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We describe a design for phase-matched Bragg scattering for single-photon conversion between two arbitrary frequencies. The bandwidth of the Bragg scattering process is calculated and immunity against competing processes is discussed.

Visible light photon counters (VLPCs) are solid-state devices providing high quantum efficiency (QE) photon detection (>88%) with photon number resolving capability and low timing jitter (~250 ps). VLPC features high QE in the 0.4-1.0μm wavelength range, as the main photon absorption mechanism is provided by electron-hole pair generation across the silicon bandgap. In this paper, we will discuss the optical and electrical operating principles of VLPCs, and propose a range of device optimization paths that improves various aspects of VLPC for advanced quantum optics and quantum information processing experiments, both in the UV and the telecom wavelength range.

Recent investigations into high pixel count imaging using multiscale optics have led to a novel optical design for a wide field, gigapixel camera. We review the mechanical design and optical performance of this imager.

We describe a scalable architecture for general‐purpose quantum computation based on trapped ions and photonic interconnect network. The quantum computer is made up of several elementary logic units (ELUs) each containing a modest number of trapped ions representing physical qubits. Each ELU is provided with an optical communication port through which a photon entangled with a communication ion is extracted. Quantum entanglement is distributed between an arbitrary pair of ELUs through a reconfigurable photonic network, which can be utilized to perform two‐qubit quantum logic operation between any pair of physical qubits in the entire quantum computer. We show that this architecture can support universal, fault‐tolerant quantum computation.

Interference and coincidence detection of two photons emitted by two remote ions can lead to an entangled state which is a critical resource for scalable quantum information processing. Currently, the success probabilities of experimental realizations of this protocol are mainly limited by low coupling efficiency of a photon emitted by an ion into a single mode fiber. Here, we consider two strategies to enhance the collection probability of a photon emitted from a trapped Yb ion, using analytic methods that can be easily applied to other types of ion or neutral atoms. Our analysis shows that we can achieve fiber coupling efficiency of over 30% with an optical cavity made of a flat fiber tip and a spherical mirror. We also investigate ways to increase the fiber coupling efficiency using high numerical aperture optics, and show that collection probability of over 15% is possible with proper control of aberration., Comment: 11 pages, 8 figures

Testing a 2-Gigapixel 8 arcsec IFOV, 120° FOV camera requires integration of precision mechanical automation, optical instrumentation, image diagnostics, electronics and networking hardware. We detail the ongoing AWARE Wide Field Camera efforts.

The Scalable Multiplexed Ion Trap II (SMIT II) program based at Georgia Tech Research Institute (GTRI) was funded by IARPA during the period from August 2008 through July 2010. The overall goal was to design, fabricate and test surface ion traps through a closely correlated, multi-disciplinary approach involving design, simulation, fabrication and test facilities at GTRI and the Nanotechnology Research Center (NRC) at Georgia Tech. During the SMIT II program, surface ion traps were produced by microfabrication with properties that match the behavior predicted by simulations and are both reproducible and reliable. The trap designs include straight sections that can contain ion chains up to 20 to 50 ions in length using anharmonic electrostatic potentials as well as trap junctions in the form of a 90 cross. Important advances have also been made in integrating optics into the surface trap architecture. Repeated transport over hundreds of microns was demonstrated with no ion loss, facilitated by the optimized software estimates of the required voltages and very accurate control on the microfabricated electrode dimensions. Ion motional frequencies are in good agreement with the simulations. In summary, excellent progress has been made in producing scalable, reliable, reproducible surface ion traps during the SMIT II program.

