Cavity-mediated collective spin-exchange interactions in a strontium superradiant laser.

Laser-cooled and quantum degenerate atoms are being pursued as quantum simulators and form the basis of today's most precise sensors. A key challenge toward these goals is to understand and control coherent interactions between the atoms. We observe long-range exchange interactions mediated by an optical cavity, which manifest as tunable spin-spin interactions on the pseudo spin-½ system composed of the millihertz linewidth clock transition in strontium. This leads to one-axis twisting dynamics, the emergence of a many-body energy gap, and gap protection of the optical coherence against certain sources of decoherence. Our observations will aid in the future design of versatile quantum simulators and the next generation of atomic clocks that use quantum correlations for enhanced metrology.

Measurement-Based Entanglement of Noninteracting Bosonic Atoms.

We demonstrate the ability to extract a spin-entangled state of two neutral atoms via postselection based on a measurement of their spatial configuration. Typically, entangled states of neutral atoms are engineered via atom-atom interactions. In contrast, in our Letter, we use Hong-Ou-Mandel interference to postselect a spin-singlet state after overlapping two atoms in distinct spin states on an effective beam splitter. We verify the presence of entanglement and determine a bound on the postselected fidelity of a spin-singlet state of (0.62±0.03). The experiment has direct analogy to creating polarization entanglement with single photons and hence demonstrates the potential to use protocols developed for photons to create complex quantum states with noninteracting atoms.

Realizing exactly solvable SU(N) magnets with thermal atoms.

We show that n thermal fermionic alkaline-earth-metal atoms in a flat-bottom trap allow one to robustly implement a spin model displaying two symmetries: the S n symmetry that permutes atoms occupying different vibrational levels of the trap and the SU(N) symmetry associated with N nuclear spin states. The symmetries make the model exactly solvable, which, in turn, enables the analytic study of dynamical processes such as spin diffusion in this SU(N) system. We also show how to use this system to generate entangled states that allow for Heisenberg-limited metrology. This highly symmetric spin model should be experimentally realizable even when the vibrational levels are occupied according to a high-temperature thermal or an arbitrary nonthermal distribution.

Influence of ligand denticity on the properties of novel 99mTc(I)-carbonyl complexes. Application to the development of radiopharmaceuticals for imaging hypoxic tissue.

An important issue in the development of metal-based radiopharmaceuticals is the selection of the labelling strategy in order to couple the metal to the pharmacophore without losing the biological activity. With the aim to evaluate the correlation between ligand denticity and biological behaviour of the corresponding (99m)Tc complexes, we designed a tridentate and a bidentate 5-nitroimidazole derivatives suitable for (99m)Tc(I) tricarbonyl complexation and with potential use as radiopharmaceuticals towards hypoxic tissue diagnosis. Ligands were synthesized using metronidazol, a pharmaceutical containing the bioreductive pharmacophore as starting material. The chelating units were connected to the pharmacophore using the click reaction of Huisgen. Both (99m)Tc complexes were obtained in high yield and were hydrophilic and stable in labelling milieu. The complex obtained from the tridentate ligand exhibited high stability in human plasma, low protein binding and a favourable biodistribution characterized by low blood and liver uptake, fast elimination and negligible uptake in other organs or tissues. Selective uptake and retention in tumour together with favourable tumour/muscle ratio makes this (99m)Tc-complex a promising candidate for further evaluation as potential hypoxia imaging agent in tumours. The bidentate ligand, on the other hand, yielded a less stable (99m)Tc-complex that experimented hydrolysis in vitro and decomposition in human plasma and showed high protein binding, high blood and liver uptake and moderate excretion. Although selective uptake and retention in tumour was also observed physicochemical and biological behaviour are inadequate for in vivo use, demonstrating that denticity of the ligand is particularly important and that tridentate ligands are preferable in order to prepare (99m)Tc-tricarbonyl complexes for Nuclear Medicine imaging.