Advanced quantum technologies最新文献

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.

Spin-orbit coupling (SOC) has broad relevances and its interplay with other interactions and potential geometry may induce novel quantum states. This work explores exotic quantum states emerging in the ground state (GS) of a strongly-correlated spin-1 Bose–Einstein condensate confined in 2D concentric annular traps with SOC. In the antiferromagnetic case, the GS density manifests various patterns of distributions, including facial-makeup states, petal states, topological fissure states, multiple-half-ring states and property-distinguished vertical and horizontal stripe states. A peculiar phenomenon of density-phase separation is noticed in the sense that the variations of density and phase tend to be independent. In ferromagnetic case, the GS exhibits a semi-circular or half-disk status of density embedded with vortices and antivortices. The spin distribution can self-arrange into an array of half-skyrmions and a half-antiskyrmion fence separating vortex-antivortex pairs is also found. This study indicates that one can manipulate the emergence of exotic quantum states and the locations of the topological defects via the interplay of the SOC, interactions and potential geometry and the abundant state variations might also provide potential resources for quantum metrology.

Dynamical phase transitions in the relaxation behavior of stochastic quantum walks are investigated, focusing on systems where coherent unitary evolution is periodically interrupted by dephasing. This interplay leads to a classicalization of the dynamics, effectively described by non-equilibrium Markovian processes that can violate detailed balance. As a result, such systems exhibit a richer and more complex spectral structure than their equilibrium counterparts. Extending recent insights from classical Markov dynamics [G. Teza et al., Phys. Rev. Lett. 130, 207103 (2023)], it is demonstrated that these quantum-classical hybrid systems can host not only first-order dynamical phase transitions – characterized by eigenvalue crossings – but also second-order transitions marked by the coalescence of eigenvalues and eigenvectors at exceptional points. Two paradigmatic models are analyzed: a quantum walk on a ring under gauge fields and a walk on a finite line with internal degrees of freedom, both exhibiting distinct mechanisms for breaking detailed balance. These findings reveal a novel class of critical behavior in open quantum systems, where decoherence-induced classicalization enables access to non-Hermitian spectral phenomena. Beyond their fundamental interest, these results offer promising implications for quantum technologies, including quantum simulation, error mitigation, and the engineering of controllable non-equilibrium quantum states.