We develop a layered quantum computer architecture, which is a systematic framework for tackling the individual challenges of developing a quantum computer while constructing a cohesive device design. We discuss many of the prominent techniques for implementing circuit-model quantum computing and introduce several new methods, with an emphasis on employing surface code quantum error correction. In doing so, we propose a new quantum computer architecture based on optical control of quantum dots. The timescales of physical hardware operations and logical, error-corrected quantum gates differ by several orders of magnitude. By dividing functionality into layers, we can design and analyze subsystems independently, demonstrating the value of our layered architectural approach. Using this concrete hardware platform, we provide resource analysis for executing fault-tolerant quantum algorithms for integer factoring and quantum simulation, finding that the quantum dot architecture we study could solve such problems on the timescale of days., 27 pages, 20 figures

We present a model as well as experimental results for a surface electrode radio-frequency Paul trap that has a circular electrode geometry well-suited for trapping of single ions and two-dimensional planar ion crystals. The trap design is compatible with microfabrication and offers a simple method by which the height of the trapped ions above the surface may be changed \emph{in situ}. We demonstrate trapping of single and few Sr+ ions over an ion height range of 200-1000 microns for several hours under Doppler laser cooling, and use these to characterize the trap, finding good agreement with our model., Comment: 10 pages, 11 figures, 1 table

High efficiency collection of photons emitted by a point source over a wide field-of-view (FoV) is crucial for many applications. Multi-scale optics over improved light collection by utilizing small optical components placed close to the optical source, while maintaining a wide FoV provided by conventional imaging optics. In this work, we demonstrate collection efficiency of 26% of photons emitted by a point-like source using a micromirror fabricated in silicon with no significant decrease in collection efficiency over a 10 mm object space., 4 pages, 4 figures

In this three-year research program, we designed and constructed a unique system capable of fusion bonding two wafers in an ultra-high vacuum environment. This system was integrated with a multi-chamber system that contains with XPS and UPS surface analysis tools and RF/DC sputtering system, to enable an experimental platform for insitu surface treatment, analysis, and bonding. We have developed various methods for preparing oxide-free silicon surfaces in UHV environment, and attempted in-situ fusion bonding of silicon wafer and InGaAs wafer. We have successfully demonstrated fusion bonding between HF-dipped silicon wafer and InGaAs wafer in UHV environment. On the device side, we have developed a detailed operational model of the VLPC devices. The device modeling capability provides us with the possibility of designing new generation of VLPC devices that feature improved performance characteristics, such as reduced timing jitter, high efficiency in the UV and telecommunication wavelength range, and lower dark counts.

Broad-range reflectance and ellipsometric spectra of high-quality epitaxial superconducting Ba 1-x K x BiO 3 thin films are reported. From these data, accurate spectral functions of Ba 1-x K x BiO 3 have been obtained. They are found to be quite similar to the in-plane spectra of the superconducting cuprates; in particular, the frequency dependence of the reflectance is nearly linear, while the dielectric loss function is nearly quadratic below the plasma edge in all of these compounds

Visible light photon counters (VLPCs) offer many attractive features as photon detectors, such as high quantum efficiency and photon number resolution. We report measurements of the single-photon timing jitter in a VLPC, a critical performance factor in a time-correlated single-photon counting measurement, in a fiber-coupled closed-cycle cryocooler. The measured timing jitter is 240 ps full-width-at-half-maximum at a wavelength of 550 nm, with a dark count rate of 25 000 counts per second. The timing jitter increases modestly at longer wavelengths to 300 ps at 1000 nm, and increases substantially at lower bias voltages as the quantum efficiency is reduced.

We present a beam steering system based on micro-electromechanical systems technology that features high speed steering of multiple laser beams over a broad wavelength range. By utilizing high speed micromirrors with a broadband metallic coating, our system has the flexibility to simultaneously incorporate a wide range of wavelengths and multiple beams. We demonstrate reconfiguration of two independent beams at different wavelengths (780 and 635 nm) across a common 5x5 array with 4 us settling time. Full simulation of the optical system provides insights on the scalability of the system. Such a system can provide a versatile tool for applications where fast laser multiplexing is necessary., Comment: 11 pages, 6 figures, submitted

We have demonstrated enhancement of point source light collection by a factor of 18 over a traditional f/2.55 imaging system (~17%) across a 15 mm object space by integrating a high numerical aperture micromirror.

