Light Shift Research Articles

Fast Control of Atom-Light Interaction in a Narrow Linewidth Cavity.

We propose a method to exploit high-finesse optical resonators for light-assisted coherent manipulation of atomic ensembles, overcoming the limit imposed by the finite response time of the cavity. The key element of our scheme is to rapidly switch the interaction between the atoms and the cavity field with an auxiliary control process as, for example, the light shift induced by an optical beam. The scheme is applicable to other atomic species, both in trapped and free fall configurations, and can be adopted to control the internal and/or external atomic degrees of freedom. Our method will open new possibilities in cavity-aided atom interferometry and in the preparation of highly nonclassical atomic states.

Coupling a Single Trapped Atom to a Whispering-Gallery-Mode Microresonator

We demonstrate trapping of a single ^{85}Rb atom at a distance of about 200nm from the surface of a whispering-gallery-mode bottle microresonator. The atom is trapped in an optical potential, which is created by retroreflecting a red-detuned focused laser beam from the resonator surface. We counteract the trap-induced light shift of the atomic transition frequency by superposing a second laser beam. This allows us to observe a vacuum Rabi splitting in the excitation spectrum of the coupled atom-resonator system. This first demonstration of stable and controlled interaction of a single atom with a whispering-gallery mode in the strong coupling regime opens up the route toward the implementation of quantum protocols and applications that harvest the chiral atom-light coupling present in this class of resonators.

Implications of Wound Healing on Subcutaneous Photovoltaic Energy Harvesting.

Cardiac pacemakers must be regularly replaced due to depleted batteries. A possible alternative is proposed by subcutaneous photovoltaic energy harvesting. The body's reaction to an implant can cause device encapsulation. Potential changes in spectral light transmission of skin can influence the performance of subcutaneous photovoltaic cells and has not yet been studied in large animal studies. Subcutaneous implants measuring changes in the light reaching the implant were developed. Three pigs received those implants and were analyzed for seven weeks. Spectral measurements with known irradiation were performed to identify possible changes in the transparency of the tissues above the implant during the wound healing process. A histological analysis at the end of the trial investigated the skin tissue above the subcutaneous photovoltaic implants. The implants measured decreasing light intensity and shifts in the light's spectrum during the initial wound healing phase. In a later stage of tissue recovery, the implants measured a generally reduced light intensity compared to the healthy tissue after implantation. The spectral distribution of the measured light at the end of the trial was similar to the first measurements. The histological analysis showed subcutaneous granulation tissue formation for all devices. The varying reduction of light intensity reaching the implants means that safety margins must be sufficiently high to ensure the power. At the end of the wound healing process, the spectral distribution of the light reaching the implant is similar to healthy tissue. Optimizations of spectral sensitivity of photovoltaic cells are possible.

Analysis of uncertainties of a cold-ytterbium atomic frequency standard using operational parameters of its optical lattice

We have assessed the effect of optical lattice laser field parameters (polarisation, intensity, and wavelength) of a cold-ytterbium atomic frequency standard on the systematic uncertainty of precision clock transition frequency measurements. The spectrum and polarisation of the laser field of the lattice have been investigated in detail directly in the spatial region of interaction of cold ytterbium atoms with the laser field. The Stark shift of the clock transition in the vicinity of the magic wavelength of the laser has been estimated as a function of the experimentally measured laser field intensity in the dipole approximation. The estimates have been used to calculate the residual systematic uncertainty in the light shift of the optical lattice laser frequency.

Light-shift induced by two unbalanced spontaneous decay rates in EIT (CPT) spectroscopies under Ramsey pulse excitation* *Project supported by the State Key Laboratory of Low Dimensional Quantum Physics Research Program, Tsinghua University (Grant No. KF201707).

Light shift is important and inevitably affects the long-term stability of an atomic clock. In this work, considering two unbalanced branches of the spontaneous decay rate in a three-level system, we studied the frequency shifts of electromagnetically induced transparency (EIT) and coherent population trapping (CPT) clocks operating under the pulse sequence regime by numerically solving the Liouville density matrix equations. The results show that the frequency shifts are larger when the two branches of spontaneous emission rate are not equal compared to the equal case. In addition, in EIT-Ramsey, the effect of the unbalanced branches of the spontaneous decay rate and relaxations of low-energy states on the frequency shift is greater than that of Rabi frequency. In CPT-Ramsey, the relaxations of low-energy states play a dominant role in frequency shift.

