Resonance Fluorescence Intensity Research Articles

Coherently driving a single quantum two-level system with dichromatic laser pulses

The excitation of individual two-level quantum systems using an electromagnetic field is an elementary tool of quantum optics, with widespread applications across quantum technologies. The efficient excitation of a single two-level system usually requires the driving field to be at the same frequency as the transition between the two quantum levels. However, in solid-state implementations, the scattered laser light can dominate over the single photons emitted by the two-level system, imposing a challenge for single-photon sources. Here, we propose a background-free method for the coherent excitation and control of a two-level quantum system using a phase-locked dichromatic electromagnetic field with no spectral overlap with the optical transition. We demonstrate this method experimentally by stimulating single-photon emission from a single quantum dot embedded in a micropillar, reaching single-photon purity of 0.988(1) and indistinguishability of 0.962(6). The phase-coherent nature of our two-colour excitation scheme is demonstrated by the dependence of the resonance fluorescence intensity on the relative phase between the two pulses. Our two-colour excitation method represents an additional and useful tool for the study of atom–photon interaction, and the generation of spectrally isolated indistinguishable single photons. A quantum two-level system can be coherently excited by a phase-locked dichromatic electromagnetic field. This technique can make single-photon generation more efficient as the pump light does not overlap in frequency with the emitted single photons.

Effects of resonant-laser excitation on the emission properties in a single quantum dot.

While many solid-state emitters can be optically excited non-resonantly, resonant excitation is necessary for many quantum information protocols as it often maximizes the non-classicality of the emitted light. Here, we study the resonance fluorescence in a solid-state system-a quantum dot-with the addition of weak, non-resonant light. In the inelastic scattering regime, changes in the resonance fluorescence intensity and linewidth are linked to both the non-resonant and resonant laser powers. Details of the intensity change indicate that charge-carrier loss from the quantum dot is resonant laser. As we enter the Mollow triplet regime, this resonant laser loss term rate is approximately 1∕50 ns-1. This work further clarifies resonance fluorescence in solid-state systems and will aid in the further improvement of solid-state non-classical light sources.

Determination of trace uranium by resonance fluorescence method coupled with photo-catalytic technology and dual cloud point extraction

In this paper, two kinds of salophens (Sal) with different solubilities, Sal1 and Sal2, have been respectively synthesized, and they all can combine with uranyl to form stable complexes: [UO22+-Sal1] and [UO22+-Sal2]. Among them, [UO22+-Sal1] was used as ligand to extract uranium in complex samples by dual cloud point extraction (dCPE), and [UO22+-Sal2] was used as catalyst for the determination of uranium by photocatalytic resonance fluorescence (RF) method. The photocatalytic characteristic of [UO22+-Sal2] on the oxidized pyronine Y (PRY) by potassium bromate which leads to the decrease of RF intensity of PRY were studied. The reduced value of RF intensity of reaction system (ΔF) is in proportional to the concentration of uranium (c), and a novel photo-catalytic RF method was developed for the determination of trace uranium (VI) after dCPE. The combination of photo-catalytic RF techniques and dCPE procedure endows the presented methods with enhanced sensitivity and selectivity. Under optimal conditions, the linear calibration curves range for 0.067 to 6.57ngmL−1, the linear regression equation was ΔF=438.0 c (ngmL−1)+175.6 with the correlation coefficient r=0.9981. The limit of detection was 0.066ngmL−1. The proposed method was successfully applied for the separation and determination of uranium in real samples with the recoveries of 95.0–103.5%. The mechanisms of the indicator reaction and dCPE are discussed.

Optical Blocking of Electron Tunneling into a Single Self-Assembled Quantum Dot.

Time-resolved resonance fluorescence (RF) is used to analyze electron tunneling between a single self-assembled quantum dot (QD) and an electron reservoir. In equilibrium, the RF intensity reflects the average electron occupation of the QD and exhibits a gate voltage dependence that is given by the Fermi distribution in the reservoir. In the time-resolved signal, however, we find that the relaxation rate for electron tunneling is, surprisingly, independent of the occupation in the charge reservoir-in contrast to results from all-electrical transport measurements. Using a master equation approach, which includes both the electron tunneling and the optical excitation or recombination, we are able to explain the experimental data by optical blocking, which also reduces the electron tunneling rate when the QD is occupied by an exciton.

