Quantum mechanics allows us to use nonclassical states of light to make measurements with a greater precision than comparable classical states. Here an experiment is presented that squeezes the polarization state of three photons. We demonstrate the deep connection that exists between squeezing and entanglement, unifying the squeezed state and multi-photon entangled state approaches to quantum metrology. For the first time we observe the phenomenon of over-squeezing where a system is squeezed to the point that further squeezing leads to a counter-intuitive increase in measurement uncertainty. Quasi-probability distributions on the surface of a Poincaré sphere are the most natural way to represent the topology of our polarization states. Using this representation it is easy to observe the squeezing and over-squeezing behaviour of our photon states. Work is also presented on two different technologies for generating nonclassical states of light. The first is based on the nonlinear process of spontaneous parametric downconversion to produce pairs of photons. With this source up to 200,000 pairs of photons/s have been collected into single-mode fibre, and over 100 double pairs/s have been detected. This downconversion source is suitable for use in a wide variety of multi-qubit quantum information applications. The second source presented is a single-photon source based on semiconductor quantum dots. The single-photon character of the source is verified using a Hanbury Brown-Twiss interferometer.

Diss. (sammanfattning) Umeå : Umeå universitet, 2005. / Härtill 6 uppsatser.

Thesis (Ph. D.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Vita. "December 2005" Includes bibliographical references.

xvii, 163 p. ; ill. (some col.) A print copy of this title is available from the UO Libraries, under the call number: SCIENCE QC446.2.C85 2008 / We present experimental and theoretical studies of a hemispherical, high-solid-angle external optical micro-cavity strongly coupled to nanoscale optical centers for cavity-quantum electrodynamics (QED) strong coupling and efficient single-photon sources. Implementations of single-photon sources based on various optical centers have been reported in the last three decades. The need for efficient single-photon sources, however, is still a major challenge in the context of quantum information processing. In order to efficiently produce single photons single optical centers are coupled to a resonant high-finesse optical micro-cavity. A cavity can channel the spontaneously emitted photons into a well-defined spatial mode and in a desired direction to improve the overall efficiency, and can alter the spectral width of the emission. It can also provide an environment where dissipative mechanisms are overcome so that a pure-quantum-state emission takes place. We engineered a hemispherical optical micro-cavity that is comprised of a planar distributed Bragg reflector (DBR) mirror, and a concave dielectric mirror having a radius of curvature 60 μm. Nanoscale semiconductor optical centers (quantum dots) are placed at the cavity mode waist at the planar mirror and are located at an antinode of the cavity field to maximize the coherent interaction rate. The three-dimensional scannable optical cavity allows both spatial and spectral selection to ensure addressing single optical centers. This unique micro-cavity design will potentially enable reaching the cavity-QED strong-coupling regime and realize the deterministic production of single photons. This cavity can also be operated with a standard planar dielectric mirror replacing the semiconductor DBR mirror. Such an all-dielectric cavity may find uses in atomic cavity-QED or cold-atom studies. We formulated a theory of single-photon emission in the cavity-QED strong-coupling regime that includes pure dipole dephasing and radiative decay both through the cavity mirror and into the side directions. This allows, for the first time, full modeling of the emission quantum efficiency, and the spectrum of the single photons emitted into the useful output mode of the, cavity. / Adviser: Michael G. Raymer

Plasmonics have been used to enhance the interaction of light with metallic nanostructures and lanthanide-doped upconversion nanocrystals. This enhancement can be achieved by using specific structures, materials, and plasmonic resonators at the emission and absorption wavelengths of the particles. This dissertation is based on four projects, which are mainly about the interaction of light and matter in metallic nanostructures and the up-conversion of nanocrystals using plasmonic resonators. In metal-insulator-metal systems, the cavity's resonant length is determined by the plasmon wavevector and the phase of reflection from the end faces. In general, the resonance length is not a simple multiple of the half-wavelength due to the significant reflection phase. As a result, in order to have a better understanding of MIM cavity resonances, the reflection phase must be calculated correctly. In the first project, the reflection phase obtained by SPPs upon reflection off the slit end-faces is calculated analytically using a simple mode matching model for real metals showing both dispersion and loss. The technique is similar to previous works, with the exception that we use the unconjugated version of the orthogonality relation. The results show good agreement with the experimental data. By having a strong grasp of the SPP dispersion, this technique aids in the design of plasmonic devices for operation at a specific wavelength. Single-photon sources are optical sources capable of emitting a single photon. A single lanthanide ion within a plasmonic nano structure with a large emission enhancement is one technique to generate a single-photon source at 1550 nm, which is a low-loss band used in fibre optics. In the second project, plasmonic double nanohole resonators are fabricated using colloidal lithography. These structures have been used to enhance the emission from low-concentration erbium emitters. The results indicate that different levels of emissions exist based on the amount of Er contained inside the nanocrystals. These findings would be an excellent starting point for developing a single-photon source operating at a 1550 nm wavelength employing erbium. Because not only can it increase the emission rate from erbium emitters, but it also helps to find and isolate a single emitter, which gives a stable single photon source. Because the surface plasmon resonance is exponentially coupled to the surface, it exhibits excellent sensitivity to changes in the refractive index near the surface. This is the underlying principle of commercially available surface plasmon resonance biosensors. Due to the wide range of applications in water quality testing and biosensing, it is critical to developing highly sensitive sensors that are compatible with commercial sensors. In the third project, we develop a design for SRSP sensing using a rectangular stripe grating and a 10 nm thick gold film. The 10 nm gold layer is sufficiently thick to enable continuous films to be formed using standard deposition procedures. We demonstrate that by employing rigorous coupled-wave analysis, the surface sensitivity of these films to an adlayer is increased by 3.3 times in angle units and the resolution is increased by fourfold while working at the commercial SPR system wavelength of 760 nm. Before trapping a particle in double nanohole apertures, we must first locate the double nanohole on the sample (gold on glass with apertures) and compare the scanning electron microscopy images with the image on the camera in the optical setup using certain markers. In the fourth project, to make DNH aperture trapping easier, we provide a polarization and transmission dependency approach for localizing and orienting DNHs on a substrate. This method provides a time and cost-effective way to ease the experimental process. This technique may also be used to localize different aperture clusters and single holes. / Graduate

