Photon statistics have moved to the forefront of modern optics, as intensity fluctuations and correlations shape multiphoton interactions and reveal information beyond mean-intensity measurements. Developing high-quality photon sources with pronounced correlations is a fundamental necessity in these fields. Here we demonstrate fluctuation-driven nonlinear statistical amplification of quantum light in spontaneous four-wave mixing using filtered amplified spontaneous emission (ASE). Extending the coherent-pump framework to fluctuating fields, we show how nonlinear weighting of pump intensity combines with bosonic bunching to amplify quantum statistics and reshape temporal correlations. In a SiN microring, ASE pumping increases the zero-delay unconditional second-order correlation from 2.01 to 7.58 and extends the Hanbury Brown--Twiss correlation time by a factor of approximately 2.4. The super-bunched quantum source nevertheless retains heralded single-photon behaviour with $g_H^{(2)}(0)\simeq0.04$, while the same ASE pump supports time--energy entanglement in a silicon waveguide with a raw Franson visibility of 89.84\%. These results establish driving-field statistics as a design dimension for quantum light, broadening the horizons for research into higher-order correlations and nonlinear physics.
Photon statistics have moved to the forefront of modern optics, as intensity fluctuations and correlations shape multiphoton interactions and reveal information beyond mean-intensity measurements. Developing high-quality photon sources with pronounced correlations is a fundamental necessity in these fields. Here we demonstrate fluctuation-driven nonlinear statistical amplification of quantum light in spontaneous four-wave mixing using filtered amplified spontaneous emission (ASE). Extending the coherent-pump framework to fluctuating fields, we show how nonlinear weighting of pump intensity combines with bosonic bunching to amplify quantum statistics and reshape temporal correlations. In a SiN microring, ASE pumping increases the zero-delay unconditional second-order correlation from 2.01 to 7.58 and extends the Hanbury Brown--Twiss correlation time by a factor of approximately 2.4. The super-bunched quantum source nevertheless retains heralded single-photon behaviour with gH(2)(0)≃0.04, while the same ASE pump supports time--energy entanglement in a silicon waveguide with a raw Franson visibility of 89.84%. These results establish driving-field statistics as a design dimension for quantum light, broadening the horizons for research into higher-order correlations and nonlinear physics.
Recently, the question of the origin of correlations in thermal light has again been debated. The alternative viewpoints suggest that (i) stimulated emission causes the correlations implied by Bose-Einstein statistics and exemplified by the Hanbury Brown-Twiss effect, or (ii) stimulated emission coherently amplifies any initial field, with no change in the nature of photon statistics, apart from the addition of, and interference with, spontaneous-emission noise. It is shown that two essentially different physical models have been considered previously, with many results being only approximate. For these models we obtain the evolution of the photon statistics by deriving exactly the generating function for the diagonal elements of the field density matrix and the quantum characteristic function. The source of Bose-Einstein correlations is seen to be merely the interference in the superposition of random independent fields from a chaotic source, spontaneous emission being one example. Extending the investigation to a nonlinear model, we show that, although there is no longer coherent amplification, it is still not correct to infer that this interaction, which produces the amplification, also leads to Bose-Einstein statistics.
On-chip quantum sources based on nonlinear processes are pivotal components in integrated photonics, driving significant advancements in quantum information technologies over recent decades. Usually, the pump coherence has been considered to be crucial for ensuring the quality of generated states, therefore incoherent light is rarely used in quantum information processing. In this work, we explore and reveal the constructive influence of pumped temporal incoherence on the quantum properties of photon sources. Taking silicon waveguides as nonlinear media, we theoretically show that temporal incoherence of light can improve pump utilization efficiency, resulting in higher source brightness in a spontaneous four-wave mixing process. Compared with coherent lasers, the frequency-uncorrelated character of incoherent light reduces spectral correlations in the generated photons, facilitating higher state purity in practice. Experimentally, we obtain a higher photon pair generation rate and the lower heralded second-order autocorrelation with an Amplified Spontaneous Emission source. Additionally, we successfully generate a polarization-entangled state with Bell inequality violation of S = 2.64 ± 0.02 and a fidelity of 95.7% ± 0.1%. Our study reveals the mechanism behind incoherently pumped quantum states and presents a method for generating photon sources using an easily accessible incoherent light. Coherence is widely seen as essential for quantum source quality. Here, authors demonstrate on-chip photon states with increased brightness and purity using incoherent light. It reveals the mechanism of pump coherence and lowers the barrier for the generation of high-quality quantum states.
We report on the properties and applications of intense and nonconventional stochastic photonic sources based on amplified spontaneous emission (ASE) [1]. First, we describe the principle of nonlinear intensity filtering using various nonlinear filters (e.g. a modified nonlinear Mach-Zehnder interferometer). The latter can alter the properties of an intense incident ASE source in a controlled manner. In particular, we demonstrated the possibility to tailor the probability density function (PDF)p(I)) (Fig. 1.a) as well as the second- and, in a more general sense, then-th order degree of coherenceg(n≥1)(τ)) associated with the likelihood and the correlation of the intensity fluctuations, respectively. Depending on the type of filter and its parameters, the resulting random intensityI(t)can exhibit large overshoots or smoother fluctuations.
