We present a novel method for reducing the inhomogeneous frequency broadening in the hyperfine splitting of the ground state of optically trapped atoms. This reduction is achieved by the addition of a weak light field, spatially mode-matched with the trapping field and whose frequency is tuned in-between the two hyperfine levels. We experimentally demonstrate the new scheme with Rb 85 atoms, and report a 50-fold narrowing of the rf spectrum.
We develop a method for extracting the physical parameters of interest for a dipole trapped cold atomic ensemble. This technique uses the spatially dependent ac-Stark shift of the trap itself to project the atomic distribution onto a light-shift broadened transmission spectrum. We develop a model that connects the atomic distribution with the expected transmission spectrum. We then demonstrate the utility of the technique by deriving the temperature, trap depth, lifetime, and trapped atom number from data that was taken in a single shot experimental measurement.
We investigate the rovibrational population redistribution of polar molecules in the electronic ground state induced by spontaneous emission and blackbody radiation. As a model system we use optically trapped LiCs molecules formed by photoassociation in an ultracold two-species gas. The population dynamics of vibrational and rotational states is modeled using an ab-initio electric dipole moment function and experimental potential energy curves. Comparison with the evolution of the v"=3 electronic ground state yields good qualitative agreement. The analysis provides important input to assess ap…
We demonstrate an optically pumped $^{87}$Rb magnetometer in a microfabricated vapor cell based on a zero-field dispersive resonance generated by optical modulation of the $^{87}$Rb ground state energy levels. The magnetometer is operated in the spin-exchange relaxation-free regime where high magnetic field sensitivities can be achieved. This device can be useful in applications requiring array-based magnetometers where radio frequency magnetic fields can induce cross-talk among adjacent sensors or affect the source of the magnetic field being measured.
Electromagnetically induced absorption (EIA) was observed on a sample of $% ^{85}Rb$ in a magneto-optical trap using low intensity cw copropagating pump and probe optical fields. At moderate trapping field intensity, the EIA spectrum is determined by the Zeeman effect produced on the atomic ground-state by the trapping quadrupolar magnetic field. The use of EIA spectroscopy for the magnetic field mapping of cold atomic samples is illustrated.
We report measurement of inelastic loss in dense and cold metastable ytterbium (Yb[$^3P_2$]). Use of an optical far-off-resonance trap enables us to trap atoms in all magnetic sublevels, removing multichannel collisional trap loss from the system. Trapped samples of Yb[$^3P_2$] are produced at a density of 2$\times10^{13}$ cm$^{-3}$ and temperature of 2 $μ$K. We observe rapid two-body trap loss of Yb[$^3P_2$] and measure the inelastic collision rate constant 1.0(3)$\times10^{-11}$ cm$^3$s$^{-1}$. The existence of the fine-structure changing collisions between atoms in the $^3P_2$ state is stro…
We investigate the dynamical process of optically trapped X$^{1}$$Σ$$^{+}$ (v" = 0) state $^{85}$Rb$^{133}$Cs molecules distributing in J" = 1 and J" = 3 rotational states. The considered molecules, formed from short-range photoassociation of mixed cold atoms, are subsequently confined in a crossed optical dipole trap. Based on a phenomenological rate equation, we provide a detailed study of the dynamics of $^{85}$Rb$^{133}$Cs molecules during the loading and holding processes. The inelastic collisions of $^{85}$Rb$^{133}$Cs molecules in the X$^{1}$$Σ$$^{+}$ (v" = 0, J" = 1 and J" = 3) states …
We report on the realization of an ultracold (<25~muK) mixture of rubidium ({87}Rb) and metastable triplet helium ({4}He) in an optical dipole trap. Our scheme involves laser cooling in a dual-species magneto-optical trap, simultaneous MW- and RF-induced forced evaporative cooling in a quadrupole magnetic trap, and transfer to a single-beam optical dipole trap. We observe long trapping lifetimes for the doubly spin-stretched spin-state mixture and measure much shorter lifetimes for other spin-state combinations. We discuss prospects for realizing quantum degenerate mixtures of alkali-metal and…
A means for precise experimental characterization of the dielectric susceptibility of an atomic gas inside and optical cavity is important for design and operation of quantum light matter interfaces, particularly in the context of quantum information processing. Here we present a numerically optimised theoretical model to predict the spectral response of an atom-filled cavity, accounting for both homogeneous and inhomogeneous broadening at high optical densities. We investigate the regime where the two broadening mechanisms are of similar magnitude, which makes the use of common approximations…
