Spin-exchange collisions in alkali vapors have been at the basis of several fundamental and applied investigations, like nuclear structure studies and tests of fundamental symmetries, ultra-sensitive atomic magnetometers, magnetic resonance and bio-magnetic imaging. Spin-exchange collisions cause loss of spin coherence, and concomittantly produce spin noise, both phenomena being central to quantum metrology. We here develop the quantum trajectory picture of spin-exchange collisions, consistent with their long-standing ensemble description using density matrices. We then use quantum trajectories to reveal the nature of spin-noise correlations that spontaneously build up in multi-species atomic vapors, frequently utilized in the most sensitive spin measurements.
A quantum network which consists of several components should ideally work on a single physical platform. Neutral alkali atoms have the potential to be very well suited for this purpose due to their electronic structure which involves long lived nuclear spins and very sensitive highly excited Rydberg states. In this paper we describe a fabrication method based on quartz glass to structure arbitrary shapes of microscopic vapor cells. We show that the usual spectroscopic properties known from macroscopic vapor cells are almost unaffected by the strong confinement.
Ultralow-power diode-laser radiation is employed to induce photodesorption of cesium from a partially transparent thin-film cesium adsorbate on a solid surface. Using resonant Raman spectroscopy, we demonstrate that this photodesorption process enables an accurate local optical control of the density of dimer molecules in alkali-metal vapors.
We explore experimentally quantum non-demolition (QND) measurements of atomic spin in a hot potassium vapor in the presence of spin-exchange relaxation. We demonstrate a new technique for back-action evasion by stroboscopic modulation of the probe light. With this technique we study spin noise as a function of polarization for atoms with spin greater than 1/2 and obtain good agreement with a simple theoretical model. We point that in a system with fast spin-exchange, where the spin relaxation rate is changing with time, it is possible to improve the long-term sensitivity of atomic magnetometry…
Spin-exchange collisions in alkali or alkali/noble gas vapors are at the basis of quantum sensing, nucleon structure studies, tests of fundamental symmetries, and medical imaging. We here show that spin-exchange collisions in hot alkali vapors naturally produce strong bipartite entanglement, which we explicitly quantify using the tools of quantum information science. This entanglement is shown to have a lifetime at least as long as the spin-exchange relaxation time, and to directly affect measurable spin noise observables. This is a formal theoretical demonstration that a hot and dense atomic …
We study the zero-field optical spin noise spectra (OSN) for a thermal state hot 87Rb vapor with strong spin exchange coupling. Our main findings are: (1) The OSN spectrum consists of two components representing a positive and a negative hyperfine spin correlation (HSC), the relative power of which varies dramatically with the detuning frequency of the probe. (2) There exist two polar frequencies at which the OSN spectrum is completely polarized with one type of HSC. (3) At the limit of far detuning, the power ratio of the positive and negative HSC component of the OSN is 4:5. (4) The total po…
We demonstrate lifetimes of atomic populations and coherences in excess of 60 seconds in alkali vapor cells with inner walls coated with an alkene material. This represents two orders of magnitude improvement over the best paraffin coatings. Such anti-relaxation properties will likely lead to substantial improvements in atomic clocks, magnetometers, quantum memory, and enable sensitive studies of collisional effects and precision measurements of fundamental symmetries.
We show how a single linearly polarized control field can produce a sharply tunable group velocity of a weak probe field at resonance in a four-level atomic configuration of alkali vapors. The dispersion can be switched from normal to anomalous along with vanishing absorption, just by changing intensity of the resonant control field. In addition, by allowing different intensities of the different polarization components of the control field, the anomalous dispersion can be switched back to the normal. This thereby creates a "valley of anomaly" in group index variation and offers two sets of co…
We introduce an all-glass, vacuum tight, fiber-integrated and alkali compatible spectroscopy device consisting of two conventional optical fibers spliced to each end of a capillary. This is mainly realized through a decentered splicing method allowing refilling of the capillary and controlling the vapor density inside. We analyze the light guidance of the setup through simulations and measurements of the transmission efficiency at different wavelengths and show that filling it with highly reactive alkali metals is possible, and that the vapor density can be controlled reliably.