Reflectance and spectroellipsometric measurements were performed on a high-quality c -axis oriented La 1.85 Sr 0.15 CuO 4 film to determine accurately the relevant spectral functions. The plasmon spectrum of La 1.85 CuO 4 consists of an optic plasmon at about 0.8 eV and possibility a broad band of acoustic plasmons. The charactristic quadratic frequency dependence of the loss function, Im (−1/ge)=βω 2 for ⩽ħω 〈 0.7 eV, has been observed. In view of similar behavior in YBa 2 Cu 3 O 7 , Bi 2 Sr 2 CaCu 2 O 8 and Tl 2 Ba 2 Ca 2 Cu 3 O 10 , this law seems to be universally obeyed in all high- T c cuprate superconductors.

The spectral functions of Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} thin films have been determined accurately from combined reflectance and spectroellipsometric measurements. The plasmon spectrum of Tl{sub 2}Ba{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10} consists of an optic plasmon at about 1.2 eV and a broad band of acoustic plasmons. The latter is revealed by the characteristic quadratic frequency dependence of the loss function, Im({minus}1/{epsilon})={beta}{omega}{sup 2}, for {h bar}{omega}{le}1 eV.

Fermion anti-bunching was directly observed by measuring the cross-covariance of the current fluctuations of partitioned electrons. A quantum point contact was used to inject single-mode electrons into a mesoscopic electron beam splitter device. The beam splitter output currents showed negative cross-covariance, indicating that the electrons arrived individually at the beam splitter and were randomly partitioned into two output channels. As the relative time delay between the outputs was changed, the observed ringing in the cross-covariance was consistent with the bandwidths used to monitor the fluctuations. The result demonstrates a fermion complement to the Hanbury Brown and Twiss experiment for photons.

A high-quantum-efficiency single-photon counting system has been developed. In this system, single photons were detected by a visible light photon counter operated at 6.9 K. The visible light photon counter is a solid state device that makes use of avalanches across a shallow impurity conduction band in silicon. Threefold tight shielding and viewports that worked as infrared blocking filters were used to eliminate the dark count caused by room-temperature radiation. Corrected quantum efficiencies as high as 88.2%±5% (at 694 nm) were observed, which we believe is the highest reported value for a single-photon detector. The dark count increased as the exponential of the quantum efficiency with changing temperature or bias voltage, and was 2.0 × 104 cps at the highest quantum efficiency.

Visible light photon counters feature noise-free avalanche multiplication and narrow pulse height distribution for single photon detection events. Such a well-defined pulse height distribution for a single photon detection event, combined with the fact that the avalanche multiplication is confined to a small area of the whole detector, opens up the possibility for the simultaneous detection of two photons. In this letter, we investigated this capability using twin photons generated by parametric down conversion, and present a high quantum efficiency (~ 47%) detection of two photons with good time resolution (~ 2 ns), which can be distinguished from a single-photon incidence with a small bit-error rate (~ 0.63%).

We propose a lateral-tandem organic photovoltaic system consisting of a dispersive-focusing element and continuously-tuned, series-connected sub-cells. The proposed system overcomes the efficiency limitation of organic photovoltaic devices by spectral re-distribution of incoming solar photons and their delivery to the wavelength-matched, resonant sub-cells. By numerical simulations, we demonstrate that optical resonance in a microcavity sub-cell with a metal/organic multilayer/metal structure can be tuned over a broad spectrum by varying the thickness of the organic multilayer. We show that the power-conversion efficiency exceeding 18% can be obtained in a lateral-tandem system employing an ideal dispersive-focusing element and the microcavity sub-cells.

Many infrared optical systems in wide-ranging applications such as surveillance and security frequently require large fields of view (FOVs). Often this necessitates a focal plane array (FPA) with a large number of pixels, which, in general, is very expensive. In a previous paper, we proposed a method for increasing the FOV without increasing the pixel resolution of the FPA by superimposing multiple sub-images within a static scene and disambiguating the observed data to reconstruct the original scene. This technique, in effect, allows each sub-image of the scene to share a single FPA, thereby increasing the FOV without compromising resolution. In this paper, we demonstrate the increase of FOVs in a realistic setting by physically generating a superimposed video from a single scene using an optical system employing a beamsplitter and a movable mirror. Without prior knowledge of the contents of the scene, we are able to disambiguate the two sub-images, successfully capturing both large-scale features and fine details in each sub-image. We improve upon our previous reconstruction approach by allowing each sub-image to have slowly changing components, carefully exploiting correlations between sequential video frames to achieve small mean errors and to reduce run times. We show the effectiveness of this improved approach by reconstructing the constituent images of a surveillance camera video.

