Spontaneous Parametric Four-wave Mixing Research Articles

Spectral and temporal atomic coherence interaction in Eu3+ : NaYF4 and Eu3+ : BiPO4.

We investigate the spectral and temporal atomic coherence interaction based on out-of-phase fluorescence (FL) and spontaneous parametric four-wave mixing (SFWM) from the hexagonal phase of Eu3+ : NaYF4 and different phases of Eu3+ : BiPO4. Spectral and temporal interactions are interrelated and reduced by about 2 times due to two-photon nested dressing in contrast to the sum of each laser excitation. As the lifetime of photons increases, off-resonance profile cross-interaction decreases because cross-interaction reverses the signal at the near time gate position and keeps it consistent at the far time gate position. Moreover, the thermal phonon dressing at 300 K exhibits 6 times more eminent and obvious temporal interaction than that at 77 K. In a different phase of Eu3+ : BiPO4, there are three dark dips having stronger self-interaction; however, Eu3+ : NaYF4 has two dark dips as Eu3+ : BiPO4 has two phonon dressing. Further, the pure hexagonal phase of Eu3+ : BiPO4 demonstrates the strongest cross-interaction and longest coherent time under the dressing effect due to the smallest dressing phonon detuning and off-resonance profile cross-interaction at PMT2 because the angle quantization is the strongest. Such results can be used for designing novel quantum devices and have potential applications in quantum memory devices.

Resonant metasurfaces for generating complex quantum states.

Quantum state engineering, the cornerstone of quantum photonic technologies, mainly relies on spontaneous parametric downconversion and four-wave mixing, where one or two pump photons spontaneously decay into a photon pair. Both of these nonlinear effects require momentum conservation for the participating photons, which strongly limits the versatility of the resulting quantum states. Nonlinear metasurfaces have subwavelength thickness and allow the relaxation of this constraint; when combined with resonances, they greatly expand the possibilities of quantum state engineering. Here, we generated entangled photons via spontaneous parametric downconversion in semiconductor metasurfaces with high-quality factor, quasi-bound state in the continuum resonances. By enhancing the quantum vacuum field, our metasurfaces boost the emission of nondegenerate entangled photons within multiple narrow resonance bands and over a wide spectral range. A single resonance or several resonances in the same sample, pumped at multiple wavelengths, can generate multifrequency quantum states, including cluster states. These features reveal metasurfaces as versatile sources of complex states for quantum information.

Correlation interference demultiplexer controlled by phase transition for Pr3+/Eu3+: YPO4

We propose a model of optical demultiplexer based on second- and third-order temporal interference of intensity-noise correlation, which is based on the superposition principle in Feynman's path integral theory. The switch from two-mode bunching to anti-bunching is controlled by gate position for pure hexagonal-phase of Pr3+/Eu3+: YPO4 crystal. We report, robust side correlation peaks caused by the destructive interference between two spontaneous parametric four-wave mixing processes from mixed (hexagonal and tetragonal)-phase of Pr3+/Eu3+: YPO4. By adjusting power of laser beam, the transition from asymmetric correlation side peaks to symmetric correlation side peaks are investigated. The robust center peak comes from the interference between two-mode and three-mode bunching. The switching from single correlation peak to multi-peaks is controlled by laser power. The multi-sharp peaks are translated into multi-dips through gate position. Such results may be used for the design of the optical multiplexer and demultiplexer. Our experimental results provide a technique to achieve larger linewidth change rate about 93% and higher channel equalization ratio about 70%.

Poissonian twin-beam states and the effect of symmetrical photon subtraction in loss estimations

We have devised an experimentally realizable model generating twin beam states whose individual beam photon statistics are varied from thermal to Poissonian keeping the non-classical mode correlation intact. We have studied the usefulness of these states for loss measurement by considering three different estimators, comparing with the correlated thermal twin beam states generated from spontaneous parametric down conversion or four-wave mixing. We then incorporated the photon subtraction operation into the model and demonstrate their advantage in loss estimations with respect to un-subtracted states at both fixed squeezing and per photon exposure of the absorbing sample. For instance, at fixed squeezing, for two photon subtraction, up to three times advantage is found. In the latter case, albeit the advantage due to photon subtraction mostly subsides in standard regime, an unexpected result is that in some operating regimes the photon subtraction scheme can also give up to 20% advantage over the correlated Poisson beam result. We have also made a comparative study of these estimators for finding the best measurement for loss estimations. We present results for all the values of the model parameters changing the statistics of twin beam states from thermal to Poissonian.

