Frequency entangled photons have potential for various quantum applications. Recently, on-chip photon-pair sources made by CMOS compatible processes have attracted attention. In this paper, we report broadband generation of photon-pairs via a spontaneous four-wave mixing process using a CMOS compatible ring resonator. We performed frequency-correlation between the signal and idler photons by frequency-resolved coincidence detection and confirmed that the signal and idler photons are correlated over 59 frequency modes, a bandwidth of 23.6 nm, which are the largest numbers achieved to date. Furthermore, we reproduced the experimentally observed joint spectral intensity from the obtained transmission spectrum of the resonator involving the information of the dispersion of the device.
Frequency entangled photons have potential for various quantum applications. Recently, on-chip photon-pair sources made by CMOS compatible processes have attracted attention. In this paper, we report broadband generation of photon-pairs via a spontaneous four-wave mixing process using a CMOS compatible ring resonator. We performed frequency-correlation between the signal and idler photons by frequency-resolved coincidence detection and confirmed that the signal and idler photons are correlated over 59 frequency modes, a bandwidth of 23.6 nm, which are the largest numbers achieved to date. Furthermore, we reproduced the experimentally observed joint spectral intensity from the obtained transmission spectrum of the resonator involving the information of the dispersion of the device.
Frequency entangled photon sources are in high demand in a variety of optical quantum technologies, including quantum key distribution, cluster state quantum computation and quantum metrology. In the recent decade, chip-scale entangled photon sources have been developed using silicon platforms, offering robustness, large scalability and CMOS technology compatibility. Here, we report the generation of frequency correlated photon pairs using a 150-GHz silicon nitride ring cavity. First, the device is characterized for studying the phase matching condition during spontaneous four-wave mixing. Next, we evaluate the joint spectrum intensity of the generated photons and confirm the photon pair generation in a total of 42 correlated frequency mode pairs, corresponding to a bandwidth of 51.25 nm. Finally, the experimental results are analyzed and the joint spectral intensity is quantified in terms of the phase matching condition.
Silicon micro-ring resonators have been demonstrated to be potential “on- chip” efficient sources of time-energy entangled photons. In these devices, photon pairs are generated by spontaneous four-wave-mixing (SFWM), an elastic scattering event involving two pump photons that results in the generation of an idler and a signal photon. The mass production of such integrated devices for quantum optic experiment requires the implementation of fast and reliable techniques to monitor the emitted two-photon state as well as the device performances. In this work we show that the joint spectral density of photon pairs that would be generated by SFWM in a silicon ring resonator can be measured with unprecedented resolution and speed, improving of several orders of magnitudes the results of traditional approaches based on coincidence measurements.
Frequency-entangled photon pairs play a vital role in various quantum technologies, including quantum computing, quantum communication, and quantum sensing. Broadening the bandwidth of frequency-entangled photon pairs enhances the performance of these technologies. Here, we report the experimental demonstration of the generation of ultra-broadband frequency-correlated photon pairs using a high-index contrast doped glass microring resonator fabricated on a silicon chip. The generated photon pairs exhibit frequency correlation between 106 mode pairs and 212 frequency combs in total, ranging from 1394.0 to 1745.9 nm with the bandwidth of 351.9 nm and covering the telecom E-, S-, C-, L-, and U-bands. The bandwidth of the photon pairs is more than three times larger than the record so far achieved with an on-chip microring resonator. This result will be useful for secure quantum communications and high-resolution quantum optical coherence tomography.
Integrated quantum photonics leverages the on-chip generation of nonclassical states of light to realize key functionalities of quantum devices. Typically, the generation of such nonclassical states relies on whispering gallery mode resonators, such as integrated optical micro-rings, which enhance the efficiency of the underlying spontaneous nonlinear processes. While these kinds of resonators excel in maximizing either the temporal confinement or the spatial overlap between different resonant modes, they are usually associated with large mode volumes, imposing an intrinsic limitation on the efficiency and footprint of the device. Here, we engineer a source of time-energy entangled photon pairs based on a silicon photonic crystal cavity, implemented in a fully CMOS-compatible platform. In this device, resonantly enhanced spontaneous four-wave mixing converts pump photon pairs into signal/idler photon pairs under the energy-conserving condition in the telecommunication C-band. The design of the resonator is based on an effective bichromatic confinement potential, allowing it to achieve up to nine close-to-equally spaced modes in frequency, while preserving small mode volumes, and the whole chip, including grating couplers and access waveguides, is fabricated in a single run on a silicon-on-insulator platform. Besides demonstrating efficient photon pair generation, we also implement a Franson-type interference experiment, demonstrating entanglement between signal and idler photons with a Bell inequality violation exceeding five standard deviations. The high generation efficiency combined with the small device footprint in a CMOS-compatible integrated structure opens a pathway toward the implementation of compact quantum light sources in all-silicon photonic platforms.
Integrated sources of single and entangled photons are currently one of the main topics in the field of integrated quantum optics [1]. Sources at telecom wavelength and compatible with the electronic \nintegrate circuit technology (CMOS) are particularly interesting for their compatibility with the existing fiber network and industrial fabrication processes [2]. As for classical communication, wavelength-division multiplexing (WDM,i.e. the possibility of simultaneously transmitting on the same channel different signals each encoded in a different frequency) could in principle be exploited also for quantum communication for increasing the transmission bit-rate. However, to date only few approaches have been proposed for generating wavelength multiplexing photon pairs in integrated platforms [3,4]. Moreover, until now no integrated photon source managed to achieve at the same time practical requirements such as narrow linewidths (required for quantum memories), compatibility with CMOS technology, multichannel emission, and stable long-term operation [5]. This is due to the fact that narrow linewidths are typically achieved with structures fundamentally incompatible with large-scale integration, while CMOS-compatible devices fail to achieve the high Q-factor required for exhibiting narrow linewidths. Here we report an integrated photon pair source based on a CMOS -compatible micro-ring resonator generating multiple, simultaneous, and independent photon pairs at different wavelengths distributed in a frequency comb, compatible with standard wavelength division multiplexing channels (DWDM, 200 GHz separation) and quantum memories (140 MHz linewidth), covering the full telecommunication band (L+C). We exploit a self-locked pumping scheme allowing an intrinsically stable operation even at the very low pump power levels typically used for photon pair generation. By enclosing the microring in an active external cavity[see Fig. 1(a)], the pump laser includes the microring itself, thus resulting in a passive self-locked pumping mechanism leading to several days of stable operation (compared to only few tens of minutes for standard schemes without active stabilization) [5]. The signal/idler photons are then separated according to their wavelength using a standard commercial DWDM filter, and then characterized by coincidence detection. Clear coincidence peaks [see Fig. 1(b)], with Coincidence to Accidental Ratios higher than 10, are obtained when selecting conjugate frequencies (while no coincidences are observed for non-conjugate signal/idler pair). Finally, Fig. 3(c) reports the measured heralded autocorrelation function, g (2)h, featured by a dip as low as 0.14<0.5, indicating the suitability of our device as heralded single photon source.\n
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.