XMDS2 is a cross-platform, GPL-licensed, open source package for numerically integrating initial value problems that range from a single ordinary differential equation up to systems of coupled stochastic partial differential equations. The equations are described in a high-level XML-based script, and the package generates low-level optionally parallelised C++ code for the efficient solution of those equations. It combines the advantages of high-level simulations, namely fast and low-error development, with the speed, portability and scalability of hand-written code. XMDS2 is a complete redesign of the XMDS package, and features support for a much wider problem space while also producing faster code.

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We demonstrate phase sensitivity in a horizontally guided, acceleration-sensitive atom interferometer with a momentum separation of 80hk between its arms. A fringe visibility of 7% is observed. Our coherent pulse sequence accelerates the cold cloud in an optical waveguide, an inherently scalable route to large momentum separation and high sensitivity. We maintain coherence at high momentum separation due to both the transverse confinement provided by the guide, and our use of optical delta-kick cooling on our cold-atom cloud. We also construct a horizontal interferometric gradiometer to measure the longitudinal curvature of our optical waveguide.

Superradiance (SR) is a cooperative phenomenon which occurs when an ensemble of quantum emitters couples collectively to a mode of the electromagnetic field as a single, massive dipole that radiates photons at an enhanced rate. Previous studies on solid-state systems either reported SR from sizeable crystals with at least one spatial dimension much larger than the wavelength of the light and/or only close to liquid-helium temperatures. Here, we report the observation of room-temperature superradiance from single, highly luminescent diamond nanocrystals with spatial dimensions much smaller than the wavelength of light, and each containing a large number (~ 103) of embedded nitrogen-vacancy (NV) centres. The results pave the way towards a systematic study of SR in a well-controlled, solid-state quantum system at room temperature.

We present a precision gravimeter based on coherent Bragg diffraction of freely falling cold atoms. Traditionally, atomic gravimeters have used stimulated Raman transitions to separate clouds in momentum space by driving transitions between two internal atomic states. Bragg interferometers utilize only a single internal state, and can therefore be less susceptible to environmental perturbations. Here we show that atoms extracted from a magneto-optical trap using an accelerating optical lattice are a suitable source for a Bragg atom interferometer, allowing efficient beamsplitting and subsequent separation of momentum states for detection. Despite the inherently multi-state nature of atom diffraction, we are able to build a Mach-Zehnder interferometer using Bragg scattering which achieves a sensitivity to the gravitational acceleration of g/g = 2.7 × 10 −9 with an integration time of 1000 s. The device can also be converted to a gravity gradiometer by a simple modification of the light pulse sequence.

We describe a scheme for creating quadrature-and intensity-squeezed atom lasers that do not require squeezed light as an input. The beam becomes squeezed due to nonlinear interactions between the atoms in the beam in an analogue to optical Kerr squeezing. We develop an analytic model of the process which we compare to a detailed stochastic simulation of the system using phase space methods. Finally we show that significant squeezing can be obtained in an experimentally realistic system and suggest ways of increasing the tunability of the squeezing.

We present a quantum multimodal treatment describing electromagnetically induced transparency ͑EIT͒ as a mechanism for storing continuous-variable quantum information in light fields. Taking into account the atomic noise and decoherences of realistic experiments, we numerically model the propagation, storage, and readout of signals contained in the sideband amplitude and phase quadratures of a light pulse using phase space methods. An analytical treatment of the effects predicted by this model is then presented. Finally, we use quantum information benchmarks to examine the properties of the EIT-based memory and show the parameters needed to operate beyond the quantum limit.

We demonstrate the feasibility of levitating a small mirror using only radiation pressure. In our scheme, the mirror is supported by a tripod where each leg of the tripod is a Fabry-Perot cavity. The macroscopic state of the mirror is coherently coupled to the supporting cavity modes allowing coherent interrogation and manipulation of the mirror motion. The proposed scheme is an extreme example of the optical spring, where a mechanical oscillator is isolated from the environment and its mechanical frequency and macroscopic state can be manipulated solely through optical fields. We model the stability of the system and find a three-dimensional lattice of trapping points where cavity resonances allow for build up of optical field sufficient to support the weight of the mirror. Our scheme offers a unique platform for studying quantum and classical optomechanics and can potentially be used for precision gravitational field sensing and quantum state generation.Recently much effort has been directed toward the development of new fabrication methods and experimental techniques for controlling optomechanical interactions at the quantum level [1,2]. Optomechanical effects have been observed in mechanical objects with masses ranging from femtograms, as in nano-optomechanical systems [3], to kilograms in the case of gravitational wave antennae [4]. Reaching the quantum regime in optomechanical systems is fundamentally interesting as one is then in a position to prepare macroscopic quantum states, which can, for example, be employed in tests of large-scale quantum decoherence [5] and models of gravity [6,7]. The main barrier to reaching the quantum regime is thermalization resulting from intrinsic coupling to environmental reservoirs. This is generally hard to avoid since most mechanical oscillators are supported by some mechanical structure that acts as a bridge for thermal fluctuations. One method to limit thermalization is to operate in cryogenic environments. Nevertheless, the dissipation of energy through the mechanical support still contributes significantly to the decoherence of the mechanical state [8]. Fabrication of a phononic-band gap structure into the substrate [9] has been proposed as one way to reduce the dissipation. Optical trapping [10] and levitation [11][12][13][14] have also been suggested as possible routes to low-dissipation quantum optomechanics. In the recent proposals, despite the mechanical support being completely removed, scattering from the levitated object leads to interaction with the environment and lowering of optomechanical coupling.Radiation pressure within an optical resonator can be used to couple the mechanical oscillations of a suspended cavity mirror with the optical mode [15,16]. Such coupling between optical and mechanical systems can be used for a variety of applications, including precision measurement [17], the creation of a mechanical quantum harmonic oscillator [15,[18][19][20], control of quantum macroscopic coherence [21], the generation of squeezed light for quantum informa...