arXiv subjects

J. Kitching

Publications and source records attributed to J. Kitching.

18 recordsLinked to original sources

arXiv2021

A simple imaging solution for chip-scale laser cooling

We demonstrate a simple stacked scheme that enables absorption imaging through a hole in the surface of a grating magneto-optical trap (GMOT) chip, placed immediately below a micro-fabricated vacuum cell. The imaging scheme is capable of overcoming the reduced optical access and surface scatter that is associated with this chip-scale platform, while further permitting both trapping and imaging of the atoms from a single incident laser beam. The through-hole imaging is used to characterise the impact of the reduced optical overlap volume of the GMOT in the chip-scale cell, with an outlook to an optimised atom number in low volume systems.

physics.atom-ph↗

arXiv2020

Laser cooling in a chip-scale platform

Chip-scale atomic devices built around micro-fabricated alkali vapor cells are at the forefront of compact metrology and atomic sensors. We demonstrate a micro-fabricated vapor cell that is actively-pumped to ultra-high-vacuum (UHV) to achieve laser cooling. A grating magneto optical trap (GMOT) is incorporated with the 4 mm-thick Si/glass vacuum cell to demonstrate the feasibility of a fully-miniaturized laser cooling platform. A two-step optical excitation process in rubidium is used to overcome surface-scatter limitations to the GMOT imaging. The unambiguous miniaturization and form-customizability made available with micro-fabricated UHV cells provide a promising platform for future compact cold-atom sensors.

physics.atom-ph↗

arXiv2020

Advanced light-shift compensation protocol in a continuous-wave microcell atomic clock

Light-shifts are known to be an important limitation to the mid- and long-term fractional frequency stability of different types of atomic clocks. In this article, we demonstrate the experimental implementation of an advanced anti-light shift interrogation protocol onto a continuous-wave (CW) microcell atomic clock based on coherent population trapping (CPT). The method, inspired by the Auto-Balanced Ramsey (ABR) spectroscopy technique demonstrated in pulsed atomic clocks, consists in the extraction of atomic-based information from two successive light-shifted clock frequencies obtained at two different laser power values. Two error signals, computed from the linear combination of signals acquired along a symmetric sequence, are managed in a dual-loop configuration to generate a clock frequency free from light-shift. Using this method, the sensitivity of the clock frequency to both laser power and microwave power variations can be reduced by more than an order of magnitude compared to normal operation. In the present experiment, the consideration of the non-linear light-shift dependence allowed to enhance light-shift mitigation. The implemented technique allows a clear improvement of the clock Allan deviation for time scales higher than 1000 s. This method could be applied in various kinds of atomic clocks such as CPT-based atomic clocks, double-resonance Rb clocks, or cell-stabilized lasers.

physics.atom-ph↗

arXiv2019

Universal methods for suppressing the light shift in atomic clocks using power modulation

We show that the light shift in atomic clocks can be suppressed using time variation of the interrogation field intensity. By measuring the clock output at two intensity levels, error signals can be generated that simultaneously stabilize a local oscillator to an atomic transition and correct for the shift of this transition caused by the interrogating optical field. These methods are suitable for optical clocks using one- and two-photon transitions, as well as for microwave clocks based on coherent population trapping or direct interrogation. The proposed methods can be widely used both for high-precision scientific instruments and for a wide range of commercial clocks, including chip-scale atomic clocks.

physics.atom-ph↗

arXiv2019

Optical pumping, decay rates and light shifts of cold-atom dark states

Coherent dark states in atoms, created by simultaneous interaction of two coherent light fields with a 3-level system, are of prime importance in quantum state manipulation. They are used extensively in quantum sensing and quantum information applications to build atomic clocks, magnetometers, atomic interferometers and more. Here we study the formation and decay of coherent dark-states in an ensemble of laser-cooled free-falling atoms. We measure the optical-pumping rate into the dark-state in the $\sigma ^+-\sigma ^-$ polarization configuration. We find that the pumping rate is linear with the optical field intensity, but about an order-of-magnitude slower than the rate predicted by the commonly used, but simplistic, three-level analytic formula. Using a numerical model we demonstrate that this discrepancy is due to the multi-level Zeeman manifold. Taking into account the slower pumping rate we explain quantitatively the relation between the light-shift and the duration of pumping into dark-state in Ramsey spectroscopy. We also measure the decay of the dark-state coherence and find that in our apparatus it is dominated by the mechanical motion of the atoms out of the probing region, while the atomic decoherence is negligible.

physics.atom-ph↗

arXiv2019

Dynamic characterization of an alkali-ion battery as a source for laser-cooled atoms

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 across the AIB when atoms are subsequently sourced back into the vapor. The time constants associated with the change in atom number in response to a change in AIB voltage are in the range of 0.5 s - 40 s. The AIB alkali reservoir is demonstrated to survive oxidization during atmospheric exposure, simplifying reservoir loading prior to vacuum implementation as a replacement for traditional resistively-heated dispensers. The AIB capabilities may provide an improved atom number stability in next-generation atomic clocks and sensors, while also facilitating fast loading and increased interrogation times.