We describe a novel method to track targets in a large field of view. This method simultaneously images multiple, encoded sub-fields of view onto a common focal plane. Sub-field encoding enables target tracking by creating a unique connection between target characteristics in superposition space and the target's true position in real space. This is accomplished without reconstructing a conventional image of the large field of view. Potential encoding schemes include spatial shift, rotation, and magnification. We briefly discuss each of these encoding schemes, but the main emphasis of the paper and all examples are based on one-dimensional spatial shift encoding. Simulation results are included to show the efficacy of the proposed sub-field encoding scheme.

Cellular interactions are subject to random fluctuations (noise) in quantities of interacting molecules. Noise presents a major challenge for the robust function of natural and engineered cellular networks. Past studies have analyzed how noise is regulated at the intracellular level. Cell–cell communication, however, may provide a complementary strategy to achieve robust gene expression by enabling the coupling of a cell with its environment and other cells. To gain insight into this issue, we have examined noise regulation by quorum sensing (QS), a mechanism by which many bacteria communicate through production and sensing of small diffusible signals. Using a stochastic model, we analyze a minimal QS motif in Gram-negative bacteria. Our analysis shows that diffusion of the QS signal, together with fast turnover of its transcriptional regulator, attenuates low-frequency components of extrinsic noise. We term this unique mechanism “diffusional dissipation” to emphasize the importance of fast signal turnover (or dissipation) by diffusion. We further show that this noise attenuation is a property of a more generic regulatory motif, of which QS is an implementation. Our results suggest that, in a QS system, an unstable transcriptional regulator may be favored for regulating expression of costly proteins that generate public goods., Author Summary Quorum sensing (QS) is a mechanism by which many bacteria regulate gene expression via the synthesis and detection of small, diffusible signals. Since its discovery, QS has been shown to control diverse physiological functions in numerous types of bacteria. It provides an elegant strategy for bacteria to sense their density and to achieve coordinated population behavior. By stochastic modeling, we show that QS can effectively reduce variability (“noise”) in the expression of its target genes. Surprisingly, the noise reduction does not significantly depend on the number of bacteria but rather results from the coupling of a bacterium and its environment through signal diffusion. Diffusion enables fast signal turnover, which, together with fast intracellular turnover of the cognate receptor of the signal, leads to noise reduction. Our work suggests a unique role of QS in achieving robust gene regulation, which is distinct from noise-regulation mechanisms that act at the intracellular level. As such, it offers novel insights into evolution of QS as well as its application in construction of synthetic gene circuits.

To provide scalability to quantum information processors utilizing trapped atoms or ions as quantum bits (qubits), the capability to address multiple individual qubits in a large array is needed. Microelectromechanical systems (MEMS) technology can be used to create a flexible and scalable optical system to direct the necessary laser beams to multiple qubit locations. We developed beam steering optics using controllable MEMS mirrors that enable one laser beam to address multiple qubit locations in a two-dimensional trap lattice. MEMS mirror settling times of approximately 10 micros were demonstrated, which allow for fast access time between qubits.

We describe microsystems approach to realizing a scalable quantum information processor in trapped ions and atoms. A flexible, MEMS-based beam steering system is demonstrated that enables random access of qubits in a 2-D array.