Laser diagnostics of the energy spectrum of Rydberg states of the lithium-7 atom

The spectra of excited lithium-7 atoms prepared in a magneto-optical trap are studied using a UV laser. The laser diagnostics of the energy of Rydberg atoms is developed based on measurements of the change in resonance fluorescence intensity of ultracold atoms as the exciting UV radiation frequency passes through the Rydberg transition frequency. The energies of various nS configurations are obtained in a broad range of the principal quantum number n from 38 to 165. The values of the quantum defect and ionization energy obtained in experiments and predicted theoretically are discussed.

Frequency-Stabilized Source of Single Photons from a Solid-State Qubit

Single quantum dots are solid-state emitters which mimic two-level atoms but with a highly enhanced spontaneous emission rate. A single quantum dot is the basis for a potentially excellent single photon source. One outstanding problem is that there is considerable noise in the emission frequency, making it very difficult to couple the quantum dot to another quantum system. We solve this problem here with a dynamic feedback technique that locks the quantum dot emission frequency to a reference. The incoherent scattering (resonance fluorescence) represents the single photon output whereas the coherent scattering (Rayleigh scattering) is used for the feedback control. The fluctuations in emission frequency are reduced to 20 MHz, just ~ 5% of the quantum dot optical linewidth, even over several hours. By eliminating the 1/f-like noise, the relative fluctuations in resonance fluorescence intensity are reduced to ~ 10E-5 at low frequency. Under these conditions, the antibunching dip in the resonance fluorescence is described extremely well by the two-level atom result. The technique represents a way of removing charge noise from a quantum device.

A Catalytic Resonance Fluorometry Method for Determination of Hydroquinone and Its Applications

Pyronin Y (PY) has a strong resonance fluorescence in sulfuric acid medium. The characteristics of the resonance fluorescence spectra and the factors affecting the spectra were studied. A catalytic resonance fluorometry method for the determination of hydroquinone was proposed based on the catalytic effect of hydroquinone on the oxidation of PY by potassium bromate. The oxidation of PY resulted in the decrease of the resonance fluorescence intensity. The influences of several variables on the sensitivity were studied. At the optimized conditions, the decrease of the resonance fluorescence intensity was in proportion to the concentration of hydroquinone in the range of 4.42-1.60 x 10(3) microg l(-1), and the detection limit was 1.46 microg l(-1). The proposed method was applied successfully for the determination of trace hydroquinone in environment samples. The relative standard deviation was less than 3.90% and the recoveries were in the range of 95.2-104.0%.

Geometry-dependent dynamics of twoΛ-type atoms via vacuum-induced coherences

The dynamics of a pair of atoms can significantly differ from the single-atom dynamics if the distance of the two atoms is small on a scale given by the relevant transition wavelengths. Here, we discuss two nearby three-level atoms in {lambda} configuration, and focus on the dependence of the optical properties on the geometry of the setup. We find that in general transitions in the two atoms can be dipole-dipole coupled by interactions via the vacuum field even if their transition dipole moments are orthogonal. We give an interpretation of this effect and show that it may crucially influence the system dynamics. In particular, for a fixed setup of driving fields and detectors, the spatial orientation of the two-atom pair decides if the system reaches a true constant steady state or if it exhibits periodic oscillations in the long-time limit. As an example observable, we study the resonance fluorescence intensity, which is either constant or is modulated periodically in the long-time limit.

Phase Control of Collective Quantum Dynamics

The manipulation of the steady-state behavior of a collection of dipole-interacting three-level atoms in a V or Lambda configuration is investigated as a function of the relative phase of two strong coherent driving fields. For larger samples, the phase is shown to be a convenient parameter to rapidly populate or depopulate completely a trapping state of the ensemble. As applications, we present the appropriately prepared atomic sample as an optical switching device and show its virtues in controlling the collective steady-state resonance fluorescence intensity.

