Session M5: Rydberg EIT and Novel Spectroscopic Techniques

Driving Rydberg-Rydberg transitions with an amplitude-modulated optical lattice

We demonstrate a novel spectroscopic method that couples Rydberg states using an amplitude-modulated optical lattice. The method is fundamentally different from traditional microwave spectroscopy: it engages the $A^2$-term rather than the $Ap$-term of the atom-field interaction Hamiltonian. The method allows us to drive microwave transitions between Rydberg states with optical spatial resolution, and it is not subject to the usual electric-dipole selection rules. Both features are attractive for quantum computing and precision metrology, such as measuring an improved value for the dipolar polarizibility of the Rb ionic core. In the experiment, cold Rb Rydberg atoms are first excited and confined in an optical lattice of wavelength 1064nm [1]. Then, the electric-quadrupole transition $58S\rightarrow59S$ is driven by modulating the intensity of the optical lattice using a tunable electro-optic fiber modulator. Maximum population transfer occurs at a lattice modulation frequency of 38.768610(30) GHz, in close agreement with calculations. We briefly explain the theoretical background of the new spectroscopic method, show experimental results and discuss applications.\\[4pt] [1] S.E. Anderson, K.C. Younge, and G. Raithel, Phys. Rev. Lett., 107, 263001 (2011)   

Characterization of Rydberg-polariton bound states

Recent experiments have realized strong interactions between single photons by coupling them to Rydberg atoms in a cold gas. In the presence of an additional ``coupling'' field, the ``probe'' photons deform into Rydberg polaritons, propagate slowly in the medium with a finite effective mass, and interact strongly with each other. For an off-resonant coupling, the interaction is conservative and, in the attractive regime, supports bound states of two, three, or more polaritons. We explore theoretically and experimentally the properties of these bound states and characterize their evolution, both for finite pulses and continuous input, with two and more photons.   

Rydberg states via CPmmW spectroscopy

Rydberg-Rydberg transitions of Ca atoms are directly observed by chirped-pulse millimeter-wave spectroscopy, which is a form of broadband, high-resolution, free induction decay (FID) spectroscopy with accurate relative intensities. At moderate to high number densities ($\sim10^6cm^{-3}$), interactions between many Rydberg atoms are mediated by an AC electric field, absorbing and radiating cooperatively. A semiclassical model describes several significant time-domain and frequency-domain cooperative effects in two-level systems and $\Lambda$-type three-level systems. Experimental evidence that supports this model will be discussed. A new experiment, employing the buffer gas cooling technique has been constructed and I expect to present preliminary results. In partically, the $>$100-fold increase in number density will permit study of ``pure electronic'' spectra of Rydberg molecules, such as BaF. We expect to produce $10^8$ state selected core-nonpenetrating Rydberg molecules in a single pulse of a laser-laser-mm-wave excitation sequence.   

Microwave-induced two-photon Autler-Townes splitting in Rydberg EIT

We study one- and two-photon microwave transitions between $^{85}$Rb Rydberg states using electromagnetically induced transparency (EIT) in a Rb vapor cell. We generate a narrow EIT transparency window for a weak probe laser tuned to the $5S_{1/2} \rightarrow 5P_{3/2}$ transition using a strong coupling laser that is resonant with a $5P_{3/2} \rightarrow$ Rydberg transition. In addition, the optically driven Rydberg level is coupled to a neighboring one with microwaves. The Rydberg-Rydberg state coupling manifests in an Autler-Townes splitting of the EIT resonance, which is used to measure Rabi frequencies and field strengths. We investigate Autler-Townes splitting on the one-photon $62S_{1/2} - 62P_{3/2}$ transition, as well as on the $62S_{1/2} - 63S_{1/2}$ and the $62D_{5/2} - 63D_{5/2}$ two-photon transitions. Our results suggest this method could find applications in precision field-strength measurements of high-power microwave and THz radiation sources.   

Quantum many-body physics of interacting photons

We study stationary light of massive photons emerging in a gas of interacting atoms via electromagnetically induced transparency. Path integral Monte Carlo simulations permit an approximation-free determination of the equilibrium phases of the resulting two-component system composed of photons and strongly interacting spin waves. Using this approach we identify a range of interesting quantum phases for varying coupling strengths between the two components, such as photonic superfluids that develop long-range diagonal order for certain parameters. An experimental realization via strongly interacting Rydberg gases will also be discussed.   

