled electrons in solid-state devices.
The Josephson current of spin-entangled electrons through the two branches of a SQUID-like structure with two quantum dots exhibits a magnetic-flux response different from the conventional Josephson current. Because of their interference, the period of maximum Josephson current changes from h/2e to h/e, which can be used for detecting the Cooper-pair splitting efficiency. The nonlocal spin entanglement provides a quantum mechanical functionale for switching on and off this novel Josephson current, and explicitly a switch is formulated by including a pilot junction. It is shown that the device can be used to measure the magnitude of split-tunneling Josephson current.
Entanglement, being at the heart of the Einstein-Podolsky-Rosen (EPR) paradox, is a necessary ingredient in processing quantum information. Cooper pairs in superconductors - being composites of two fully entangled electrons - can be split adiabatically, thus forming entangled electrons. We fabricated such electron splitter by contacting an aluminum superconductor strip at the center of a suspended InAs nanowire; terminated at both ends with two normal metallic drains. Intercepting each half of the nanowire by gate - induced Coulomb blockaded quantum dot strongly impeded the flow of Cooper pairs due to large charging energy, while still permitting passage of single electrons. Here, we provide conclusive evidence of extremely high efficiency Cooper pairs splitting via observing positive average (conductance) and time (shot noise) correlations of the split electrons in the two opposite drains of the nanowire. Moreover, The actual charge of the injected quasiparticles was verified by shot noise measurements.
The two electrons of a Cooper pair in a conventional superconductor form a spin singlet and therefore a maximally entangled state. Recently, it was demonstrated that the two particles can be extracted from the superconductor into two spatially separated contacts via two quantum dots in a process called Cooper pair splitting (CPS). Competing transport processes, however, limit the efficiency of this process. Here we demonstrate efficiencies up to 90%, significantly larger than required to demonstrate interaction-dominated CPS, and on the right order to test Bell's inequality with electrons. We compare the CPS currents through both quantum dots, for which large apparent discrepancies are possible. The latter we explain intuitively and in a semiclassical master equation model. Large efficiencies are required to detect electron entanglement and for prospective electronics-based quantum information technologies.