Integrated Photonic Sensing

Loss is a critical roadblock to achieving photonic quantum-enhanced technologies. We explore a modular platform for implementing integrated photonics experiments and consider the effects of loss at different stages of these experiments, including state preparation, manipulation and measurement. We frame our discussion mainly in the context of quantum sensing and focus particularly on the use of loss-tolerant Holland-Burnett states for optical phase estimation. In particular, we discuss spontaneous four-wave mixing in standard birefringent fibre as a source of pure, heralded single photons and present methods of optimising such sources. We also outline a route to programmable circuits which allow the control of photonic interactions even in the presence of fabrication imperfections and describe a ratiometric characterisation method for beam splitters which allows the characterisation of complex circuits without the need for full process tomography. Finally, we present a framework for performing state tomography on heralded states using lossy measurement devices. This is motivated by a calculation of the effects of fabrication imperfections on precision measurement using Holland-Burnett states.Comment: 19 pages, 7 figure

Quantum Optical Systems for the Implementation of Quantum Information Processing

We review the field of Quantum Optical Information from elementary considerations through to quantum computation schemes. We illustrate our discussion with descriptions of experimental demonstrations of key communication and processing tasks from the last decade and also look forward to the key results likely in the next decade. We examine both discrete (single photon) type processing as well as those which employ continuous variable manipulations. The mathematical formalism is kept to the minimum needed to understand the key theoretical and experimental results

Optimal quantum control of atomic wave packets in optical lattices

In this work, I investigate the motional control and the transport of single neutral atoms trapped in an optical conveyor belt. The main goal is to prepare the atoms in the vibrational ground state of the trapping potential with high efficiency and keep the atoms in this state after fast non-adiabatic transport. In this group, the conveyor belt is used in two systems: (i) In an atom-cavity system, the three-dimensional ground state is prepared by means of carrier-free Raman sideband cooling for the first time. (ii) I use one-dimensional microwave sideband cooling in a state-dependent optical lattice and analyze with a new temperature model the influence of the anharmonic shape of the trapping potential. In the next step, I present a numerical simulation of atom transport. Optimal quantum control theory is used to find transport sequences for different durations without heating atoms out of the ground state. The measurements with these new sequences demonstrate that atoms can be transported by a factor two faster, with higher fidelity and robustness against experimental imperfections. Additionally, I analyze the dynamics of atom transport for sequences of multiple transport steps, which are required for quantum walk experiments. A proof-of-principle measurement demonstrates open-loop live feedback optimization of transport sequences with the experiment. This technique can further compensate experimental imperfections that are not taken into account in the numerical calculation. In the last part, I examine the fundamental limit of fast atom transport, the so-called quantum speed limit. It is defined as the minimum time that a quantum state requires to evolve into an orthogonal one. I investigate the dependencies of this boundary on different trap depths and the finite radial temperature

Coupling qualitative and quantitative analyses of pharmaceutical materials enabled by second harmonic generation microscopy

The detection and characterization of crystallinity is critical throughout the drug development process. From the initial establishment of an active pharmaceutical ingredient’s (API) crystal structure to stability testing and quality control, the phase of an API affects the solubility, bioavailability, stability, and efficacy of a drug product. Second harmonic generation (SHG) microscopy has recently been developed as a selective and rapid method for imaging crystallinity in drug formulations. While SHG microscopy can enable the high signal-to-noise (SNR) detection of crystallinity, the intrinsic chemical information content within SHG images is relatively low. In cases of trace crystallinity and/ or small crystal volumes, new tools capable of rapid, qualitative crystal characterization are needed to fill this measurement gap. Several strategies for increasing the chemical information content of SHG microscopy were developed. Following combined computational and experimental studies to help determine the body of crystalline API structures amenable to imaging by SHG microscopy, measurements by confocal Raman spectroscopy and synchrotron X-ray diffraction were performed on regions of interest (ROI) identified by SHG. In both cases, spatial restriction of the spectroscopic technique to these regions of interest lowered the detection limits of Raman and synchrotron X-ray diffraction by several orders of magnitude. To further expand the capabilities of SHG microscopy, nonlinear optical Stokes ellipsometric (NOSE) microscopy was developed to assess crystal structure characteristics through the polarization dependence of SHG. Rapid (8 MHz) polarization modulation enabled NOSE microscopies at video rates (up to 15 Hz). Following development and validation, NOSE microscopy was used in conjunction with an iterative, nonlinear least-squares fitting algorithm to discriminate polymorphic crystal forms of the small molecule D-mannitol. Finally, to extend the linear dynamic range of photon counting measurements as described here-in, a novel digital filter derived from linear discriminant analysis (LDA) was developed and validated via theoretical and experimental nonlinear optical (NLO) measurements

