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Memory-assisted quantum key distribution resilient against multiple-excitation effects
摘要： Memory-assisted measurement-device-independent quantum key distribution (MA-MDI-QKD) has recently been proposed as a technique to improve the rate-versus-distance behavior of QKD systems by using existing, or nearly-achievable, quantum technologies. The promise is that MA-MDI-QKD would require less demanding quantum memories than the ones needed for probabilistic quantum repeaters. Nevertheless, early investigations suggest that, in order to beat the conventional memory-less QKD schemes, the quantum memories used in the MA-MDI-QKD protocols must have high bandwidth-storage products and short interaction times. Among different types of quantum memories, ensemble-based memories offer some of the required specifications, but they typically suffer from multiple excitation effects. To avoid the latter issue, in this paper, we propose two new variants of MA-MDI-QKD both relying on single-photon sources for entangling purposes. One is based on known techniques for entanglement distribution in quantum repeaters. This scheme turns out to offer no advantage even if one uses ideal single-photon sources. By finding the root cause of the problem, we then propose another setup, which can outperform single memory-less setups even if we allow for some imperfections in our single-photon sources. For such a scheme, we compare the key rate for different types of ensemble-based memories and show that certain classes of atomic ensembles can improve the rate-versus-distance behavior.
关键词： quantum cryptography,quantum networks,quantum key distribution (QKD),quantum memory,single-photon source,quantum communications
更新于2025-09-23 15:22:29
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Improving the Secret Key Rate of Coherent Quantum Key Distribution with Bayesian Inference
摘要： Laser phase noise is one of the major limitations in continuous-variable quantum key distribution, when the local oscillator is placed at the receiver site. Thus, improving phase noise mitigation can improve the secret key rate. This paper provides an experimental investigation of different Bayesian methods for that purpose. It is shown that, compared to a previously reported method, the excess noise power can be reduced by about 15%. In some scenarios, this can improve the secret key rate by a factor of 9.
关键词： phase noise,Bayes procedures,quantum communications
更新于2025-09-23 15:21:21
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Hyper-Entanglement in Time and Frequency
摘要： Hyper-entanglement, i.e. entanglement in more than one degree of freedom, enables a multiplicative increase in Hilbert space size. Such systems can be treated as multi-partite even though the number of state particles is not increased, making them highly attractive for applications in high-capacity quantum communications and information processing. Until now, such states have been realized only using combinations of fully independent degrees of freedom, described by commuting operators, such as polarization and optical paths. Time and frequency, in turn, are linked and described by non-commuting operators. Here, using two discrete forms of energy-time entanglement we demonstrate that time and frequency can be used for genuine multi-partite hyper-entangled states. This is achieved by increasing the time-frequency product to far exceed the Heisenberg uncertainty limit, effectively making the time and frequency degrees independent.
关键词： time and frequency,hyper-entanglement,quantum communications,information processing,Heisenberg uncertainty limit
更新于2025-09-12 10:27:22
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Scaling Phononic Quantum Networks of Solid-State Spins with Closed Mechanical Subsystems
摘要： Phononic quantum networks feature distinct advantages over photonic networks for on-chip quantum communications, providing a promising platform for developing quantum computers with robust solid-state spin qubits. Large mechanical networks including one-dimensional chains of trapped ions, however, have inherent and well-known scaling problems. In addition, chiral phononic processes, which are necessary for conventional phononic quantum networks, are difficult to implement in a solid-state system. To overcome these seemingly unsolvable obstacles, we have developed a new network architecture that breaks a large mechanical network into small and closed mechanical subsystems. This architecture is implemented in a diamond phononic nanostructure featuring alternating phononic crystal waveguides with specially designed band gaps. The implementation also includes nanomechanical resonators coupled to color centers through phonon-assisted transitions as well as quantum state transfer protocols that can be robust against the thermal environment.
关键词： quantum communications,diamond phononic nanostructure,Phononic quantum networks,quantum state transfer,solid-state spin qubits
更新于2025-09-10 09:29:36
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Bunching and antibunching in four wave mixing NV center in diamond
摘要： The determination of classical and quantum states through photon bunching and anti-bunching like phenomena may have potential applications in quantum information processing and long-distance quantum communications. We report the photon bunching and multi anti-bunching like phenomena by generating multi-order ?uorescence and four-wave mixing (FWM) at room temperature using the Nitrogen-vacancy (NV) center in diamond. We have implied FWM process to demonstrate the interference pattern emerging from NV of nano-crystals in classical, nonclassical and intermediate (classical and nonclassical) regimes. Intersystem crossing is controlled by the ?uence of incident beams. The interference pattern from dominant ionization of NV- to NVo and NVo to NV- suggests the bunching and anti-bunching like phenomena of photons, respectively.
关键词： antibunching,quantum information processing,quantum communications,diamond,four-wave mixing,photon bunching,NV center
更新于2025-09-10 09:29:36