On the possibility of investigating the dispersion of the energy bands of a crystal using resonant x-ray emission spectra

It is shown that, when the dispersion of the energy bands of crystals is investigated by resonant x-ray emission (RXE), an ambiguity can arise in the determination of ktr — the transition point in k space — as a result of the characteristic features of the band structure and the value of the matrix elements. It is proposed that calculations of the distribution of partial contributions to interband optical transitions in the Brillouin zone (BZ) be used as a means of obtaining a simplified estimate of ktr. The basic properties of this distribution are examined for lithium hydride, which is a convenient model object having a simple band structure and interband transitions which have been studied in detail. It is shown that the k points of the general position, which form a complex figure in the BZ, make the main contribution to the interband transitions. The contribution of high-symmetry points is much smaller mainly because of their small representativeness. This make it easier to understand the reason for the possible nonmonotonic variation of ktr in RXE measurements of the dispersion of the energy bands of crystals or the sharp changes in the resonance-fluorescence intensity.

Laser-Phase-Noise-Induced Stochastic-Resonance Fluorescence

Abstract Stochastic fluctuations of coherent and incoherent components of the resonance fluorescence intensity induced by Wiener-Levy laser phase noise are investigated. Statistical properties of the atomic dipole moment and stochastic Mollow spectra of atomic dipole fluctuations for different values of the laser linewidth and Rabi frequency are calculated. It is shown that these spectra exhibit a triplet structure which is purely classical and entirely laser-noise dependent.

Satellite measurements of hydroxyl in the mesosphere

The global distribution of hydroxyl (OH) in the middle atmosphere was recently measured by the Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) on a satellite deployed and retrieved by the space shuttle. During 75 orbits, MAHRSI acquired 1800 daytime limb scans of the OH ultraviolet solar resonance fluorescence intensity. Each limb scan extends over the altitude region from 30 to 90 km and across 10° of latitude between 53°S and 63°N. OH number densities were retrieved using a Twomey regularization scheme constrained by the smoothness of the retrieved profile. Results provide a detailed description of the diurnal variation of mesospheric OH. Midmorning OH densities had a well defined peak of about 6 ×106 cm³ near 70 km, a broad minimum centered near 64 km, and rose to about 1 × 107 cm³ at 50 km. This profile is in substantial disagreement with photochemical model predictions [Summers et al., this issue]. The observations are compared with the two previous measurements.

The photophysics and photochemistry of complexes of s-tetrazine and acetylene

The photochemistry and photophysics of complexes of s-tetrazine (T) with acetylene have been studied in a supersonic free jet using laser induced fluorescence spectroscopy. Two complexes of the form T–C2H2 and a complex of the form T–(C2H2)2 were observed. One of the monoacetylene complexes has a stacked structure and one has a planar structure. In all cases low frequency vibrational structure was observed in the emission spectrum, and this allowed measurement of the frequencies of intermolecular vibrations. At some levels of excitation, all three complexes had broad features in their emission spectra. It was shown that in these cases, the density of states was sufficiently high that the molecular complexes were in the statistical limit, and therefore the broad structure was attributed to intramolecular vibrational relaxation (IVR). At higher levels of excitation, dissociation of the complexes was observed, and in some instances both IVR and dissociation were observed. Rate constants were measured by comparing the relative intensity of emission produced by these two decay channels with the intensity of resonance fluorescence. These rate constants were found to vary depending on the complex and upon the initially excited state of a given complex. When dissociation was observed, not all energetically allowed vibrational states were observed. The diacetylene complex was observed to dissociate to produce both monoacetylene complexes, but never the monomer.

Laser-phase-noise-induced stochastic-resonance fluorescence.

Stochastic fluctuations of coherent and incoherent components of the resonance fluorescence intensity induced by Wiener-Levy laser phase noise are investigated. Statistical properties of the atomic dipole moment for different values of the laser linewidth and different strength of the driving field are calculated. The stochastic Mollow spectra of atomic dipole fluctuations are derived. It is shown that these spectra exhibit a triplet structure which is purely classical and entirely laser-noise dependent.

Quantum beats in two-atom resonance fluorescence.

We study the resonance fluorescence emitted by two laser-driven coupled identical two-level atoms and allow for an arbitrary separation between the atoms and an arbitrary orientation of the interatomic axis in the laser field. Quantum beats arise in the resonance fluorescence intensity profile when an interatomic axis orientation is not perpendicular to the driving field propagation direction and are well resolved for an interatomic separation comparable to the resonant wavelength. These beats vanish for noninteracting atoms as well as for atoms separated by distances much smaller than the resonant wavelength. We also consider the time-dependent resonance fluorescence photon statistics that also exhibit quantum beats. Sub-Poissonian photon statistics occur for large interatomic separations and, for small separations, sub- and super-Poissonian statistics arise depending on the atomic orientation in the external driving field.

