Quantum information science (QIS) is a pioneering field of research at the interface of physics and information science. By harnessing the unique properties of quantum mechanics to code, transmit and process information (Qbit), QIS offers significant opportunities to revolutionise information processing and communication strategies. Of the various physical systems currently investigated, single particles of light (photons) are destined to play a central role due to their inherent low noise, ease of manipulation at the single photon level and light-speed transmission. Photonics Qbits can be conveniently generated through the process of spontaneous parametric down-conversion, whereby a photon from a laser beam incident onto a non-linear crystal can spontaneously split into two daughter photons, conserving momentum and energy. Our approach aims at exploiting the high-maturity of both telecom and integrated non-linear optics as enabling technologies. This should lead to the demonstration of ultrafast photon-pair sources, as well as, when one of the photon is used as a trigger, of ultrafastest heralded Fourier transform single photon sources, all in a guided-wave fashion. In this talk, we will present a photon pair source, based on high-brightness periodically poled lithium niobate waveguide, pumped by a state-of-the-art telecom laser operating at a repetition rate of 10 GHz. We will also show how high quality telecommunication components enable the implementation of an ultrafast Fourier transform limited heralded single-photon source complying with the demand of next generation high bit rates quantum networks.
Quantum information science (QIS) is a pioneering field of research at the interface of physics and information science. By harnessing the unique properties of quantum mechanics to code, transmit and process information (Qbit), QIS offers significant opportunities to revolutionise information processing and communication strategies. Of the various physical systems currently investigated, single particles of light (photons) are destined to play a central role due to their inherent low noise, ease of manipulation at the single photon level and light-speed transmission. Photonics Qbits can be conveniently generated through the process of spontaneous parametric down-conversion, whereby a photon from a laser beam incident onto a non-linear crystal can spontaneously split into two daughter photons, conserving momentum and energy. Our approach aims at exploiting the high-maturity of both telecom and integrated non-linear optics as enabling technologies. This should lead to the demonstration of ultrafast photon-pair sources, as well as, when one of the photon is used as a trigger, of ultrafastest heralded Fourier transform single photon sources, all in a guided-wave fashion. In this talk, we will present a photon pair source, based on high-brightness periodically poled lithium niobate waveguide, pumped by a state-of-the-art telecom laser operating at a repetition rate of 10 GHz. We will also show how high quality telecommunication components enable the implementation of an ultrafast Fourier transform limited heralded single-photon source complying with the demand of next generation high bit rates quantum networks.
We report on a guided wave heralded photon source based on the creation of non-degenerate photon pairs by spontaneous parametric down conversion in a Periodically Poled Lithium Niobate waveguide. Using the signal photon at 1310 nm as a trigger, a gated detection process permits announcing the arrival of single photons at 1550 nm at the output of a single mode optical fiber with the best probability to date of 0.38. The multi-photon emission probability is reduced by a factor of 10 compared to poissonian light sources. Relying on guided wave technologies such as integrated optics and fiber optics components, our source offers stability, compactness and efficiency and can serve as a paradigm for guided wave devices applied to quantum communication and computation using existing telecom networks.
We demonstrate a miniaturized, scalable high rate, pulsed single-photon source in the telecom band obtained by heralding a spontaneous parametric downconversion source pumped with a highly tunable GHz repetition rate pulsed laser in an all-guided wave scheme. For developing this source, we first perform second harmonic generation of ultrashort pump pulses varying with GHz rate at the telecom wavelength. Our investigation demonstrates a trade-off between the spectral brightness and the single-photon purity of the heralded single-photon source by controlling the repetition rate of pump pulses. For a 5 GHz repetition rate, a periodically poled lithium niobate waveguide in type-0 configuration produces the highest spectral brightness ∼8.5×106pairs/s/mW/GHz. We quantify the single-photon purity using the second-order autocorrelation function g(2), which reaches the lowest value of ∼(3.4 ± 0.038) × 10−4 for 20 GHz repetition rate pulses, generating heralded single photons at 45 kHz rate. Our all-guided wave configuration offers easy integration and alignment, paving the way for developing scalable, integrable, tunable purity single-photon sources for quantum technology applications, such as quantum communication and quantum networks.
Quantum information protocols tend to involve more and more entangled photon pairs, for enabling advanced quantum tasks. To compensate for the low success efficiency of these protocols, one can increase the repetition rate of the emitted pairs, up to current telecom standard (40 GHz). In this context, we propose a realization of ultra-fast photon pair sources, intended for either heralded quantum state engineering or entanglement swapping at telecom wave- length. In this paper, we present preliminary results consisting of a two-photon interference experiment using four photons where the achieved raw visibility of the Hong-Ou-Mandel (HOM) dip exceeds 98.6 %. The interfering photons are generated through spontaneous parametric down conversion process (SPDC) in two independent, separate, periodically poled lithium niobate (PPLN) waveguides.