We report on a scheme to cool and compress trapped clouds of highly magnetic 52Cr atoms. This scheme combines sequences of gray molasses, which freeze the velocity distribution, and free evolutions in the (close to) harmonic trap, which periodically exchange the spatial and velocity degrees of freedom. Taken together, the successive gray molasses pulses cool all external degrees of freedom, which leads to an increase of the phase-space density (PSD) by a factor of about 250, allowing to reach a high final PSD of about 1.7*10^-3. These experiments are performed within an optical dipole trap, in…
We propose a scheme that combines velocity-selective coherent population trapping (CPT) and Raman sideband cooling (RSC) for subrecoil cooling of optically trapped atoms outside the Lamb-Dicke regime. This scheme is based on an inverted $\mathsf{Y}$ configuration in an alkali-metal atom. It consists of a $Λ$ formed by two Raman transitions between the ground hyperfine levels and the $D$ transition, allowing RSC along two paths and formation of a CPT dark state. Using state-dependent difference in vibration frequency of the atom in a circularly polarized trap, we can tune the $Λ$ to make only t…
We study binary collisions of metastable calcium atoms ($^{40}$Ca) in an optical dipole trap. Collisions between $^{3}$P$_{0}$-atoms and between $^{3}$P$_{0}$ and $^{1}$S$_{0}$-atoms are considered. In the former case, the elastic and inelastic collision parameters are found to be $5.4\times 10^{-11}\,\mathrm{cm}^{3}\mathrm{s}^{-1}$ and $3.6\times 10^{-11}\,\mathrm{cm}^{3}\mathrm{s}^{-1}$, respectively. A fraction of the collisions between $^{3}$P$_{0}$-atoms is found to produce cold trapped atoms in the singlet $^{1}$S$_{0}$ state, suggesting that the internal energy for these collisions is d…
Ultra-cold atoms trapped in an optical dipole trap and prepared in a coherent superposition of their hyperfine ground states, decohere as they interact with their environment. We demonstrate than the loss in coherence in an "echo" experiment, which is caused by mechanisms such as Rayleigh scattering, can be suppressed by the use of a new pulse sequence. We also show that the coherence time is then limited by mixing to other vibrational levels in the trap and by the finite lifetime of the internal quantum states of the atoms.
We report the production of $^{87}$RbCs Feshbach molecules in a crossed-beam dipole trap. A mixture of $^{87}$Rb and $^{133}$Cs is cooled close to quantum degeneracy before an interspecies Feshbach resonance at 197\,G is used to associate up to $\sim5000$ molecules with a temperature of $\sim300$\,nK. The molecules are confined in the dipole trap with a lifetime of 0.21(1)\,s, long enough for future experiments exploring optical transfer to the absolute ground state. We have measured the magnetic moment of the Feshbach molecules in a magnetic bias field range between 181 and 185\,G to demonstr…
Calcium monofluoride (CaF) molecules are loaded into an optical dipole trap (ODT) and subsequently laser cooled within the trap. Starting with magneto-optical trapping, we sub-Doppler cool CaF and then load $150(30)$ CaF molecules into an ODT. Enhanced loading by a factor of five is obtained when sub-Doppler cooling light and trapping light are on simultaneously. For trapped molecules, we directly observe efficient sub-Doppler cooling to a temperature of $60(5)$ $μ\text{K}$. The trapped molecular density of $8(2)\times10^7$ cm$^{-3}$ is an order of magnitude greater than in the initial sub-Dop…
We perform spectroscopy on the hyperfine splitting of $^{85}$Rb atoms trapped in far-off-resonance optical traps. The existence of a spatially dependent shift in the energy levels is shown to induce an inherent dephasing effect, which causes a broadening of the spectroscopic line and hence an inhomogeneous loss of atomic coherence at a much faster rate than the homogeneous one caused by spontaneous photon scattering. We present here a number of approaches for reducing this inhomogeneous broadening, based on trap geometry, additional laser fields, and novel microwave pulse sequences. We then sh…
We report on the realization of a stable mixture of ultracold lithium and ytterbium atoms confined in a far-off-resonance optical dipole trap. We observe sympathetic cooling of 6Li by 174Yb and extract the s-wave scattering length magnitude |a6Li-174Yb| = (13 \pm 3)a0 from the rate of inter-species thermalization. Using forced evaporative cooling of 174Yb, we achieve reduction of the 6Li temperature to below the Fermi temperature, purely through inter-species sympathetic cooling.
