Single Hyperfine State Research Articles

Resolved Raman sideband cooling of a single optically trapped cesium atom.

We developed a resolved Raman sideband cooling scheme that can efficiently prepare a single optically trapped cesium (Cs) atom in its motional ground states. A two-photon Raman process between two outermost Zeeman sublevels in a single hyperfine state is applied to reduce the phonon number. Our scheme is less sensitive to the variation in the magnetic field than the commonly used scheme where the two outermost Zeeman sublevels belonging to the two separate ground hyperfine states are taken. Fast optical pumping with less spontaneous emission guarantees the efficiency of the cooling process. After cooling for 50 ms, 82% of the Cs atoms populate their three-dimensional ground states. Our scheme improves the long-term stability of Raman sideband cooling in the presence of magnetic field drift and is thus suitable for cooling other trapped atoms or ions with abundant magnetic sublevels.

Optical pumping effects on high-contrast Rydberg electromagnetically induced transparency

We discuss the interplay between high-contrast Rydberg-state electromagnetically induced transparency (EIT) and optical pumping (OP) in a thermal 87Rb medium. By pumping the population to one single hyperfine state, we can enhance the interaction strength and, in principle, amplify the EIT peak. According to the measurements, the EIT peak height can be improved by a factor of two or reduced by one order of magnitude, and linewidth was slightly narrowed by the pumping effect. The EIT feature is predicted quantitatively using a Doppler-free non-perturbation numerical calculation. In both simulations and measurements, Rydberg-EIT enhancement through OP is dependent on the intensity of the probe field and the optical density. Our work clarifies the underlying mechanisms of optical pumping, making relevant studies useful in developing Rydberg-based electrometry.

Elastic rate coefficients forLi+H2collisions in the calibration of a cold-atom vacuum standard

Ongoing efforts at the National Institute of Standards and Technology in creating a cold-atom vacuum standard device have prompted theoretical investigations of atom-molecule collision processes that characterize its operation. Such a device will operate as a primary standard for the ultrahigh-vacuum and extreme-high-vacuum regimes. This device operates by relating loss of ultracold lithium atoms from a conservative trap by collisions with ambient atoms and molecules to the background density and thus pressure through the ideal gas law. The predominant background constituent in these environments is molecular hydrogen H2. We compute the relevant Li+H2 Born-Oppenheimer potential energy surface, paying special attention to its uncertainty. Coupled-channel calculations are then used to obtain total rate coefficients, which include momentum-changing elastic and inelastic processes. We find that inelastic rotational quenching of H2 is negligible near room temperature. For a (T = 300)-K gas of H2 and 1.0-μK gas of Li atoms prepared in a single hyperfine state, the total rate coefficients are 6.0(1) × 10-9 cm3/s for both 6Li and 7Li isotopes, where the number in parentheses corresponds to a one-standard-deviation combined statistical and systematic uncertainty. We find that a 10-K increase in the H2 temperature leads to a 1.9% increase in the rate coefficients for both isotopes. For Li temperatures up to 100 μK, changes are negligible. Finally, a semiclassical Born approximation significantly overestimates the rate coefficients. The difference is at least ten times the uncertainty of the coupled-channel result.

Coherence time of over a second in a telecom-compatible quantum memory storage material

Quantum memories for light will be essential elements in future long-range quantum communication networks. These memories operate by reversibly mapping the quantum state of light onto the quantum transitions of a material system. For networks, the quantum coherence times of these transitions must be long compared to the network transmission times, approximately 100 ms for a global communication network. Due to a lack of a suitable storage material, a quantum memory that operates in the 1550 nm optical fiber communication band with a storage time greater than 1 us has not been demonstrated. Here we describe the spin dynamics of $^{167}$Er$^{3+}:$Y$_{2}$SiO$_{5}$ in a high magnetic field and demonstrate that this material has the characteristics for a practical quantum memory in the 1550 nm communication band. We observe a hyperfine coherence time of 1.3 seconds. Further, we demonstrate efficient optical pumping of the entire ensemble into a single hyperfine state, the first such demonstration in a rare-earth system and a requirement for broadband spin-wave storage. With an absorption of 70 dB/cm at 1538 nm and $\Lambda$-transitions enabling spin-wave storage, this material is the first candidate identified for an efficient, broadband quantum memory at telecommunication wavelengths.

