Quantum-correlated Photon Pairs Research Articles

Engineering the passband shape of coupled-cavity filters for low loss and/or narrow bandwidth.

Emerging applications of photonic integrated circuits are calling for extremely narrowband and/or low-insertion-loss bandpass filters. Both properties are limited by cavity losses or intrinsic quality factors. However, the choice of inter-cavity and bus couplings establishes trade-offs between these two properties and the passband shape, which have been little explored. Using the widely used second-order resonant system as an example, we present new, to the best of our knowledge, classes of filter passband shapes that provide the lowest insertion loss and the narrowest bandwidth for a given loss Q. A normalized design and novel properties based on a temporal coupled-mode theory model are presented, including a design tool to apply these results. These results may benefit loss-sensitive filtering applications such as quantum-correlated photon pair sources and RF-photonic integrated circuits.

Generating quantum correlated photon pairs in a hybrid silicon–BTO platform

Here, we show photon pair generation from ring resonator and waveguide structures in a hybrid silicon–BTO on an insulator platform with a pulsed pump. Our analysis of single photon and coincidence generation rates show that spontaneous four-wave mixing is comparable to that expected from SOI devices with similar characteristics and find γeff of (14.7 ± 1.3) and (2.0 ± 0.3) MHz/mW2 for ring resonator and waveguide structures, respectively.

Coincidence measurements of two quantum-correlated photon pairs widely separated in the frequency domain

Quantum correlation is a key concept characterizing the properties of quantum light sources and is important for developing quantum applications with superior performance. In particular, it enables photon pairs that are widely separated in the frequency domain, one in the visible region, the other in the infrared region, to be used for quantum infrared sensing without direct detection of infrared photons. Here, simultaneous multiwavelength and broadband phase matching in a nonlinear crystal could provide versatile photon-pairs source for broadband infrared quantum sensing. This paper describes direct generation and detection of two quantum-correlated photon pairs produced via simultaneous phase-matched processes in periodic crystals. These simultaneous photon pairs provide a correlated state with two frequency modes in a single pass. To confirm the correlation, we constructed an infrared-photon counting system with two repetition-synchronized fiber lasers. We performed coincidence measurements between two pairs, 980 nm and 3810 nm, and 1013 nm and 3390 nm, which yielded coincidence-to-accidental ratios of 6.2 and 6.5, respectively. We believe that our novel correlated light source with two separate pairs in the visible and infrared region complements a wide-range of multi-dimensional quantum infrared processing applications.

Spatial and spectral characterization of photon pairs at telecommunication wavelengths from type-0 spontaneous parametric downconversion

The thorough characterization of entangled-photon sources is vital for their optimal use in quantum communication. However, this task is not trivial at telecommunication wavelengths. While cameras and spectrometers are well developed for visible and near-infrared spectra, this does not apply in the mid-infrared range. Here, we present a spatial and spectral characterization of photon pairs emitted in a type-0 phase-matched spontaneous parametric downconverted source. We experimentally show how these photon properties are modified by the crystal temperature. This parameter allows easy modification of photon-pair properties to fit multiplexing schemes based on only one entanglement photon source. Our results pave the way for the optimal design and use of spatial and spectral properties of quantum-correlated photon pairs at telecommunication wavelengths.

Generation of photon pairs by stimulated emission in ring resonators.

Third-order parametric downconversion (TOPDC) describes a class of nonlinear interactions in which a pump photon is converted into a photon triplet. This process can occur spontaneously or it can be stimulated by seeding fields. Here we show that stimulated TOPDC (StTOPDC) can be exploited for the generation of quantum correlated photon pairs. We model StTOPDC in a microring resonator, predicting observable pair generation rates in a microring engineered for third-harmonic generation, and we examine the peculiar features of this approach when compared with second-order spontaneous parametric downconversion and spontaneous four-wave mixing. We conclude that if the experimental difficulties associated with implementing StTOPDC can be overcome, it may soon be possible to demonstrate this process in resonant integrated devices.

Ray tracing with quantum correlated photons to image a three-dimensional scene

To capture a three-dimensional (3D) image, conventional methods often require multiple two-dimensional images of the scene from different perspectives. Here we show the reconstruction of a 3D scene with a fixed camera using quantum correlated photon pairs from a single source. Correlated photon pairs are effectively mirror images of each other so, by measuring the emission position of one photon, and the emission angle of the other, the entire propagation trajectory of the pair, and, subsequently, the 3D scene, can be reconstructed. The high photon correlation and low photon flux from a quantum source also makes it well suited for 3D imaging of light sensitive samples.

Generation of Quantum Correlated Photon Pairs by Using Third-Order Nonlinearity in Optical Fibers

Generation of Quantum Correlated Photon Pairs by Using Third-Order Nonlinearity in Optical Fibers

Integrated photonic high extinction short and long pass filters based on lateral leakage.

