RESUMEN

Photonic crystal slab devices with subwavelength periods can be tailored to provide remarkable functionality, such as ultrahigh reflectivity in a structure only 200 nm in thickness. Accurate measurement of the characteristics of these structures is essential to compare their performance to theoretical expectations and to better understand the origin of unexpected behavior. In this work, we present a simple non-invasive method employing diffraction of a visible wavelength reference in the Littrow configuration for measuring the period of a photonic crystal slab. We have measured periods of our devices with uncertainty below 0.5 nm and expect that the uncertainty could easily be improved by an order of magnitude. In addition to facilitating development, our approach can be used to explore possible variations in the period of the photonic crystal due to its operating environment and aging.

RESUMEN

We demonstrate the tunable quantum beat of single photons through the co-development of core nonlinear nanophotonic technologies for frequency-domain manipulation of quantum states in a common physical platform. Spontaneous four-wave mixing in a nonlinear resonator is used to produce non-degenerate, quantum-correlated photon pairs. One photon from each pair is then frequency shifted, without degradation of photon statistics, using four-wave mixing Bragg scattering in a second nonlinear resonator. Fine tuning of the applied frequency shift enables tunable quantum interference of the two photons as they are impinged on a beamsplitter, with an oscillating signature that depends on their frequency difference. Our work showcases the potential of nonlinear nanophotonic devices as a valuable resource for photonic quantum information science.

RESUMEN

Single self-assembled InAs/GaAs quantum dots are promising bright sources of indistinguishable photons for quantum information science. However, their distribution in emission wavelength, due to inhomogeneous broadening inherent to their growth, has limited the ability to create multiple identical sources. Quantum frequency conversion can overcome this issue, particularly if implemented using scalable chip-integrated technologies. Here, we report the first demonstration of quantum frequency conversion of a quantum dot single-photon source on a silicon nanophotonic chip. Single photons from a quantum dot in a micropillar cavity are shifted in wavelength with an on-chip conversion efficiency ≈ 12 %, limited by the linewidth of the quantum dot photons. The intensity autocorrelation function g(2)(τ) for the frequency-converted light is antibunched with g(2)(0)=0.290±0.030, compared to the before-conversion value g(2)(0)=0.080±0.003. We demonstrate the suitability of our frequency conversion interface as a resource for quantum dot sources by characterizing its effectiveness across a wide span of input wavelengths (840 nm to 980 nm), and its ability to achieve tunable wavelength shifts difficult to obtain by other approaches.

RESUMEN

Single self-assembled InAs/GaAs quantum dots are a promising solid-state quantum technology, with which vacuum Rabi splitting, single-photon-level nonlinearities, and bright, pure, and indistinguishable single-photon generation having been demonstrated. For such achievements, nanofabrication is used to create structures in which the quantum dot preferentially interacts with strongly-confined optical modes. An open question is the extent to which such nanofabrication may also have an adverse influence, through the creation of traps and surface states that could induce blinking, spectral diffusion, and dephasing. Here, we use photoluminescence imaging to locate the positions of single InAs/GaAs quantum dots with respect to alignment marks with < 5 nm uncertainty, allowing us to measure their behavior before and after fabrication. We track the quantum dot emission linewidth and photon statistics as a function of distance from an etched surface, and find that the linewidth is significantly broadened (up to several GHz) for etched surfaces within a couple hundred nanometers of the quantum dot. However, we do not observe appreciable reduction of the quantum dot radiative efficiency due to blinking. We also show that atomic layer deposition can stabilize spectral diffusion of the quantum dot emission, and partially recover its linewidth.

RESUMEN

Ultrafast pulsed laser interferometry (PLI) can measure picometer displacements at sub-nanosecond time scales, such as acoustic waves and vibrations in microstructures. In this Letter, the effects of pulse characteristics on the accuracy of PLI are investigated through measurements and modeling. The results show that the effective wavelength of PLI, λeff, varies significantly as a function of overlap between the interfering pulses due to pulse asymmetry and nonlinear chirp. This variation presents a serious limitation on the accuracy of PLI if unaddressed. However, it is shown that a continuous-wave laser interferometer can be used to determine λeff with an uncertainty near 0.01%, making it possible to use PLI for accurate displacement measurements.