Digital silicon photomultipliers (dSiPMs) and single-photon avalanche diode (SPAD) imagers are optical sensing systems formed from the integration of time-to-digital converters (TDCs) with arrays of highly sensitive photodetectors known as SPADs. TDCs are high-performance mixed-signal circuits capable of timestamping events with picosecond level resolution. The digital operation mechanisms of SPADs allow for their outputs to be sent to TDCs, where the timestamps of individual photon detections are recorded. In recent years, time-resolved SPAD-based sensors have been a heavily studied topic due to their exceptional performance potential in biomedical imaging applications, including time-of-flight (ToF) positron emission tomography (PET), fluorescence lifetime imaging microscopy (FLIM), and diffuse optical tomography (DOT). This work targets the optimization of these sensors in low-cost standard complementary metal-oxide-semiconductor (CMOS) processes. Firstly, this thesis provides a detailed review of the work accomplished in CMOS TDCs and their integration in SPAD-based sensors. Next, a feedback time amplification TDC was designed and tested in the TSMC 65 nm process that can achieve < 5 ps timing resolution in a very compact area of 0.016 mm2. The design is then described for a multi-time-gated array of p+/n-well SPADs that aims to mitigate SPAD dark noise while providing high-speed imaging by applying shifted gate windows simultaneously to an array of SPADs. The p+/n-well SPAD is first characterized in a passive quench configuration where it demonstrated a maximum dark count rate of 44.9 kHz, 18.1% peak PDP at 420 nm, and 0.82 ns timing jitter at a 0.7 V excess bias. While the current multi-time-gated prototype is not fully functional, the measurement results for individual pixels of the multi-time-gated array showed a 3.25 ns median gate window with a 2.2x 10-4 dark count probability for a 0.7 V excess bias, with 440 ps timing resolution and ~1 LSBrms timing jitter. Based on the results, limitations of the current design and sources for future improvement are then discussed in detail. / Thesis / Master of Applied Science (MASc) / Medical imaging plays a key role in the diagnosis of diseases like cancer, and as such, the optimized performance of medical imaging systems is a large area of research. Recently, highly sensitive photodetectors known as single-photon avalanche diodes (SPADs) were integrated with high-performance timing circuits known as time-to-digital converters (TDCs) to form digital silicon photomultipliers (dSiPMs) and SPAD imagers. DSiPMs and SPAD imagers are capable of timestamping the detection of individual photons with a very high level of accuracy in order to generate biomedical images. This thesis focuses on the design and measurement of these sensors using standard fabrication processes with the aim of working towards high-performance medical imaging sensors at a low cost. Firstly, we review the results achieved in TDCs and SPAD-based sensors within the recent literature. Following that, we present the design and performance results of a custom-designed TDC that aims to achieve state-of-the-art performance within a small area in order to maintain low-cost and optimal integration with SPADs. Next, the design is described for an array of custom time-gated SPADs with integrated TDCs. Finally, the SPAD is characterized in two different configurations to identify sources of improvement for future design iterations.

