As stated in the text, Figs. 3 and 4 (transmission versus probe laser detuning) were taken at an energy of 10 nJ in a 0.5-mm-diam beam. We should have noted that when the probe energy is increased to 150 n3 (— 10" W/cm ) the absorption cross section at the transmission maximum increases by a factor of approximately 2. At this energy density, with or without the coupling laser present, transmitted probe energy is no longer linear with incident probe energy.

Observation of Electromagnetically Induced Transparency in Collisionally Broadened Lead Vapor

We review recent progress in inducing and harnessing stimulated Brillouin scattering (SBS) in integrated photonic circuits. Exciting SBS in a chip-scale device is challenging due to the stringent requirements on materials and device geometry. We discuss these requirements, which include material parameters, such as optical refractive index and acoustic velocity, and device properties, such as acousto-optic confinement. Recent work on SBS in nano-photonic waveguides and micro-resonators is presented, with special attention paid to photonic integration of applications such as narrow-linewidth lasers, slow- and fast-light, microwave signal processing, Brillouin dynamic gratings, and nonreciprocal devices.

Inducing and harnessing stimulated Brillouin scattering in photonic integrated circuits

Chip-scale atomic devices combine elements of precision atomic spectroscopy, silicon micromachining, and advanced diode laser technology to create compact, low-power, and manufacturable instruments with high precision and stability. Microfabricated alkali vapor cells are at the heart of most of these technologies, and the fabrication of these cells is discussed in detail. We review the design, fabrication, and performance of chip-scale atomic clocks, magnetometers, and gyroscopes and discuss many applications in which these novel instruments are being used. Finally, we present prospects for future generations of miniaturized devices, such as photonically integrated systems and manufacturable devices, which may enable embedded absolute measurement of a broad range of physical quantities.

/pdf/chip-scale-atomic-devices-2t0mgeutgr.pdf

Chip-scale atomic devices

“Cavity-optomechanics” aims to study the quantum properties of mechanical systems. A common strategy implemented in order to achieve this goal couples a high finesse photonic cavity to a high quality factor mechanical resonator. Then, using feedback forces such as radiation pressure, one can cool the mechanical mode of interest into the quantum ground state and create non-classical states of mechanical motion. On the path towards achieving these goals, many near-term applications of this field have emerged. After briefly introducing optomechanical systems and describing the current state-of-the-art experimental results, this article summarizes some of the more exciting practical applications such as ultra-sensitive, high bandwidth accelerometers and force sensors, low phase noise x-band integrated microwave oscillators and optical signal processing such as optical delay-lines, wavelength converters, and tunable optical filters. In this rapidly evolving field, new applications are emerging at a fast pace, but this article concentrates on the aforementioned lab-based applications as these are the most promising avenues for near-term real-world applications. New basic science applications are also becoming apparent such as the generation of squeezed light, testing gravitational theories and for providing a link between disparate quantum systems.

Applications of cavity optomechanics

Room-temperature, easy-to-operate quantum memories are essential building blocks for future long distance quantum information networks operating on an intercontinental scale, because devices like quantum repeaters, based on quantum memories, will have to be deployed in potentially remote, inaccessible locations. Here we demonstrate controllable, broadband and efficient storage and retrieval of weak coherent light pulses at the single-photon level in warm atomic cesium vapor using the robust far off-resonant Raman memory scheme. We show that the unconditional noise floor of this technically simple quantum memory is low enough to operate in the quantum regime, even in a room-temperature environment.

https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.107.053603

Single-photon-level quantum memory at room temperature.