The preparation of single photons in a pure quantum state is a subject of great interest in physics, enabling the control of light at an unprecedented level. The ease with which certain degrees of freedom of photon states, such as polarisation, can be manipulated, along with the inherent resilience of photons to decoherence, makes them well suited for use as qubits. Recent rapid developments in the transmission and processing of quantum information, as well as the likely technological impact of potential real-world applications such as quantum cryptography and quantum computation, mean that the demand for high performance single photon sources is likely to increase in the near future. One approach to producing single photon states, which are known to be in a well-defined spatio-temporal mode without destructively measuring them, is to take advantage of nonlinear optics. Nonlinear processes can be used to realise frequency conversion by generating a single, correlated pair of photons from an intense pump laser source. The detection of one of the photons from a pair can then be used to indicate the presence of the other photon in the pair, a procedure known as heralding. This thesis describes the development of a source of heralded single photons at 1550 nm, generated directly in the core of a photonic crystal fibre (PCF). By taking advantage of low loss fibre components for the required spectral filtering of the generated photon state, a heralding fidelity of 52% was achieved. The source was designed to be used with a picosecond pulsed fibre laser, making it relatively low cost and maintenance free. With 148 mW of average pump power a heralded output photon rate of 6.4 × 104 s-1 was observed, demonstrating the brightness of the source. The purity of the generated single photons was established by measuring non-classical interference, with a visibility of 70%, between the photons output from this source and a source based on a PPLN waveguide. The fabrication of a series of birefringent PCFs for the generation of spectrally pure state photons at 1550 nm is also discussed. These PCFs will be useful for incorporation in the next generation of high performance, fibre-based photon sources.
Entangled photons generation is an interesting field of research, since progress in this area will directly affect the development of photonic quantum technologies, including quantum computing, simulation and sensing. Several methods have been sifted to increase the performances of entangled photon sources and the integrated optics approach represents a promising strategy. In particular, integrated waveguide sources represent a robust tool, thanks to their stability and the enhancement of nonlinear light-crystal interaction provided by waveguide field confinement. Here, we show the versatility of a hybrid approach, realizing an integrated optical source for the generation of entangled photon-pairs at telecom wavelength. The nonlinear active medium used is lithium niobate, while the routing and manipulation of the generated signal is performed in aluminum-borosilicate glass photonic circuits. The system is composed of three cascaded devices. First, a balanced directional coupler at the fundamental wavelength equally splits the pump in the lithium niobate waveguides, which generate single-photon pairs through type 0 spontaneous parametric down-conversion process. A third chip, encompassing directional couplers and waveplates, closes the interferometer and recombines the generated photons, thus giving access to different quantum states of light: path-entangled or polarization-entangled states. A thermal phase shifter, which controls the relative phase between the interferometer arms, gives an additional degree of freedom for engineering the output state of the presented photon pairs source. All these components are entirely fabricated by femtosecond laser micromachining, a direct and very versatile technique that allows to process different kind of materials and realize high quality optical circuits.
Periodically poled lithium niobate waveguides (PPLN/W) are nowadays considered to be one of the most useful toolboxes for quantum communication experiments. Thanks to the high optical confinement over longer lengths than in bulk configurations (a few cm in our case), such structures provide highly efficient non-linear interactions, both in down- and up-conversion regimes. Within the framework of long-distance quantum communication at telecom wavelength, PPLN/Ws have therefore been proved to be a key ingredient for building ultra-bright sources of energy-time, time-bin, as well as polarization entangled pairs of photons, up-conversion based detectors for telecom photon detection and photonic quantum interfaces for coherent wavelength conversion, as well as quantum relays in the entanglement swapping configuration. During the presentation, we will discuss some recent experimental advances regarding two quantum relay scenarios employed to extend the maximum achievable distance of quantum communication. Based on picosecond regime operation, the first relies on the entanglement swapping configuration, and the other on single qubit teleportation using a telecom oriented chip dedicated to one-way quantum communication. In the first realization, we demonstrate that the utilization of PPLN/Ws and standard components available from the telecommunications industry, associated with the picosecond operation regime enables reaching near-perfect two-photon interference (or coalescence) while maintaining high effective photon pair rates. Using pairs of photons emitted around 1550 nm and appropriate filtering stages, we obtain the highest coalescence net visibility, i.e., of 99%, ever reported. As coalescence is seen a major step towards entanglement swapping, we believe that our picosecond guided-wave scheme provides an efficient trade-off between CW and femtosecond regimes, and emphasize why it should lead to realistic quantum relay and repeater schemes, namely by offering an reduced-constraint solution to the synchronization issue when two completely independent lasers are employed. We shall focus on our experimental demonstration and detail a comparative study of performance with similar reported experiments. As a second realization, we will give further directions towards the integration of several functions on a single optical chip, such as a photon pair generator and electro-optically controllable couplers. The idea is to realize a telecom-like quantum relay chip on lithium niobate through which teleportation of single qubits can be done so as to provide the necessary relay function in a compact, stable, efficient, and user-friendly fashion. We will discuss preliminary results obtained with this device for fully fiber-based one-way quantum communication systems. We will conclude by emphasizing the large potential of what we call "guided-wave quantum communication" developed in our laboratory.