Generalised Ramsey methods for suppressing light shifts in atomic clocks based on the coherent population trapping effect

We study the possibility of suppressing light shifts in Ramsey spectroscopy of coherent population trapping (CPT) using generalised autobalanced Ramsey spectroscopy (GABRS) and combined error signal in Ramsey spectroscopy (CESRS). We consider CPT resonances excited by a coherent bichromatic field in an open Λ-system with a ‘trap’ state. Using a rigorous mathematical proof and numerical calculations, these methods are shown to lead to complete suppression of the light shift and its fluctuations. Implementation of GABRS and CESRS in CPT clocks can markedly improve accuracy and long-term stability of these devices. These methods can also be applied in atomic CPT magnetometers and interferometers.

Implementation of one-qubit quantum gates with individual addressing of two rubidium atoms in two optical dipole traps

We report the results of experiments on implementing individually addressable one-qubit quantum gates on a microwave transition with two 87Rb atoms in two optical dipole traps. Addressing is carried out using additional focused laser light, which results in a differential light shift of the microwave transition frequency. In the absence of addressing in each of the atoms, Rabi oscillations are obtained on the microwave clock transition 5S1/2 (F = 2, mF = 0) → 5S1/2(F = 1, mF = 0) between two working levels of qubits with a frequency of up to 5.1 kHz, a contrast up to 98 %, and a coherence time up to 4 ms. When addressing is turned on, the probability of a microwave transition in the addressed atom is suppressed to an average value of less than 5 %. The Rabi oscillations remaining in the other atom have the same contrast and correspond to the implementation of individually addressable basic one-qubit quantum operations (Hadamard gate and NOT gate) from different initial states of a qubit with an average fidelity of 92% ± 3 %. After renormalising this fidelity to the error in the preparation and measurement of quantum states of qubits, an estimate of 97% ± 3% is obtained for the fidelity of individual qubit rotations.

Controlling Growth of Poly (Triethylene Glycol Acrylate-Co-Spiropyran Acrylate) Copolymer Liquid Films on a Hydrophilic Surface by Light and Temperature.

A quartz crystal microbalance with dissipation monitoring (QCM-D) was employed for in situ investigations of the effect of temperature and light on the conformational changes of a poly (triethylene glycol acrylate-co-spiropyran acrylate) (P (TEGA-co-SPA)) copolymer containing 12–14% of spiropyran at the silica–water interface. By monitoring shifts in resonance frequency and in acoustic dissipation as a function of temperature and illumination conditions, we investigated the evolution of viscoelastic properties of the P (TEGA-co-SPA)-rich wetting layer growing on the sensor, from which we deduced the characteristic coil-to-globule transition temperature, corresponding to the lower critical solution temperature (LCST) of the PTEGA part. We show that the coil-to-globule transition of the adsorbed copolymer being exposed to visible or UV light shifts to lower LCST as compared to the bulk solution: the transition temperature determined acoustically on the surface is 4 to 8 K lower than the cloud point temperature reported by UV/VIS spectroscopy in aqueous solution. We attribute our findings to non-equilibrium effects caused by confinement of the copolymer chains on the surface. Thermal stimuli and light can be used to manipulate the film formation process and the film’s conformational state, which affects its subsequent response behavior.

Accurate measurement of the residual field in a magnetic shield using optically pumped 133Cs atoms

Determining the residual field in a magnetic shield is essential in quantum measurement. However, it faces some problems which limit the measuring accuracy. In order to overcome the main problems for the measuring method based on magnetic resonance, a method which detects the electron paramagnetic resonance frequency of 133Cs atoms is reported. By using a rotating exciting magnetic field and choosing appropriate frequency of probe light, the influences of the Bloch-Siegert effect on the measurement of the residual field is eliminated, and by extracting the sums of the residual field and the fictitious field caused by light shifts under different pump light powers and using a second-degree polynomial fitting, the influences of light shifts on the measurement of the residual field is eliminated, thus the residual field is obtained accurately. The test results demonstrate that a high measuring accuracy of 0.01 nT can be achieved for this method.

