A cold-atom Ramsey clock with a low volume physics package.

We demonstrate a Ramsey-type microwave clock interrogating the 6.835 GHz ground-state transition in cold [Formula: see text]Rb atoms loaded from a grating magneto-optical trap (GMOT) enclosed in an additively manufactured loop-gap resonator microwave cavity. A short-term stability of [Formula: see text] is demonstrated, in reasonable agreement with predictions from the signal-to-noise ratio of the measured Ramsey fringes. The cavity-grating package has a volume of [Formula: see text]67 cm[Formula: see text], ensuring an inherently compact system while the use of a GMOT drastically simplifies the optical requirements for laser cooled atoms. This work is another step towards the realisation of highly compact portable cold-atom frequency standards.

Ultra-low noise, bi-polar, programmable current sources.

We present the design process and implementation of fully open-source, ultra-low noise programmable current source systems in two configurations. Although originally designed as coil drivers for Optically Pumped Magnetometers (OPMs), the device specifications make them potentially useful in a range of applications. The devices feature a bi-directional current range of ±10 and ±250 mA on three independent channels with 16-bit resolution. Both devices feature a narrow 1/f noise bandwidth of 1 Hz, enabling magnetic field manipulation for high-performance OPMs. They exhibit a low noise of 146 pA/Hz and 4.1 nA/Hz, which translates to 15 and 16 ppb/Hz noise relative to full scale.

Micro-fabricated components for cold atom sensors.

Laser cooled atoms have proven transformative for precision metrology, playing a pivotal role in state-of-the-art clocks and interferometers and having the potential to provide a step-change in our modern technological capabilities. To successfully explore their full potential, laser cooling platforms must be translated from the laboratory environment and into portable, compact quantum sensors for deployment in practical applications. This transition requires the amalgamation of a wide range of components and expertise if an unambiguously chip-scale cold atom sensor is to be realized. We present recent developments in cold-atom sensor miniaturization, focusing on key components that enable laser cooling on the chip-scale. The design, fabrication, and impact of the components on sensor scalability and performance will be discussed with an outlook to the next generation of chip-scale cold atom devices.

Optical characterisation of micro-fabricated Fresnel zone plates for atomic waveguides.

We optically assess Fresnel zone plates (FZPs) that are designed to guide cold atoms. Imaging of various ring patterns produced by the FZPs gives an average RMS error in the brightest part of the ring of 3% with respect to trap depth. This residue is attributed to the imaging system, incident beam shape and FZP manufacturing tolerances. Axial propagation of the potentials is presented experimentally and through numerical simulations, illustrating prospects for atom guiding without requiring light sheets.

Cold-atom clock based on a diffractive optic.

Clocks based on cold atoms offer unbeatable accuracy and long-term stability, but their use in portable quantum technologies is hampered by a large physical footprint. Here, we use the compact optical layout of a grating magneto-optical trap (gMOT) for a precise frequency reference. The gMOT collects 107 87Rb atoms, which are subsequently cooled to 20 µK in optical molasses. We optically probe the microwave atomic ground-state splitting using lin⊥lin polarised coherent population trapping and a Raman-Ramsey sequence. With ballistic drop distances of only 0.5 mm, the measured short-term fractional frequency stability is 2×10-11/τ.

High-precision control of static magnetic field magnitude, orientation, and gradient using optically pumped vapour cell magnetometry.

An integrated system of hardware and software allowing precise definition of arbitrarily oriented magnetic fields up to |B| = 1 µT within a five-layer Mumetal shield is described. The system is calibrated with reference to magnetic resonance observed between Zeeman states of the 6S1/2 F = 4 133Cs ground state. Magnetic field definition over the full 4π solid angle is demonstrated with one-sigma tolerances in magnitude, orientation, and gradient of δ|B| = 0.94 nT, δθ = 5.9 mrad, and δ|∇B|=13.0 pT/mm, respectively. This field control is used to empirically map Mx magnetometer signal amplitude as a function of the static field (B0) orientation.

Design and fabrication of diffractive atom chips for laser cooling and trapping.

It has recently been shown that optical reflection gratings fabricated directly into an atom chip provide a simple and effective way to trap and cool substantial clouds of atoms (Nshii et al. in Nat Nanotechnol 8:321-324, 2013; McGilligan et al. in Opt Express 23(7):8948-8959, 2015). In this article, we describe how the gratings are designed and microfabricated and we characterise their optical properties, which determine their effectiveness as a cold atom source. We use simple scalar diffraction theory to understand how the morphology of the gratings determines the power in the diffracted beams.

Phase-space properties of magneto-optical traps utilising micro-fabricated gratings.

We have used diffraction gratings to simplify the fabrication, and dramatically increase the atomic collection efficiency, of magneto-optical traps using micro-fabricated optics. The atom number enhancement was mainly due to the increased beam capture volume, afforded by the large area (4cm(2)) shallow etch (~ 200nm) binary grating chips. Here we provide a detailed theoretical and experimental investigation of the on-chip magneto-optical trap temperature and density in four different chip geometries using (87)Rb, whilst studying effects due to MOT radiation pressure imbalance. With optimal initial MOTs on two of the chips we obtain both large atom number (2×10(7)) and sub-Doppler temperatures (50 µK) after optical molasses.

