No abstract

Fano resonances and bound states with energy in the continuum are ubiquitous phenomena in different areas of physics. Observations, however, have been limited so far to single-particle processes. In this work we experimentally investigate the multi-particle case and observe Fano interference in a non-interacting two-particle Fano-Anderson model by considering propagation of two-photon states in engineered photonic lattices. We demonstrate that the quantum statistics of the particles, either bosonic or fermionic, strongly affects the decay process. Remarkably, we find that the Fano resonance, when two discrete levels are coupled to a continuum, is suppressed in the fermionic case.Decay of excited states has been a topic of great interest since the early times of quantum mechanics [1] [6][7][8], and plasmonic nanostructures [9]. Fano interference is observed when different decay channels interfere, giving rise to broadening and asymmetric deformations of natural line shapes. In general, the destructive interference between different decay channels is associated to the formation of bound states in the continuum [2,10], which inhibit the complete decay of the excited state. The interplay between bound states in the continuum and Fano/Feshbach resonances has been highlighted in several works (see, for instance, [11][12][13][14]). Experimental studies on Fano resonances [4], quantum decay processes [15,16] and bound states in the continuum [17][18][19][20][21] have focused up to now on single-particle dynamics. Interestingly, recent works [22][23][24][25][26][27][28] showed that particle statistics and contact interactions can deeply modify the decay dynamics. Fermions and bosons may show very different decay behaviour, in particular in many cases fermions tend to decay faster [22][23][24]. However, no experimental observation of this phenomenon has been reported yet.In this work we investigate, experimentally, the decay process of two non-interacting particles to a common continuum, by probing an engineered photonic lattice with two-photon states. The lattice, consisting of a threedimensional array of coupled optical waveguides, is fabricated in a glass substrate by femtosecond laser micromachining [29][30][31]. While the bosonic dynamics is naturally observed for identically polarised photons, an antisymmetric polarisation-entangled state of the two photons is used to simulate the fermionic behavior [32][33][34][35][36].We focus on systems described by the Fano-Anderson [2,4] or Friedrichs-Lee Hamiltonian [37,38], which is a paradigmatic model to study quantum mechanical decay, Fano interference phenomena and bound states in the continuum [10,13,14,27]. The simplest case is provided by two discrete states coupled to a common tightbinding continuum of modes, i.e. a quantum wire [27]. In detail, we consider a system composed of two sites |1 and |2 , respectively with energy 1 and 2 , side-coupled with hopping rates κ 1 and κ 2 , to a common semi-infinite chain of coupled sites (a quantum wire), each with energy = 0 (s...

We associate Sr atom pairs on sites of a Mott insulator optically and coherently into weaklybound ground-state molecules, achieving an efficiency above 80%. This efficiency is 2.5 times higher than in our previous work [S. Stellmer, B. Pasquiou, R. Grimm, and F. Schreck, Phys. Rev. Lett. 109, 115302 (2012)] and obtained through two improvements. First, the lifetime of the molecules is increased beyond one minute by using an optical lattice wavelength that is further detuned from molecular transitions. Second, we compensate undesired dynamic light shifts that occur during the stimulated Raman adiabatic passage (STIRAP) used for molecule association. We also characterize and model STIRAP, providing insights into its limitations. Our work shows that significant molecule association efficiencies can be achieved even for atomic species or mixtures that lack Feshbach resonances suitable for magnetoassociation.

We report on spectroscopic studies of hot and ultracold RbSr molecules, and combine the results in an analysis that allows us to fit a potential energy curve (PEC) for the X(1) 2 Σ + ground state bridging the short-to-long-range domains. The ultracold RbSr molecules are created in a µK sample of Rb and Sr atoms and probed by two-colour photoassociation spectroscopy. The data yield the long-range dispersion coefficients C6 and C8, along with the total number of supported bound levels. The hot RbSr molecules are created in a 1000 K gas mixture of Rb and Sr in a heat-pipe oven and probed by thermoluminescence and laser-induced fluorescence spectroscopy. We compare the hot molecule data with spectra we simulated using previously published PECs determined by three different ab-initio theoretical methods. We identify several band heads corresponding to radiative decay from the B(2) 2 Σ + state to the deepest bound levels of X(1) 2 Σ + . We determine a mass-scaled high-precision model for X(1) 2 Σ + by fitting all data using a single fit procedure. The corresponding PEC is consistent with all data, thus spanning short-to-long internuclear distances and bridging an energy gap of about 75% of the potential well depth, still uncharted by any experiment. We benchmark previous ab-initio PECs against our results, and give the PEC fit parameters for both X(1) 2 Σ + and B(2) 2 Σ + states. As first outcomes of our analysis, we calculate the s-wave scattering properties for all stable isotopic combinations and corroborate the locations of Fano-Feshbach resonances between alkali Rb and closed-shell Sr atoms recently observed [Barbé et al., Nat. ]. These results and more generally our strategy should greatly contribute to the generation of ultracold alkali -alkaline-earth dimers, whose applications range from quantum simulation to state-controlled quantum chemistry.

We produce 84 Sr2 molecules using Bose-enhanced Raman photoassociation. We apply the stimulated Raman adiabatic passage (STIRAP) technique on a Bose-Einstein condensate (BEC) to produce more than 8 × 10 3 ultracold molecules. This chemical reaction is only made possible because of the Bose enhancement of the optical transition dipole moment between the initial atomic state and an intermediate molecular state. We study the effect of Bose enhancement by measuring the transition Rabi frequency in a BEC and by comparing it with measurements for two atoms in sites of a Mott insulator. By breaking the dimers' bond and directly observing the separated atoms, we measure the molecular inelastic collision rate parameters. We discuss the possibility of applying Bose-enhanced STIRAP to convert a BEC of atoms into a BEC of molecules, and argue that the required efficiency for STIRAP is within experimental reach.