Borromean three-body FRET in frozen Rydberg gases

Controlling the interactions between ultracold atoms is crucial for quantum simulation and computation purposes. Highly excited Rydberg atoms are considered in this prospect for their strong and controllable interactions known in the dipole-dipole case to induce non-radiative energy transfers between atom pairs, similarly to fluorescence resonance energy transfer (FRET) in biological systems. Here we predict few-body FRET processes in Rydberg atoms and observe the first three-body resonance energy transfer in cold Rydberg atoms using cold caesium atoms. In these resonances, additional relay atoms carry away an energy excess preventing the two-body resonance, leading thus to a Borromean type of energy transfer. These few-body processes present strong similarities with multistep FRET between chromophores sometimes called donor-bridge-acceptor or superexchange. Most importantly, they generalize to any Rydberg atom and could lead to new implementations of few-body quantum gates or entanglement.

Rydberg atoms are promising platform for quantum simulations, due to their strong and controllable dipole–dipole interactions. Here, the authors predict few-body processes in Rydberg atoms which resemble fluorescence resonance energy transfer in biological setting, and observe them in cold caesium atoms.

Laser controlled tunneling in a vertical optical lattice

Raman laser pulses are used to induce coherent tunneling between neighboring sites of a vertical 1D optical lattice. Such tunneling occurs when the detuning of a probe laser from the atomic transition frequency matches multiples of the Bloch frequency, allowing for a spectroscopic control of the coupling between Wannier-Stark (WS) states. In particular, we prepare coherent superpositions of WS states of adjacent sites, and investigate the coherence time of these superpositions by realizing a spatial interferometer. This scheme provides a powerful tool for coherent manipulation of external degrees of freedom of cold atoms, which is a key issue for quantum information processing.

Magnetoelectric directional nonreciprocity in gas-phase molecular nitrogen

We report the direct observation of the nonreciprocity of the velocity of light, induced by electric and magnetic fields. This bilinear magneto-electro-optical effect appears in crossed electric and magnetic fields perpendicular to the light wave vector, as a refractive index difference between two counterpropagating directions. Using a high finesse ring cavity, we have measured this magnetoelectric nonreciprocity in molecular nitrogen at ambient temperature and atmospheric pressure; for light polarized parallel to the magnetic field it is 2η(∥exp)(N2) = (4.7±1)×10(-23)  m  V(-1)  T(-1) for λ = 1064  nm, in agreement with the expected order of magnitude. Our measurement opens the way to a deeper insight into light-matter interaction beyond the electric dipole approximation. We were able to measure a nonreciprocity as small as Δn =(5±2)×10(-18), which makes its observation in quantum vacuum a conceivable challenge.

Expression of class II major histocompatibility complex molecules correlates with human colon tumor vaccine efficacy

Vaccination of colon cancer patients with X-irradiated autologous tumor cells and Bacillus Calmette-Guérin results in a significant reduction in tumor recurrence. A study was undertaken to determine whether the expression of tumor-associated antigens, expression of major histocompatibility complex molecules, or the cellular composition of the vaccine cells correlates with vaccine efficacy. A significant increase in the percentage of histocompatibility leukocyte antigen (HLA) class II molecule-expressing tumor cells was the only marker with a positive correlation. Because HLA class II molecule expression is not a prognostic marker in control patients, it was hypothesized that HLA class II molecules are involved in the induction of tumor immunity in patients treated with the autologous colon tumor vaccine. Enhancement of HLA class II molecule-expressing cells could be induced in X-irradiated colon tumor cells injected into the skin of mice when the cells were mixed with gamma-interferon. Therefore, addition of gamma-interferon to the colon tumor vaccine, resulting in increased numbers of HLA class II molecule-expressing cells, could potentiate the generation of tumor immunity.

Isolation and characterization of a monoclonal antibody specific for epithelial cells

Monoclonal antibodies were generated to antigens on human foreskin keratinocytes to identify epithelial-specific molecules. Spleen cells from BALB/c mice, immunized with membrane preparations from primary explants of foreskin epithelial cells, were fused with the NS-1 mouse myeloma line. Hybridoma supernatants were screened for the desired immunological reactivity using enzyme-linked immunosorbant binding assays. Hybridomas secreting antibodies reacting with epithelial cells, but not fibroblasts or lymphocytes, were cloned by limiting dilution, and two stable clones producing immunoglobulin M K antibodies were selected for study. Evaluation of fixed paraffin-embedded human tissue by an indirect immunoperoxidase technique revealed that the antibodies bound most strongly to normal stratified squamous and transitional epithelium, and squamous and transitional cell carcinomas. Antibodies from the cloned hybridomas also reacted with primary cell cultures of foreskin keratinocytes, pulmonary epithelium, fetal liver, and amnion cells, but not with primary cultures of nonepithelial cells. Further testing by enzyme-linked immunosorbent assays revealed that the antibodies reacted with some long-term cell lines derived from epithelial tumors. Nonepithelial cell lines were not stained by the antibodies. Indirect immunofluorescent studies indicated that staining was confined to the cell surface. These antibodies may prove useful in studies of differentiation markers of human epithelial cells.