Many infrared optical systems in wide-ranging applications such as surveillance and security frequently require large fields of view. Often this necessitates a focal plane array (FPA) with a large number of pixels, which, in general, is very expensive. In this paper, we propose a method for increasing the field of view without increasing the pixel resolution of the FPA by superimposing the multiple subimages within a scene and disambiguating the observed data to reconstruct the original scene. This technique, in effect, allows each subimage of the scene to share a single FPA, thereby increasing the field of view without compromising resolution. To disambiguate the subimages, we develop wavelet regularized reconstruction methods which encourage sparsity in the solution. We present results from numerical experiments that demonstrate the effectiveness of this approach.

Extension of coded apertures to the MWIR introduces the effects of diffraction and other distortions not observed in shorter wavelength systems. A new approach is being developed under the DARPA/SPO funded LACOSTE (Large Area Coverage Optical search-while Track and Engage) program, that addresses the effects of diffraction while gaining the benefits of coded apertures, thus providing flexibility to vary resolution, possess sufficient light gathering power, and achieve a wide field of view (WFOV). The photonic MEMS "eyelid" array technology is currently being instantiated in this DARPA Surveillance program study as the "heart", mediating the flow of the incoming signal. However, speed, lifetime, packaging and scalability are critical factors for the MEMS "eyelid" technology which will determine system efficacy as well as military and commercial usefulness. The electronic eyelid array is the fundamental addressable unit for adaptive code generation and will allow the system to multiplex in time for increased resolution. The binary code which determines whether a 500μm eyelid is open or closed is referred to as the "eyelid code." Groups of eyelids can work together as a "super aperture" by virtue of a "macro-code." A macro code becomes relevant to describe how dispersed eyelids across the 0.19m x 0.19m aperture will function together. Dynamic aperture arrays were fabricated on both quartz and sapphire substrates for operation in the visible to MWIR. Both 8x8 and 40x40 element arrays were designed, fabricated, and tested with macro-codes consisting of 4, 8, and 16 unique combinations. The die were packaged and tested in ambient for robust eyelid operations. The point spread function was also measured in an optical setup with the eyelid arrays located in the aperture plane.

Microwave propagation through an electric-field-coupled metamaterial lens with a refractive index gradient is experimentally investigated. A gradient in the refractive index of the metamaterial is introduced by continuous tuning of a single parameter in the metamaterial elements. Experimental field maps, acquired in a planar waveguide, demonstrate that the planar gradient index lens can be used to collimate radiation from a line source, thereby forming a beam.

Scalable quantum information processing in ion traps or neutral atoms requires highly integrated and functional optical systems for qubit manipulation and detection. We discuss and demonstrate integrated optics technologies that are relevant for this application.

Recent experimental progress in quantum information processing with trapped ions have demonstrated most of the fundamental elements required to realize a scalable quantum computer. The next set of challenges lie in realization of a large number of qubits and the means to prepare, manipulate and measure them, leading to error-protected qubits and fault tolerant architectures. The integration of qubits necessarily require integrated optical approach as most of these operations involve interaction with photons. In this paper, we discuss integrated optics technologies and concrete optical designs needed for the physical realization of scalable quantum computer., Comment: 22 pages, 8 figures

We demonstrate a high quantum efficiency single photon detector with operating wavelength extended into the ultraviolet range (250nm-1000nm). Quantum efficiency of 6% is demonstrated at 300 nm, with estimated internal efficiency of 24%.

Utilizing simultaneous Coulomb blockade for electrons and holes in a p-n junction, we can realize a device where a single electron and a single hole are injected into the active region to produce a single photon with well-regulated time interval. The photons emitted from such a device can be studied with single photon counting detectors using a Si solid-state photomultiplier. We report locking of the photon emission with external driving pulse, in the regime where one electron and one hole are injected into the active region on the average.

Quantum computation provides non-trivial advantages over classical computation, by enabling fundamentally more efficient algorithms for important problems like factoring and database search. Free space Gaussian beams controlled by MEMS micromirrors were proposed as a means to precisely address the ions on a chip. Here, we investigate the design space of such elements based on an existing ion-trap experimental setup and characterize their performance. This design approach can be readily adapted to meet the requirements for a variety of other trapped ion or neutral atom experiments

Realizing ion trap based large-scale quantum information processor requires integrated optics technologies. We design and characterize basic optical beam steering system using micromirrors as a first step towards constructing high-quality functional integrated optics.

