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arXiv:2211.14979 · Physical Review A

Enhancing the stimulated emission of polarization-entangled photons using passive optical components

Ryo Nozaki, Yoshiro Sato, Yoshitaka Shimada, Taku Suzuki, Kei Yasuno, Yuta Ikai, Wataru Ueda, Kaito Shimizu, Emi Yukawa, Kaoru Sanaka

Published Feb 7, 2023• 4 citations
arXivHTMLPDF

Abstract

Bright sources of polarization-entangled photon pairs are essential components for quantum information technologies. In many methods proposed so far, it is necessary to introduce a resonator that combines active optical components, such as an electric optical modulator to enhance the stimulated emission of polarization-entangled photons. In these methods, however; it is technically difficult to perform the time-series operation to output the stimulated entangled photons in the resonator by synchronizing laser pulses. In this paper, we propose a scheme to scale up the stimulated emission of polarization-entangled photon pairs using a resonator with only passive optical components. We show the theoretical aspects of the scheme and perform a proof-of-principle experimental demonstration of the scheme in a double-pass configuration.

DOI
10.1103/physreva.107.023707

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•Jan 1, 2002•1 citation
Bright sources of polarization-entangled photon pairs are essential components for quantum information technologies. In many methods proposed so far, it is necessary to introduce a resonator that combines active optical components, such as an electric optical modulator to enhance the stimulated emission of polarization-entangled photons. In these methods, however; it is technically difficult to perform the time-series operation to output the stimulated entangled photons in the resonator by synchronizing laser pulses. In this paper, we propose a scheme to scale up the stimulated emission of polarization-entangled photon pairs using a resonator with only passive optical components. We show the theoretical aspects of the scheme and perform a proof-of-principle experimental demonstration of the scheme in a double-pass configuration.
Abstract Single-photon sources based on semiconductor quantum dots find several applications in quantum information processing due to their high single-photon indistinguishability, on-demand generation, and low multiphoton emission. In this context, the generation of entangled photons represents a challenging task with a possible solution relying on the interference in probabilistic gates of identical photons emitted at different pulses from the same source. In this work, we implement this approach via a simple and compact design that generates entangled photon pairs in the polarization degree of freedom. We operate the proposed platform with single photons produced through two different pumping schemes, the resonant excited one and the longitudinal-acoustic phonon-assisted configuration. We then characterize the produced entangled two-photon states by developing a complete model taking into account relevant experimental parameters, such as the second-order correlation function, Hong–Ou–Mandel visibility, multiphoton emission and pump laser filtering. Our source shows long-term stability and high quality of the generated entangled states, thus constituting a reliable building block for optical quantum technologies.
We introduce the notion of laser-like operation for polarization entangled photons. The proposed device has a two-mode output which contains quantum correlations both between the polarization degree of freedom for particles in separate modes and between the photon numbers in the modes. The proposed device will operate in the new and virtually unexplored regime of many-particle entanglement. We present the design and provide experimental data in support of the main operation mechanism. In particular we show the generation of a rotational symmetric four-photon entangled state obtained by stimulated emission of the familiar antisymmetric two-particle Bell state. The produced states allow for novel quantum cryptography and quantum information protocols and for tests of spin-s Bell inequalities.
Recently, a novel Resolution Enhancement Technology (RET) have been proposed to overcome the Rayleigh resolution limit by using both entangled photon pair and two-photon absorption resist. However, the illumination intensity is not enough to attain the reasonable throughput. We propose a new method which enables to enhance the resolution over the Rayleigh limit with more strong intensity source by using two-photon absorption resist, where the absorbed two photons have different polarization each other. Since it is recently reported that the stimulated emission of polarization-entangled photons has been achieved, we investigate the effect of such entangled four photons to the resolution enhancement instead of entangled photon pair. Moreover, we also study the application of two-mode squeezing state.
