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].

We trap and cool a gas composed of 40 K and 87 Rb, using a two-species magneto-optical trap (MOT). This trap represents the first step towards cooling the Bose-Fermi mixture to quantum degeneracy. Laser light for the MOT is derived from laser diodes and amplified with a single high power semiconductor amplifier chip. The four-color laser system is described, and the single-species and two-species MOTs are characterized. Atom numbers of 1 × 10 7 40 K and 2 × 10 9 87 Rb are trapped in the two-species MOT. Observation of trap loss due to collisions between species is presented and future prospects for the experiment are discussed. PACS number(s): 32.80. Pj, 03.75.Fi, 05.30.Fk The first experimental realizations of Bose-Einstein condensation in dilute atomic gases [1][2][3] brought with them an ever-increasing interest in the quantum behavior of such systems. These systems exhibit weak and controllable interactions, and are typically simpler to describe theoretically than their condensed matter counterparts. The quantum statistics of fermions, however, initially prevented the production of a quantum degenerate Fermi gas of atoms. Specifically, the challenge came in maintaining the rethermalizing collisions necessary for forced evaporative cooling of the gas -the Pauli exclusion principle forbids s-wave collisions between identical fermions at the ultralow temperatures necessary to reach quantum degeneracy. To circumvent this limitation, the first experiment to produce a quantum degenerate Fermi gas [4] used two spin states of a single fermionic isotope, thus allowing the rethermalizing collisions necessary for evaporative cooling. Sympathetic cooling of fermionic atoms to quantum degeneracy using a thermal bath of bosonic atoms has more recently been demonstrated in systems using 6 Li and 7 Li [5,6].In this paper we report on the simultaneous trapping of 40 K (a fermion) and 87 Rb (a boson) using a two-species magneto-optical trap (MOT). This MOT will be used as a pre-cooling stage prior to forced evaporation of the 87 Rb and sympathetic cooling of the 40 K gas. To produce the four frequencies of light necessary to operate the MOT, we have developed a relatively simple laser scheme that includes the use of a single high power semiconductor amplifier. With this system we are able to trap 2×10 9 87 Rb atoms and 1×10 7 40 K atoms simultaneously. In addition we can monitor either species during the operation of the MOT, and have observed number loss in the 40 K cloud due to the presence of trapped rubidium.A MOT for trapping two different elements requires twice as many laser frequencies as a single-species MOT. All of the light for our MOT is generated by laser diodes and amplified by a single high power tapered semiconductor amplifier chip (Toptica Photonics TAE 780 [7,8]). The design of the laser system and MOT optics exploits the similar wavelengths of the D 2 lines in rubidium and potassium, whose energy levels are shown schematically in Fig. 1. Note the inverted structure and considerably smaller splittings for...

We study modulation spectroscopy of the potassium D 2 transitions at 766.7 nm.The vapour pressure, controlled by heating a commercial reference cell, is optimized using conventional saturated absorption spectroscopy. Subsequent heterodyne detection yields sub-Doppler frequency discriminants suitable for stabilizing lasers in experiments with cold atoms. Comparisons are made between spectra obtained by direct modulation of the probe beam, and those using modulation transfer from the pump via nonlinear mixing. Finally, suggestions are made for further optimization of the signals. Submitted to: J. Phys. B: At. Mol. Phys.

Cavity quantum electrodynamics describes the fundamental interactions between light and matter, and how they can be controlled by shaping the local environment. For example, optical microcavities allow high-efficiency detection and manipulation of single atoms. In this regime, fluctuations of atom number are on the order of the mean number, which can lead to signal fluctuations in excess of the noise on the incident probe field. Here we demonstrate, however, that nonlinearities and multi-atom statistics can together serve to suppress the effects of atomic fluctuations when making local density measurements on clouds of cold atoms. We measure atom densities below 1 per cavity mode volume near the photon shot-noise limit. This is in direct contrast to previous experiments where fluctuations in atom number contribute significantly to the noise. Atom detection is shown to be fast and efficient, reaching fidelities in excess of 97% after 10 μs and 99.9% after 30 μs.

We present experiments on ensemble cavity quantum electrodynamics with cold potassium atoms in a high-finesse ring cavity. Potassium-39 atoms are cooled in a two-dimensional magneto-optical trap and transferred to a three-dimensional trap which intersects the cavity mode. The apparatus is described in detail and the first observations of strong coupling with potassium atoms are presented. Collective strong coupling of atoms and light is demonstrated via the splitting of the cavity transmission spectrum and the avoided crossing of the normal modes.