Advanced quantum technologies最新文献

Quantum digital signature is used to authenticate the identity of the signer with information theoretical security while providing non-forgery and non-repudiation services. In traditional multi-receiver quantum digital signature schemes without an arbitrator, the transferability of one-to-one signature is always required to achieve unforgeability, with complicated implementation and heavy key consumption. In this article, an arbitrated quantum digital signature scheme is proposed, in which the signature can be verified by multiple receivers simultaneously, and meanwhile, the transferability of the signature is still kept. This scheme can be simplified performed to various quantum secure networks, due to the proposed efficient signature calculation procedure with low secure key consumption and low computation complexity, by employing one-time universal hashing algorithm and a one-time pad encryption scheme. The evaluation results show that this scheme uses at least two orders of magnitude less key than existing signature schemes with transferability when signing files of the same length with the same number of receivers and security parameter settings.

k-uniform mixed states are a significant class of states characterized by all k-party reduced states being maximally mixed.Novel methodologies are constructed for constructing k-uniform mixed states with the highest possible purity. By using the orthogonal partition of orthogonal arrays, a series of new k-uniform mixed states is derived. Consequently, an infinite number of higher-dimensional k-uniform mixed states, including those with highest purity, can be generated.

The on-chip resonant excitation of single quantum dots (QDs) via integrated microlasers represents an effective and scalable method for integrated quantum photonics applications based on on-demand single-photon emitters. In this study, the design and numerical optimization of the evanescent coupling between whispering gallery modes (WGMs) of a micropillar resonator and a nearby single-mode ridge waveguide in the Al(Ga)As/GaAs material system are presented. In this study, such systems are examined within a wavelength range of 930 nm, which is suitable for resonant excitation of typical self-assembled InGaAs quantum dots. In particular, the coupling and the transmitted optical power of a WGM resonator to a ridge waveguide are examined for a range of gap spacings, with the objective of optimizing the photon coupling efficiency and Q-factor of the monolithically integrated nanophotonic system. The findings of this study enable to identify the best device parameters for subsequent device fabrication. The findings establish a foundation for the production of highly effective photonic quantum circuits through the use of WGM microlasers integrated into evanescently coupled waveguide systems, including resonantly excited single quantum dots.

A spin-photon interface based on the luminescence of a singly charged quantum dot in a micropillar cavity allows for the creation of photonic entangled states. Current devices suffer from cavity birefringence, which limits the generation of spin-photon entanglement. In this study, we conduct a theoretical analysis of the light absorption and emission by the interface with an anisotropic cavity and derive the maximal excitation and spin-photon entanglement conditions. It is shown that the concurrence of the spin-photon state equal to one and complete quantum dot population inversion can be reached for a micropillar cavity with any degree of birefringence by tuning the quantum dot resonance strictly between the cavity modes. This sweet spot is also valid for generating a multiphoton cluster state, as demonstrated by calculating the three-tangle and fidelity with the maximally entangled state.

The interconversion of a variety of entangled states can facilitate the information transmission and decline the risk of error rates. Here two faithful protocols to achieve deterministic interconversion between three-logic-qubit W state and three-logic-qubit Greenberger–Horne–Zeilinger state in decoherence-free subspace (DFS), resorting to the state-selective property of the quantum dot (QD)-cavity systems and robust-fidelity quantum control gates are presented. Moreover, the single-photon detectors introduced can effectively herald and mitigate potential failures from imperfect interaction between the QD-cavity system and photons, significantly enhancing experimental feasibility. Through comprehensive analysis and evaluation, the protocols demonstrate exceptional conversion efficiencies and deliver near-perfect fidelities. Additionally, the DFS makes system coherence over extended periods to overcome the decoherence effect caused by specific environmental noise, paving the way for quantum information processing.

