Spss Quantum

[Chris]

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Single-photon sources (SPSs) are a fundamental building block for optical implementations of quantum information protocols. Among SPSs, multiple crystal heralded single-photon sources seem to give the best compromise between high pair production rate and low multiple photon events. In this work, we study their performance in a practical quantum-key-distribution experiment, by evaluating the achievable key rates. The analysis focuses on the two different schemes, symmetric and asymmetric, proposed for the practical implementation of heralded single-photon sources, with attention on the performance of their composing elements. The analysis is based on the protocol proposed by Bennett and Brassard in 1984 and on its improvement exploiting decoy state technique. Finally, a simple way of exploiting the postselection mechanism for a passive, one decoy state scheme is evaluated.

Schematic of the SMHPS [11]. Each nonlinear crystal (NLC) is fed with pulses such that the mean number of generated pair per pulse is μ/γk, with k=log2m and γ is the transmittance of 2-to-1 optical switches. The idler of each NLC is fed into a detector with quantum efficiency η.

Schematics of the AMHPS [16]. Each nonlinear crystal (NLC) is pumped with a different intensity in order to compensate the different number of traversed 2-to-1 optical switches, each characterized by its transmittance γ. The idler of each NLC is fed into a detector with quantum efficiency η.

Schematic of the MHPS [13]. Each nonlinear crystal (NLC) is fed with a pulse such that the mean number of generated pairs is μ. The idler photon is fed into a detector (APD), while the signal one is routed through an optical switch (O.S.) to the output.

QKD has gained significant attention worldwide due to its ability to provide security based on quantum mechanics principles, surpassing classical cryptography's capabilities. Specifically, it securely enables information transmission by preventing general attacks by eavesdroppers.

In QKD protocols, the utilization of on-demand quantum light sources can improve maximum tolerable loss and security. Semiconductor SPSs can revolutionize large-scale quantum communication. Semiconductor quantum dots (QDs) can serve as a foundation for quantum communication applications due to the deterministic single-photon emission with low multiphoton contribution and high brightness.

Specifically, these QDs can emit indistinguishable single photons on demand with exceptional purity and efficiency, thereby providing significant advantages for QKD. A scheme involving QDs can enhance the key rate significantly for measurement-device-independent QKD, which requires high Hong-Ou-Mandel interference visibility between two single-photon sources.

Quantum repeaters can also be realized using QDs as they can emit photonic cluster states and allow inherent quantum information storage. Quantum communication studies using QDs have displayed their ability to connect metropolitan areas and university campuses.

However, the progress to intercity distances has been hindered due to the absence of bright single-photon signals within the telecommunication bands. Recently, a breakthrough has been achieved by researchers that enabled bright single-photon emission with high emission rates, due to Purcell enhancement, directly from a QD device in the telecommunication C-band.

In this work, researchers performed the first intercity QKD experiment using a bright, deterministic single-photon source. A semiconductor QD embedded in a circular Bragg grating structure efficiently emitted high-rate single photons in the telecommunication C-band and was used along with polarization encoding based on the standard BB84 protocol.

The experimental setups included the superconducting nanowire detector (SNSPD), receiver, fiber spools, and the transmitter. The clock-variable pulsed fiber laser was coupled into free space in the transmitter to excite the QD after passing through a beam splitter.

Additionally, the Attodry1100 system was equipped with a Thorlabs aspheric lens with a 0.7 numerical aperture to collect the single photons from the device. Thorlabs polarizer, quarter-waveplate, and zero-order half-waveplate were employed to encode and purify the polarization states. These components were controlled by the Thorlabs electronic stages.

A fiber-based Bragg grating was utilized by the receiver to split the single-photon signals and reference laser. The encoded single photons were detected by the SNSPDs after passing through two plate polarizing beam splitters and a 50:50 beam splitter.

Researchers successfully showed the first intercity QKD experiments using a deterministic telecom SPS by harnessing single-photon emissions from a semiconductor QD emitting within the telecom C-band and having excitation rates up to the GHz range.

Additionally, an asymptotic maximum tolerable loss of 28.11 dB was observed, corresponding to a 144 km channel length in repeaterless quantum communication with standard fiber-optic networks, indicating the competitiveness of semiconductor SPSs for quantum communication applications.

It approached the levels achieved by established decoy-state weak coherent pulse-based QKD protocols even without further optimization of the setup performance and the source, which indicated the viability of integrating semiconductor SPSs seamlessly into large-scale, high-capacity, and realistic quantum communication networks.

To summarize, the findings of this work demonstrated that deterministic semiconductor sources possess the potential to excel in quantum repeater applications and measurement-device-independent protocols.

Samudrapom Dam is a freelance scientific and business writer based in Kolkata, India. He has been writing articles related to business and scientific topics for more than one and a half years. He has extensive experience in writing about advanced technologies, information technology, machinery, metals and metal products, clean technologies, finance and banking, automotive, household products, and the aerospace industry. He is passionate about the latest developments in advanced technologies, the ways these developments can be implemented in a real-world situation, and how these developments can positively impact common people.

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N2 - A high-quality single-photon source (SPS) is one of the most critical components in photonic quantum information technologies (e.g. QKD, cryptography, linear quantum computing, etc.) where qubits are encoded within individual photons. Moreover, the scalability of these technologies relies heavily on their integration into existing photonic systems, so controlling their quantum properties is crucial. Besides their advantages, current material platforms present limitations due to their complex fabrication procedures and inherent attributes. In the search for reliable SPSs, Transition Metal Dichalcogenides (TMDCs) have emerged as a promising platform. Despite the recency of the field, they have exhibited satisfactory integration potential into photonic cavities, purity close to the state-of-the-art, and the ability to be used in quantum information protocols. The poster presents on-chip quantum emitters from monolayer WSe2 with controlled polarization and high purity, via strain and defect engineering. We explain the drawbacks of current nanopillar designs for strain application, which we use to justify the new proposed geometries. Moreover, we analyze the entire fabrication process from the structure fabrication, the flake exfoliation and transfer, to the defect introduction through electron beam irradiation. Finally, we characterize the samples with different imaging techniques and present the properties of theproduced quantum emitters.

AB - A high-quality single-photon source (SPS) is one of the most critical components in photonic quantum information technologies (e.g. QKD, cryptography, linear quantum computing, etc.) where qubits are encoded within individual photons. Moreover, the scalability of these technologies relies heavily on their integration into existing photonic systems, so controlling their quantum properties is crucial. Besides their advantages, current material platforms present limitations due to their complex fabrication procedures and inherent attributes. In the search for reliable SPSs, Transition Metal Dichalcogenides (TMDCs) have emerged as a promising platform. Despite the recency of the field, they have exhibited satisfactory integration potential into photonic cavities, purity close to the state-of-the-art, and the ability to be used in quantum information protocols. The poster presents on-chip quantum emitters from monolayer WSe2 with controlled polarization and high purity, via strain and defect engineering. We explain the drawbacks of current nanopillar designs for strain application, which we use to justify the new proposed geometries. Moreover, we analyze the entire fabrication process from the structure fabrication, the flake exfoliation and transfer, to the defect introduction through electron beam irradiation. Finally, we characterize the samples with different imaging techniques and present the properties of theproduced quantum emitters.

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