Phase transition filter from controllable hybrid line shape of correlation and squeezing of Pr3+: YPO4 and Eu3+: YPO4

We report the symmetry-dependent intensity–noise correlation and the intensity-difference squeezing of spontaneous parametric four-wave mixing (SP-FWM) and fluorescence (FL) hybrid signals from the different phases [hexagonal (H) + tetragonal (T), T + H] of Pr3+: YPO4 and Eu3+: YPO4 crystals. The competition between FL and SP-FWM in hybrid signals determines the amplitude and hybrid line shape of the two-mode and three-mode correlation. The correlation amplitude switches from positive to negative due to strong double dressing caused by a high transition probability and a dipole moment of the (more H + less T)-phase of Pr3+: YPO4. This switching phenomenon is used to realize a metal–oxide semiconductor field-effect transistor-based logic inverter. Furthermore, the line shape of correlation changes from broad to sharp due to weak dressing, transition probability, and a low dipole moment of the (more T + less H)-phase of Pr3+: YPO4. Based on these results, we proposed the model of a tunable correlation filter. Gate position, frequency detuning, and laser power control the amplitude and hybrid line shape. Our experimental results provide an advanced technique of bandwidth contrast of about 0.9%. Such notch filters have potential applications in quantum communications.

Narrowband and broadband single-photon sources using custom-tapered waveguides

In this paper, we present a thorough investigation for a spontaneous parametric four-wave mixing process in third-order nonlinear waveguides with various continuous tapering patterns. It has been previously shown that these devices can quasi-phase-match the four-wave mixing process and enhance its conversion efficiency by orders of magnitude. By altering the tapering profile curve we found that these devices can enable single-photon sources with either narrow or broadband spectral widths at on-demand frequencies. Using our model, we were also able to identify the waveguide length at which the single-photon spectral purity is maximized.

Hybrid communication assisted by coherent oscillator using resonant excitation of Nitrogen–vacancy center in diamond

We propose the multi-channel hybrid communication assisted by a coherent oscillator, by configuring the diamond Nitrogen–vacancy center using spontaneous parametric four-wave mixing. For one-channel hybrid communication, composite signal of fluorescence (information) and Stokes (carrier) is sent to the receiver; information is recovered by subtracting intensities of composite signal and reference coherent signal (from coherent oscillator) at demodulator. Further, we achieved two-channel and three-channel hybrid communication through two-mode and three-mode intensity–noise correlation, respectively. Two-mode correlation of hybrid signal (produced through photon subtraction) and anti-Stokes demonstrates the nonclassical behavior by violating Cauchy–Schwarz inequality, verified through corresponding squeezing (−5 dB). Such phenomenon of non-classical behavior was also verified by non-Gaussian negativity of Wigner function. Our hybrid communication model is based on temporal width- and coherence time-contrast, which can be controlled by wavelength (power) of input beams. The coherence time-contrast is about 90%.

Temporal and spectral hybrid interference from phase transition of Eu3+/Pr3+: YPO4 and evolution of amplifier and multiplexer

We study the temporal and spectral oscillation originated from the interference between the fluorescence (FL) and spontaneous parametric four-wave mixing (SP-FWM) signals. The FL and SP-FWM are generated from different phases of Eu3+ or Pr3+ doped YPO4 under the nonlinear SP-FWM process. We discuss and compare the spectral interfering oscillations and self-Rabi oscillations controlled via multiple phase transitions (hexagonal-phase and mixed-phase) of Eu3+: YPO4 and Pr3+: YPO4. The coexistence mechanism of interference and self-oscillations in time domain is also investigated. Further, we discuss the cross-Rabi oscillation in correlated light beams, which evolves from FL signal (having Sinc profile) to SP-FWM (having Cosine profile) in the hybrid signal regime. Based on these results, we have realized wavelength division multiplexing, and temporal amplifier with the temporal interference being controlled by the gate position, and frequency detuning. Our experimental results provide a technique to achieve higher channel equalization ratio about 85%.

Three-type Fano interference controlled by the phase transition of Eu3+/Pr3+:YPO4

We study the Fano interference from different phase transitions of Eu3+:YPO4 and Pr3+:YPO4 crystals through simultaneous detection of bright and dark states. For this study, we employed tetragonal (T), hexahedral (H), and (H + T)-phases of YPO4 crystals. The Fano interfering bright and dark states are classified based on dressed spontaneous parametric four-wave mixing, dressed multi-order fluorescence, and hybrid signal regimes. Further, the Fano interference between conti-nuous and discrete states can be controlled from partly-(constructive–destructive)-interference through a phase transition, nonlinear phase, and dressing. The (H + T)-phase Pr3+:YPO4 suggests more obvious Fano interference in contrast to T- or H-phase Pr3+:YPO4. We report that the Pr3+:YPO4 and Eu3+:YPO4 demonstrates the dressed multi-level- and dressed single-level Fano interference, respectively, with further three types of Fano interference that can be distinguished at different time delays. The experimental measurement agrees with theoretical simulations. Such results may be used for the design of new types of quantum electronic or spintronic devices such as Fano-transistors.