RESUMEN

Chronic migraine (CM) is a disabling painful condition that is associated with dementia and thrombotic disease. It has been proposed that carbon monoxide (CO) and iron may play a role in CM, and CO and iron are products of the heme oxygenase system which is widespread within the brain. Further, CO and iron enhance plasmatic coagulation in part via a fibrinogen-dependent mechanism. Thus, our goal was to determine whether patients with CM had experienced carboxyhemefibrinogen formation, iron bound fibrinogen formation and plasmatic hypercoagulability. Nonsmokers with CM were recruited after informed, written consent. Blood was collected, anticoagulated with sodium citrate, and then centrifuged with plasma stored at -80ºC. Carboxyhemefibrinogen formation, iron bound fibrinogen formation and coagulation kinetics were determined via thrombelastographic methods. Patient results were compared with laboratory values generated from normal control plasmas. Incidence (95% confidence intervals) of the various parameters was determined using the Clopper-Pearson method. Twenty-six CM patients (24 female) were recruited; they were 46±12 years old. With regard to fibrinogen modification, 88.5% (69.8%-97.6%) of CM patients had formation of carboxyhemefibrinogen, iron bound fibrinogen, or both. With regard to coagulation, 42.3% (23.4%-63.1%) of patients had abnormally decreased time to clot initiation, 80.8% (60.6%-93.4%) had abnormally large velocity of clot formation, and 46.2% (26.6%-66.7%) had abnormally strong clot strength. Patients with CM have a large incidence of carboxyhemefibrinogen and iron bound fibrinogen formation and hypercoagulability. Confirmatory and potential therapeutic clinical trials targeting CO and iron modified hypercoagulation as a source of pain and vascular disease in CM patients are indicated.

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Asunto(s)

RESUMEN

We study mode competition in a multimode "phonon laser" comprised of an optical cavity employing a highly reflective membrane as the output coupler. Mechanical gain is provided by the intracavity radiation pressure, to which many mechanical modes are coupled. We calculate the gain and find that strong oscillation in one mode suppresses the gain in other modes. For sufficiently strong oscillation, the gain of the other modes actually switches sign and becomes damping, a process we call "anomalous cooling." We demonstrate that mode competition leads to single-mode operation and find excellent agreement with our theory, including anomalous cooling.

RESUMEN

The material properties of silicon nitride (SiN) play an important role in the performance of SiN membranes used in optomechanical applications. An optimum design of a subwavelength high-contrast grating requires accurate knowledge of the membrane thickness and index of refraction, and its performance is ultimately limited by material absorption. Here we describe a cavity-enhanced method to measure the thickness and complex index of refraction of dielectric membranes with small, but nonzero, absorption coefficients. By determining Brewster's angle and an angle at which reflection is minimized by means of destructive interference, both the real part of the index of refraction and the sample thickness can be measured. A comparison of the losses in the empty cavity and the cavity containing the dielectric sample provides a measurement of the absorption.

RESUMEN

Resonant elastic scattering from InAs quantum dots (QDs) is studied by heterodyne spectroscopy. We show theoretically that heterodyne spectroscopy of a two-level quantum emitter is not sensitive to the inelastic fluorescence component. In practice, we easily measure the elastic emission even when the fluorescence is dominated by inelastic scattering. We are able to distinguish the resonant elastic fluorescence from a large background of scattered pump light by modulating the QD transition frequency with a surface acoustic wave. The signal linewidth is 250 Hz, limited by vibration-induced phase noise in the optical fibers used for resonant optical drive and fluorescence collection.

RESUMEN

This case report describes the successful treatment of chronic headache from intracranial hypotension with bilateral transforaminal (TF) lumbar epidural blood patches (EBPs). The patient is a 65-year-old male with chronic postural headaches. He had not had a headache-free day in more than 13 years. Conservative treatment and several interlaminar epidural blood patches were previously unsuccessful. A transforaminal EBP was performed under fluoroscopic guidance. Resolution of the headache occurred within 5 minutes of the procedure. After three months without a headache the patient had a return of the postural headache. A second transforaminal EBP was performed again with almost immediate resolution. The patient remains headache-free almost six months from the time of first TF blood patch. This is the first published report of the use of transforaminal epidural blood patches for the successful treatment of a headache lasting longer than 3 months.