The ability to slow down the propagation of light touches both fundamental aspects of light–matter interactions and practical applications in photonic communication and computation1,2,3. Optical quantum interference can substantially reduce the speed of light while offering additional dramatic optical effects based on the ability to control electronic quantum states4,5. Recent efforts are increasingly being directed towards harnessing these effects in integrated photonic structures6,7. Here, we report the first demonstration of slow light and electromagnetically induced transparency in a self-contained, planar atomic spectroscopy chip. Using hot rubidium atoms in hollow-core waveguides, we demonstrate 44% optical transparency with a group index of 1,200, or more than sevenfold slower light than in photonic-crystal waveguides8. Optical pulse delays of 16 ns with a delay-bandwidth product of 0.8 are observed. This implementation of atomic quantum state control in integrated photonic structures will enable coherent photonics at ultralow power levels. Researchers exploit atomic quantum state control in a fully integrated photonic atomic spectroscopy chip to reduce the group velocity of light by a factor of 1,200 — the lowest group velocity ever reported for a solid-state material. The findings will enable the creation of on-chip nonlinear optical devices with enhanced quantum coherence operating at ultralow power levels.

Slow light on a chip via atomic quantum state control

Atomic vapors of alkali metals are widely used to slow and stop light in tabletop experiments. In order to take advantage of the underlying quantum interference effects in future commercial devices, highly reactive alkali atoms must be incorporated into small volumes with integrated optical access. With integration in mind, we describe the development of a hollow-core waveguide technology based on the combination of vapor-filled hollow waveguides and conventional solid-core waveguides on a silicon chip. We discuss the underlying principles of the waveguide design, the development of different approaches to building on-chip vapor cells, the demonstration of linear and nonlinear rubidium spectroscopy on a chip, and the prospects for quantum interference effects such as slow light and giant Kerr nonlinearities using this approach. Ultrasmall active vapor volumes on the order of 100 picoliters with simultaneously high optical density in excess of two illustrate the potential of planar hollow-core waveguides for linear and nonlinear optical spectroscopy of atoms confined on a chip.

Planar Hollow-Core Waveguide Technology for Atomic Spectroscopy and Quantum Interference in Alkali Vapors

A versatile approach to Rb atomic vapor cell construction is proposed and tested. The construction method employs pinch-off copper cold-welds and epoxy to create hermetic seals between dissimilar geometries and materials. Accelerated testing revealed expected lifetimes of 3 days at 90 °C operation and in excess of 1 yr at 25 °C operation. The reaction of Rb with epoxy was determined to be the largest contributor to failure.

Versatile approach to Rb vapor cell construction

Harnessing the unique optical quantum interference effects associated with electromagnetically induced transparency
(EIT) on a chip promises new opportunities for linear and nonlinear optical devices. Here, we review the status of
integrated atomic spectroscopy chips that could replace conventional rubidium spectroscopy cells. Both linear and
nonlinear absorption spectroscopy with excellent performance are demonstrated on a chip using a self-contained Rb
reservoir and exhibiting a footprint of only 1.5cm x 1cm. In addition, quantum interference effects including V-scheme
and Λ-scheme EIT are observed in miniaturized rubidium glass cells whose fabrication is compatible with on-chip
integration.

Quantum interference effects in rubidium vapor on a chip

The authors report on an approach to the construction of long-lasting rubidium atomic vapor cells. The method uses pinch-off copper cold-welds, low temperature solders, and electroplated copper to create long-lasting hermetic seals between containment chambers of dissimilar geometries and materials. High temperature epoxy, eutectic lead/tin solder, and indium solder were considered as sealing materials. These seals were analyzed using accelerated lifetime testing techniques. Vapor cells with epoxy and bare metal solder seals had a decrease in the rubidium atomic density within days after being heated to elevated temperatures. They also exhibited broadened spectra as a result of rubidium reacting with the seals. However, indium solder seals with a passivation coating of electroplated copper did not exhibit a significant decrease in linewidth or atomic density after being held at 95 °C for 30 days. The authors conclude that this particular seal has no rubidium chemical reaction failure mode and when used in combination with copper cold welding has the potential to create multiplatform vapor cells with extremely long lifetimes.

/pdf/versatile-rb-vapor-cells-with-long-lifetimes-2gj1hhrhzm.pdf

John F. Hulbert

Papers

Slow light on a chip via atomic quantum state control

Planar Hollow-Core Waveguide Technology for Atomic Spectroscopy and Quantum Interference in Alkali Vapors

Versatile approach to Rb vapor cell construction

Quantum interference effects in rubidium vapor on a chip

Versatile Rb vapor cells with long lifetimes