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

A new open-source parallel genetic algorithm, the Birmingham parallel genetic algorithm, is introduced for the direct density functional theory global optimisation of metallic nanoparticles. The program utilises a pool genetic algorithm methodology for the efficient use of massively parallel computational resources. The scaling capability of the Birmingham parallel genetic algorithm is demonstrated through its application to the global optimisation of iridium clusters with 10 to 20 atoms, a catalytically important system with interesting size-specific effects. This is the first study of its type on Iridium clusters of this size and the parallel algorithm is shown to be capable of scaling beyond previous size restrictions and accurately characterising the structures of these larger system sizes. By globally optimising the system directly at the density functional level of theory, the code captures the cubic structures commonly found in sub-nanometre sized Ir clusters.

The Birmingham cluster genetic algorithm is a package that performs global optimisations for homo- and bimetallic clusters based on either first principles methods or empirical potentials. Here, we present a new parallel implementation of the code which employs a pool strategy in order to eliminate sequential steps and significantly improve performance. The new approach meets all requirements of an evolutionary algorithm and contains the main features of the previous implementation. The performance of the pool genetic algorithm is tested using the Gupta potential for the global optimisation of the Au10Pd10 cluster, which demonstrates the high efficiency of the method. The new implementation is also used for the global optimisation of the Au10 and Au20 clusters directly at the density functional theory level.

Resolving the structure of clusters in the gas phase often requires the comparison of experimental data to quantum chemical calculations. Herein, we present the variation of a straightforward approach, in which photodissociation spectra of isolated clusters are compared to optical response calculations in order to elucidate cluster structures. Our absorption spectra were measured using a newly built longitudinal beam depletion spectroscopy apparatus and recorded in the photon energy range ħω = 1.9-3.5 eV. Cluster geometries were obtained using the unbiased Birmingham Cluster Genetic Algorithm coupled with density functional theory, while the optical response was calculated in the framework of time-dependent density functional theory. Experiments and excited state calculations are in excellent agreement using long-range corrected exchange correlation functionals for both ground and excited state calculations. Our methodology indicates a contribution of Y shaped Au4(+) whereas for Ag4(+) only the ground state isomer has to be considered to explain the experimental absorption spectrum. Our extended methodology shows two nearly degenerate isomers of Au4(+) probably being present in the molecular beam and therefore shows promise for the further structure determination of pure and binary transition-metal clusters.

The controversial nature of chemical bonding between noble gases and noble metals is addressed. Experimental evidence of exceptionally strong Au-Ar bonds in Ar complexes of mixed Au-Ag trimers is presented. IR spectra reveal an enormous influence of the attached Ar atoms on vibrational modes, particularly in Au-rich trimers, where Ar atoms are heavily involved owing to a relativistically enhanced covalency. In Ag-rich trimers, vibrational transitions of the metal framework predominate, indicating a pure electrostatic character of the Ag-Ar bonds. The experimental findings are analyzed by means of DFT calculations, which show how the relativistic differences between Au and Ag are manifested in stronger Au-Ar binding energies. Because of the ability to vary composition and charge distribution, the trimers serve as ideal model systems to study the chemical nature of the bonding of noble gases to closed-shell systems containing gold.

We present experimental and theoretical studies of the optical response of mixed Ag(n)Au(+)(4-n) (n=1-3) clusters in the photon energy range ℏω = 1.9-3.5 eV. Absorption spectra are recorded by a newly built longitudinal molecular beam depletion spectroscopy apparatus providing lower limits to absolute photodissociation cross sections. The experimental data are compared to optical response calculations in the framework of long-range corrected time-dependent density functional theory with initial cluster geometries obtained by the unbiased Birmingham Cluster Genetic Algorithm coupled with density functional theory. Experiments and excited state calculations shed light on the structural and electronic properties of the mixed Ag-Au tetramer cations.

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The de Broglie wave nature of matter is a paradigmatic example of fundamental quantum physics and enables precise measurements of forces, fundamental constants and even material properties. However, even though matter-wave interferometry is nowadays routinely realized in many laboratories, this feat has remained an outstanding challenge for the vast class of native polypeptides, the building blocks of life, which are ubiquitous in biology but fragile and difficult to handle. Here, we demonstrate the quantum wave nature of gramicidin, a natural antibiotic composed of 15 amino acids. Femtosecond laser desorption of a thin biomolecular film with intensities up to 1 TW/cm 2 transfers these molecules into a cold noble gas jet. Even though the peptide's de Broglie wavelength is as tiny as 350 fm, the molecular coherence is delocalized over more than 20 times the molecular size in our all-optical time-domain Talbot-Lau interferometer. We compare the observed interference fringes for two different interference orders with a model that includes both a rigorous treatment of the peptide's quantum wave nature as well as a quantum chemical assessment of its optical properties to distinguish our result from classical predictions. The successful realization of quantum optics with this polypeptide as a prototypical biomolecule paves the way for quantumassisted molecule metrology and in particular the optical spectroscopy of a large class of biologically relevant molecules.The wave-particle duality of massive matter has become an important aspect of modern physics. Atom interferometry [1, 2] enabled new tests from quantum physics [3] to general relativity [4,5], cosmology [6] inertial sensing [7,8] precision measurements of fundamental constants [9] and forces [10]. The de Broglie wave nature has been shown for large molecules, from fullerenes [11] and molecular clusters [12] up to even high-mass particles [13]. Such experiments probe the quantum-toclassical interface and can even be used as a unique tool to characterize neutral molecules in the gas phase [14,15] with the potential for minimally invasive high-precision spectroscopy [16].However until today, quantum optics with massive native biomolecules has remained elusive in particular due to the challenges in forming stable and intense molecular beams which can be detected with high efficiency and selectivity. Measurements on neutral biomolecules in the gas phase will, however, become valuable as they are solvent-free and allow predicting and evaluating biomolecular electronic properties independent of any coupling matrix environments [17]. Here, we present the first realization of matter-wave interferometry of gramicidin A1, a linear antibiotic polypeptide composed of 15 amino acids with a mass m = 1882 amu = 3.13 × 10 −24 kg, naturally produced by the soil bacterium Bacillus brevis. Interference experiments with this biomolecular prototype brings us a step closer towards quantum experiments with living organisms [18].A typical matter-wave experiment requires an efficient so...