RESUMEN

Ultralow-loss concave micromirrors with radius of curvature below 60 microm were fabricated by laser ablation and reflective coatings. A 10-microm-long microcavity with a mode volume of 40 microm(3) was set up with two such mirrors, and the cavity linewidth was measured both spectrally and temporally. The smallest linewidth obtained was 96 MHz, corresponding to a quality factor of 3.3x10(6) and a finesse in excess of 1.5x10(5). With these parameters, we estimate that a variety of solid-state quantum emitters coupled to the cavity may enter the strong coupling regime.

RESUMEN

In typical epitaxial quantum dots (QDs) the ideally degenerate optical excitons are energy split, preventing the formation of two-photon entanglement in a biexciton decay. We use an external field, here a continuous-wave laser tuned to the QD in the ac Stark limit, to cancel the splitting and create two-photon entanglement. Quantum-state tomography is used to construct the two-photon density matrix. When the splitting is removed it satisfies well-known entanglement tests. Our approach shows that polarization-entangled photons can be routinely produced in semiconductor nanostructures.

RESUMEN

The photoluminescence spectrum of a single quantum dot was recorded as a secondary resonant laser optically dressed either the vacuum-to-exciton or the exciton-to-biexciton transitions. High-resolution polarization-resolved measurements using a scanning Fabry-Pérot interferometer reveal splittings of the linearly polarized fine-structure states that are nondegenerate in an asymmetric quantum dot. These splittings manifest as either triplets or doublets and depend sensitively on laser intensity and detuning. Our approach realizes complete resonant control of a multiexcitonic system in emission, which can be either pulsed or continuous wave, and offers direct access to the emitted photons.

RESUMEN

We present a heterodyne Michelson interferometer for vibration measurement in which feedback is used to obviate the need to unwrap phase data. The Doppler shift of a vibrating target mirror is sensed interferometrically and compensated by means of a voltage-controlled oscillator driving an acousto-optic modulator. For frequencies within the servo bandwidth, the oscillator control voltage provides a direct measurement of the target velocity. Outside the servo bandwidth, phase-sensitive detection is used to evaluate high-frequency displacements. This approach is of great interest for the frequently-occurring situation where vibration amplitudes at low frequency exceed an optical wavelength, but knowledge of the vibration spectrum at high frequency is important as well.

RESUMEN

A system designed to apply Fabry-Perot interferometry to the measurement of displacements is described. Two adjacent modes of a Fabry-Perot cavity are probed, and both the absolute optical frequencies and their difference are used to determine displacements via changes in cavity length. Light is coupled to the cavity via an optical fiber, making the system ideal for remote sensing applications. Continuous interrogation is not necessary, as the cavity length is encoded in the free spectral range. The absolute uncertainty is determined to be below 10 pm, which for the largest displacement measured corresponds to a relative uncertainty of 4 x 10(-10). To my knowledge this is the smallest relative uncertainty in a displacement measurement ever demonstrated.

RESUMEN

Ultrashort laser pulses have thus far been used in two distinct modes. In the time domain, the pulses have allowed probing and manipulation of dynamics on a subpicosecond time scale. More recently, phase stabilization has produced optical frequency combs with absolute frequency reference across a broad bandwidth. Here we combine these two applications in a spectroscopic study of rubidium atoms. A wide-bandwidth, phase-stabilized femtosecond laser is used to monitor the real-time dynamic evolution of population transfer. Coherent pulse accumulation and quantum interference effects are observed and well modeled by theory. At the same time, the narrow linewidth of individual comb lines permits a precise and efficient determination of the global energy-level structure, providing a direct connection among the optical, terahertz, and radio-frequency domains. The mechanical action of the optical frequency comb on the atomic sample is explored and controlled, leading to precision spectroscopy with an appreciable reduction in systematic errors.