Synthesis scaly Ag-TiO2 loaded fly ash magnetic bead particles for treatment of xanthate wastewater

It is a challenging problem which Titanium dioxide (TiO 2 ) has low utilization of visible light and difficult recovery. In this work, the Ag-TiO 2 -FAMB photocatalyst was prepared by the sol-gel method, with Ag as the dopant and Fly Ash Magnetic Bead (FAMB) as the carrier to improve its photocatalytic performance and recovery rate. The samples prepared were characterized by XRD, SEM, EDS, VSM, UV–vis diffuse reflection. The effects of the amount of photocatalyst, initial pH value and concentration of xanthate, and the intensity of light on the degradation of xanthate were investigated. Free radical quenching test, full-spectrum ultraviolet scanning, and ion test are used to explore the potential mechanism of xanthate degradation. The test results show that the synthesized Ag-TiO 2 is scaly and uniformly supported on the surface of FAMB and its response of the photocatalyst to visible light shifts to 475 nm. When the photocatalyst concentration is 3.0 mg/L, the initial pH value is 5.0, the initial concentration of xanthate is 10.0 mg/L and the light intensity is 250 W, the degradation rate of xanthate reaches 98.5% after 30 h of light. The photocatalyst recovered by the external magnetic field was reused 5 times, and the degradation rate of xanthate remained above 83.8%. Superoxide radical (·O 2 - ) is the main active species for photocatalytic degradation of xanthate, and xanthate peroxide (ROCSSO - ) is an intermediate product, which is finally degraded into CO 2 , SO 4 2- , H 2 O. • FAMB as a carrier for preparing photocatalytic materials. • The new type Ag-TiO 2 -FAMB uses visible light wavelength to extend to 475 nm. • The new type Ag-TiO 2 -FAMB can be magnetically recycled and reused.

P‐80: Enhancement of Ultra‐Narrow‐Border Displays

In this paper, we conduct relevant tests on ultra‐narrow border display with light leakage and color shift under wide viewing angle in low gray scale at T0(T0 meas no aging test). When combining the tests results with the simulation results of the LC master, we have comprehensively analyzed the possible causes of light leakage and color shift in low gray scale at T0, and proposed solutions which can be used to enable high quality ultranarrow border displays.

Quantum lock-in detection of a vector light shift

We demonstrate detection of a vector light shift (VLS) using the quantum lock-in method. The method offers precise and accurate VLS measurement without being affected by real magnetic field fluctuations. We detect a VLS on a Bose--Einstein condensate (BEC) of $^{87}$Rb atoms caused by an optical trap beam with a resolution less than 1 Hz. We also demonstrate elimination of a VLS by controlling the beam polarization to realize a long coherence time of a transversally polarized $F$ = 2 BEC. Quantum lock-in VLS detection should find wide application, including the study of spinor BECs, electric-dipole moment searches, and precise magnetometry.

Weekend Light Shifts Evoke Persistent Drosophila Circadian Neural Network Desynchrony.

We developed a method for single-cell resolution longitudinal bioluminescence imaging of PERIOD (PER) protein and TIMELESS (TIM) oscillations in cultured male adult Drosophila brains that captures circadian circuit-wide cycling under simulated day/night cycles. Light input analysis confirms that CRYPTOCHROME (CRY) is the primary circadian photoreceptor and mediates clock disruption by constant light (LL), and that eye light input is redundant to CRY; 3-h light phase delays (Friday) followed by 3-h light phase advances (Monday morning) simulate the common practice of staying up later at night on weekends, sleeping in later on weekend days then returning to standard schedule Monday morning [weekend light shift (WLS)]. PER and TIM oscillations are highly synchronous across all major circadian neuronal subgroups in unshifted light schedules for 11 d. In contrast, WLS significantly dampens PER oscillator synchrony and rhythmicity in most circadian neurons during and after exposure. Lateral ventral neuron (LNv) oscillations are the first to desynchronize in WLS and the last to resynchronize in WLS. Surprisingly, the dorsal neuron group-3 (DN3s) increase their within-group synchrony in response to WLS. In vivo, WLS induces transient defects in sleep stability, learning, and memory that temporally coincide with circuit desynchrony. Our findings suggest that WLS schedules disrupt circuit-wide circadian neuronal oscillator synchrony for much of the week, thus leading to observed behavioral defects in sleep, learning, and memory.