Collective jumps in a system of three-level atoms

The collective jumps in the steady-state intensity of resonance fluorescence and the collective population trapping in a system of three-level atoms interacting with an intense external field are considered. It is shown that for a proper choice of parameters the atomic populations and the steady-state intensity of resonance fluoresence from such a system display discontinuous behaviour (jumps) in a collective limit N→∞. Potential applications of collective jumps to measure weak transition linewidths are shortly discussed.

Measurements of the gJ factors of the 6s^2S_1/2 and 6p^2P_1/2 states in ^198Hg^+

Measurements of 198Hg+gJ factors by two methods are reported. The first method was based on optical wavelength measurements of the Zeeman components of the 6s2S1/2 (ground state) to 6p2P1/2 transition at 194 nm. The lines were observed by the absorption of tunable 194-nm radiation by Hg+ ions created in a rf discharge. The results were gJ(6s2S1/2) = 2.0036(20) and gJ(6p2P1/2) = 0.6652(20). The second method was based on microwave-optical double resonance of ions confined in a Penning trap. They were optically pumped by the 194-nm source, which was tuned to a particular Zeeman component. An increase in the resonance-fluorescence intensity was observed when the microwave frequency was tuned to the ground-state Zeeman resonance. The result is gJ(6s2S1/2) = 2.003 174 5(74).

Resonance fluorescence as a probe to elucidate mechanisms of intramolecular relaxation processes

Density matrix formalism is used to study resonance fluorescence processes of isolated gaseous molecules. The Wangsness–Bloch–Fano theory is applied to the irreversible intramolecular relaxation process. In the present treatment, it is assumed that the rotational angular momentum J is a constant of motion in the zeroth order approximation. Thus intramolecular interactions can be classified as tensor operators with respect to J. The fluorescence decay patterns depend on excitation bandwidths and monitoring conditions. Under narrow band excitation, the population (monopole), orientation (dipole), and alignment (quadrupole) of the excited state density matrix ρe can be prepared. For a sharply prepared angular momentum state under pulsed excitation, the population does not undergo radiationless decay and the resonance fluorescence intensity is a sum of three exponentials in general. For cw experiments, where lifetime limited linewidth or polarized fluorescence intensities are measured, the population can decay via an intramolecular relaxation channel providing the orientation component is initially prepared. Explicit J dependences of lifetimes are given for pulsed experiments. Under broad band excitation, quantum beats due to the coherence of ρe are derived from the Liouville equation. Most important of all, the population can decay under pulsed, broad-band excitation conditions. The scalar part of the nonadiabatic coupling becomes an additional contributor to the intramolecular relaxation process in this last case.

Theory of time- and frequency-resolved resonance Raman and resonance fluorescence induced by realistic coherent pulses of arbitrary strength

Closed-form expressions are derived for the time-resolved and frequency-resolved resonance fluorescence (RF) and resonance Raman (RR) produced by coherent, realistic, quasi-rectangular pulses of arbitrary strength. Saturation effects, such as optical nutation, dynamic Stark splitting and dynamic Stark shifts of RF and RR are shown to be strongly dependent on the rise and fall times of the pulse. It is predicted that at high pulse intensities, optical nutation and the intensity of RF, but not of RR, disappear rapidly with increasing frequency offset Δω = ω - ω mn of the average pulse frequency ω from the molecular transition frequency ω mn . This result strongly influences the saturation effects in Doppler-broadened time- and frequency-resolved spectra and points to the necessity of revising the interpretation of recent experimental observations.

Kinetic behaviour of OH X2Π and A2σ+using molecular resonance fluorescence spectrometry

A method for the investigation of OH X2Π(v″= 0) radical kinetics in a discharge-flow system at 300 K, with detection of OH by molecular resonance fluorescence, using the OH A2Σ+–X2Π(0, 0) transition, is described. Quenching cross sections for OH A2Σ+(by H2O, N2, Ar and He) were determined from steady-state kinetic analysis, and the effects of electronic quenching on the kinetic measurements were shown to be unimportant. The intensity of resonance fluorescence, under the conditions used, varied in direct proportion to [OH, X2Π, v″= 0] up to concentrations of 5 × 1014 cm–3.