Hybrid Switch of Correlation and Squeezing Using Resonant and Off-Resonant Excitation Spectrum in Nitrogen-Vacancy Center Diamond

Optical hybrid communication is one of the key fields of quantum communications, where scientists are focusing to integrate classical and quantum system as single hybrid system. In this regard, we realized optical hybrid switch using second-order fluorescence (FL) and spontaneous parametric four-wave mixing (SPFWM). The hybrid signal contains Stokes and the FL signal which can be distinguished using power of incident beam. In addition, we investigate the resonant and off-resonant excitation spectrum of negatively charged Nitrogen-vacancy (NV−) center in diamond. The hybrid switch is realized by results obtained in time domain and intensity noise correlation. The optical hybrid switch can be controlled by power of incident beams. The hybrid index and temporal width contrast of the hybrid switch are about 4 and 90%, respectively.

Logic NOT gates of the intensity–noise correlation and squeezing in a diamond nitrogen-vacancy center

Color defects in a diamond nitrogen-vacancy (NV) center represent an important physical system for emergent quantum technologies such as logic gates and registers at room temperature. We realized an optical logic NOT gate by inducing a phase shift in a diamond NV center under nonlinear Kerr effect of spontaneous parametric four-wave mixing (SP-FWM). Also, we discussed the intensity–noise correlation and intensity-difference squeezing of SP-FWM and composite signals (SP-FWM+fluorescence) under self-phase modulation (SPM) and cross-phase modulation (XPM) induced by the nonlinear Kerr effect in V-type and double V-type atomic systems. Our experimental results provide an advanced technique of switching contrast by approximately 90%. Different parameters, such as the power of input laser beam and boxcar gate position, were also configured to control the SPM and XPM, which determine the switching phenomenon for correlation and squeezing.

Controlling fluorescence and noise correlation by phonon and double dressing in two types of Pr3+:YSO

We investigate the effect of single dressing and double dressing on fourth-order fluorescence (FL) and spontaneous four-wave mixing. The single dressing effect changes to a double dressing effect as we change the detuning (power) of the input beam from off-resonant (low power) to resonant point (high power). We also demonstrate the spectral and temporal nature of fourth-order FL and its Autler–Townes splitting caused by the competition of the phonon effect (at different temperatures) with a single and double dressed state in Pr3+:Y2SiO5 crystal. To further explore the competition between the phonon and dressing effects, we investigated intensity-noise correlation of spontaneous parametric four-wave mixing at 110 K. Our results demonstrate the dependency of YSO crystal on temperature, detuning, and power, which can be controlled by the competition between a phonon with single and double dressing.

Hybrid correlation and squeezing with Rabi oscillation in the diamond nitrogen-vacancy center at room temperature

For the first time, the energy level structure of the nitrogen-vacancy center in diamond is introduced in conjunction with a spontaneous parametric four-wave mixing (SP-FWM) process and fluorescence (FL) generation in heteronuclear-like (V-type level) systems. The obtained output signals are characterized by their decaying components and differentiated by Rabi oscillation, while their lifetimes are modulated by changing the power of the laser field. Two- and three-mode correlation and squeezing among the SP-FWM and FL composite signals are investigated theoretically and experimentally. By selecting different time delayed positions and changing the power of the laser field, competition between the SP-FWM and FL composite signals is demonstrated; this can also control the two-stage line shape of hybrid correlation and the magnitude of squeezing. Such results may find potential applications in optical transistors and optical hybrid communications.

Spontaneous parametric four wave mixing and fluorescence lifetime manipulation in the diamond nitrogen vacancy center

We report the lifetime of spontaneous parametric four wave mixing (SP-FWM) and multiorder fluorescence in two-, three-, and four-level systems of negatively charged nitrogen vacancy (NV−) in diamond. The lifetime of SP-FWM is enhanced at high power by the induced dark state from coupling fields. The reduction and enhancement in fluorescence lifetime are attributed to destructive and constructive quantum interference, respectively. The quantum interference is induced by interaction among different decay pathways of spontaneous emission by closely spaced energy levels, which can be controlled by dipole–dipole interaction and the mutual orientations of dipole moments. The lifetime is observed to be longer in two-level as compared to three-level and four-level systems. The different measured lifetimes suggest the sensitivity of these NV systems to quantum interference and the dressing effect. These outcomes may provide new insights in development of all-optical communication devices and quantum storage on photonic chips.