Fluorescence lifetime imaging (FLIM) has the potential to provide rapid screening and detection of diseases. However, time-resolved fluorescence measurements require high-performance detectors with single-photon sensitivity and sub-nanosecond time resolution. These systems should also be compact, reliable, inexpensive, and easily deployable for laboratory and clinical applications. It is with these applications in mind that the development of single photon avalanche diodes (SPAD) and time-to-digital converter (TDC) prototype integrated circuits (IC) in standard digital CMOS have been pursued in this thesis. SPAD and TDC ICs were designed and fabricated in 130 nm IBM CMOS technology and then intensively studied. Several different SPAD pixels were modeled and designed, and the electro-optical performance was characterized and comparatively studied. By repurposing existing design layers of a standard CMOS process, the fabricated SPAD pixel test structures achieved up to 20× improvement of dark count rate (DCR) compared to previous designs. Optical measurements also showed up to 10× improvement in the detection limits for low-level light. Detailed dark noise characterization was performed at various temperatures using free-running and time-gated modes of operation. Optimal operating conditions were found for minimal afterpulsing effects. The SPAD’s capability to accurately measure fast fluorescence decays was also demonstrated in a practical setting with the lifetime measurements of two fluorophores, Rhodamine 6G and Ruby crystal, which have fluorescence lifetimes of approximately 4 ns and 3 ms, respectively. A fast and accurate TDC prototype circuit for time-correlated single-photon counting (TCSPC) applications was designed, fabricated and characterized. With a coarse-fine delay line architecture, the TDC size was reduced without compromising its linearity and jitter performance. Extensive characterization of the fabricated SPAD and TDC ICs shows that the measured performance met the stated design goals. / Thesis / Doctor of Philosophy (PhD)

Single-photon avalanche diodes (SPADs) capable of single photon detection are promising optical sensors for use as receivers in optical wireless communication (OWC) systems. In SPAD-based receivers, the intersymbol interference (ISI) effect caused by dead time is an important drawback that limits performance. In this thesis, we propose two novel SPAD operation receivers to reduce the ISI effect in SPAD-based OWC. To validate the feasibility of these two modes, we design a free-running SPAD front-end circuit with post-layout transient simulation results. This SPAD circuit is improved by a novel mixed passive-active quench and reset front-end circuit that achieves a very short dead time. Based on the traditional free-running mode, we design the clock-driven mode and time-gated mode to reduce the ISI effect through time-controlled operating signals. In this work, we develop a new simulation system to assess the ISI effect in On-Off Keying (OOK) modulated communication and pulse position modulated (PPM) communication. To accurately evaluate these three modes, we build a OWC platform to test our proposed SPAD receiver manufactured by TSMC 65 nm process. The Test results demonstrate that the clock-driven mode and time-gated mode receivers can improve the bit error rate (BER) performance in low data rate communication and high data rate high optical power communication, respectively. Moreover, compared to the free-running mode, the two proposed time-controlled modes achieve higher data rate communication and better noise tolerance ability in SPAD-based OWC. / Thesis / Master of Applied Science (MASc) / Optical communication involves using light as a signal to transmit information, and it is currently a highly popular field of research. However, optical receivers used in this type of communication often require specific conditions, which can limit the overall performance of the communication system. To address this issue, we have developed an optical sensor tailored for optical communication. This sensor boasts exceptional sensitivity, allowing it to detect individual particles of light, thereby substantially reducing the demand for signal intensity in the optical communication system. Moreover, we have devised three operational circuits that enhance the sensor's responsiveness to signals under specific communication conditions. We have created a mathematical model to evaluate the proposed optical sensor and the designed circuits, and subsequently manufactured the optical sensor. Both the simulation results and the actual test outcomes unequivocally demonstrate that our proposed sensor has the potential to enhance the performance of optical communication systems.

No description available.

Accurate attenuation correction is essential for quantitative positron emission tomography. Typically, this correction is based on a coincidence transmission measurement using an external source of positron emitter, which is positioned close to the detectors. This technique suffers from poor statistical quality and high dead time losses, especially with a high transmission source strength. We have proposed and tested the use of single photon transmission measurement with a rotating rod source, to measure the attenuation correction factors (ACFs). The singles projections are resampled into the coincidence geometry using the detector positions and the r,)d source location. A nonparalyzable dead time correction algorithm was developed for the block detectors used in the McMaster PET scanner. Transaxial resolution is approximately 6 mm, which is comparable to emission scanning performance. Axial resolution is about 25 mm, with only crude source collimation. ACFs are underestimated by approximately 10% due to increased crossplane scatter, compared to coincidence transmission scanning. Effective source collimation is necessary to obtain suitable axial resolution and improved accuracy. The response of the correction factors to object density is linear to within 15%, when comparing singles transmission measurement to current coincidence transmission measurement. The major advantage of using singles transmission measurement IS a dramatically increased count rate. A factor of seven increase in count rate over coincidence scanning is possible with a 2 mCi transmission rod source. There are no randoms counted in singles transmission scans, which makes the measured count rate nearly linearly proportional with source activity. Singles detector dead time is approximately 6% in the detectors opposite a 2 mCi rod source. Present hardware and software precludes the application of this technique in a clinical environment. We anticipate that real time acquisition of detector singles can reduce the transmission scanning time to under 2 minutes, and produce attenuation coefficient images with under 2% noise. This is a significant improvement compared to the current coincidence transmission technique. / Thesis / Master of Science (MS)