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arXiv:1004.1414 · Physical Review Letters

CNOT and Bell-state analysis in the weak-coupling cavity QED regime

Cristian Bonato, Florian Haupt, Sumant S. R. Oemrawsingh, Jan Gudat, Dapeng Ding, Martin P. van Exter, Dirk Bouwmeester

Published Apr 23, 2010• 280 citations
arXivHTMLPDF

Abstract

We propose an interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a microcavity operating in the weak-coupling regime. This interface, based on spin selective photon reflection from the cavity, can be used to construct a CNOT gate, a multiphoton entangler and a photonic Bell-state analyzer. Finally, we analyze experimental feasibility, concluding that the schemes can be implemented with current technology.

DOI
10.1103/physrevlett.104.160503

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We propose an interface between the spin of a photon and the spin of an electron confined in a quantum dot embedded in a microcavity operating in the weak-coupling regime. This interface, based on spin selective photon reflection from the cavity, can be used to construct a CNOT gate, a multiphoton entangler and a photonic Bell-state analyzer. Finally, we analyze experimental feasibility, concluding that the schemes can be implemented with current technology.
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This thesis presents a viable route towards the implementation of quantum computing utilizing quantum dots embedded in optical microcavities. Following the introduction of the big picture and long-term visionary goal, general concepts fundamental to this field of research are described: quantum dots and microcavities, forming the physical system explored; and cavity quantum electrodynamics, the theoretical language used to describe their interaction.\n\nThe physical structure and the optical mode composition in oxide-apertured micropillar cavities is analyzed. Permanent tuning methods achieving polarization degenerate cavities resonant with a quantum dot transition are illustrated. Active positioning of single quantum dots is developed providing an accuracy suitable to measure the interaction between a quantum dot and a cavity in the strong coupling limit. The possibility to waveguide-couple photonic crystal cavities on the same sample is explored. A theoretical description of the quantum-dot confined electron dynamics is presented. \nPresented are ideas how a hybrid quantum system could serve for implementation of a controlled NOT gate, and therewith be the building block for a quantum computer, exploiting the weak coupling regime. A Bell-state analyzer is the second scheme that is discussed. \nResults from reflection spectroscopy measurements on single quantum dots in a micropillar cavity are presented.
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We propose a scheme for preparation of the N-dimension spin Greenberger–Horne–Zeilinger state by exploiting quantum dots (QDs) embedded in microcavities. Numerically analysed results show that with the spin-selective photon reflection from the cavity, we can complete the scheme assisted by one polarized photon with high fidelity and 100% successful probability in principle. Furthermore, the set-up is just composed of simple linear optical elements, delay lines and conventional photon detectors, which are feasible with existing experimental technology. Moreover, QDs have numerous admirable features in weak-coupling regime, which are practicable in realistic cavity quantum electrodynamics system shown by previous numerical simulations and experiments. Therefore, our scheme might be realized in near future.
We present a quantum key distribution scheme using a weak-coupling cavity QED regime based on quantum dense coding. Hybrid entanglement states of photons and electrons are used to distribute information. We just need to transmit photons without storing them in the scheme. The electron confined in a quantum dot, which is embedded in a microcavity, is held by one of the legitimate users throughout the whole communication process. Only the polarization of a single photon and spin of electron measurements are applied in this protocol, which are easier to perform than collective-Bell state measurements. Linear optical apparatus, such as a special polarizing beam splitter in a circular basis and single photon operations, make it more flexible to realize under current technology. Its efficiency will approach 100% in the ideal case. The security of the scheme is also discussed.