Rotational Doppler Frequency Shift from Time‐Evolving High‐Order Pancharatnam–Berry Phase: A Metasurface Approach

AbstractThe Doppler frequency shift of sound or electromagnetic waves has been widely investigated in many different contexts and, nowadays, represents a formidable tool in medicine, engineering, astrophysics, and optics. Such effect is commonly described in the framework of the universal energy‐momentum conservation law. In particular, the rotational Doppler effect has been recently demonstrated using light carrying orbital angular momentum. When a wave undergoes a cyclic adiabatic transformation of its Hamiltonian, it is known to acquire the so‐called Pancharatnam–Berry (PB) phase. In this work, an experimental evidence of the direct connection between the high‐order PB phase time evolution on the Poincaré sphere and the rotational Doppler frequency shift of light is provided. A metasurface operating at telecom wavelengths is employed to impose a total (spin and orbital) angular momentum (TAM) on the light wave, while two TAM converters ensure a closed cycle on the Poincaré sphere. By rotating one of the converters, a significant Doppler frequency shift is observed without variation of the output TAM. The proposed metasurface‐based approach offers new advanced ways to engineer the frequency content of light.

A pulsed-Laser Rb atomic frequency standard for GNSS applications

We present the results of 10 years of research related to the development of a Rubidium vapor cell clock based on the principle of pulsed optical pumping (POP). Since in the pulsed approach, the clock operation phases take place at different times, this technique demonstrated to be very effective in curing several issues affecting traditional Rb clocks working in a continuous regime, like light shift, with a consequent improvement of the frequency stability performances. We describe two laboratory prototypes of POP clock, both developed at INRIM. The first one achieved the best results in terms of frequency stability: an Allan deviation of σy(τ) = 1.7 × 10−13 τ−1/2, being τ the averaging time, has been measured. In the prospect of a space application, we show preliminary results obtained with a second more recent prototype based on a loaded cavity-cell arrangement. This clock has a reduced size and exhibited an Allan deviation of σy(τ) = 6 × 10−13 τ−1/2, still a remarkable result for a vapor cell device. In parallel, an ongoing activity performed in collaboration with Leonardo S.p.A. and aimed at developing an engineered space prototype of the POP clock is finally mentioned. Possible issues related to space implementation are also briefly discussed. On the basis of the achieved results, the POP clock represents a promising technology for future GNSSs.

Characterization and Suppression of Background Light Shifts in an Optical Lattice Clock

Experiments involving optical traps often require careful control of the ac Stark shifts induced by strong confining light fields. By carefully balancing light shifts between two atomic states of interest, optical traps at the magic wavelength have been especially effective at suppressing deleterious effects stemming from such shifts. Highlighting the power of this technique, optical clocks today exploit Lamb-Dicke confinement in magic-wavelength optical traps, in some cases realizing shift cancellation at the ten parts per billion level. Theory and empirical measurements can be used at varying levels of precision to determine the magic wavelength where shift cancellation occurs. However, lasers exhibit background spectra from amplified spontaneous emission or other lasing modes which can easily contaminate measurement of the magic wavelength and its reproducibility in other experiments or conditions. Indeed, residual light shifts from laser background have plagued optical lattice clock measurements for years. In this work, we develop a simple theoretical model allowing prediction of light shifts from measured background spectra. We demonstrate good agreement between this model and measurements of the background light shift from an amplified diode laser in an Yb optical lattice clock. Additionally, we model and experimentally characterize the filtering effect of a volume Bragg grating bandpass filter, demonstrating that application of the filter can reduce background light shifts from amplified spontaneous emission well below the $10^{-18}$ fractional clock frequency level. This demonstration is corroborated by direct clock comparisons between a filtered amplified diode laser and a filtered titanium:sapphire laser.