Hybrid correlation and squeezing with spontaneously generated coherence effect

We investigate intensity noise correlation of hybrid signals generated through spontaneous parametric four-wave mixing and fourth-order fluorescence signals from the nitrogen-vacancy center in diamond. The degree of hybrid correlation changes with power, frequency detuning, and experimental temperature. A theoretical model including spontaneously generated coherence in the dressed-state picture is set up to explain this phenomenon. We also observed damped Rabi oscillations in spontaneous parametric four-wave mixing and attributed it to quantum interference between two four-wave mixing transition paths.

Intracavity Spontaneous Parametric Down-Conversion in Bragg Reflection Waveguide Edge Emitting Diode**Supported by the National Key Basic Research Program of China under Grant Nos 2013CB933304 and 2014CB643904, the National Natural Science Foundation of China under Grant Nos 61435012 and 61274125, and the Strategic Priority Research Program (B) of Chinese Academy of Sciences under Grant No XDB01010200.

A four-wavelength Bragg reflection waveguide edge emitting diode based on intracavity spontaneous parametric down-conversion and four-wave mixing (FWM) processes is made. The structure and its tuning characteristic are designed by the aid of FDTD mode solution. The laser structure is grown by molecular beam epitaxy and processed to laser diode through the semiconductor manufacturing technology. Fourier transform infrared spectroscopy is applied to record wavelength information. Pump around 1.071 μm, signal around 1.77 μm, idler around 2.71 μm and FWM signal around 1.35 μm are observed at an injection current of 560 mA. The influences of temperature, carrier density and pump wavelength on tuning characteristic are shown numerically and experimentally.

Hybrid Three-Mode Correlation and Squeezing in a Pr3+:YSO Crystal

We report the generation of three-mode hybrid intensity-noise correlation and intensity-difference squeezing of spontaneous parametric four-wave mixing (SP-FWM) and fourth-order fluorescence (FL) signals in the heteronuclear-like (three-level Λ-type) molecular structure of a Pr3+:Y2SiO5 (Pr3+:YSO) crystal using the nonlinear cross-Kerr effect under a polarized dressing effect. In the semi-classical view of a Kerr nonlinear medium, the amplitude of two-mode hybrid correlations of this kind is subject to a limit determined by the hybrid maximally entangled state. Whereas the degree of correlation and squeezing is determined by the dressing effects of the input laser fields participating in the SP-FWM process. We also find that the variations in magnitude of three-mode hybrid intensity-noise correlation and intensity-difference squeezing are consistent with nonlinear cross-Kerr processes. Such a three-mode hybrid signal may have potential applications in long-distance communication, dense coding, all-optical communication and quantum storage on photonic chips.

Evolution of intensity noise and hybrid correlation

We report the evolution of spontaneous parametric four-wave mixing (SP-FWM) as a small peak in the dip of Autler–Townes splitting in the medium of coherent non linear crystal of Pr3+:Y2SiO5. We demonstrate the results of a composite signal with evolution from pure fluorescence to a hybrid state of light to pure SP-FWM. By investigating the composite signal in frequency/time domains and studying hybrid correlations (positive/negative or anti-correlation) among three channels, i.e. Stokes (anti-Stokes) with composite signal, we demonstrate the evolution of SP-FWM processes from fluorescence. Such correlations can have potential applications in all-optical communication and quantum teleportation.

Correlation and squeezing for optical transistor and intensity router applications in diamond NV center.

We study an optical transistor (switch and amplifier) and router by spontaneous parametric four-wave mixing and fluorescence in diamond nitrogen-vacancy (NV) center. The routing results from three peaks of fluorescence signal in the time domain, while the switching and amplification are realized by correlation and squeezing. The intensity switching speed is about 17 ns. The optical transistor and router are controlled by the power of incident beams. Our experimental results provide that the advance technique of peak division and channel equalization ratio of about 90% are applicable to all optical switching and routing.

Franson Interference Generated by a Two-Level System.

We report a Franson interferometry experiment based on correlated photon pairs generated via frequency-filtered scattered light from a near-resonantly driven two-level semiconductor quantum dot. In contrast to spontaneous parametric down-conversion and four-wave mixing, this approach can produce single pairs of correlated photons. We have measured a Franson visibility as high as 66%, which goes beyond the classical limit of 50% and approaches the limit of violation of Bell's inequalities (70.7%).