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Controlled insertion ofone andtwoatomsinto a high-finesse optical cavity

Wolfgang Alt, Tobias Kampschulte, Mkrtych Khudaverdyan, Sebastian Reick, Ariane Stiebeiner, Institutfur Physik, Johannes Gutenberg-Universitdt

Published Jan 1, 2006• 0 citations
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Abstract

Entangled quantum states haveapplications asamodelsystem forstrongly correlated manybodystates, asresource forquantum information processing andasatool forenhanced precision measurements. Deterministic entanglement schemes create thedesired state bytransferring thesystem under theaction ofacarefully chosen Hamiltonian into an entangled state. Thesystem mustfollow a unitary evolution, anduncontrolled parasitic interactions withthe environment leading tospontaneous decay orpartial measurements ofthestate havetobeavoided. Entangled states canalsobecreated inaprobabilistic manner: By performing asuitable partial measurement ofthesystem's state, the probe measurement outcomeindicates whether thesystemhasbeen laser projected into thedesired state ornotbythemeasurement's backaction. Suchprobabilistic schemescan relaxthestringent requirements onthesuppression ofdissipation inourcavity-QED system [1,2]. cavity Inourexperiment, we loada chosen numberofdoppler-cooled mirror

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Entangled quantum states haveapplications asamodelsystem forstrongly correlated manybodystates, asresource forquantum information processing andasatool forenhanced precision measurements. Deterministic entanglement schemes create thedesired state bytransferring thesystem under theaction ofacarefully chosen Hamiltonian into an entangled state. Thesystem mustfollow a unitary evolution, anduncontrolled parasitic interactions withthe environment leading tospontaneous decay orpartial measurements ofthestate havetobeavoided. Entangled states canalsobecreated inaprobabilistic manner: By performing asuitable partial measurement ofthesystem's state, the probe measurement outcomeindicates whether thesystemhasbeen laser projected into thedesired state ornotbythemeasurement's backaction. Suchprobabilistic schemescan relaxthestringent requirements onthesuppression ofdissipation inourcavity-QED system [1,2]. cavity Inourexperiment, we loada chosen numberofdoppler-cooled mirror
Entangled quantum states have applications as a model system for strongly correlated many body states, as resource for quantum information processing and as a tool for enhanced precision measurements. Deterministic entanglement schemes create the desired state by transferring the system under the action of a carefully chosen Hamiltonian into an entangled state. The system must follow a unitary evolution, and uncontrolled parasitic interactions with the environment leading to spontaneous decay or partial measurements of the state have to be avoided. The paper present an experiment, on loading a chosen number of Doppler-cooled caesium atoms from a magneto-optical trap into a standing wave optical dipole trap. The positions of the individual atoms are then determined with sub-micrometer precision, enabling to prepare, to manipulate and to read out the quantum state of each atom. Using the dipole trap as an optical conveyor belt, the atoms are transported into the mode of a high-finesse optical cavity.
Every quantum system subjected to measurements is an open quantum system. The cavity QED system is elegant in that it probes the interaction between two quantum systems, the atom and the field, while its loss mechanisms are well understood and can be externally monitored. The study of cross-correlations in cavity QED is important for understanding how entanglement evolves in open quantum systems. As quantum information science grows we need to learn more about entanglement and how it can be quantified and measured. Correlation functions have been used to compare an electromagnetic field (intensity) of one mode with the electromagnetic field (intensity) of the same mode at a later time or different spatial location. In quantum optics, correlation functions have been calculated and measured to probe the nonclassical field that results from the interaction of a single mode of the electromagnetic field and an ensemble of two-level atoms (the canonical cavity QED system). This field can exhibit antibunching, squeezing, and can violate inequalities required for a classical field. Entanglement in the steady state of a cavity QED system cannot be measured directly with traditional correlation functions (Hanbury-Brown and Twiss type experiments). Cross-correlations, however, interrogate directly both modes of the entangled pair, the transmitted (cavity) and the fluorescent (atom) intensities, and can act as an entanglement witness. This thesis presents the implementation of a cross-correlation measurement in a cavity QED system. The work has required the construction of an apparatus that incorporates laser cooling and trapping with quantum optics to carefully control both the external (center of mass motion) and internal (atomic state) degrees of freedom of a collection of atoms that interact with a single mode of a high finesse Fabry-Perot cavity. We examine theoretically and experimentally a new intensity cross-correlation function which probes the evolution of the cavity field conditioned on the detection of a fluorescent photon from an atom in the cavity. The results open the possibility to generalize the dynamics of entanglement as a physical resource necessary for the nascent quantum information science.
Abstract The presence of mirrors modifies both the coherent coupling of an atom to a light mode and its spontaneous emission into the mode [1]. We study such cavity QED effects experimentally with single ions and optical cavities. We focus on two examples which are equally interesting as fundamental systems and for application in quantum information processing. (i) By retroreflecting the fluorescence of a single trapped Ba+ ion with a mirror 25 cm away, we observe inhibition and enhancement of the atom's spontaneous emission. When two ions are trapped, the distant mirror creates super‐ and subradiance. (ii) With a single trapped Ca+ ion we demonstrate coherent coupling of its narrow S1/2 – D5/2 “qubit” transition to a mode of a high‐finesse optical cavity. We also achieve deterministic coupling of the cavity standing wave to the ion's vibrational state by controlling the ion's position with nanometer‐precision and selectively exciting vibrational state‐changing transitions.