A surface-patterned chip as a strong source of ultracold atoms for quantum technologies.

Laser-cooled atoms are central to modern precision measurements. They are also increasingly important as an enabling technology for experimental cavity quantum electrodynamics, quantum information processing and matter-wave interferometry. Although significant progress has been made in miniaturizing atomic metrological devices, these are limited in accuracy by their use of hot atomic ensembles and buffer gases. Advances have also been made in producing portable apparatus that benefits from the advantages of atoms in the microkelvin regime. However, simplifying atomic cooling and loading using microfabrication technology has proved difficult. In this Letter we address this problem, realizing an atom chip that enables the integration of laser cooling and trapping into a compact apparatus. Our source delivers ten thousand times more atoms than previous magneto-optical traps with microfabricated optics and, for the first time, can reach sub-Doppler temperatures. Moreover, the same chip design offers a simple way to form stable optical lattices. These features, combined with simplicity of fabrication and ease of operation, make these new traps a key advance in the development of cold-atom technology for high-accuracy, portable measurement devices.

Enhanced frequency up-conversion in Rb vapor.

We demonstrate highly efficient generation of coherent 420 nm light via up-conversion of near-infrared lasers in a hot rubidium vapor cell. By optimizing pump polarizations and frequencies we achieve a single-pass conversion efficiency of 260% per Watt, significantly higher than in previous experiments. A full exploration of the coherent light generation and fluorescence as a function of both pump frequencies reveals that coherent blue light is generated close to (85)Rb two-photon resonances, as predicted by theory, but at high vapor pressure is suppressed in spectral regions that do not support phase matching or exhibit single-photon Kerr refraction. Favorable scaling of our current 1 mW blue beam power with additional pump power is predicted.

A versatile and reliably reusable ultrahigh vacuum viewport.

We present a viewport for use in ultrahigh vacuum (UHV) based upon the preflattened solder seal design presented in earlier work [Cox et al., Rev. Sci. Instrum. 74, 3185 (2003)]. The design features significant modifications to improve long term performance. The windows have been leak tested to less than 10(-10) atm cm(3)/s. From atom number measurements in an optical dipole trap loaded from a vapor cell magneto-optical trap inside a vacuum chamber accommodating these viewports, we measure a trap lifetime of 9.5 s suggesting a pressure of around 10(-10) Torr limited by background rubidium vapor pressure. We also present a simplified design where the UHV seal is made directly to a vacuum pipe.

Tunable, Single-frequency, Diode-pumped 2.3mum VECSEL.

We report high-performance single-frequency operation of a directly diode-pumped GaSb-based vertical-external-cavity surface-emitting laser (VECSEL) at 2.3mum. Tunability of 70nm and a maximum single frequency output of 0.68W is demonstrated.

Injection-locking technique for heterodyne optical phase locking of a diode laser.

A novel technique is demonstrated for heterodyne optical phase locking of a diode laser to a single-frequency source by injection seeding. By modulation of the drive current of the diode laser at as much as several gigahertz, FM sidebands are imposed upon the output. We demonstrate that it is possible to phase lock either sideband to an injected beam. The carrier of the diode laser output is therefore locked in phase with the injected light but with a frequency difference given by the modulation of the drive current. The phase fluctuations between the lasers are analyzed, and the variance is found to be (4.4( degrees ))(2) , corresponding to 99.4% of the diode carrier light locked to the injected beam.

Bright tunable ultraviolet squeezed light.

We have produced bright tunable squeezed light by second-harmonic generation in a singly resonant cavity. We have investigated the effect of input coupling and fundamental power on the squeezing. Up to 400 mW of continuous-wave mode-locked tunable squeezed light was produced at wavelengths as short as 389 nm, and more than 1.5 dB of squeezing was inferred.

Optical comb generator as an efficient short-pulse source.

We demonstrate a novel technique for converting a continuous-wave laser beam into a stable train of short pulses with a high repetition rate. The system, which is generally applicable, is based on a purely passive coupled-cavity optical frequency comb generator, which ensures a high overall efficiency. The repetition rate of the device is determined by the drive frequency of an electro-optic modulator and the pulse width by the rf power applied to the modulator. We have observed pulses down to 3.3 ps long at a 5.34-GHz repetition rate and an overall efficiency of 11%. The experimental results for pulse shape and width show excellent quantitative agreement with the results of a simple model.

Efficient optical frequency-comb generator.

We have demonstrated a method that efficiently transfers the power from a single-frequency laser into a wideband frequency comb. The comb was produced by a 2.7-GHz electro-optic modulator in a resonant optical cavity. A coupled cavity technique was used to transfer 8.5% of the laser power into a comb with a span of 400 modes, or more than 1 THz.