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Basso Basset F, Valeri M, Roccia E, Muredda V, Poderini D, Neuwirth J, Spagnolo N, Rota MB, Carvacho G, Sciarrino F, Trotta R. Quantum key distribution with entangled photons generated on demand by a quantum dot. SCIENCE ADVANCES 2021; 7:eabe6379. [PMID: 33741595 PMCID: PMC7978422 DOI: 10.1126/sciadv.abe6379] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2020] [Accepted: 02/03/2021] [Indexed: 05/31/2023]
Abstract
Quantum key distribution-exchanging a random secret key relying on a quantum mechanical resource-is the core feature of secure quantum networks. Entanglement-based protocols offer additional layers of security and scale favorably with quantum repeaters, but the stringent requirements set on the photon source have made their use situational so far. Semiconductor-based quantum emitters are a promising solution in this scenario, ensuring on-demand generation of near-unity-fidelity entangled photons with record-low multiphoton emission, the latter feature countering some of the best eavesdropping attacks. Here, we use a coherently driven quantum dot to experimentally demonstrate a modified Ekert quantum key distribution protocol with two quantum channel approaches: both a 250-m-long single-mode fiber and in free space, connecting two buildings within the campus of Sapienza University in Rome. Our field study highlights that quantum-dot entangled photon sources are ready to go beyond laboratory experiments, thus opening the way to real-life quantum communication.
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Affiliation(s)
| | - Mauro Valeri
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy
| | - Emanuele Roccia
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy
| | - Valerio Muredda
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy
| | - Davide Poderini
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy
| | - Julia Neuwirth
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy
| | - Nicolò Spagnolo
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy
| | - Michele B Rota
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy
| | - Gonzalo Carvacho
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy
| | - Fabio Sciarrino
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy.
| | - Rinaldo Trotta
- Department of Physics, Sapienza University of Rome, 00185 Rome, Italy.
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Gao X, Yang L, Bo F, Li J, Zhang G, Xu J. Vector beams in planar photonic crystal cavities with rotating air holes. OPTICS LETTERS 2020; 45:1587-1590. [PMID: 32164023 DOI: 10.1364/ol.381458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Accepted: 02/04/2020] [Indexed: 06/10/2023]
Abstract
We report a method to generate angularly polarized vector beams with a topological charge of one by rotating air holes to form two-dimensional photonic crystal (PC) cavities. The mode volume and resonance wavelength of these cavities are tuned from ${0.33}{(\lambda /n)^3}$0.33(λ/n)3 to ${12}{(\lambda /n)^3}$12(λ/n)3 and in a wide range of 400 nm, respectively, by controlling the range of fixed air holes near the center of the structure. As a benefit, the half-maximum divergence angles of the vector beam can be widely changed from 90° to $\sim{60}^\circ $∼60∘. By adjusting the shift direction of the air holes in the PC cavities, optical vector beams with different far-field morphology are obtained. The scheme provides not only an alternative method to generate optical vector beams, but also an effective strategy to control far-field morphology and polarizations, which holds promising applications such as optical microscopy and micro-manipulation.
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Lin W, Ota Y, Iwamoto S, Arakawa Y. Spin-dependent directional emission from a quantum dot ensemble embedded in an asymmetric waveguide. OPTICS LETTERS 2019; 44:3749-3752. [PMID: 31368959 DOI: 10.1364/ol.44.003749] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Accepted: 06/27/2019] [Indexed: 06/10/2023]
Abstract
In this study, we examine a photonic wire waveguide embedded with an ensemble of quantum dots (QDs) that directionally emits into the waveguide depending on the spin state of the ensemble. The directional emission is facilitated by the spin-orbit interaction of light. The waveguide has a two-step stair-like cross section and QDs are embedded only in the upper step, such that the circular polarization of emission from the spin-polarized QDs controls the direction of the radiation. We numerically verify that more than 70% of the radiation from the ensemble emitter is toward a specific direction in the waveguide. We also examine a microdisk resonator with a stair-like edge, which supports selective coupling of the QD ensemble radiation into a whispering gallery mode that rotates unidirectionally. Our study provides a foundation for spin-dependent optoelectronic devices.
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