physics.atom-ph↗

arXiv2019

Reduction of light shifts in Ramsey spectroscopy with a combined error signal

Light-induced frequency shifts can be a key limiting contribution to the mid and long-term frequency instability in atomic clocks. In this letter, we demonstrate the experimental implementation of the combined error signal interrogation protocol to a cold-atom clock based on coherent population trapping (CPT) and Ramsey spectroscopy. The method uses a single error signal that results from the normalized combination of two error signals extracted from two Ramsey sequences of different dark periods. The single combined error signal is used to stabilize the atomic clock frequency. Compared to the standard Ramsey-CPT interrogation, this method reduces the clock frequency sensitivity to light-shift variations by more than one order of magnitude. This method can be applied in various kinds of Ramsey-based atomic clocks, sensors and instruments.

physics.atom-ph↗

arXiv2019

A magneto-optic trap using a reversible, solid-state alkali-metal source

We demonstrate a novel way to form and deplete a vapor-cell magneto-optic trap (MOT) using a reversible, solid-state alkali-metal source (AMS) via an applied polarized voltage. Using ~100 mW of electrical power, a trapped-atom number of 5x10^6 has been achieved starting from near zero and the timescales of the MOT formation and depletion of ~1 s. This fast, reversible, and low power alkali-atom source is desirable in both tabletop and portable cold-atom systems. The core technology of this device should translate readily to other alkali and alkaline-earth elements that could find a wide range of uses in cold-atom systems and instruments.

physics.atom-ph↗

arXiv2018

Ramsey Spectroscopy with Displaced Frequency Jumps

Sophisticated Ramsey-based interrogation protocols using composite laser pulse sequences have been recently proposed to provide next-generation high-precision atomic clocks with a near perfect elimination of frequency shifts induced during the atom-probing field interaction. We propose here a simple alternative approach to the auto-balanced Ramsey (ABR) interrogation protocol and demonstrate its application to a cold-atom microwave clock based on coherent population trapping. The main originality of the method, based on two consecutive Ramsey sequences with different dark periods, is to sample the central Ramsey fringes with frequency-jumps finely-adjusted by an additional frequency-displacement concomitant parameter, scaling as the inverse of the dark-period. The advantage of this displaced frequency-jumps Ramsey (DFJR) method is that the local oscillator frequency is used as a single physical variable to control both servo loops of the sequence, simplifying its implementation and avoiding noise associated with controlling the LO phase. Compared to the usual Ramsey-CPT technique, the DFJR scheme reduces the sensitivity of the clock frequency to variations of the CPT sideband ratio and to the one-photon laser detuning by more than an order of magnitude. This simple method could be applied in a wide variety of Ramsey-spectroscopy based applications including frequency metrology with CPT-based and optical atomic clocks, mass spectrometry, and precision spectroscopy.

physics.atom-ph↗

arXiv2018

Photonic integration of an optical atomic clock

Laboratory optical atomic clocks achieve remarkable accuracy (now counted to 18 digits or more), opening possibilities to explore fundamental physics and enable new measurements. However, their size and use of bulk components prevent them from being more widely adopted in applications that require precision timing. By leveraging silicon-chip photonics for integration and to reduce component size and complexity, we demonstrate a compact optical-clock architecture. Here a semiconductor laser is stabilized to an optical transition in a microfabricated rubidium vapor cell, and a pair of interlocked Kerr-microresonator frequency combs provide fully coherent optical division of the clock laser to generate an electronic 22 GHz clock signal with a fractional frequency instability of one part in 10^13. These results demonstrate key concepts of how to use silicon-chip devices in future portable and ultraprecise optical clocks.

physics.optics↗

arXiv2018

Combined error signal in Ramsey spectroscopy of clock transitions

We have developed a universal method to form the reference signal for the stabilization of arbitrary atomic clocks based on Ramsey spectroscopy. Our approach uses an interrogation scheme of the atomic system with two different Ramsey periods and a specially constructed combined error signal (CES) computed by subtracting two error signals with the appropriate calibration factor. CES spectroscopy allows for perfect elimination of probe-induced light shifts and does not suffer from the effects of relaxation, time-dependent pulse fluctuations and phase-jump modulation errors and other imperfections of the interrogation procedure. The method is simpler than recently developed auto-balanced Ramsey spectroscopy techniques [Ch. Sanner, et al., Phys. Rev. Lett. 120, 053602 (2018); V. I. Yudin, et al., Phys. Rev. Appl. 9, 054034 (2018)], because it uses a single error signal that feeds back on the clock frequency. CES universal technique can be applied to many applications of precision spectroscopy.