Novel yellow light emission from vanadyl ions-doped calcium-lithium hydroxyapatite nanopowders: structural, optical, and photoluminescence properties

Phosphor luminescent materials, especially those activated with transition metal ions, have been extensively investigated during the last decade because of their potential in various applications such as displays, medical imaging, lighting, and fluorescent lamps. In this study, a mechanochemical approach was used for the synthesis of novel yellow light-emitting vanadyl ion (VO2+)-doped calcium-lithium hydroxyapatite (CLHA) nanophosphors. The structural, morphological, optical, photoluminescence, and chromaticity properties of the as-prepared nanopowders were systematically examined. Phase structural analysis showed that the as-prepared samples were highly crystalline and corresponded to the hexagonal crystal phase of hydroxyapatite. X-ray photoelectron spectroscopy investigation indicated the existence of elements. The spectroscopic results indicate that the doped VO2+ ions belong to the tetragonally distorted octahedral site symmetry. The chromaticity results show that the chromaticity coordinates (x, y) for the VO2+-doped CLHA nanopowders were (0.448, 0.401), (0.430, 0.384), and (0.423, 0.377). The emission colors are positioned in the orange, orange-yellow, and pale-yellow regions, respectively, for VO2+-doped CLHA nanopowders. Thus, the light emission properties shift from orange to yellow as the dopant concentration increases from 0.01 to 0.05 mol%. These results demonstrate that phosphor materials doped with transition metal ions are suitable for display device applications.

Convolutional Neural Networks(CNN) based Eye-Gaze Tracking System using Machine Learning Algorithm

To avoid the rising number of car crash deaths, which are mostly caused by drivers' inattentiveness, a paradigm shift is expected. The knowledge of a driver's look area may provide useful details about his or her point of attention. Cars with accurate and low-cost gaze classification systems can increase driver safety. When drivers shift their eyes without turning their heads to look at objects, the margin of error in gaze detection increases. For new consumer electronic applications such as driver tracking systems and novel user interfaces, accurate and effective eye gaze prediction is critical. Such systems must be able to run efficiently in difficult, unconstrained conditions while using reduced power and expense. A deep learning-based gaze estimation technique has been considered to solve this issue, with an emphasis on WSN based Convolutional Neural Networks (CNN) based system. The proposed study proposes the following architecture, which is focused on data science: The first is a novel neural network model that is programmed to manipulate any possible visual feature, such as the states of both eyes and head location, as well as many augmentations; the second is a data fusion approach that incorporates several gaze datasets. However, due to different factors such as environment light shifts, reflections on glasses surface, and motion and optical blurring of the captured eye signal, the accuracy of detecting and classifying the pupil centre and corneal reflection centre depends on a car environment. This work also includes pre-trained models, network structures, and datasets for designing and developing CNN-based deep learning models for Eye-Gaze Tracking and Classification.

Light-shift comparison of electromagnetically induced transparency and coherent population trapping in continuous-wave and Ramsey spectroscopies

In the atomic frequency standard, the light shift inevitably affects the long-term stability of the atomic clock. In this work, we accurately calculated the light shifts of electromagnetically induced transparency (EIT) and coherent population trapping (CPT) clocks operating under continuum and pulse sequence regimes by numerically solving the Liouville density matrix equation, including all the relaxation terms of a three-level system. The results show that the light shifts under pulse excitation are smaller than those under continuous excitation and the light shifts of the CPT process are much smaller than those of the EIT process under both excitations. It is also found that the light shifts in the continuous excitation increase and those in the pulse excitation decrease with an increase in the Rabi frequency. The light shifts will increase with an increase of the relaxations of the ground states for both the processes under both regimes. Compared to all process atomic clocks, the light shift of pulse-excited atomic clocks is the smallest, which will be suitable for many applications.

Semiconductor nanopillars for programmable directional lasing emissions

Mie resonances facilitate an efficient manipulation of light on the subwavelength scale in high-refractive-index metasurfaces. These ultra-thin high-refractive-index nanostructures have been utilized in wave-front engineering devices for amplitude and phase modulation on the subwavelength scale in dielectric metasurfaces with high transmission efficiencies. We seek to establish a guideline for the desired phase modulation of each element in the metasurfaces integrated with light-emitting devices. Numerical simulations of gallium arsenide (GaAs) nanopillar metasurfaces are carried out over the visible and near-infrared spectral ranges. We analyze the scattering properties of the nanopillars of various sizes along with reflection, transmission, absorption, and phase-change spectra of the nanopillar arrays. We study phase-change properties of nanopillars of varied radii along the spectrum and elaborate on the scattering features of the metasurfaces to create a library of phase-change characteristics. The results indicate that the nanostructures respond with strong resonances and the corresponding phase-change features in the visible and near-infrared frequencies. By the variation of the nanopillar dimensions, one can control the light phase change and shift the features along the spectrum.