Alkali vapor cells with antirelaxation coating (especially paraffin-coated cells) have been a central tool in optical pumping and atomic spectroscopy experiments for 50 years. We have discovered a dramatic change of the alkali vapor density in a paraffin-coated cell upon application of an electric field to the cell. A systematic experimental characterization of the phenomenon is carried out for electric fields ranging in strength from 0-8 kV/cm for paraffin-coated cells containing rubidium and cells containing cesium. The typical response of the vapor density to a rapid (duration < 100 ms) cha…
We present an experimental investigation of alkali atom vapor cells coated with a high quality anti-relaxation coating material based on alkenes. The prepared cells with single compound alkene based coating showed the longest spin relaxation times which have been measured up to now with room temperature vapor cells. Suggestions are made that chemical binding of a cesium atom and an alkene molecule by attack to the C=C bond plays a crucial role in such improvement of anti-relaxation coating quality.
We describe and characterize a device for alkali vapor pressure modulation on the 100ms timescale in a single-cell cold atom experiment. Its mechanism is based on optimized heat conduction between a current-modulated alkali dispenser and a heat sink at room temperature. We have studied both the short-term behavior during individual pulses and the long-term pressure evolution in the cell. The device combines fast trap loading and relatively long trap lifetime, enabling high repetition rates in a very simple setup. These features make it particularly suitable for portable atomic sensors.
We demonstrate a method to produce vacuum tight, metal free, bakeable and alkali compatible feedthroughs for optical fibers. The manufacturing process mainly relies on encasing fibers made of fused silica with glass materials with lower melting points by heating. We analyze the vacuum and optical performance of the devices by various methods including helium leak checking and several spectroscopic schemes, among others electromagnetically induced transparency involving Rydberg states.
Spin noise sets fundamental limits to the precision of measurements using spin-polarized atomic vapors, such as performed with sensitive atomic magnetometers. Spin squeezing offers the possibility to extend the measurement precision beyond the standard quantum limit of uncorrelated atoms. Contrary to the current understanding, we show that even in the presence of spin relaxation, spin squeezing can lead to a significant reduction of spin noise, and hence an increase in magnetometric sensitivity, for a long measurement time. This is the case when correlated spin relaxation due to binary alkali-…
Optical pumping of an optically thick atomic vapor typically requires a quenching buffer gas, such as N$_{2}$, to prevent radiation trapping of unpolarized photons which would depolarize the atoms. We show that optical pumping of a trace contamination of Rb present in K metal results in a 4.5 times higher polarization of K than direct optical pumping of K in the absence of N$_{2}$. Such spin-exchange polarization transfer from optically-thin species is useful in a variety of areas, including spin-polarized nuclear scattering targets and electron beams, quantum-non-demolition spin measurements,…
Light shifts are an important source of noise and systematics in optically pumped magnetometers. We demonstrate that the long spin coherence time in paraffin-coated cells leads to spatial averaging of the light shifts over the entire cell volume. This renders the averaged light shift independent, under certain approximations, of the light-intensity distribution within the sensor cell. These results and the underlying mechanism can be extended to other spatially varying phenomena in anti-relaxation-coated cells with long coherence times.