Correlated single photons provide a means to drive applications such as quantum computing and quantum communications. Correlated single photons can be generated via parametric down conversion in second–order nonlinear media or spontaneous four–wave mixing in third–order nonlinear media. In particular, complementary metal–oxide–semiconductor (CMOS) technology allows for seamless integration with electronics, providing the potential for a completely on-chip solution for quantum information processing. Ultra–silicon–rich nitride platform is a backend CMOS compatible platform, that has already been used to obtain high gain optical parametric amplification, wideband supercontinuum and enhanced nonlinearity in photonic crystal waveguides due to its large nonlinearity. In this work, we demonstrate correlated photon pair generation based on spontaneous four–wave mixing using ultra-silicon-rich nitride waveguides for the application in CMOS–based optical quantum technologies. A CW pump at a wavelength of 1555.747nm amplified using an EDFA is filtered through five wavelength division multiplexers (WDM) with a bandwidth of 1.2nm, providing 175dB suppression of EDFA induced pump sideband noise. The filtered quasi–TE pump, adjusted using a fiber polarization controller, is coupled into an ultra–silicon–rich nitride waveguide using a lensed fiber. A SiO2 cladded waveguide with a width of 550nm and height of 300nm possesses a high nonlinear parameter of 530W^-1/m with anomalous dispersion necessary for spontaneous four-wave mixing. The waveguide output is coupled into a lensed fiber and 7 cascaded WDMs are used to provide 245dB of residual pump filtration. The pump–suppressed output is spectrally separated into signal/idler part using WDMs. We refer to lower (higher) frequency photon as the signal (idler). The spontaneously generated signal and idler photons are filtered using cascaded tunable band pass filters (OTF) centered at 1571.24nm and cascaded WDMs centered at 1540.56nm, respectively. The bandwidth of the tunable OTF and WDM is 0.5nm and 1.2nm, therefore the correlated signal/idler photons are observed within the bandwidth window of 0.5nm induced by the OTF. The signal and idler photons are measured using InGaAs/InP avalanche photodetectors. The time correlation between signal and idler photons is obtained using a time interval analyzer with a detection efficiency of 20% and dead time of 15μs.The time bin is set to 81ps and the photon collection time is 240s. The coincidence peak is located ~11ns in the time–bin histogram due to the optical-path difference between the tunable OTF and WDM at respective signal and idler sides. The experimental raw coincidence counts (Hz), calculated by subtracting the accidental rate from the coincidence peak, show a quadratic increase with respect to coupled pump power. At the maximum coupled power of 5mW, the raw coincidence count is ~1Hz. We achieve a raw coincidence–to–accidental ratio (CAR) of up to 3. Therefore, we succeeded to observe correlated photon pair generation based on spontaneous four–wave mixing using the ultra–silicon–rich-nitride waveguide as a CMOS compatible platform, for future applications in quantum technologies.
Developments in quantum technologies lead to new applications that require radiation sources with specific photon statistics. A widely used Poissonian statistics are easily produced by lasers; however, some applications require super- or sub-Poissonian statistics. Statistical properties of a light source are characterized by the second-order coherence function g^(2)(0). This function distinguishes stimulated radiation of lasers with g^(2)(0)=1 from light of other sources. For example, g^(2)(0)=2 for black-body radiation, and g^(2)(0)=0 for single-photon emission. One of the applications requiring super-Poissonian statistics (g^(2)(0)>1) is ghost imaging with thermal light. Ghost imaging also requires light with a narrow linewidth and high intensity. Currently, rather expensive and inefficient light sources are used for this purpose. In the last year, a superluminescent diode based on amplified spontaneous emission (ASE) has been considered as a new light source for ghost imaging. Even though ASE has been widely studied, its photon statistics has not been settled - there are neither reliable theoretical estimates of the second-order coherence function nor unambiguous experimental data. Our computer simulation clearly establishes that coherence properties of light produced by ASE are similar to that of a thermal source with g^(2)(0)=2 independent of pump power. This result manifests the fundamental difference between ASE and laser radiation.
Understanding nonequilibrium transport and fluctuations driven by nonclassical light in nonlinear quantum optical systems is challenging. Here, we formulate a driven quantum master equation in the rotating frame combined with full counting statistics, retaining the drive-induced frequency shifts in the system-reservoir interactions and providing a unified description of drive-assisted incoherent transitions based on the rotated system dressed-basis. Applied to a Kerr resonator and a nonlinear Jaynes-Cummings model, the approach reveals pronounced multiphoton-resonant enhancement of the drive input energy current, with significant high peaks under two-photon driving compared to the single-photon case. The two-photon resonance relations are analytically obtained. Resonance structure in the nonlinear Jaynes-Cummings model nonlinearly relies on qubit-photon couplings, with additional dressed-state branches. A low-energy-state approximation attributes the resonant current enhancement to dressed-state hybridization and efficient activation of incoherent energy exchange processes. Beyond the average current, two-photon-driving induced energy exchange picture near resonance also substantially modifies the second-order current fluctuation and higher-order current cumulant, while increasing the time-normalized signal-to-noise ratio. Adding two-photon loss introduces extra incoherent photon-pair exchange pathways and further reshapes the current and its fluctuations. We hope these results may deepen interpretation of photon driving and quantum dissipation cooperatively governing nonequilibrium energy transport and fluctuations.