. (2013) A surface-patterned chip as a strong source of ultracold atoms for quantum technologies. Nature Nanotechnology, 8 (5). pp. 321-324. Copyright © 2013 MacMillanA copy can be downloaded for personal non-commercial research or study, without prior permission or chargeThe content must not be changed in any way or reproduced in any format or medium without the formal permission of the copyright holder(s) Laser cooled atoms are central to modern precision measurements 1-6 . They are also increasingly important as an enabling technology for experimental cavity quantum electrodynamics 7,8 , quantum information processing 9-11 and matter wave interferometry 12 . Although significant progress has been made in miniaturising atomic metrological devices 13,14 , 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 benefit from the advantages of atoms in the microKelvin regime 15,16 . However, simplifying atomic cooling and loading using microfabrication technology has proved difficult 17,18 . In this letter we address this problem, realising 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, at sub-Doppler temperatures. Moreover, the same chip design offers a simple way to form stable optical lattices. These features, combined with the simplicity of fabrication and the ease of operation, make these new traps a key advance in the development of cold-atom technology for high-accuracy, portable measurement devices.

We report on the design, fabrication, and characterization of a unidirectional quantum cascade ring laser operating at a wavelength of around 3.4 μm at 200 K. A unidirectional operation is achieved by incorporating an “S-shaped” crossover waveguide in a manner that it couples light from the counterclockwise direction to the preferred clockwise direction. The ring laser unidirectionality is confirmed by measuring the counterpropagating wave suppression ratio (CWSR) as a function of injection current. At 1.5 times the threshold current, the CWSR is 9 that is 90% of the light is emitted in the favored (clockwise) direction.

The design, fabrication and characterization of a monolithic double-ring quantum-cascade laser (DRQCL) are described. At a wavelength of 4.6 μm, we demonstrate tunable, single-mode operation of a DRQCL and use it as a source for spectroscopy of CO gas.

Quantum cascade lasers (QCLs) are semiconductor lasers based on intersubband transitions in quantum wells [1]. Semiconductor lasers in ring format do not need cleaved facets or gratings to achieve optical feedback required for lasing and could support either bidirectional or unidirectional operation [2].In this paper, we report on QCL in this ring format for unidirectional operation and coupled ring tuning. A key advantage of unidirectional lasers (ULs) is that in the preferred emission direction, they can have up to double the quantum efficiency of bidirectional lasers. This behaviour was first reported in interband lasers by Hohimer and Vawter [3], by incorporating an "S-crossarm" waveguide into the ring in a manner that introduces an non reciprocal loss and gain in the counterclockwise (CCW) and clockwise (CW) direction respectively. Using similar technique, we recently reported on a unidirectional quantum cascade ring laser (UQCRL) with 90 % emission in the preferred CW direction [4]. We will report on the competing mode behaviour that gives rise to unidirectional operation. Shown in Fig.1(a) and (b) are an SEM image of the processed UQCRL and the plot of CW/CCW L-I respectively.Also we report an investigation into wavelength tuning characteristics of coupled ring QCLs. Coupled ring lasers have the potential of achieving M times the tuning range of a single ring laser, where M is the Vernier effect tuning enhancement factor associated with coupled waveguide [5]. Fig.1(c) and (d) are the SEM image of the processed coupled ring and the plot of wavelength versus DC current injected into ring 2 respectively. Current in ring 1 was held constant at 400 mA (pulsed).

We have made magneto-optical traps (MOTs) on a chip which is able to cool and trap ~10 8 atoms directly from a ~1cm 3 thermal background of 87 Rb. Diffraction gratings are used to manipulate the light from a single input beam to create the beams required for a MOT [1,2]. The gratings are etched into the surface of a silicon or GaAs wafer by either electron beam, or photo-lithography making them simple to fabricate and integrate into other atom chip architectures. We have developed a variety of gratings for utilisation both inside and outside a vacuum chamber --facilitating their incorporation into both new and existing devices. Unlike previously integrated cold atom sources on a chip [3,4] the atoms now sit above the surface where they can be easily imaged, manipulated and transferred into other on-chip potentials.We have demonstrated sub-Doppler cooling with the chip MOT, which enables its use as a source for e.g. quantum gas experiments. Moreover, we explain how the same specialised optics could also be used to make a straightforward, extremely stable, optical lattice for use in advanced clocks [5] and atomic quantum simulators [6,7]. Our devices significantly simplify the initial capturing of atoms, representing substantial progress towards fully integrated atomic physics experiments and devices. They also offer a simple way to integrate many atom sources on a single device. Mineral prospecting, defence and quantum information are key development areas which can benefit from this simple, yet powerful, technology.