We report the finding of "triply magic" conditions (the doubly magic frequency-intensity conditions of an optical dipole trap plus the magic magnetic field) for the microwave transitions of optically trapped alkali-metal atoms. The differential light shift (DLS) induced by a degenerate two-photon process is adopted to compensate a DLS associated with the one-photon process. Thus, doubly magic conditions for the intensity and frequency of the optical trap beam can be found. Moreover, the DLS decouples from the magnetic field in a linearly polarized optical dipole trap, so that the magic conditi…
Optical trapping of molecules with long coherence times is crucial for many protocols in quantum information and metrology. However, the factors that limit the lifetimes of the trapped molecules remain elusive and require improved understanding of the underlying molecular structure. Here we show that measurements of vibronic line strengths in weakly and deeply bound $^{88}$Sr$_2$ molecules, combined with \textit{ab initio} calculations, allow for unambiguous identification of vibrational quantum numbers. This, in turn, enables the construction of refined excited potential energy curves that in…
Cold inelastic collisions between confined cesium (Cs) atoms and Cs$\_2$ molecules are investigated inside a CO$\_2$ laser dipole trap. Inelastic atom-molecule collisions can be observed and measured with a rate coefficient of $\sim 2.5 \times 10^{-11} $cm$^3$ s$^{-1}$, mainly independent of the molecular ro-vibrational state populated. Lifetimes of purely atomic and molecular samples are essentially limited by rest gas collisions. The pure molecular trap lifetime ranges 0,3-1 s, four times smaller than the atomic one, as is also observed in a pure magnetic trap. We give an estimation of the i…
A reaction microscope (ReMi) has been combined with a magneto-optical trap (MOT) for the kinematically complete investigation of atomic break-up processes. With the novel MOTReMi apparatus, the momentum vectors of the fragments of laser-cooled and state-prepared lithium atoms are measured in coincidence and over the full solid angle. %Earlier attempts to realize this combination failed due to intrinsic incompatibilities of the magnetic fields required for MOT and ReMi. The first successful implementation of a MOTReMi could be realized due to an optimized design of the present setup, a nonstand…
Doppler broadening plays an important role in laser rovibrational spectroscopy of trapped deuterated molecular hydrogen ions (HD$^+$), even at the millikelvin temperatures achieved through sympathetic cooling by laser-cooled beryllium ions. Recently, Biesheuvel \textit{et al.} \cite{Biesheuvel2016} presented a theoretical lineshape model for such transitions which not only considers linestrengths and Doppler broadening, but also the finite sample size and population redistribution by blackbody radiation, which are important in view of the long storage and probe times achievable in ion traps. H…
Optically trapped ensembles are of crucial importance for frequency measurements and quantum memories, but generally suffer from strong dephasing due to inhomogeneous density and light shifts. We demonstrate a drastic increase of the coherence time to 21 s on the magnetic field insensitive clock transition of Rb-87 by applying the recently discovered spin self-rephasing. This result confirms the general nature of this new mechanism and thus shows its applicability in atom clocks and quantum memories. A systematic investigation of all relevant frequency shifts and noise contributions yields a s…
In this work, we measure the properties of ensembles of rubidium atoms trapped in solid neon that are relevant for use as quantum sensors of magnetic fields: the spin coherence of the trapped atoms and the ability to optically control and measure their spin state. We use the rubidium atoms as an AC magnetometer (by employing an appropriate dynamical decoupling sequence) and demonstrate NMR detection of Ne-21 atoms co-trapped in the neon matrix.