Si solid state photomultipliers utilize impact ionization of shallow impurity donor levels to create an avalanche multiplication when triggered by a photoexcited hole. The distribution of pulse height from a single photon detection event shows narrow dispersion, which implies that the avalanche multiplication process in these devices is inherently noise-free. We have measured the excess noise factor using two different techniques, digital pulse height analysis and analog noise power measurement. The results demonstrate nearly noise-free avalanche multiplication accomplished in these devices.

Summary form only given. It has been demonstrated that large-scale transparent optical switches can be built using micro-electro-mechanical systems (MEMS) technology. An added advantage of transparent switches is that the switching function is independent of data rate and data format. In this paper, we discuss a three-dimensional MEMS optical crossconnect (OXC) switch fabric, with a focus on the optical performance.

As telecom networks increase in complexity there is a need for systems capable of manage numerous optical signals. Many of the channel-manipulation functions can be done more effectively in the optical domain. MEMS devices are especially well suited for this functions since they can offer large number of degrees of freedom in a limited space, thus providing high levels of optical integration. We have designed, fabricated and tested optical MEMS devices at the core of Optical Cross Connects, WDM spectrum equalizers and Optical Add-Drop multiplexors based on different fabrication technologies such as polySi surface micromachining, single crystal SOI and combination of both. We show specific examples of these devices, discussing design trade-offs, fabrication requirements and optical performance in each case.

We report drift-free two-axis tilting MEMS mirrors fabricated from single crystal silicon. These micromirrors survive 1000 G mechanical shocks and exhibit angular stability better than 4 millidegrees under simulated office vibrations. Two hermetically sealed mirror arrays were used to build a low-loss nonblocking 1000/spl times/1000-port optical cross-connect switch.

Summary form only given. We discuss recent progress in two single-photonic devices: a single-photon turnstile device and a solid-state photomultiplier. A single photon turnstile device is based on the simultaneous Coulomb-blockade effect for electrons and holes in a mesoscopic, double barrier, pn-tunnel junction. By periodically modulating the bias voltage between the electron and hole resonant tunneling conditions, we can periodically inject a single electron and a single hole into the central island, which will be followed by single-photon emission. A double-barrier GaAs-AlGaAs pn-tunnel junction wafer is grown by molecular beam epitaxy.

A 1296-port MEMS transparent optical crossconnect with 5.1dB/spl plusmn/1.1dB insertion loss at 1550 nm is reported. Measured worst-case optical crosstalk in a fabric was n38 dB and nominal switching rise/fall times were 5 ms. A 2.07 petabit/s switch capacity was verified upon cross-connecting a forty-channel by 40 Gb/s DWDM data stream through a prototype fabric.

The ability to individually manipulate the increasing number of qubits is one of the many challenges towards scalable quantum information processing with trapped ions. Using micro-mirrors fabricated with micro-electromechanical systems technology, we focus laser beams on individual ions in a linear chain and steer the focal point in two dimensions. We demonstrate sequential single qubit gates on multiple 171Yb+ qubits and characterize the gate performance using quantum state tomography. Our system features negligible crosstalk to neighboring ions (

System requirements for many military electro-optic and IR camera systems reflect the need for both wide-field-of-view situational awareness as well as high-resolution imaging for target identification. In this work we present a new imaging system architecture designed to perform both functions simultaneously and the AWARE 10 camera as an example at visible wavelengths. We first describe the basic system architecture and user interface followed by a laboratory characterization of the system optical performance. We then describe a field experiment in which the camera was used to identify several maritime targets at varying range. The experimental results indicate that users of the system are able to correctly identify ~10 m targets at between 4 and 6 km with 70% accuracy.