In this contribution we present a new approach to achieve high extinction short and long pass wavelength filters in the integrated photonic platform of lithium niobate on insulator. The filtering of unwanted wavelengths is achieved by employing lateral leakage and is related to the bound state in the continuum phenomenon. We show that it is possible to control the filter edge wavelength by adjusting the waveguide dimensions and that an extinction of hundreds of dB/cm is readily achievable. This enabled us to design a pump wavelength suppression of more than 100 dB in a 3.5 mm long waveguide, which is essential for on-chip integration of quantum-correlated photon pair sources. These findings pave the way to integrate multi wavelength experiments on chip for the next generation of photonic integrated circuits.

Quantum-correlated photon-pair generation via cascaded nonlinearity in an ultra-compact lithium-niobate nano-waveguide.

We generate quantum-correlated photon pairs using cascaded χ(2):χ(2) traveling-wave interactions for second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC) in a single periodically-poled thin-film lithium-niobate (TFLN) waveguide. When pulse-pumped at 50 MHz, a 4-mm-long poled region with nearly 300%/Wcm2 SHG peak efficiency yields a generated photon-pair probability of 7±0.2 × 10-4 with corresponding coincidence-to-accidental ratio (CAR) of 13.6±0.7. The CAR is found to be limited by Stokes/anti-Stokes Raman-scattering noise generated primarily in the waveguide. A Raman peak of photon counts at 250 cm-1 Stokes shift from the fundamental-pump wavenumber suggests most of the noise that limits the CAR originates within the lithium niobate material of the waveguide.

Generation of broadband correlated photon-pairs in short thin-film lithium-niobate waveguides.

An efficient source of quantum-correlated photon-pairs that is integrable with existing silicon-electronics fabrication techniques is desirable for use in quantum photonic integrated circuits. Here we demonstrate signal-idler photon pairs with high coincidence-to-accidental count ratios of over 103 on a coarse wavelength-division-multiplexing grid that spans 140 nm by using a 300-μm-long poled region in a thin-film periodically-poled lithium-niobate ridge waveguide bonded to silicon. The pairs are generated via spontaneous parametric downconversion pumped by a continuous-wave tunable laser source. The small mode area of the waveguide allows for efficient interaction in a short length of the waveguide and, as a result, permits photon-pair generation over a broad range of signal-idler wavelengths.

Tunable Quantum Beat of Single Photons Enabled by Nonlinear Nanophotonics

We demonstrate the tunable quantum beat of single photons through the co-development of core nonlinear nanophotonic technologies for frequency-domain manipulation of quantum states in a common physical platform. Spontaneous four-wave mixing in a nonlinear resonator is used to produce non-degenerate, quantum-correlated photon pairs. One photon from each pair is then frequency shifted, without degradation of photon statistics, using four-wave mixing Bragg scattering in a second nonlinear resonator. Fine tuning of the applied frequency shift enables tunable quantum interference of the two photons as they are impinged on a beamsplitter, with an oscillating signature that depends on their frequency difference. Our work showcases the potential of nonlinear nanophotonic devices as a valuable resource for photonic quantum information science.

Compressive characterization of telecom photon pairs in the spatial and spectral degrees of freedom.

In the past few years, physicists and engineers have demonstrated the possibility of utilizing multiple degrees of freedom of the photon to perform information processing tasks for a wide variety of applications. Furthermore, complex states of light offer the possibility of encoding and processing many bits of information in a single photon. However, the challenges involved in the process of extracting large amounts of information, encoded in photonic states, impose practical limitations to realistic quantum technologies. Here, we demonstrate characterization of quantum correlated photon pairs in the spatial and spectral degrees of freedom. Our technique utilizes a series of random projective measurements in the spatial basis that do not perturb the spectral properties of the photon. The sparsity in the spatial properties of downconverted photons allows us to exploit the potential of compressive sensing to reduce the number of measurements to reconstruct spatial and spectral properties of correlated photon pairs at telecom wavelength. We demonstrate characterization of a photonic state with 12 × 109 dimensions using only 20% of the measurements with respect to the conventional raster scan technique. Our characterization technique opens the possibility of increasing and exploiting the complexity and dimensionality of quantum protocols that utilize multiple degrees of freedom of light with high efficiency.

Wavelength Tunable Source of Correlated Photon Pairs Based on Photonic Crystal Fiber

Quantum-correlated photon pairs with tunable wavelength are highly desirable in a number of quantum technologies. In this letter, we demonstrate a wavelength tunable source of the correlated photon pairs based on pulse-pumped spontaneous four-wave mixing in photonic-crystal fiber. The wavelengths of the correlated signal and idler photons can be continuously tuned at room temperature by adjusting the wavelength of pump originating from an ytterbium-doped fiber laser. The tuning range of the idler photons is 757–880 nm and the range of the signal photons is 1310–1610 nm, which covers the 1310- and 1550-nm telecom bands.

Engineering spectrally unentangled photon pairs from nonlinear microring resonators by pump manipulation.

The future of integrated quantum photonics relies heavily on the ability to engineer refined methods for preparing the quantum states needed to implement various quantum protocols. An important example of such states is quantum-correlated photon pairs, which can be efficiently generated using spontaneous nonlinear processes in integrated microring-resonator structures. In this work, we propose a method for generating spectrally unentangled photon pairs from a standard microring resonator. The method utilizes interference between a primary and a delayed secondary pump pulse to effectively increase the pump spectral width inside the cavity. This enables on-chip generation of heralded single photons with state purities in excess of 99% without spectral filtering.