Controlling the Hyperfine State of Rovibronic Ground-State Polar Molecules

We report the preparation of a rovibronic ground-state molecular quantum gas in a single hyperfine state and, in particular, the absolute lowest quantum state. This addresses the last internal degree of freedom remaining after the recent production of a near quantum degenerate gas of molecules in their rovibronic ground state, and provides a crucial step towards full control over molecular quantum gases. We demonstrate a scheme that is general for bialkali polar molecules and allows the preparation of molecules in a single hyperfine state or in an arbitrary coherent superposition of hyperfine states. The scheme relies on electric-dipole, two-photon microwave transitions through rotationally excited states and makes use of electric nuclear quadrupole interactions to transfer molecular population between different hyperfine states.

Scheme for generating a sequence of single photons of alternating polarization

Single-photons of well-defined polarization that are deterministically generated in a single spatio-temporal field mode are the key to the creation of multi-partite entangled states in photonic networks. Here, we present a novel scheme to produce such photons from a single atom in an optical cavity, by means of vacuum-stimulated Raman transitions between the Zeeman substates of a single hyperfine state. Upon each transition, a photon is emitted into the cavity, with a polarization that depends on the direction of the Raman process.

Superfluidity ofp-wave ands-wave atomic Fermi gases in optical lattices

We consider p-wave pairing of single hyperfine state and s-wave pairing of two hyperfine states ultracold atomic gases trapped in quasi-two-dimensional optical lattices. First, we analyse superfluid properties of p-wave and s-wave symmetries in the strictly weak coupling BCS regime where we discuss the order parameter, chemical potential, critical temperature, atomic compressibility and superfluid density as a function of filling factor for tetragonal and orthorhombic optical lattices. Second, we analyse superfluid properties of p-wave and s-wave superfluids in the evolution from BCS to BEC regime at low temperatures ($T \approx 0$), where we discuss the changes in the quasiparticle excitation spectrum, chemical potential, atomic compressibility, Cooper pair size and momentum distribution as a function of filling factor and interaction strength for tetragonal and orthorhombic optical lattices.

Quantum-based microwave power measurements: Proof-of-concept experiment

We present an initial proof-of-concept experiment to measure microwave power based on quantum-mechanical principles. Ground-state cesium atoms exposed to microwaves at 9.192 631 770 GHz oscillate between two hyperfine states at a rate that is proportional to the rf magnetic field strength. This provides a quantum-based method of measuring rf field strength that depends only on the fundamental parameters in the proportionality constant. A small fountain apparatus was used to prepare laser-cooled cesium atoms in a single hyperfine state, which were then launched through a cylindrical cavity operating in the TE011 mode. After passing through the cavity, the fraction of atoms in the two hyperfine states was measured. Rabi oscillations between the two states were observed as a function of microwave field strength. The scaling with field strength and with time in the cavity agreed with theory to within 0.4%. The field strength in the cavity was used, together with measured S parameters, to determine the microwave power incident at a reference plane outside the fountain apparatus. The difference between the quantum-based microwave power measurement and a traditional microwave power measurement was less than 5% of the measured power.

Schematic phase diagram and collective excitations in the collisional regime for trapped boson–fermion mixtures at zero temperature

We discuss the ground state and the small-amplitude excitations of dilute boson–fermion mixtures confined in spherical harmonic traps at T=0, assuming repulsive boson–boson interactions and with each component being in a single hyperfine state. From previous studies of the equilibrium density profiles we propose a schematic phase diagram in a plane defined by the variables a bf/ a bb and a bb k f (0), where a bb and a bf are the boson–boson and boson–fermion scattering lengths and k f (0) is the Fermi wave number at the centre of the trap. With this background we turn to the equations of motion for density fluctuations in the collisional regime and discuss some general features of the eigenmodes. We display analytic solutions for sound waves in a quasi-homogeneous mixture and for surface modes at weak fermion–boson coupling.