Fiber-based entangled photon sources are a key resource in emerging quantum technologies due to compactness, long-term stability and alignment-free operation. Fast control of the quantum state properties is also necessary in practical scenarios, where a universal source can be employed with different temporal and spectral configurations. Here, we report on a flexible source design that produces high-quality entanglement from continuous-wave up to GHz-pulsed operation modes. Our approach uses off-the-shelf optical components in a Sagnac configuration to generate polarization-entangled photon pairs at telecom wavelength. This design further allows phase modulation above MHz speeds with high fidelity. Together with its 60 nm spectral bandwidth, the proposed system is entirely suitable for wavelength-multiplexed and reconfigurable quantum networks, where state modulation or active bandwidth allocation is required.
Efficient Generation of Entangled Photon-Pairs The first experiments with correlated photons have been performed in the context of EPR-Bell experiments on the realistic and local properties of quantum mechanics. The source used there produced pairs of polarization entangled photons from a 2-photon decay of Calcium atoms. The technical requirements of these experiments were high (vacuum systems, stronge dye-lasers, etc.) whereas the efficiency of the source was quite low. An important step forward was the introduction of spontaneous parametric down conversion (SPDC), which has become the most common source in quantum optics for generating correlated or entangled photon pairs. In this process photons of an intense pump laser convert to photon pairs in an optical nonlinear crystal. Conservation of energy and momentum leads to strong correlations between the generated photons. With this kind of two-photon source it was possible to realize or improve many experiments on the foundations of quantum mechanics addressing the EPR-Paradoxon and in the new field of quantum information. But again, more advanced experiments and applications suffer from the limited ef- ficiency of the fluorescence process. Many photon pairs are lost by spatial and spectral filtering, which is necessary to achieve polarization entanglement and long coherence times. Different techniques have been implemented to increase the number of photon pairs using two-crystal arrangements, focusing techniques or periodically poled crystals. Most of these methods have the disadvantage that no entangled photons have been observed. It is the aim of this work to increase the yield and to improve the mode definition of entangled photon pairs generated by resonant enhancement of the pump mode and the fluorescence modes. As a first step a linear cavity for the pump mode was realized. Since the conversion probability is proportional to the pump power it was possible to increase the photon pair count rate by factor of 7 over the previous source. Besides the possibility of further improvement on already established pair correlation experiments, such an enhancement allows to build a compact source for photon pairs, in which an expensive argon-ion laser is replaced by a cheap diode laser. Among other applications such sources are of strong interest for quantum cryptography. 3 In many quantum information experiments optical fibers are use to carry the photons over long distance. Therefore, light from the parametric down-conversion source has to be efficiently coupled into fibers. In the second part we report on a new method to optimize collection efficiency by matching the angular distribution of the parametric fluorescence to the spatial mode of an optical fiber. By using this technique, we detected 366500 polarization-entangled photon pairs per second in the near-infrared region in single-mode optical fibers for 465 mW pump power (at 351.1 nm) with a 2 mm BBOcrystal. The entanglement of the photon pairs was verified by measuring polarization correlations of more than 96% in a HV-basis and in a ±45◦-basis. To our knowledge, such enormous count rates of highly entangled photon pairs have not been reached yet with any other technique. In the third part of this thesis we investigated the process of parametric downconversion in a cavity which is resonant to certain longitudinal down-conversion modes only. The idea of placing the parametric down-conversion source inside a cavity is not new. Such a device is usually referred to as a single or double resonant optical parametric oscillator (OPO) and is mainly used to generate squeezed quantum states. In that kind of application the system is operating close to but still under the threshold of oscillation. In our application the situation is quite different. The system is operating far below threshold so that mainly spontaneous emission occurs. In that mode correlations between single photons can still be observed. But bouncing the light back and forth inside the cavity increases the interaction length and hence enhances the signal levels of the down-conversion fields. Further, by resonating two certain modes only, the bandwidth is reduced by orders of magnitude and the coherence time is found to be inverse proportional to the bandwidth. A similar experiment has already been realized with a type-I parametric down-converter in the resonator. We have tried to realize a compact double resonant OPO far below threshold with a type-II parametric down-converter in a high-finesse cavity to realize a bright source of entangled photon pairs with extremely narrow bandwidth.