physics.atom-ph↗

arXiv2018

AC Stark Shifts of Dark Resonances Probed with Ramsey Spectroscopy

The off-resonant AC Stark shift for coherent population trapping (CPT) resonances probed with Ramsey spectroscopy is investigated experimentally and theoretically. Measurements with laser-cooled $^{87}$Rb atoms show excellent quantitative agreement with a simple theory. The shift depends on the relative intensity of the two CPT light fields, but depends only weakly on the total intensity. Since the origin of the shift is through couplings of the interrogation light to off-resonant excited state hyperfine levels, the size and sign of the shift depend on the specific interrogation scheme. However, the simple theory shows that for several commonly used interrogation schemes the off-resonant shift goes to zero at specific values of this relative intensity.

physics.atom-ph↗

arXiv2017

Generalized auto-balanced Ramsey spectroscopy of clock transitions

When performing precision measurements, the quantity being measured is often perturbed by the measurement process itself. This includes precision frequency measurements for atomic clock applications carried out with Ramsey spectroscopy. With the aim of eliminating probe-induced perturbations, a method of generalized auto-balanced Ramsey spectroscopy (GABRS) is presented and rigorously substantiated. Here, the usual local oscillator frequency control loop is augmented with a second control loop derived from secondary Ramsey sequences interspersed with the primary sequences and with a different Ramsey period. This second loop feeds back to a secondary clock variable and ultimately compensates for the perturbation of the clock frequency caused by the measurements in the first loop. We show that such a two-loop scheme can lead to perfect compensation of measurement-induced light shifts and does not suffer from the effects of relaxation, time-dependent pulse fluctuations and phase-jump modulation errors that are typical of other hyper-Ramsey schemes. Several variants of GABRS are explored based on different secondary variables including added relative phase shifts between Ramsey pulses, external frequency-step compensation, and variable second-pulse duration. We demonstrate that a universal anti-symmetric error signal, and hence perfect compensation at finite modulation amplitude, is generated only if an additional frequency-step applied during both Ramsey pulses is used as the concomitant variable parameter. This universal technique can be applied to the fields of atomic clocks, high-resolution molecular spectroscopy, magnetically induced and two-photon probing schemes, Ramsey-type mass spectrometry, and to the field of precision measurements. Some variants of GABRS can also be applied for rf atomic clocks using CPT-based Ramsey spectroscopy of the two-photon dark resonance.

physics.atom-ph↗

arXiv2009

Optical detection of NMR J-spectra at zero magnetic field

Scalar couplings of the form J I_1 \cdot I_2 between nuclei impart valuable information about molecular structure to nuclear magnetic-resonance spectra. Here we demonstrate direct detection of J-spectra due to both heteronuclear and homonuclear J-coupling in a zero-field environment where the Zeeman interaction is completely absent. We show that characteristic functional groups exhibit distinct spectra with straightforward interpretation for chemical identification. Detection is performed with a microfabricated optical atomic magnetometer, providing high sensitivity to samples of microliter volumes. We obtain 0.1 Hz linewidths and measure scalar-coupling parameters with 4-mHz statistical uncertainty. We anticipate that the technique described here will provide a new modality for high-precision "J spectroscopy" using small samples on microchip devices for multiplexed screening, assaying, and sample identification in chemistry and biomedicine.

physics.atom-ph↗

arXiv2008

Nuclear quadrupole resonances in compact vapor cells: the crossover from the NMR to the NQR interaction regimes

We present the first experimental study that maps the transformation of nuclear quadrupole resonances from the pure nuclear quadrupole regime to the quadrupole-perturbed Zeeman regime. The transformation presents an interesting quantum-mechanical problem, since the quantization axis changes from being aligned along the axis of the electric-field gradient tensor to being aligned along the magnetic field. We achieve large nuclear quadrupole shifts for I = 3/2 131-Xe by using a 1 mm^3 cubic cell with walls of different materials. When the magnetic and quadrupolar interactions are of comparable size, perturbation theory is not suitable for calculating the transition energies. Rather than use perturbation theory, we compare our data to theoretical calculations using a Liouvillian approach and find excellent agreement.

quant-ph↗

arXiv2005

Magnetometry with millimeter-scale anti-relaxation-coated alkali-metal vapor cells

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.

physics.atom-ph↗

arXiv2004

Investigation of microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells

Using laser optical pumping, widths and frequency shifts are determined for microwave transitions between ground-state hyperfine components of $^{85}$Rb and $^{87}$Rb atoms contained in vapor cells with alkane anti-relaxation coatings. The results are compared with data on Zeeman relaxation obtained in nonlinear magneto-optical rotation (NMOR) experiments, a comparison important for quantitative understanding of spin-relaxation mechanisms in coated cells. By comparing cells manufactured over a forty-year period we demonstrate the long-term stability of coated cells, an important property for atomic clocks and magnetometers.

physics.atom-ph↗

arXiv2003

Theory of dark resonances for alkali vapors in a buffer-gas cell

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.

physics.atom-ph↗