Quantum Memories. A Review based on the European Integrated Project "Qubit Applications (QAP)"

We perform a review of various approaches to the implementation of quantum memories, with an emphasis on activities within the quantum memory sub-project of the EU Integrated Project "Qubit Applications". We begin with a brief overview over different applications for quantum memories and different types of quantum memories. We discuss the most important criteria for assessing quantum memory performance and the most important physical requirements. Then we review the different approaches represented in "Qubit Applications" in some detail. They include solid-state atomic ensembles, NV centers, quantum dots, single atoms, atomic gases and optical phonons in diamond. We compare the different approaches using the discussed criteria.Comment: 22 pages, 12 figure

Modern optical astronomy: technology and impact of interferometry

The present `state of the art' and the path to future progress in high spatial resolution imaging interferometry is reviewed. The review begins with a treatment of the fundamentals of stellar optical interferometry, the origin, properties, optical effects of turbulence in the Earth's atmosphere, the passive methods that are applied on a single telescope to overcome atmospheric image degradation such as speckle interferometry, and various other techniques. These topics include differential speckle interferometry, speckle spectroscopy and polarimetry, phase diversity, wavefront shearing interferometry, phase-closure methods, dark speckle imaging, as well as the limitations imposed by the detectors on the performance of speckle imaging. A brief account is given of the technological innovation of adaptive-optics (AO) to compensate such atmospheric effects on the image in real time. A major advancement involves the transition from single-aperture to the dilute-aperture interferometry using multiple telescopes. Therefore, the review deals with recent developments involving ground-based, and space-based optical arrays. Emphasis is placed on the problems specific to delay-lines, beam recombination, polarization, dispersion, fringe-tracking, bootstrapping, coherencing and cophasing, and recovery of the visibility functions. The role of AO in enhancing visibilities is also discussed. The applications of interferometry, such as imaging, astrometry, and nulling are described. The mathematical intricacies of the various `post-detection' image-processing techniques are examined critically. The review concludes with a discussion of the astrophysical importance and the perspectives of interferometry.Comment: 65 pages LaTeX file including 23 figures. Reviews of Modern Physics, 2002, to appear in April issu

Electron spin resonance of nitrogen-vacancy centers in optically trapped nanodiamonds

Using an optical tweezers apparatus, we demonstrate three-dimensional control of nanodiamonds in solution with simultaneous readout of ground-state electron-spin resonance (ESR) transitions in an ensemble of diamond nitrogen-vacancy (NV) color centers. Despite the motion and random orientation of NV centers suspended in the optical trap, we observe distinct peaks in the measured ESR spectra qualitatively similar to the same measurement in bulk. Accounting for the random dynamics, we model the ESR spectra observed in an externally applied magnetic field to enable d.c. magnetometry in solution. We estimate the d.c. magnetic field sensitivity based on variations in ESR line shapes to be ~50 microTesla/Hz^1/2. This technique may provide a pathway for spin-based magnetic, electric, and thermal sensing in fluidic environments and biophysical systems inaccessible to existing scanning probe techniques.Comment: 29 pages, 13 figures for manuscript and supporting informatio