Random spin-exchange collisions in warm alkali vapor cause rapid decoherence and act to equilibriate the spin state of the atoms. In contrast, here we demonstrate experimentally and theoretically a coherent coupling of one alkali specie to another specie, mediated by these random collisions. We show that, the minor specie (potassium) inherits the magnetic properties of the dominant specie (rubidium), including its lifetime (T1), coherence time (T2), gyromagnetic ratio, and SERF magnetic-field threshold. We further show that this coupling can be completely controlled by varying the strength of …
Antirelaxation surface coatings allow long spin relaxation times in alkali-metal cells without buffer gas, enabling faster diffusion of the alkali atoms throughout the cell and giving larger signals due to narrower optical linewidths. Effective coatings were previously unavailable for operation at temperatures above 80 C. We demonstrate that octadecyltrichlorosilane (OTS) can allow potassium or rubidium atoms to experience hundreds of collisions with the cell surface before depolarizing, and that an OTS coating remains effective up to about 170 C for both potassium and rubidium. We consider th…
We present an application of the Faraday effect to produce a narrow band atomic filter in an alkali metal vapor. In our experiment two Raman beams separated in frequency by the ground state hyperfine splitting in 87Rb are produced using an EOM and then filtered using the Faraday effect in an isotopically pure 85Rb thermal vapor. An experimental transmission spectra for the filter is presented along with a theoretical calculation. The performance of the filter is then demonstrated and characterized using a Fabry-Perot etalon. For a temperature of 70 degrees and a longitudinal magnetic field of …
Alkali-metal atomic magnetometers suffer from heading errors in geomagnetic fields as the measured magnetic field depends on the orientation of the sensor with respect to the field. In addition to the nonlinear Zeeman splitting, the difference between Zeeman resonances in the two hyperfine ground states can also generate heading errors depending on initial spin polarization. We examine heading errors in an all-optical scalar magnetometer that uses free precession of polarized $^{87}\text{Rb}$ atoms by varying the direction and magnitude of the magnetic field at different spin polarization regi…
Dynamic nonlinear magneto-optical-rotation signals with frequency- and amplitude-modulated laser light have been observed and investigated with a spherical glass cell of 3-mm diameter containing Cs metal with inner walls coated with paraffin. Intrinsic Zeeman relaxation rates of $γ/(2π)\approx 20 $Hz and lower have been observed. Favorable prospects of using millimeter-scale coated cells in portable magnetometers and secondary frequency references are discussed.
We develop an analytical theory of dark resonances that accounts for the full atomic-level structure, as well as all field-induced effects such as coherence preparation, optical pumping, ac Stark shifts, and power broadening. The analysis uses a model based on relaxation constants that assumes the total collisional depolarization of the excited state. A good qualitative agreement with experiments for Cs in Ne is obtained.
We have developed a torsion balance to detect the rotation of a cell containing spin-polarized gaseous atoms to study angular momentum transfer from gaseous atoms to solid. A cesium vapor cell was hung from a thin wire in a vacuum chamber, and irradiated from the bottom with circularly polarized light tuned to the $D_2$ transition to polarize cesium atoms in the cell. By varying the light helicity at the resonance frequency of the torsion balance, we induced forced rotational oscillation of the cell and detected radiation torque exerted on the cesium vapor cell through the cesium atoms inside.…
Nuclear slowing-down factors in alkali-metal vapors
Institute of Electronic Structure and Laser, Foundation for Research and Technology（电子结构与激光研究所，研究与技术基金会）；Department of Physics, Princeton University（普林斯顿大学物理系）
We present a first-principles analysis of the noise spectra of alkali-metal-metal vapors in and out of the spin-exchange-relaxation-free (SERF) regime, and we predict non-intuitive features with a potential to further improve the sensitivity of SERF media, and which must be taken into account in their use in quantum optical applications. Studying the process of spin-noise spectroscopy (SNS), we derive analytic formulas for the observable noise spectra, and for the correlation functions among different hyperfine components, which give additional insight into the spin dynamics. The analytic resu…
