Advanced quantum technologies最新文献

Symmetry breaking is commonly employed to optimize the functionalities of cavities, such as the single-wavelength resonance, directional output, or high quality-factor (Q). Due to the mutual influence and restriction of these performance metrics, it is a great challenge to realize high-Q multiple-wavelength resonances with each wavelength's emission being directional and distinguished. Here, a non-circular inner and circular outer (NICO) cavity is proposed, and dual-wavelength resonant modes with different in-plane emission directions for the two wavelengths are realized. More importantly, the Q of the two modes in the NICO cavity remains unchanged (100%) compared to the fully circular cavity. To gradually change the inner ellipse shape to the outer-circle shape, only the coordinates (not the refractive index) are transformed. This transformation makes the cavity easy to fabricate in the experiment. Both the band-gap confinement effect of the outer circle layers and the gradual change from the inner ellipse shape to the outer-circle shape significantly halt the Q-spoiling phenomena. Solutions of increasing refractive index differences and further breaking symmetry are provided to improve the Q factors (as high as 10¹³) and narrow the emission divergence angles (by approximately twice), as well as increase the splitting wavelengths (by ≈6 times).

Enhancing and controlling optomechanically induced higher-order sideband generation is essential to achieve high-sensitivity sensing. This study theoretically explores the amplified charge-dependent generation of optical second-order sidebands (OSS) within a cavity optomechanical system, facilitated by an atomic ensemble. Findings reveal that the presence of an atomic ensemble not only enhances OSS generation but also shows a more pronounced charge dependence in the output OSS spectrum compared to a single optomechanical cavity system. This enhancement inspires to explore charge measurements with higher sensitivity. The results demonstrate that the sensitivity of charge measurement can be elevated by over four orders of magnitude when additional atomic ensembles are incorporated. The proposed scheme presents a promising approach for charge measurement and holds significant potential for applications in quantum sensing.

2D ferromagnetic (FM) semiconductors/half-metals offer promising prospects for quantum information technologies in miniature devices. However, the low Curie temperature (T_C) severely limits their application in spintronic devices. Here, two stable FM transition metal chalcogenides, Ti₃S₂X₂ (X = Se, Te) monolayers, based on first-principles calculations are presented. It is found that the Ti₃S₂Se₂ monolayer is a bipolar magnetic semiconductor with an indirect bandgap of 0.094 eV, while Ti₃S₂Te₂ exhibits be FM half-metallic feature. Notably, the T_Cs of Ti₃S₂Se₂ monolayer and Ti₃S₂Te₂ monolayer are 641 and 408 K, respectively, much higher than room temperature. Moreover, the T_Cs and electronic properties of both Ti₃S₂X₂ (X = Se, Te) monolayers can be modulated by applying biaxial strains. These promising properties make Ti₃S₂X₂ (X = Se, Te) monolayers ideal candidates for 2D spintronic devices.

Periodically driving a quantum many-body system can drastically change its properties, leading to exotic non-equilibrium states of matter without a static analog. In this scenario, parametric resonances and the complexity of an interacting many-body system are pivotal in establishing non-equilibrium states. A Floquet-engineered transverse field Ising model for the controlled propagation in one dimension of spin waves is reported. The underlying mechanisms behind the proposal rely on high-frequency drivings using characteristic parametric resonances of the spin lattice. Many-body resonances modulating spin-spin exchange or individual spin gaps inhibit interactions between spins thus proving a mechanism for controlling spin-wave propagation and a quantum switch. The schemes may be implemented in circuit QED with direct applications in coupling–decoupling schemes for system-reservoir interaction and routing in quantum networks.

Quantum secret sharing (QSS) plays a crucial role in quantum cryptography as a privacy preserving scheme. Designing an efficient QSS protocol requires addressing three key challenges: 1) dynamic agent membership (handling agents joining or leaving during execution), 2) adversarial resilience (ensuring robustness against dishonest agents), and 3) practical optimization (improving computational and communication efficiency while minimizing implementation cost). In this paper, a verifiable dynamic $��(�t�,�n�)�$ threshold QSS (VDQSS) protocol with authentication capability is proposed. The protocol employs single particles for both authentication and share distribution, combining homogeneous linear recursion (HLR) with mutually unbiased bases (MUBs) to reconstruct multiple secrets. This approach significantly enhances security while reducing protocol complexity. The correctness and practicality of the protocol are validated through experimental simulations. Analytical results demonstrate its robustness against common attacks, providing reliable security guarantees for quantum communications. Compared to existing QSS protocols, the protocol offers enhanced simplicity and practical applicability.

Floquet engineering, a powerful technique for manipulating quantum systems, has shown great promise in controlling mobility edges in quasiperiodic systems. A one-dimensional quasiperiodic mosaic Aubry-André-Harper model with a time-periodic driving potential is investigated. Using Avila's global theory, analytical solutions are derived for the mobility edges in the Floquet system under high-frequency conditions. These solutions are numerically validated through the computations of the fractal dimension and the mean normalized participation ratio. Notably, as the ratio of drive amplitude to frequency progressively increases, the absolute energy of mobility edges exhibits a recurring pattern characterized by sequential reduction and resurgence within the spectrum. Remarkably, the localized phases also appear repeatedly at the zeros of the zeroth-order Bessel function. These phenomena collectively manifest the unique feature inherent to Floquet quantum systems. The findings demonstrate the flexible manipulation of the mobility edges via Floquet engineering, while providing a novel insight into Anderson localization.

Applications of quantum systems with non-linear light–matter interaction have to deal with a peculiar instability in the ultra- and deep strong coupling regime, the so-called “spectral collapse.” To solve this problem, the present work investigates a generalized quantum Rabi model (QRM) with two- and four-photon terms in view of applications for critical quantum metrology. In the introduced model, the spectral collapse occurring in the standard two-photon QRM is stabilized by the presence of the quartic potential. The collapse is then transformed into a quantum phase transition, which occurs in the low-frequency limit of the light mode, whose remnant at finite ratio between qubit and mode frequencies can be applied to critically enhanced quantum metrology. It is found that the four-photon term entails a much higher measurement precision compared to the standard two-photon QRM. The mechanism behind the higher precision can be traced to the different behavior of the ground state wave function as the system is tuned through the transition. As the standard two-photon QRM, despite the absence of the spectral collapse, the proposed model allows for a finite preparation time for the probe state (PTPS).

Photon polarization serves as an essential quantum information carrier in quantum information and measurement applications. Routing of arbitrarily polarized single photons and polarization-entangled photons is a crucial technology for scaling up quantum information applications. Here, a low-loss, noiseless, polarization-maintaining routing of arbitrarily polarized single photons and, crucially, multi-photon entangled states is demonstrated where the entanglement is encoded in orthogonal polarization bases, at the telecom L-band. The interferometer-based router is constructed by optics with a low angle of incidence and cross-aligned electro-optic crystals, achieving the polarization-maintaining operation with a minimal number of optical components. The routing of arbitrarily-polarized heralded single photons with a 0.057 dB (1.3%) loss, a $�>$22 dB switching extinction ratio, and $�>$99% polarization process fidelity to ideal identity operation is demonstrated. Moreover, the high-quality router achieves the routing of two-photon N00N-type entangled states with a highly maintained interference visibility of $�\approx$97%. The demonstrated router scheme preserving multi-photon polarization state paves the way toward polarization-encoded photonic quantum network as well as multi-photon entanglement synthesis via spatial- and time-multiplexing techniques.