The main focus of the discussion in this chapter is the detection of single photons. The ultimate goal for sensitive photodetection would be the detection of single photons with high quantum efficiency (QE) and low error probability. Experimental techniques for single-photon detection have made tremendous progress in recent years. Successful development of such a sensitive photodetector will be useful for various optical precision measurements like spectroscopy and interferometry. Besides these conventional applications, the development of a high-performance single-photon counter has been crucial for recent progress in quantum information technology utilizing single photons [215], such as quantum cryptography [35, 176, 177], quantum computation [174, 236] and quantum teleportation [28, 67], and fundamental tests of quantum mechanics such as a loophole-free test of Bell inequality experiment [43, 44, 6, 59, 135, 204].

The previous chapters of this book concentrated on the intensity noise suppression of light generated by a p-n junction light emitter in the macroscopic limit, where the charging energy due to a single carrier traversing the depletion region of the junction is negligible compared to the characteristic thermal energy of the system. With today’s semiconductor fabrication and cryogenic technologies, it is possible to reach the opposite regime where the single carrier charging energy, e2/C, is larger than the thermal energy, kBT. The next two chapters will describe p-n junctions operating in this mesoscopic limit, where a single-carrier injection event completely suppresses the rate for a subsequent carrier-injection event. Such limit was first discussed in the context of mesoscopic M-I-M junctions [10, 11], and is commonly referred to as Coulomb blockade effect [79].

The noise characteristics of semiconductor lasers as seen in experiments strongly depend on laser structure. In general, transverse-junction-stripe (TJS) lasers demonstrate lower noise and more often produce squeezing. The maximum squeezing was observed in the TJS lasers which were made from wafers grown by an old liquid-phase epitaxy (LPE) technique [198]. This technique has become obsolete, and wafers are now grown using the metal-organic chemical vapor deposition (MOCVD) technique. MOCVDgrown lasers showed higher noise than the LPE-grown lasers. Until recently, the MOCVD process had not been optimized for the generation of a high level of squeezing.

The model and discussion presented in Chap. 10 demonstrate the possibility of observing the Coulomb blockade effect in mesoscopic p-n junctions and further imply the possible realization of a “single-photon turnstile device” that generates single photons with a well-defined time interval. Since the arrival time of each photon can be predicted, such single photon states are called “heralded single photons” [104, 269]. This chapter describes the experimental progress towards realization of such single-photon states using a mesoscopic semiconductor p-n junction. The first half of the chapter discusses the fabrication of a mesoscopic p—n junction in a GaAs material system. The second half describes the electrical and optical characteristics of these devices measured at low temperatures. A Coulomb staircase was observed in the electrical measurement, which clearly demonstrates the Coulomb blockade effect present in these devices. Device operation in the turnstile mode indicates that the time interval between single photons is regulated to better than the Poissonian limit. This implies that nonclassical single photons can be generated from a mesoscopic p—n junction utilizing the Coulomb blockade effect.

Amplitude-squeezed light can enhance the sensitivity of interferometric measurements in the same way as it does for spectroscopy. The ultimate limits of a measurement are sought in many fundamental physics experiments which are trying to measure very weak interactions. One example of such difficult but exciting experiments is the detection of gravitational wave which has remained elusive since Einstein predicted the existence of a gravitational wave in general relativity theory. A very-large-scale optical interferometer is now considered as the most promising gravitational wave detector owing to the recent progress of lasers and other optical-component technologies [39]. Inoue, Yamamoto, and Bjork proposed a new scheme to realize sub-shotnoise interferometry using amplitude-squeezed light generated directly from a constant-current-driven semiconductor laser [107]. The idea was to inject the amplitude-squeezed light from an injection-locked semiconductor laser into the open port of a dark fringe interferometer. The output noise of the interferometer was reduced to the noise level of the squeezed laser when the interferometer was operated at a dark-fringe.

Frequency modulation (FM) spectroscopy is a very sensitive technique for measuring very small interactions. It was originally proposed as a method for locking a microwave source to a cavity [192] but was later extended to optical carrier frequencies by Bjorklund in the early 1980s [24]. Applications of FM spectroscopy include trace molecular detection, Raman spectroscopy, combustion control, fluorescence spectroscopy, process monitoring, and laser stabilization [41, 86, 148, 153].