A Bose-Einstein condensate (BEC) with periodically modulated interactions (PMI) has emerged as a novel kind of periodic superfluid, which has been recently experimentally created using optical Feshbach resonance. In this paper, we are motivated to investigate the superfluidity of a BEC with PMI trapped in an optical lattice (OL). In particular, we explore the effects of PMI on the sound speed and the dynamical structure factor of the model system. Our numerical results, combined with the analytical results in both the weak-potential limit and the tight-binding limit, have shown that the PMI ca…
We present precision spectroscopy on electrically trapped formaldehyde (H$_2$CO), demonstrating key attributes which will enable molecular spectroscopy with unprecedented precision. Our method makes use of a microstructured electric trap with homogeneous fields in the trap center and rotational transitions with minimal Stark broadening at a 'magic' offset electric field. Using molecules cooled to the low millikelvin temperature regime via optoelectrical Sisyphus cooling, we reduce Stark broadening on the $J=5\leftarrow4$ ($K=3$) transition at 364 GHz to well below 1 kHz, observe Doppler-limite…
Two-dimensional crystals of ions stored in Penning traps are a leading platform for quantum simulation and sensing experiments. For small amplitudes, the out-of-plane motion of such crystals can be described by a discrete set of normal modes called the drumhead modes, which can be used to implement a range of quantum information protocols. However, experimental observations of crystals with Doppler-cooled and even near-ground-state-cooled drumhead modes reveal an unresolved drumhead mode spectrum. In this work, we establish in-plane thermal fluctuations in ion positions as a major contributor …
We perform Raman spectroscopy of optically trapped non interacting \Rb atoms, and observe revivals of the atomic coherence at integer multiples of the trap period. The effect of coherence control methods such as echo and dynamical decoupling is investigated experimentally, analytically and numerically, along with the effect of the anharmonicity of the trapping potential. The latter is shown to be responsible for incompleteness of the revivals. Coherent Raman control of trapped atoms can be useful in the context of free-oscillation atom intefrerometry and spatial multi-mode quantum memory.
Rapid progress in cooling and trapping of molecules has enabled first experiments on high resolution spectroscopy of trapped diatomic molecules, promising unprecedented precision. Extending this work to polyatomic molecules provides unique opportunities due to more complex geometries and additional internal degrees of freedom. Here, this is achieved by combining a homogeneous-field microstructured electric trap, rotational transitions with minimal Stark broadening at a 'magic' offset electric field, and optoelectrical Sisyphus cooling of molecules to the low millikelvin temperature regime. We …
We propose a novel cooling scheme for realising single photon sideband cooling on particles trapped in a state-dependent optical potential. We develop a master rate equation from an ab-initio model and find that in experimentally feasible conditions it is possible to drastically reduce the average occupation number of the vibrational levels by applying a frequency sweep on the cooling laser that sequentially cools all the motional states. Notably, this cooling scheme works also when a particle experiences a deeper trap in its internal ground state than in its excited state, a condition for whi…
Optically trapped dielectric objects are well suited for reaching the quantum regime of their center of mass motion in an ultra-high vacuum environment. We show that ground state cooling of an optically trapped nanosphere is achievable when starting at room temperature, by sympathetic cooling of a cold atomic gas optically coupled to the nanoparticle. Unlike cavity cooling in the resolved sideband limit, this system requires only a modest cavity finesse and it allows the cooling to be turned off, permitting subsequent observation of strongly-coupled dynamics between the atoms and sphere. Nanos…
Exponential enhancement of sensitivity in Ramsey interferometry with optically thick ensemble of atoms
Kazan Quantum Center, Kazan National Research Technical University n.a. A.N. Tupolev-KAI（喀山量子中心，喀山国立研究技术大学（A.N. 图波列夫-CAI））；Department of Physics, McGill University（麦吉尔大学物理系）
We show that nonlinear dynamics in diode lasers with optical injection leads to frequency tunable microwave sidebands which are suitable for atomic physics experiments. We demonstrate the applicability of the sidebands in an experiment where rubidium atoms are magneto-optically trapped with both the trap and the re-pump optical frequencies derived from one optically injected laser. We find linewidth narrowing in the optical spectrum of the injected laser at both the injection frequency and the sideband frequency. With strong optical injection which leads to frequency locking we find a complete…
We observe a sixfold Purcell broadening of the D$_2$ line of an optically trapped $^{87}\text{Rb}$ atom strongly coupled to a fiber cavity. Under external illumination by a near-resonant laser, up to $90\%$ of the atom's fluorescence is emitted into the resonant cavity mode. The sub-Poissonian statistics of the cavity output and the Purcell enhancement of the atomic decay rate are confirmed by the observation of a strongly narrowed antibunching dip in the photon autocorrelation function. The photon leakage through the higher-transmission mirror of the single-sided resonator is the dominant con…
We demonstrate the cancellation of the differential ac Stark shift of the microwave hyperfine clock transition in trapped $^{87}$Rb atoms. Recent progress in metrology exploits so-called "magic wavelengths," whereby an atomic ensemble can be trapped with laser light whose wavelength is chosen so that both levels of an optical atomic transition experience identical ac Stark shifts. Similar magic-wavelength techniques are not possible for the microwave hyperfine transitions in the alkalis, due to their simple electronic structure. We show, however, that ac Stark shift cancellation is indeed achi…
