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arXiv:1209.0992 · Physical Review B

Spin-entangled two-particle dark state in quantum transport through coupled quantum dots

Christina Pöltl, Clive Emary, Tobias Brandes

Published Jan 14, 2013• 19 citations
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Abstract

We present a transport setup of coupled quantum dots that enables the creation of spatially separated spin-entangled two-electron dark states. We prove the existence of an entangled transport dark state by investigating the system Hamiltonian without coupling to the electronic reservoirs. In the transport regime, the entangled dark state, which corresponds to a singlet, has a strongly enhanced Fano factor compared to the dark state, which corresponds to a mixture of the triplet states. Furthermore, we calculate the concurrence of the occupying electrons to show the degree of entanglement in the transport regime.

DOI
10.1103/physrevb.87.045416

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We present a transport setup of coupled quantum dots that enables the creation of spatially separated spin-entangled two-electron dark states. We prove the existence of an entangled transport dark state by investigating the system Hamiltonian without coupling to the electronic reservoirs. In the transport regime, the entangled dark state, which corresponds to a singlet, has a strongly enhanced Fano factor compared to the dark state, which corresponds to a mixture of the triplet states. Furthermore, we calculate the concurrence of the occupying electrons to show the degree of entanglement in the transport regime.
We propose a simple setup of three coupled quantum dots in the Coulomb blockade regime as a source for spatially separated currents of spin-entangled electrons. The entanglement originates from the singlet ground state of a quantum dot with an even number of electrons. To preserve the entanglement of the electron pair during its extraction to the drain leads, the electrons are transported through secondary dots. This prevents one-electron transport by energy mismatch, while joint transport is resonantly enhanced by conservation of the total two-electron energy.
Spin entanglement between two spatially separated electrons can be generated in nonequilibrium interacting quantum dots, coherently coupled to a common lead. In this system entangled two-electron states develop which are Werner states with an imbalance between singlet and triplet probabilities. We propose a multi-terminal, multiply connected set-up for the generation and detection of this imbalance. In particular, we identify a regime in which the formation of spin entanglement leads to a cancellation of Aharonov–Bohm oscillations.
Spin entanglement between two spatially separated electrons can be generated in nonequilibrium interacting quantum dots, coherently coupled to a common lead. In this system entangled two-electron states develop which are Werner states with an imbalance between singlet and triplet probabilities. We propose a multi-terminal, multiply connected set-up for the generation and detection of this imbalance. In particular, we identify a regime in which the formation of spin entanglement leads to a cancellation of Aharonov–Bohm oscillations.
We propose schemes for generating spatially separated spin entanglement in systems of two quantum dots with onsite Coulomb repulsion weakly coupled to a joint electron reservoir. An enhanced probability for the formation of spin entanglement is found in nonequilibrium situations with one extra electron on each dot, either in the transient state after rapid changes of the gate voltage or in the steady state with applied bias voltage. In both cases, so-called Werner states with spin-singlet fidelity exceeding 1∕21∕21∕2 are generated, which indicates entanglement.
The adiabatic passage of two correlated electrons in three coupled quantum dots is shown to provide a robust and controlled way of distilling, transporting, and detecting spin entanglement, as well as measuring the rate of spin disentanglement. By employing tunable interdot coupling the scheme creates from an unentangled two-electron state, a superposition of spatially separated singlet and triplet states. A single measurement of a dot population (charge) collapses the wave function to either of these states, realizing the entanglement to the charge conversion. The scheme is robust, with the efficiency close to 100%, for a large range of realistic spectral parameters.