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Journal of Physics Condensed Matter

Generation of entangled photon pairs by semiconductor quantum dots in a structure of quantum cellular automata

Mang Feng, Jun‐Hong An, Wei-Min Zhang

Published Jul 17, 2007• 2 citations
Publisher

Abstract

We propose a unique scheme to generate entangled photon pairs by six semiconductor quantum dots in a structure of quantum cellular automata. By means of interdot electronic tunneling, single-electron spin manipulation, and auxiliary excitons, we can convert the entanglement from the charge degrees of freedom of the electrons to the spin degrees of freedom of the electrons, and then to the polarization of the photons. Our scheme presents a source of entangled photon pairs without using spin–spin coupling, which could work repeatedly, deterministically and efficiently. Both the experimental challenge and the feasibility with present technologies are discussed. In comparison with former relevant work, our proposal not only gives an alternative method to generate entangled photons, but is applicable to other quantum information processing tasks with free electrons.

DOI
10.1088/0953-8984/19/32/326215

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We propose a unique scheme to generate entangled photon pairs by six semiconductor quantum dots in a structure of quantum cellular automata. By means of interdot electronic tunneling, single-electron spin manipulation, and auxiliary excitons, we can convert the entanglement from the charge degrees of freedom of the electrons to the spin degrees of freedom of the electrons, and then to the polarization of the photons. Our scheme presents a source of entangled photon pairs without using spin–spin coupling, which could work repeatedly, deterministically and efficiently. Both the experimental challenge and the feasibility with present technologies are discussed. In comparison with former relevant work, our proposal not only gives an alternative method to generate entangled photons, but is applicable to other quantum information processing tasks with free electrons.
Taking the excess electron spin in a unit cell of semiconductor multiple quantum-dot structure as a qubit, we can implement scalable quantum computation without resorting to spin-spin interactions. The technique of single electron tunnelings and the structure of quantum-dot cellular automata (QCA) are used to create a charge entangled state of two electrons which is then converted into spin entanglement states by using single spin rotations. Deterministic two-qubit quantum gates can also be manipulated using only single spin rotations with help of QCA. A single-short read-out of spin states can be realized by coupling the unit cell to a quantum point contact.
We show that electron recombination using positively charged excitons in single quantum dots provides an efficient method to transfer entanglement from electron spins onto photon polarizations. We propose a scheme for the production of entangled four-photon states of GHZ type. From the GHZ state, two fully entangled photons can be obtained by a measurement of two photons in the linear polarization basis, even for quantum dots with observable fine structure splitting for neutral excitons and significant exciton spin decoherence. Because of the interplay of quantum mechanical selection rules and interference, maximally entangled electron pairs are converted into maximally entangled photon pairs with unity fidelity for a continuous set of observation directions. We describe the dynamics of the conversion process using a master-equation approach and show that the implementation of our scheme is feasible with current experimental techniques.
We propose a scheme to generate hyper-entangled photon pairs from single quantum dots (SQDs). Single photons emitted by SQD are manipulated to be entangled after post-selection. Crucially, exciton fine-structure splitting, which was previously deemed undesirable in similar schemes, is used here to produce photon pairs entangled in both frequency and polarization degrees of freedom. This hyper-entangled two-photon state is potentially more powerful than a normal entangled state for quantum state engineering and quantum information processing.
Using electron spin states in a unit cell of three semiconductor quantum dots as qubit states, a scalable quantum computation scheme is advocated without invoking qubit-qubit interactions. Single electron tunneling technology and coherent quantum-dot cellular automata architecture are used to generate an ancillary charge entangled state which is then converted into spin entangled state. Without using charge measurement and ancillary qubits, we demonstrate universal quantum computation based on free electron spin and coherent quantum-dot cellular automata.
Abstract Single-photon sources based on semiconductor quantum dots find several applications in quantum information processing due to their high single-photon indistinguishability, on-demand generation, and low multiphoton emission. In this context, the generation of entangled photons represents a challenging task with a possible solution relying on the interference in probabilistic gates of identical photons emitted at different pulses from the same source. In this work, we implement this approach via a simple and compact design that generates entangled photon pairs in the polarization degree of freedom. We operate the proposed platform with single photons produced through two different pumping schemes, the resonant excited one and the longitudinal-acoustic phonon-assisted configuration. We then characterize the produced entangled two-photon states by developing a complete model taking into account relevant experimental parameters, such as the second-order correlation function, Hong–Ou–Mandel visibility, multiphoton emission and pump laser filtering. Our source shows long-term stability and high quality of the generated entangled states, thus constituting a reliable building block for optical quantum technologies.
Without resorting to spin-spin coupling, we propose a scalable spin quantum computing scheme assisted with a semiconductor multiple-quantum-dot structure. The techniques of single electron transitions and the nanostructure of quantum-dot cellular automata (QCA) are used to generate charge entangled states of two electrons, which are then converted into spin entanglement states using single-spin rotations only. Deterministic two-qubit quantum gates are also manipulated using only single-spin rotations with the help of QCA. A single-shot readout of spin states can be carried out by coupling the multiple dot structure to a quantum point contact. As a result, deterministic spin-interaction-free quantum computing can be implemented in semiconductor nanostructure.