Spontaneous emission of a photon by an atom is described theoretically in three dimensions with the initial wave function of a finite-mass atom taken in the form of a finite-size wave packet. Recoil and wave-packet spreading are taken into account. The total atom-photon wave function is found in the momentum and coordinate representations as the solution of an initial-value problem. The atom-photon entanglement arising in such a process is shown to be closely related to the structure of atom and photon wave packets which can be measured in the coincidence and single-particle schemes of measurements. Two predicted effects, arising under the conditions of high entanglement, are anomalous narrowing of the coincidence wave packets and, under different conditions, anomalous broadening of the single-particle wave packets. Fundamental symmetry relations between the photon and atom single-particle and coincidence wave packet widths are established.The relationship with the famous scenario of Einstein-Podolsky-Rosen is discussed.

The narrowing of electron and ion wave packets in the process of photoionization is investigated, with the electron-ion recoil taken fully into account. Packet localization of this type is directly related to entanglement in the joint quantum state of the electron and ion, and to Einstein-Podolsky-Rosen localization. Experimental observation of such packet-narrowing effects is suggested via coincidence registration by two detectors, with a fixed position of one and varying position of the other. A similar effect, typically with an enhanced degree of entanglement, is shown to occur in the case of photodissociation of molecules.

We present a unique matter-wave interferometer whose phase scales with the cube of the time the atom spends in the interferometer. Our scheme is based on a full-loop Stern-Gerlach interferometer incorporating four magnetic field gradient pulses to create a state-dependent force. In contrast to typical atom interferometers which make use of laser light for the splitting and recombination of the wave packets, this realization uses no light and can therefore serve as a high-precision surface probe at very close distances.

Microgravity eases several constraints limiting experiments with ultracold and condensed atoms on ground. It enables extended times of flight without suspension and eliminates the gravitational sag for trapped atoms. These advantages motivated numerous initiatives to adapt and operate experimental setups on microgravity platforms. We describe the design of the payload, motivations for design choices, and capabilities of the Bose-Einstein Condensate and Cold Atom Laboratory (BECCAL), a NASA-DLR collaboration. BECCAL builds on the heritage of previous devices operated in microgravity, features rubidium and potassium, multiple options for magnetic and optical trapping, different methods for coherent manipulation, and will offer new perspectives for experiments on quantum optics, atom optics, and atom interferometry in the unique microgravity environment on board the International Space Station.

Strong and/or short laser pulses provide one avenue for rapid separation of composite quantum systems. Daughter particles can exhibit subtle aspects of quantum entanglement. We show that a Gaussian approximation provides a unifying overview of rapidly separating systems in many contexts, and propose using combined single-particle and coincidence measurements of wave-packet widths of bipartite systems for experimental observation of the degree of entanglement.

We show that the wave packet of a biphoton generated via spontaneous parametric down conversion is strongly anisotropic. Its anisotropic features manifest themselves very clearly in comparison of measurements performed in two different schemes: when the detector scanning plane is perpendicular or parallel to the plane containing the crystal optical axis and the laser axis. The first of these two schemes is traditional whereas the second one gives rise to such unexpected new results as anomalously strong narrowing of the biphoton wave packet measured in the coincidence scheme and very high degree of entanglement. The results are predicted theoretically and confirmed experimentally.

We propose and experimentally demonstrate a method to prepare a nonspreading atomic wave packet. Our technique relies on a spatially modulated absorption constantly chiseling away from an initially broad de Broglie wave. The resulting contraction is balanced by dispersion due to Heisenberg's uncertainty principle. This quantum evolution results in the formation of a nonspreading wave packet of Gaussian form with a spatially quadratic phase. Experimentally, we confirm these predictions by observing the evolution of the momentum distribution. Moreover, by employing interferometric techniques, we measure the predicted quadratic phase across the wave packet. Nonspreading wave packets of this kind also exist in two space dimensions and we can control their amplitude and phase using optical elements.PACS numbers: 03.75. Be, 42.50.Vk, 03.75.Dg Nonspreading wave packets have attracted interest since the early days of quantum mechanics. Already in 1926 Schrödinger [1] found that the displaced Gaussian ground state of a harmonic oscillator experiences conformal evolution because a classical force prevents the wave packet from spreading. Even in free space the correlations between position and momentum stored in an initially Airy-function-shaped wave packet can prevent spreading [2]. Here we propose and experimentally observe the formation and propagation of nondispersive atomic wave packets in an imaginary (absorptive) potential accessible in atom optics [3,4,5]. Although there is no classical force, there are correlations continuously imposed by Heisenberg's uncertainty relation resulting in the stabilization of the wave packet.Localized wave packets due to stabilization are well known in the context of periodically driven quantum systems [6] and studied with increasing interest for electronic wave packets in Rydberg atoms [7,8,9,10]. Our approach to create nondispersive atomic wave packets relies on three ingredients: (i) an absorption process [11] cuts away the unwanted parts of a broad wave creating a packet that is continuously contracting in position space, (ii) this process leads due to Heisenberg's uncertainty relation to a broadening in momentum space and consequently to a faster spreading in real space, and (iii) the absorptive narrowing and the quantum spreading are balanced, leading to a nonspreading wave packet. In the following we will refer to such a wave packet as Michelangelo packet [12].Complex potentials for matter waves [13] emerge from the interaction of near resonant light with an open twolevel system shown in Fig. 1(a). For a standing light wave tuned exactly on resonance an array of purely imaginary harmonic potentials arises. When the Rabi frequency Ω 0 is of the order of the excited state linewidth Γ the local saturation parameter |Ω 0 sin(kx)/Γ|, and thus the upper level population, is of the order of unity except in a small vicinity of the field nodes. Consequently, our system decays approximately with the rate Γ. Therefore, in the time domain t ≫ 1/Γ the atomic wave function vanishes almost...

We show that the wave packet of a biphoton generated via spontaneous parametric down-conversion is strongly anisotropic. Its anisotropic features manifest themselves very clearly in comparison with measurements performed in two different schemes: When the detector scanning plane is perpendicular or parallel to the plane containing the crystal optical axis and the laser axis. The first of these two schemes is traditional whereas the second one gives rise to such unexpected results, such as anomalously strong narrowing of the biphoton wave packet measured in the coincidence scheme and very high degree of entanglement. The results are predicted theoretically and confirmed experimentally.