β-NMR on single-crystal surfaces: Method

A new and highly sensitive β-NMR method to study adsorbates on single-crystal surfaces is presented. Contrary to conventional NMR, this method combines (via optical pumping) a high, nonthermal polarization of the adsorbed species with a particle counting method. Here, the β-active isotope 8Li is produced in the nuclear reaction D(7Li, 8Li)H using a high-pressure deuterium gas target. The fast 8Li ions are subsequently implanted into a hot graphite block where they thermally diffuse to the surface and desorb. The desorbing thermal velocity 8Li atoms are shaped into an atomic beam. Using a frequency modulated laser beam the atoms are transferred into a single hyperfine state by optical pumping. The so-achieved nuclear polarization of the atoms (before impinging on the single-crystal surface) is approximately 0.8 and can be switched in sign by an adiabatic high-frequency transition. The atoms adsorb on the single-crystal surface and their polarization—either freely decaying on the surface or driven by an external radio-frequency field—is observed via the decay asymmetry of the nuclear β-decay of the 8Li nuclei. This method realizes an effective sensitivity to the active NMR isotope of 5×103 atoms/cm2, which corresponds to a stationary coverage of 10−11 of a monolayer. The typical electron count rate is 400 Hz during β-NMR experiments.

High density polarized hydrogen gas target for storage rings

A target of gaseous polarized hydrogen was formed by injecting polarized hydrogen atoms (produced by Stern–Gerlach spin separation) into a storage cell consisting of a cylindrical tube open at both ends. The target was placed in a storage ring to study the target characteristics (nuclear polarization, target thickness, radiation resistance). A weak transverse guide field (5 G) was applied to define the polarization direction. When atoms in a single hyperfine state were selected, the nuclear polarization of the target was measured to be 0.80±0.02. The areal density of the target under these conditions was (5.5±0.2)×1013 H/cm2, while for two spin states (applicable to experiments in high energy rings where a strong magnetic field can be applied to the target) the target thickness was found to be (8.2±0.3)×1013 H/cm2. The target polarization was unaffected by prolonged exposure of the target to beams up to 1 mA.

Precise Proton-Polarization Standards Determined with a Lamb-Shift Ion Source Incorporating a Nuclear Spin Filter

The polarization of an 8-12-MeV proton beam produced by a Lamb-shift ion source has been determined with 0.4% absolute accuracy by an atomic-beam technique. The procedure, which involves selection of a single hyperfine state of fast $\mathrm{H}(2s)$ atoms, is ideally suited to routine monitoring of beam polarization. Absolute $p\ensuremath{-}^{4}\mathrm{He}$ elastic-scattering analyzing powers measured with the calibrated beam are reported, and existing double-scattering data are compared with these results.

Measurement of the2S122−2P322Energy Separation (ΔE−S) in Hydrogen (n=2)

We have measured the $2{S}_{\frac{1}{2}}\ensuremath{-}2{P}_{\frac{3}{2}}$ energy separation ($\ensuremath{\Delta}E\ensuremath{-}S$) in the $n=2$ state of atomic hydrogen by an atomic-beam radio-frequency method. We used a beam of metastable atoms in the single hyperfine state ${\ensuremath{\beta}}_{A}(F,{m}_{F}=0,0)$. The electric dipole transitions ${\ensuremath{\beta}}_{A}\ensuremath{-}b(F,{m}_{F}=1,+1)$ and ${\ensuremath{\beta}}_{A}\ensuremath{-}d(F,{m}_{F}=1,\ensuremath{-}1)$ were observed at fixed frequencies by sweeping the Zeeman magnetic field parallel to the beam axis. Measurements of the frequencies of the rf field used to drive the transition and the magnetic fields at the line centers of the resonance curves, along with the theory of Zeeman splitting were used to determine the zero-field splitting ($\ensuremath{\Delta}E\ensuremath{-}S$). Our final value of ($\ensuremath{\Delta}E\ensuremath{-}S$) is 9911.250 \ifmmode\pm\else\textpm\fi{} 0.063 MHz, where the quoted uncertainty is one average deviation from the mean. Using the revised experimental value of the Lamb shift, ${S}_{H}=1057.90\ifmmode\pm\else\textpm\fi{}0.10$ MHz, we obtain $\ensuremath{\Delta}E=10 969.15+0.12$ MHz. The corresponding value for ${\ensuremath{\alpha}}^{\ensuremath{-}1}$ is 137.0356 \ifmmode\pm\else\textpm\fi{} 0.0007.