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We propose a quantum theory of rotating light beams and study some of its properties. Such beams are polychromatic and have either a slowly rotating polarization or a slowly rotating transverse mode pattern. We show there are, for both cases, three different natural types of modes that qualify as rotating, one of which is a new type not previously considered. We discuss differences between these three types of rotating modes on the one hand and non-rotating modes as viewed from a rotating frame of reference on the other, thus resolving some paradoxes mentioned recently.

We give an overview of different types of entanglement that can be generated in experiments, as well as of various protocols that can be used to verify or quantify entanglement. We propose several criteria that, we argue, should be applied to experimental entanglement verification procedures. Explicit examples demonstrate that not following these criteria will tend to result in overestimating the amount of entanglement generated in an experiment or in inferring entanglement when there is none. We distinguish protocols meant to refute or eliminate hidden-variable models from those meant to verify entanglement.

We propose a quantum theory of rotating light beams and study some of its properties. Such beams are polychromatic and have either a slowly rotating polarization or a slowly rotating transverse mode pattern. We show that there are, for both cases, three different natural types of modes that qualify as rotating, one of which is a type not previously considered. We discuss differences between these three types of rotating modes on the one hand and nonrotating modes as viewed from a rotating frame of reference on the other. We present various examples illustrating the possible use of rotating photons, mostly for quantum information processing purposes. We introduce in this context a rotating version of the two-photon singlet state.

We give an overview of different types of entanglement that can be generated in experiments, as well as of various protocols that can be used to verify or quantify entanglement. We propose several criteria that, we argue, should be applied to experimental entanglement verification procedures. Explicit examples demonstrate that not following these criteria will tend to result in overestimating the amount of entanglement generated in an experiment or in inferring entanglement when there is none. We distinguish protocols meant to refute or eliminate hidden-variable models from those meant to verify entanglement.

The ability to distribute quantum resources over long distances is a key element for the development of several practical applications in the field of quantum information. In this way, major efforts have been made in the past decade to extend the maximum distances for the observation of entanglement or for the realization of quantum cryptography. Using optical fibers as the quantum channel, entanglement has already been achieved between photons separated by 50 km of fiber, and quantum cryptography is now a commercial technology that allows quantum key distributon over distances up to around 100 km. Progress has also been made towards entanglement distribution in free space, with the achieved distances of about 10 km on ground atmosphere being a substantial step toward the development of satellite-based quantum communication.

We propose a quantum theory of rotating light beams and study some of its properties. Such beams are polychromatic and have either a slowly rotating polarization or a slowly rotating transverse mode pattern. We show that there are, for both cases, three different natural types of modes that qualify as rotating, one of which is a type not previously considered. We discuss differences between these three types of rotating modes on the one hand and nonrotating modes as viewed from a rotating frame of reference on the other. We present various examples illustrating the possible use of rotating photons, mostly for quantum information processing purposes. We introduce in this context a rotating version of the two-photon singlet state.

We report the observation of heralded entanglement between remote atomic ensembles. The detection of an emitted photon projects the ensembles into an entangled state with one joint excitation stored in the whole system.

We show that Itano's arguments confirm our conclusion, that entanglement of the atom with the laser field contributes a small but nonzero amount to the total decoherence of an atom in a laser field. This small effect scales as 1/(n) over bar with (n) over bar the average number of photons in the laser pulse.

We show that Itano's arguments confirm our conclusion, that entanglement of the atom with the laser field contributes a small but nonzero amount to the total decoherence of an atom in a laser field. This small effect scales as 1/(n) over bar with (n) over bar the average number of photons in the laser pulse.

We present detailed discussions of cooling and trapping mechanisms for an atom in an optical trap inside an optical cavity, as relevant to recent experiments. The interference pattern of cavity QED and trapping fields in space makes the trapping wells, in principle, distinguishable from one another. This adds considerable flexibility to creating effective trapping and cooling conditions and to detection possibilities. Friction and diffusion coefficients are calculated in and beyond the low excitation limit and full three-dimensional simulations of the quasiclassical motion of a Cs atom are performed.

We construct three-dimensional solutions of Maxwell’s equations that describe Gaussian light beams focused by a strong lens. We investigate the interaction of such beams with single atoms in free space and the interplay between angular and quantum properties of the scattered radiation. We compare the exact results with those obtained with paraxial light beams and from a standard input-output formalism. We put our results in the context of quantum information processing with single atoms.

We construct three-dimensional solutions of Maxwell’s equations that describe Gaussian light beams focused by a strong lens. We investigate the interaction of such beams with single atoms in free space and the interplay between angular and quantum properties of the scattered radiation. We compare the exact results with those obtained with paraxial light beams and from a standard input-output formalism. We put our results in the context of quantum information processing with single atoms.

We present detailed discussions of cooling and trapping mechanisms for an atom in an optical trap inside an optical cavity, as relevant to recent experiments. The interference pattern of cavity QED and trapping fields in space makes the trapping wells, in principle, distinguishable from one another. This adds considerable flexibility to creating effective trapping and cooling conditions and to detection possibilities. Friction and diffusion coefficients are calculated in and beyond the low excitation limit and full three-dimensional simulations of the quasiclassical motion of a Cs atom are performed.

We calculate exact three-dimensional solutions of Maxwell equations corresponding to strongly focused light beams, and study their interaction with a single atom in free space. We show how the naive picture of the atom as an absorber with a size given by its radiative cross section σ = 3λ²/2π must be modified. The implications of these results for quantum-information-processing capabilities of trapped atoms are discussed.

A Comment on the Letter by David A. Meyer, Phys. Rev. Lett. 82, 1052 (1999). The authors of the Letter offer a Reply.

We show that quantum information may be transferred between atoms in different locations by using “phantom” or “dark” photons: the atoms are coupled through electromagnetic fields, but the corresponding field modes do not have to be fully populated. In the case where atoms are placed inside optical cavities, errors in quantum information processing due to photon absorption inside the cavity are diminished in this way. This effect persists up to intercavity distances of about a meter for the current levels of cavity losses, and may be useful for distributed quantum computing.

We show that quantum information may be transferred between atoms in different locations by using “phantom” or “dark” photons: the atoms are coupled through electromagnetic fields, but the corresponding field modes do not have to be fully populated. In the case where atoms are placed inside optical cavities, errors in quantum information processing due to photon absorption inside the cavity are diminished in this way. This effect persists up to intercavity distances of about a meter for the current levels of cavity losses, and may be useful for distributed quantum computing.

An overview of our work on quantum communication in quantumnetworks is given. We discuss physical implementations for quantum networks based on cavity-QED, including error correction schemes for the transmission of qubits over noisy channels and for noisy local entanglement and joint measurement operations on atoms. We define the "photonic channel", and outline the most recent developments concerning the "quantum repeater".

A quantum network where the data stored, processed, and communicated consists of quantum bits, would offer exciting possibilities including teleportation, dense coding, quantum money, secured quantum key distribution, and perhaps distributed quantum computing. But how to implement such a network? In this contribution we describe a concrete physical implementation consisting of atoms placed inside high-Q optical cavities, connected by optical fibers, that allow the atoms to communicate with each other using a cavity photon as the information carrier.