We propose in this White Paper a concept for a space experiment using cold atoms to search for ultra-light dark matter, and to detect gravitational waves in the frequency range between the most sensitive ranges of LISA and the terrestrial LIGO/Virgo/KAGRA/INDIGO experiments. This interdisciplinary experiment, called Atomic Experiment for Dark Matter and Gravity Exploration (AEDGE), will also complement other planned searches for dark matter, and exploit synergies with other gravitational wave detectors. We give examples of the extended range of sensitivity to ultra-light dark matter offered by AEDGE, and how its gravitational-wave measurements could explore the assembly of super-massive black holes, first-order phase transitions in the early universe and cosmic strings. AEDGE will be based upon technologies now being developed for terrestrial experiments using cold atoms, and will benefit from the space experience obtained with, e.g., LISA and cold atom experiments in microgravity.KCL-PH-TH/2019-65, CERN-TH-2019-126
Three magnetic-field induced heteronuclear Feshbach resonances were identified in collisions between bosonic 87Rb and fermionic 40K atoms in their absolute ground states. Strong inelastic loss from an optically trapped mixture was observed at the resonance positions of 492, 512, and 543+/-2 G. The magnetic-field locations of these resonances place a tight constraint on the triplet and singlet cross-species scattering lengths, yielding (-281+/-15)a(0) and (-54+/-12)a(0), respectively. The width of the loss feature at 543 G is 3.7+/-1.5 G wide; this broad Feshbach resonance should enable experimental control of the interspecies interactions.
A microfabricated Fabry-Perot optical resonator has been used for atom detection and photon production with less than 1 atom on average in the cavity mode. Our cavity design combines the intrinsic scalability of microfabrication processes with direct coupling of the cavity field to singlemode optical waveguides or fibers. The presence of the atom is seen through changes in both the intensity and the noise characteristics of probe light reflected from the cavity input mirror. An excitation laser passing transversely through the cavity triggers photon emission into the cavity mode and hence into the single-mode fiber. These are first steps towards building an optical microcavity network on an atom chip for applications in quantum information processing.PACS numbers: 42.50. Pq, 03.67.Lx, 03.75.Be When a neutral atom is placed in a high-finesse optical cavity, the electric dipole coupling between the atom and the light field can lead to quantum coherence between the two. This fact forms the basis of cavity quantum electrodynamics (QED) [1]. Recently, there has been considerable interest in the possibility of applying cavity QED to problems in quantum information processing, as reviewed, for example, in Ref. [2]. Single photons have been generated on demand from falling [3] and trapped [4] atoms in high-finesse Fabry-Perot cavities, and recent experiments have investigated the cavityassisted generation of single photons from atomic ensembles [5]. These are important steps towards building multiple-cavity quantum information networks, such as those proposed in Ref. [6]. However, experiments so far have been limited to single cavities by the technical demands of achieving high enough finesse. Outstanding challenges now are to make the cavities smaller, to fabricate them in large numbers with the possibility of multiple interconnects, and to load them conveniently and deterministically with atoms. This would pave the way to circuit-model quantum computers [7], to one-way computations based on cluster states [8], and to other schemes requiring multiple cavities [9].As a first move in this direction, two recent experiments have used a small magnetic guide to load atoms into a cavity [10]. However the cavities in these experiments were 2-3 cm long and therefore not more scalable than a conventional Fabry-Perot cavity. By contrast, Aoki et al. have dropped atoms close to a microscopic toroidal cavity and observed evidence of strong coupling [11]. These resonators can be microfabricated in large arrays, however they are not easily used for controlled atom-cavity coupling because of the need to position the atom very precisely in the evanescent field just outside the surface of the resonator. For this reason it is of interest to consider microscopic Fabry-Perot cavities, whose open structure gives access to the central part of the cavity field. In one recent design [12], the two mirrors of such a resonator are formed by optical fibers whose tips have been modified into concave reflectors. This design can achieve small mode...
A quantum degenerate, dilute gas mixture of bosonic and fermionic atoms was produced using 87 Rb and 40 K. The onset of degeneracy was confirmed by observing the spatial distribution of the gases after time-of-flight expansion. Further, the magnitude of the interspecies scattering length between the doubly spin polarized states of 87 Rb and 40 K, |a RbK |, was determined from crossdimensional thermal relaxation. The uncertainty in this collision measurement was greatly reduced by taking the ratio of interspecies and intraspecies relaxation rates, yielding |a RbK | = 250 ± 30 a0, which is a lower value than what was reported in [M. Modugno et al., Phys. Rev. A 68, 043626 (2003)]. Using the value for |a RbK | reported here, current T = 0 theory would predict a threshold for mechanical instability that is inconsistent with the experimentally observed onset for sudden loss of fermions in [G. Modugno et al., Science 297, 2240].
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