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Nature

Observation of entanglement between a single trapped atom and a single photon

B. B. Blinov, David L. Moehring, Luming Duan, Christopher R. Monroe

Published Mar 1, 2004• 673 citations
Publisher
DOI
10.1038/nature02377

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Email Share Share with Facebook Share on X Post on reddit Share with LinkedIn Add to Mendeley Add to BibSonomy Share with WeChat Get Citation Copy Citation Text D. L. Moehring, B. B. Blinov, M. J. Madsen, L. Duan, and C. Monroe, "Observation of entanglement between a single trapped atom and a single photon," in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, Technical Digest (CD) (Optica Publishing Group, 2004), paper IPDA5. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Conference on Lasers and Electro-Optics•Jan 1, 2004•29 citations

Interfacing single ions and single photons for quantum networks

Carsten Schuck

Experiments in quantum optics are motivated by fundamental questions about the quantum mechanical description of matter and light as well as by applications in quantum technologies such as quantum information processing. Exploiting the quantum character of both matter and light has turned out to be extremely rewarding for novel technological applications in the emerging fields of quantum communication and computation. Here we consider the implementation of quantum information technology with trapped ions and single photons, focusing on two key issues: the entanglement of distant atoms and the controlled interaction of a single photon with a single atom. This thesis describes the construction of a double ion trap apparatus including the necessary frequency-stabilized laser systems, and first experiments to investigate the generation of distant atomic entanglement, the implementation of a simple quantum network and controlled single-atom single-photon interaction. The experimental setup comprises two ion traps at a distance of one meter, which are independent but identical in construction. We introduce novel realizations of a photoionization method for calcium atoms, a laser frequency stabilization scheme and a radio frequency pulse sequencer. Linear Paul traps are used to load individual or strings of calcium ions. High-numerical aperture objectives mounted on sub-micrometer positioning systems allow us to address and manipulate a single ion with strongly focused light fields and collect the emitted fluorescence photons from a large solid angle. With these bidirectional single-atom single-photon interfaces the essential building blocks of a quantum network with atoms and photons are available. One of the main objectives we pursue with the double-trap apparatus is the generation of entanglement between ions in different traps, which is one of the key tasks in a quantum network. We compare single- and two-photon schemes for probabilistic entanglement creation and analyze how the performance of the schemes depends on photon detection efficiency. As a first step towards the experimental realization of such schemes we measure the second order correlation function of fluorescence photons emitted from two distant trapped ions. We observe high-contrast quantum (Hong-Ou-Mandel) interference, proving the indistinguishability of photons emitted from different ions, which is a prerequisite for the considered entanglement schemes. To investigate the interaction of single photons and a single atom in free space we combine the ion trap apparatus with a tunable, narrowband spontaneous parametric down-conversion source. The high-numerical aperture objectives allow us to efficiently couple bandwidth-tunable photons to a single trapped ion. Such atom-photon interaction at the single-particle level is the most fundamental process in quantum optics and lies literally at the focus of many experimental implementations of quantum information processing protocols and of studies of the (quantum) limits of matter -light interaction, which were so far restricted to weak coherent light fields. Here we observe individual atomic absorption events of one photon of an entangled pair by employing a quantum jump detection scheme. To characterize and control the interaction process we modify the spectral properties of the down conversion photons and perform single-photon spectroscopy of a single ion. To go beyond experiments with cohe rent fields we study temporal correlations between the absorption of photons from the spontaneous parametric down conversion source by a single ion and the detection of the corresponding partner photon. For the applied scheme we observe promising indications that the quantum correlations of photons produced in spontaneous parametric down conversion are preserved in the resonant interaction with a single atom. The implementation of more efficient atom-light coupling and entanglement transfer schemes with our apparatus is outlined.

•Jan 1, 2010•3 citations
We report the observation of entanglement between a single trapped atom and a single photon at a wavelength suitable for low-loss communication over large distances, thereby achieving a crucial step towards long range quantum networks. To verify the entanglement, we introduce a single atom state analysis. This technique is used for full state tomography of the atom-photon qubit pair. The detection efficiency and the entanglement fidelity are high enough to allow in a next step the generation of entangled atoms at large distances, ready for a final loophole-free Bell experiment.
Email Share Share with Facebook Share on X Post on reddit Share with LinkedIn Add to Mendeley Add to BibSonomy Share with WeChat Get Citation Copy Citation Text D. L. Moehring, B. B. Blinov, M. J. Madsen, L. Duan, and C. Monroe, "Observation of entanglement between a single trapped atom and a single photon," in Conference on Lasers and Electro-Optics/International Quantum Electronics Conference and Photonic Applications Systems Technologies, Technical Digest (CD) (Optica Publishing Group, 2004), paper IPDA5. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article
Experiments in quantum optics are motivated by fundamental questions about the quantum mechanical description of matter and light as well as by applications in quantum technologies such as quantum information processing. Exploiting the quantum character of both matter and light has turned out to be extremely rewarding for novel technological applications in the emerging fields of quantum communication and computation. Here we consider the implementation of quantum information technology with trapped ions and single photons, focusing on two key issues: the entanglement of distant atoms and the controlled interaction of a single photon with a single atom. This thesis describes the construction of a double ion trap apparatus including the necessary frequency-stabilized laser systems, and first experiments to investigate the generation of distant atomic entanglement, the implementation of a simple quantum network and controlled single-atom single-photon interaction. The experimental setup comprises two ion traps at a distance of one meter, which are independent but identical in construction. We introduce novel realizations of a photoionization method for calcium atoms, a laser frequency stabilization scheme and a radio frequency pulse sequencer. Linear Paul traps are used to load individual or strings of calcium ions. High-numerical aperture objectives mounted on sub-micrometer positioning systems allow us to address and manipulate a single ion with strongly focused light fields and collect the emitted fluorescence photons from a large solid angle. With these bidirectional single-atom single-photon interfaces the essential building blocks of a quantum network with atoms and photons are available. One of the main objectives we pursue with the double-trap apparatus is the generation of entanglement between ions in different traps, which is one of the key tasks in a quantum network. We compare single- and two-photon schemes for probabilistic entanglement creation and analyze how the performance of the schemes depends on photon detection efficiency. As a first step towards the experimental realization of such schemes we measure the second order correlation function of fluorescence photons emitted from two distant trapped ions. We observe high-contrast quantum (Hong-Ou-Mandel) interference, proving the indistinguishability of photons emitted from different ions, which is a prerequisite for the considered entanglement schemes. To investigate the interaction of single photons and a single atom in free space we combine the ion trap apparatus with a tunable, narrowband spontaneous parametric down-conversion source. The high-numerical aperture objectives allow us to efficiently couple bandwidth-tunable photons to a single trapped ion. Such atom-photon interaction at the single-particle level is the most fundamental process in quantum optics and lies literally at the focus of many experimental implementations of quantum information processing protocols and of studies of the (quantum) limits of matter -light interaction, which were so far restricted to weak coherent light fields. Here we observe individual atomic absorption events of one photon of an entangled pair by employing a quantum jump detection scheme. To characterize and control the interaction process we modify the spectral properties of the down conversion photons and perform single-photon spectroscopy of a single ion. To go beyond experiments with cohe rent fields we study temporal correlations between the absorption of photons from the spontaneous parametric down conversion source by a single ion and the detection of the corresponding partner photon. For the applied scheme we observe promising indications that the quantum correlations of photons produced in spontaneous parametric down conversion are preserved in the resonant interaction with a single atom. The implementation of more efficient atom-light coupling and entanglement transfer schemes with our apparatus is outlined.