An electrically-controllable, solid-state, reversible device for sourcing and sinking alkali vapor is presented. When placed inside an alkali vapor cell, both an increase and decrease of the rubidium vapor density by a factor of two are demonstrated through laser absorption spectroscopy on 10 to 15 s time scales. The device requires low voltage (5 V), low power (<3.4 mW peak power), and low energy (<10.7 mJ per 10 s pulse). The absence of oxygen emission during operation is shown through residual gas analysis, indicating Rb is not lost through chemical reaction but rather by ion transport thro…
We demonstrate an all-optical $^{133}$Cs scalar magnetometer, operating in nonzero magnetic field,in which the magnetic resonance is driven by an effective oscillating magnetic field provided by the AC Stark shift of an intensity-modulated laser beam. We achieve a projected shot-noise-limited sensitivity of 1.7 fT/Hz$^{1/2}$ and measure a technical noise floor of 40 fT/Hz$^{1/2}$. These results are essentially identical to a coil-driven scalar magnetometer using the same setup. This all-optical scheme offers advantages over traditional coil-driven magnetometers for use in arrays and in magneti…
In this work, we demonstrate a microwave magnetic field imaging technique based on Rabi resonance with a cesium atom vapor cell. Rabi resonance signals are generated when atoms interact with a phase-modulated microwave (MW) field and are detected by a photodiode and camera. A low noise, high quantum efficiency camera is used to capture a series of frames for different phase modulation frequencies. Rabi frequencies of each spatial point in the field can be measured by scanning the frames. Thus, the strength of the MW magnetic field distribution is obtained by combing the Rabi frequencies, measu…
We demonstrate a new technique for the accurate measurement of diffusion coefficients for alkali vapor in an inert buffer gas. The measurement was performed by establishing a spatially periodic density grating in isotopically pure $^{87}$Rb vapor and observing the decaying coherent emission from the grating due to the diffusive motion of the vapor through N$_2$ buffer gas. We obtain a diffusion coefficient of $0.245 \pm0.002 ~\textrm{cm}^{2}/\textrm{s}$ at 50$\degree$C and 564~Torr. Scaling to atmospheric pressure, we obtain $D_0 = 0.1819 \pm 0.0024~\textrm{cm}^2/\textrm{s}$. To the best of ou…
Atom-light interactions in nano-scale systems hold great promise for novel technologies based on integrated emitters and optical modes. We present the design architecture, construction method, and characterization of an all-glass alkali-metal vapor cell with nanometer-scale internal structure. Our cell has a glue-free design which allows versatile optical access, in particular with high numerical aperture optics, and incorporates a compact integrated heating system in the form of an external deposited ITO layer. By performing spectroscopy in different illumination and detection schemes, we inv…
Rydberg-assisted atomic electrometry using alkali-metal atoms contained inside a vacuum environment for detecting external electric fields (E-fields) at frequencies $<$ a few kHz has been quite challenging due to the low-frequency E-field screening effect that is caused by the alkali-metal atoms adsorbed on the inner surface of the container. We report a very slow E-field screening phenomenon with a time scale up to $\sim$ second on a rubidium (Rb) vapor cell that is made of monocrystalline sapphire. Using this sapphire-made Rb vapor cell with optically induced, internal bias E-field, we demon…
We report an experimental observation of degenerate mirrorless lasing in forward direction under excitation of a dilute atomic Rb vapor with a single linearly polarized cw laser light resonant with cycling Fe > Fg atomic D2 transitions. Light polarized orthogonally to the laser light is generated for the input light intensity exceeding a threshold value of about 3 mW/cm^2. Application of a transverse magnetic field directed along the input light polarization reveals a sharp about 20 mG wide magnetic resonance centered at B = 0. Increasing the incident light intensity from 3 to 300 mW/cm^2, the…
The nonlinear Zeeman effect can induce splittings and asymmetries of magnetic-resonance lines in the geophysical magnetic-field range. We demonstrate a scheme to suppress the nonlinear Zeeman effect all optically based on spin locking. Spin locking is achieved with an effective oscillating magnetic field provided by the AC Stark-shift of an intensity-modulated and polarization-modulated laser beam. This results in the collapse of the multi-component asymmetric magnetic-resonance line with about 100 Hz width in the Earth-field range into a peak with a central component width of 25Hz. The techni…