High-extinction ratio integrated photonic filters for silicon quantum photonics.

We present the generation of quantum-correlated photon pairs and subsequent pump rejection across two silicon-on-insulator photonic integrated circuits. Incoherently cascaded lattice filters are used to provide over 100 dB pass-band to stop-band contrast with no additional external filtering. Photon pairs generated in a microring resonator are successfully separated from the input pump, confirmed by temporal correlations measurements.

Temporal Quantum Correlations in Inelastic Light Scattering from Water

Water is one of the most prevalent chemicals on our planet, an integral part of both our environment and our existence as a species. Yet it is also rich in anomalous behaviors. Here we reveal that water is a novel-yet ubiquitous-source for quantum correlated photon pairs at ambient conditions. The photon pairs are produced through Raman scattering, and the correlations arise from the shared quantum of a vibrational mode between the Stokes and anti-Stokes scattering events. We confirm the nonclassical nature of the produced photon pairs by showing that the cross-correlation and autocorrelations of the signals violate a Cauchy-Schwarz inequality by over 5 orders of magnitude. The unprecedented degree of violating the inequality in pure water, as well as the well-defined polarization properties of the photon pairs, points to its usefulness in quantum information.

Multifrequency sources of quantum correlated photon pairs on-chip: a path toward integrated Quantum Frequency Combs

Abstract Recent developments in quantum photonics have initiated the process of bringing photonic-quantumbased systems out-of-the-lab and into real-world applications. As an example, devices to enable the exchange of a cryptographic key secured by the laws of quantum mechanics are already commercially available. In order to further boost this process, the next step is to transfer the results achieved by means of bulky and expensive setups into miniaturized and affordable devices. Integrated quantum photonics is exactly addressing this issue. In this paper, we briefly review the most recent advancements in the generation of quantum states of light on-chip. In particular, we focus on optical microcavities, as they can offer a solution to the problem of low efficiency that is characteristic of the materials typically used in integrated platforms. In addition, we show that specifically designed microcavities can also offer further advantages, such as compatibility with telecom standards (for exploiting existing fibre networks) and quantum memories (necessary to extend the communication distance), as well as giving a longitudinal multimode character for larger information transfer and processing. This last property (i.e., the increased dimensionality of the photon quantum state) is achieved through the ability to generate multiple photon pairs on a frequency comb, corresponding to the microcavity resonances. Further achievements include the possibility of fully exploiting the polarization degree of freedom, even for integrated devices. These results pave the way for the generation of integrated quantum frequency combs that, in turn, may find important applications toward the realization of a compact quantum-computing platform.

Energy correlations of photon pairs generated by a silicon microring resonator probed by Stimulated Four Wave Mixing

Compact silicon integrated devices, such as micro-ring resonators, have recently been demonstrated as efficient sources of quantum correlated photon pairs. The mass production of integrated devices demands the implementation of fast and reliable techniques to monitor the device performances. In the case of time-energy correlations, this is particularly challenging, as it requires high spectral resolution that is not currently achievable in coincidence measurements. Here we reconstruct the joint spectral density of photons pairs generated by spontaneous four-wave mixing in a silicon ring resonator by studying the corresponding stimulated process, namely stimulated four wave mixing. We show that this approach, featuring high spectral resolution and short measurement times, allows one to discriminate between nearly-uncorrelated and highly-correlated photon pairs.

冷原子系综中量子关联光子对的产生

冷原子系综中量子关联光子对的产生

Quantum-correlated photon pairs generated in a commercial 45 nm complementary metal-oxide semiconductor microelectronic chip

Correlated photon pairs are a fundamental building block of quantum photonic systems. While pair sources have previously been integrated on silicon chips built using customized photonics manufacturing processes, these often take advantage of only a small fraction of the established techniques for microelectronics fabrication and have yet to be integrated in a process that also supports electronics. Here we report the first demonstration of quantum-correlated photon pair generation in a device fabricated in an unmodified advanced (sub-100-nm) complementary metal-oxide semiconductor (CMOS) process, alongside millions of working transistors. The microring resonator photon pair source is formed in the transistor layer structure, with the resonator core formed by the silicon layer typically used for the transistor body. With ultralow CW on-chip pump powers ranging from 4.8 to 400 μW, we demonstrate pair generation rates between 165 Hz and 332 kHz using >80% efficient WSi superconducting nanowire single-photon detectors. Coincidences-to-accidentals ratios consistently exceeding 40 were measured, with a maximum of 55. In the process of characterizing this source, we also accurately predict pair generation rates from the results of classical stimulated four-wave mixing measurements. This proof-of-principle device demonstrates the potential of commercial CMOS microelectronics as an advanced quantum photonics platform with the capability of large volumes and pristine process control, where state-of-the-art high-speed digital circuits could interact with quantum photonic circuits.