Detection of barium 6sng to 6snh, 6sni and 6snk microwave transitions using selective excitation to autoionizing states

In this experiment, we measure the $6sng\longrightarrow 6snh$, $6sni$ and $6snk$, $15\le n\le18$, microwave transitions of barium. The high angular momentum Rydberg states of barium are detected by the selective laser excitation to the autoionizing states. This detection technique is based on the difference in the optical cross sections of the $6snl\longrightarrow6p_{1/2}nl$ and $6snl^{\prime}\longrightarrow 6p_{1/2}nl^{\prime}$ isolated core excitation (ICE) transitions where the outermost electron remains a spectator during the excitation. We analyze the measured data jointly with the data from the previous work of Gallagher et al.\footnote{T. F. Gallagher, R. Kachru, and N. H. Tran, Phys. Rev. A 26, 2611 (1982).} and Snow and Lundeen\footnote{E. L. Snow, and S. R. Lundeen, Phys. Rev. A 76, 052505 (2007).} using the non-adiabatic core polarization model. We extract the dipole ($\alpha_d$) and quadrupole ($\alpha_q$) polarizabilities of barium to be $\alpha_d=124.82(12)\;a_0^3$ and $\alpha_q=2517(18)\;a_0^5$, respectively. The results indicate that the detection technique provides an alternative and reliable way to experimentally extract the values of the ionic dipole and quadrupole polarizabilities of the alkaline-earth atoms.   

Population transfer collisions involving nD Rydberg atoms in a CO$_{2}$ optical dipole trap

There has been an increasing interest in cold Rydberg atoms over the last several years. The primary reason for this attention is that interactions between Rydberg atoms are strong and lead to many interesting and useful phenomena, which require high atomic density samples. In this work, we have loaded Rb atoms into a CO$_{2}$ optical dipole trap. After the loading, we turn off the dipole trap and excite the Rydberg state using a combination of two cw laser beams at 780 nm and 480 nm respectively. Finally, the Rydberg atoms are detected using pulsed field ionization technique. By analyzing the electrons signal, we can study the population transfer from the nD state to the (n$+$2)P as a function of the atomic density for 37$\le $n$\le $ 45. As the atomic density increases, the excitation of the nD state saturates, suggesting the occurrence of dipole blockade. Nevertheless, the (n$+$2)P is quadratically proportional to the nD population. We have also investigated the role of a dc electrical field in such process. This work was supported by Fapesp and INCT-IQ.   

Spin-Polarized Hydrogen Rydberg Time-of-Flight: Experimental Measurement of the Velocity-Dependent H Atom Spin Polarization

We have developed a new experimental methodology allowing direct detection of the velocity dependent spin-polarization of hydrogen atoms produced in molecular photodissociation. The technique, which we term Spin-Polarized Hydrogen Rydberg Time-of-Flight, employs a double- resonance excitation scheme and experimental geometry which yields the two coherent laboratory-frame anisotropy parameters 1 and 1 as a function of recoil speed for scattering perpendicular to the laser propagation direction. The technique, apparatus, and optical layout we employ is described here in detail and demonstrated in application to HBr and DBr photolysis at 213 nm. We also discuss the theoretical foundation for the approach, as well as the resolution and sensitivity we achieve.   

Two-photon adiabatic passage for excitation of Rydberg states

We study the excitation of the Rb atom to a Rydberg state in the blockaded regime and the excitation of two Rb atoms to Rydberg states in the regime of a weak blockade. For a single atom excitation, we describe a technique to realize two-photon adiabatic passage involving $5S_{1/2}$, $5P_{1/2,3/2}$ and the Rydberg state modeled by a three level ladder system. The technique is based on using a pair of linearly chirped pulses, initially detuned off the one-photon resonance and satisfying the two-photon resonance condition at the time of peak pulse intensity. Secondly, we consider the excitation of two atoms to Rydberg states in the presence of dipole-dipole interaction between them. We find that an efficient excitation to the two-atom Rydberg state can be realized with two-photon adiabatic passage using chirped pulses with equal Rabi frequencies and chirp rates. High transfer efficiency can be achieved for pulse Rabi frequencies $\Omega_{p,S}\ge V_{int}$, where $\Omega_{p,S}$ is the Rabi frequency of the pump and Stokes pulses and $V_{int}$ is the Rydberg-Rydberg interaction strength. The use of chirped pulses for performing two-photon transitions has a benefit of passing through the two-photon resonances whose frequencies are known only to a certain level of approximation.   

Probing Atom-Surface Interactions Using Rb Rydberg Atoms

Alkali Rydberg atoms close to a dielectric surface can resonantly excite surface phonon-polaritons, by decaying into a nearby Rydberg state. In our experiment, rubidium atoms are trapped in a mirror-MOT and are brought close to a dielectric surface in a magnetic trap, where Rydberg excitiation takes place. We are exploring the controlled coupling of Rydberg atoms to surfaces such as quartz, LaF$_3$, and PPLN. Engineered materials such as PPLN allow for control over surface phonon-polariton resonance frequencies and bandwidths, enabling increased coupling strength. Engineering the surface allows for coupling to surface phonon-polaritions at much greater distances.