The nonlinear Zeeman effect can induce splitting and asymmetries of magnetic-resonance lines in the geophysical magnetic field range. This is a major source of "heading error" for scalar atomic magnetometers. We demonstrate a method to suppress the nonlinear Zeeman effect and heading error based on spin locking. In an all-optical synchronously pumped magnetometer with separate pump and probe beams, we apply a radio-frequency field which is in-phase with the precessing magnetization. In an earth-range field, a multi-component asymmetric magnetic-resonance line with ? 60 Hz width collapses into …
Atomic spin sensors offer precision measurements using compact, microfabricated packages, placing them in a competitive position for both market and research applications. Performance of these sensors such as dynamic range may be enhanced through magnetic field control. In this work, we discuss the design of miniature coils for three-dimensional, localized field control by direct placement around the sensor, as a flexible and compact alternative to global approaches used previously. Coils are designed on biplanar surfaces using a stream-function approach and then fabricated using standard prin…
A new configuration for observation of magneto-optical subnatural-linewidth resonances of electromagnetically induced absorption (EIA) in alkali vapor has been verified experimentally. The configuration includes using two counter-propagating pump and probe light waves with mutually orthogonal linear polarizations, exciting an open optical transition of an alkali atom in the presence of a buffer gas. The main advantage of the novel observation scheme consists in the possibility of obtaining simultaneously high-contrast and quite narrow nonlinear signals. Here a 2.5-cm long rubidium-87 vapor cel…
Alkali metal dispensers have become an indispensable tool in the production of atomic vapors for magnetometry, alkali vapor cell clocks, and laser cooling experiments. A primary advantage of these dispensers is that they contain alkali metal in an inert form that can be exposed to air without hazard. However, their high temperature of operation (>600 C) is undesirable for many applications, as it shifts the atomic speed distribution to higher values and presents a radiative heat source that can raise the temperature of its surroundings. For this reason, dispensers are typically not used in lin…
We investigate a solid-state, reversible, alkali-ion battery (AIB) capable of regulating the density of alkali atoms in a vacuum system used for the production of laser-cooled atoms. The cold-atom sample can be used with in-vacuum chronoamperometry as a diagnostic for the voltage-controlled electrochemical reaction that sources or sinks alkali atoms into the vapor. In a combined reaction-diffusion-limited regime, we show that the number of laser-cooled atoms in a magneto-optical trap can be increased both by initially loading the AIB from the vapor for longer, and by using higher voltages acro…
We report on widefield microwave vector field imaging with sub um resolution using a microfabricated alkali vapor cell. The setup can additionally image dc magnetic fields, and can be configured to image microwave electric fields. Our camera-based widefield imaging system records 2D images with a 6x6 mm2 field of view at a rate of 10 Hz. It provides up to 50 um spatial resolution, and allows imaging of fields as close as 150 um above structures, through the use of thin external cell walls. This is crucial in allowing us to take practical advantage of the high spatial resolution, as feature siz…
Using a simple and cost-effective water jet process, silicon etch depth limitations are overcome to realize a $6\,$mm deep atomic vapor cell. While the minimum silicon feature size was limited to a $1.5\,$mm width in these first generation vapor cells, we successfully demonstrate a two-chamber geometry by including a $\sim$25~mm meandering channel between the alkali pill chamber and main interrogation chamber. We evaluate the impact of the channel conductance on the introduction of alkali vapor density during the pill activation process, and mitigate glass damage and pill contamination near th…
We consider ultracold collisions of ground-state, heteronuclear alkali dimers that are susceptible to four-center chemical reactions 2 AB -> A2 + B2 even at sub-microKelvin temperature. These reactions depend strongly on species, temperature, electric field, and confinement in an optical lattice. We calculate ab initio van der Walls coefficients for these interactions, and use a quantum formalism to study the scattering properties of such molecules under an external electric field and optical lattice. We also apply a quantum threshold model to explore the dependence of reaction rates on the va…
