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We present a brief overview of recently proposed detection schemes for axion, axion-like pseudoscalar particle and topological defect dark matter. We focus mainly on the possibility of using atomic and molecular systems for dark matter detection. For axions and axion-like particles, these methods are complementary probes to ongoing photon–axion interconversion experiments and astrophysical observations. For topological defects, these methods are complementary to conventional astrophysical search schemes based on gravitational signatures.

The quadrupole linear Paul trap is one of the key instruments in building highly stable atomic clocks. However, a frequency reference based on a single trapped ion is limited in stability due to the time needed for the interrogation cycle which cannot be further shortened. A promising strategy is the utilization of multiple trapped ions. The ions of the same kind then repulse each other with the Coulomb force, which is countered by the ponderomotive force of the time depended field in the trap. A few ions form a chain along the axis of a linear Paul trap. Adding more ions (a few tens or hundreds) gives rise to Coulomb crystals. We created an efficient simulation code which calculates the motion of such collections of ions in quasi-static radiofrequency fields of real linear quadrupole traps (including the micromotion). We include a model for laser cooling of the ions. The simulation tool can be used to study the formation and the dynamics of Coulomb crystals under conditions corresponding to various experimental setups.

The Human Spaceflight, Microgravity, and Exploration (HME) Directorate of the European Space Agency is strongly involved in fundamental physics research. One of the major activities in this field is represented by the ACES (Atomic Clock Ensemble in Space) mission. ACES will demonstrate the high performances of a new generation of atomic clocks in the microgravity environment of the International Space Station (ISS). Following ACES, a vigorous research program has been recently approved to develop a second generation of atomic quantum sensors for space applications: atomic clocks in the optical domain, aiming at fractional frequency stability and accuracy in the low 10^-18 regime; inertial sensors based on matter-wave interferometry for the detection of tiny accelerations and rotations; a facility to study degenerate Bose gases in space. Tests of quantum physics on large distance scales represent another important issue addressed in the HME program. A quantum communication optical terminal has been proposed to perform a test of Bell's inequalities on pairs of entangled photons emitted by a source located on the ISS and detected by two ground stations. In this paper, present activities and future plans will be described and discussed.

An optical lattice clock was realized for ⁸⁷Sr atoms and its absolute frequency has been measured. Projected uncertainty in the lattice clock is illustrated for the case of ⁸⁷Sr. We discuss application of the clock scheme to other atom species, in search for better lattice clocks as well as for the variation of fine-structure constant.

The Human Spaceflight, Microgravity, and Exploration (HME) Directorate of the European Space Agency is strongly involved in fundamental physics research. One of the major activities in this field is represented by the ACES (Atomic Clock Ensemble in Space) mission. ACES will demonstrate the high performances of a new generation of atomic clocks in the microgravity environment of the International Space Station (ISS). Following ACES, a vigorous research program has been recently approved to develop a second generation of atomic quantum sensors for space applications: atomic clocks in the optical domain, aiming at fractional frequency stability and accuracy in the low 10⁻¹⁸ regime; inertial sensors based on matter-wave interferometry for the detection of tiny accelerations and rotations; a facility to study degenerate Bose gases in space. Tests of quantum physics on large distance scales represent another important issue addressed in the HME program. A quantum communication optical terminal has been proposed to perform a test of Bell's inequalities on pairs of entangled photons emitted by a source located on the ISS and detected by two ground stations. In this paper, present activities and future plans will be described and discussed.

We generate input states with reduced quantum uncertainty (spin-squeezed states) for a hyperfine atomic clock by collectively coupling an ensemble of laser-cooled and trapped ⁸⁷Rb atoms to an optical resonator. A quantum non-demolition measurement of the population difference between the two clock states with far-detuned light produces an entangled state whose projection noise is reduced by as much as 9.4(8) dB below the standard quantum limit (SQL) for uncorrelated atoms. When the observed decoherence is taken into account, we attain 4.2(8) dB of spin squeezing, confirming entanglement, and 3.2(8) dB of improvement in clock precision over the SQL. The method holds promise for improving the performance of optical-frequency clocks.