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1. Dynamic control of photon lifetime for quantum random number generation

   https://doi.org/10.1364/OPTICA.433102  

   Okawachi, Yoshitomo ; Kim, Bok Young ; Zhao, Yun ; Ji, Xingchen ; Lipson, Michal ; Gaeta, Alexander L. ( November 2021 , Optica)

   In a passive cavity geometry, there exists a trade-off between resonant enhancement and response time, which is inherently limited by the cavity photon lifetime. We demonstrate frequency-selective, dynamic control of the photon lifetime using a silicon-nitride coupled-ring resonator. The photon lifetime is tuned by controlling an avoided mode crossing using thermo-optic tuning of the cavity resonance with integrated heaters. Using this effect, we achieve fast turn-on/off of a${\mathrm{\chi <\#comment/>}}^{(3)}$degenerate optical parametric oscillator (DOPO) and on-chip true random number generation. Our approach allows us to overcome the$Q$-limited generation rate of a single-ring-based DOPO and offers a path toward the development of a scalable integrated high-quality entropy source for modern cryptographic systems.

    

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2. Interpretable inverse-designed cavity for on-chip nonlinear photon pair generation

   https://doi.org/10.1364/OPTICA.502732  

   Jia, Zhetao ; Qarony, Wayesh ; Park, Jagang ; Hooten, Sean ; Wen, Difan ; Zhiyenbayev, Yertay ; Seclì, Matteo ; Redjem, Walid ; Dhuey, Scott ; Schwartzberg, Adam ; et al ( November 2023 , Optica)

   Inverse design is a powerful tool in wave physics for compact, high-performance devices. To date, applications in photonics have mostly been limited to linear systems and it has rarely been investigated or demonstrated in the nonlinear regime. In addition, the “black box” nature of inverse design techniques has hindered the understanding of optimized inverse-designed structures. We propose an inverse design method with interpretable results to enhance the efficiency of on-chip photon generation rate through nonlinear processes by controlling the effective phase-matching conditions. We fabricate and characterize a compact, inverse-designed device using a silicon-on-insulator platform that allows a spontaneous four-wave mixing process to generate photon pairs at a rate of 1.1 MHz with a coincidence to accidental ratio of 162. Our design method accounts for fabrication constraints and can be used for scalable quantum light sources in large-scale communication and computing applications.

    

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3. Single-Photon Emitters in SiN Integrated Quantum Photonics

   https://doi.org/10.1364/QUANTUM.2022.QW4B.5  

   Senichev, Alexander ; Peana, Samuel ; Martin, Zachariah O. ; Yesilyurt, Omer ; Sychev, Demid ; Lagutchev, Alexei S. ; Boltasseva, Alexandra ; Shalaev, Vladimir M. ( January 2022 , Quantum 2.0 Conference 2022 Optica Publishing Group 2022)

   We report on the generation of single-photon emitters in silicon nitride. We demonstrate monolithic integration of these quantum emitters with silicon nitride waveguides showing a room-temperature off-chip count-rate of ~10⁴counts/s and clear antibunching behavior.

    

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4. Quantum dot single-photon sources with ultra-low multi-photon probability

   https://doi.org/10.1038/s41534-018-0092-0  

   Hanschke, Lukas ; Fischer, Kevin A. ; Appel, Stefan ; Lukin, Daniil ; Wierzbowski, Jakob ; Sun, Shuo ; Trivedi, Rahul ; Vučković, Jelena ; Finley, Jonathan J. ; Müller, Kai ( September 2018 , npj Quantum Information)

   High-quality sources of single photons are of paramount importance for quantum communication, sensing, and metrology. To these ends, resonantly excited two-level systems based on self-assembled quantum dots have recently generated widespread interest. Nevertheless, we have recently shown that for resonantly excited two-level systems, emission of a photon during the presence of the excitation laser pulse and subsequent re-excitation results in a degradation of the obtainable single-photon purity. Here, we demonstrate that generating single photons from self-assembled quantum dots with a scheme based on two-photon excitation of the biexciton strongly suppresses the re-excitation. Specifically, the pulse-length dependence of the multi-photon error rate reveals a quadratic dependence in contrast to the linear dependence of resonantly excited two-level systems, improving the obtainable multi-photon error rate by several orders of magnitude for short pulses. We support our experiments with a new theoretical framework and simulation methodology to understand few-photon sources.

    

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5. Photon-photon interactions in Rydberg-atom arrays

   https://doi.org/10.22331/q-2022-03-30-674  

   Zhang, Lida ; Walther, Valentin ; Mølmer, Klaus ; Pohl, Thomas ( March 2022 , Quantum)

   We investigate the interaction of weak light fields with two-dimensional lattices of atoms with high lying atomic Rydberg states. This system features different interactions that act on disparate length scales, from zero-range defect scattering of atomic excitations and finite-range dipole exchange processes to long-range Rydberg-state interactions, which span the entire array and can block multiple Rydberg excitations. Analyzing their interplay, we identify conditions that yield a nonlinear quantum mirror which coherently splits incident fields into correlated photon-pairs in a single transverse mode, while transmitting single photons unaffected. In particular, we find strong anti-bunching of the transmitted light with equal-time pair correlations that decrease exponentially with an increasing range of the Rydberg blockade. Such strong photon-photon interactions in the absence of photon losses open up promising avenues for the generation and manipulation of quantum light, and the exploration of many-body phenomena with interacting photons. 

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