A systematic analysis of the advantages and challenges associated with the satellite-based implementation of the high dimensional extended B92 (HD-Ext-B92) and high-dimensional BB84 (HD-BB84) protocol is analyzed. The method used earlier for obtaining the key rate for the HD-Ext-B92 is modified here and subsequently the variations of the key rate, probability distribution of key rate (PDR), and quantum bit error rate (QBER) with respect to dimension and noise parameter of a depolarizing channel is studied using the modified key rate equation. Further, the variations of average key rate (per pulse) with zenith angle and link length in different weather conditions in day and night considering extremely low noise for dimension $��d�=�32�$ are investigated using elliptic beam approximation. The effectiveness of the HD-(extended) protocols used here in creating satellite-based quantum key distribution links (both up-link and down-link) are established by appropriately modeling the atmosphere and analyzing the variation of average key rates with the probability distribution of the transmittance (PDT). The analysis performed here has revealed that in higher dimensions, HD-BB84 outperforms HD-Ext-B92 in terms of both key rate and noise tolerance. However, HD-BB84 experiences a more pronounced saturation of QBER in high dimensions.

A scheme is proposed to prepare quantum entanglement and quantum steering between two indirectly coupled microwave cavity modes within a hybrid cavity magnonic system. The system consists of two microwave cavities individually coupled to a common YIG sphere driven by a two-tone Floquet field, while the output field of the second microwave cavity is fed back into the input port of the first microwave cavity via a coherent feedback loop. Floquet driving can effectively generate two interactions between magnons and photons. Magnons with higher dissipation can serve as a cooling channel for the two cavity modes. Optimal quantum correlations between the cavity modes can be achieved when the competition between these two interactions reaches equilibrium. Subsequently, a comparative analysis is performed on the evolution of quantum correlation with and without coherent feedback, revealing that the presence of a coherent feedback loop in the system not only significantly enhances entanglement and steering but also induces inherent asymmetry in quantum steering regardless of the decay rates within subsystems. Moreover, under the influence of the coherent feedback loop, the enhanced quantum correlations exhibit increased robustness against rising environmental temperatures. This work significantly expands the validity of implementation and provides a promising avenue for the preparation of stable quantum correlations.

A high-dimensional quantum gate not only enables the processing of more information through parallel quantum channels but also enhances fault tolerance in a higher Hilbert space. In this paper, a protocol is presented for implementing a three-qudit $��4�\times �4�\times �4�$-Dimensional (D) Toffoli gate for a hybrid system, where the first control qudit, the second control qudit, and the target qudit of four dimension are encoded in the spatial-polarization state of a flying photon, the electron-spin state of the first two quantum dots (QDs), and the one of the remaining two QDs, respectively. Besides, the high-dimensional Toffoli gate does not require any assistance. Moreover, the gate operates deterministically in principle, as the photon is easy to manipulate feasibly using simple optical elements, and four QDs have a long electron-spin coherent time used for storage and manipulation. Furthermore, the success probability and fidelity of the high-dimensional Toffoli gate, in alignment with current technological capabilities, demonstrate satisfactory results. This indicates that it is feasible in experimental settings and promises a quantum computing paradigm that excels in speed, error resilience, and scalability for intricate quantum operations.

The detection of laser-induced photo-currents in diamond is shown with about 100 fA resolution in the pico- to nanoampere range. A micro-electronic approach enables to work without using lock-in techniques. For that purpose, a commercially available and low-cost precision integrating amplifier is utilized on a home-built printed circuit board. This technique is applied to three different diamond samples with different defect concentrations. Two ultra-pure diamond samples with shallow implanted defects, predominantly nitrogen-vacancy (NV) centers and substitutional nitrogen (P1 centers), are investigated. The third sample is an electron-irradiated type Ib diamond with a much higher intrinsic defect concentration. For all samples, spatially resolved photo-current maps as well as laser power and bias voltage-dependent measurements are recorded. Furthermore, photo-currents are successfully recorded without an applied bias voltage. Finally, the technique is used to perform continuous wave photoelectric detection of magnetic resonances (PDMR) using NV centers. The presented approach paves the way for time-resolved photo-current measurements of individual defects and pulsed PDMR measurements without lock-in technology.