Advanced quantum technologies最新文献

Hybrid quantum systems provide versatile physical properties that could be qualified for high-fidelity quantum information storage, distribution, and processing in a quantum network. This work proposes to synthesize a hybrid generalized Jaynes-Cummings (JC) model among two mircowave (MW) cavities and a Rydberg atom, where the Rydberg transition occurs by simultaneously absorbing or emitting two MW photons distributed in different cavities. Based on this synthesized Rydberg two-mode two-photon JC (TMTP-JC) model, a hybrid MW-MW-atom Toffoli gate is constructed with the atomic qubit encoded on two stable ground states. Furthermore, the Rydberg atom is considered as an interface in an MW-optical quantum network and a scheme is demonstrated for generating a three-body photonic entangled state among the two MW cavities and an optical cavity, assisted by the synthesized Rydberg TMTP-JC interaction. The proposed setup provides a Rydberg-state–mediated interface for constructing MW-MW-atom three-qubit gates and entangling three-body MW-MW-optical photons, which may bridge the gap for modular, scalable, and cross-platform quantum networks.

Nonreciprocal devices, such as isolator or circulator, are crucial for information routing and processing in quantum networks. Traditional nonreciprocal devices, which rely on the application of bias magnetic fields to break time-reversal symmetry and Lorentz reciprocity, tend to be bulky and require strong static magnetic fields. This makes them challenging to implement in highly integrated large-scale quantum networks. Therefore, a multifunctional nonreciprocal quantum device based on the integration and tunable interaction of superconducting quantum circuit (SQC) is designed. This device can switch between two-port isolator, three-port symmetric circulator, and antisymmetric circulator under the control of external magnetic flux. Furthermore, both isolator and circulator can achieve nearly perfect unidirectional signal transmission. It is believed that this scalable and integrable nonreciprocal device can provide new insight for the development of large-scale quantum networks.

The conventional method for generating entangled states in qubit systems relies on applying precise two-qubit entangling gates alongside single-qubit rotations. However, achieving high-fidelity entanglement demands high accuracy in two-qubit operations, requiring complex calibration protocols. In this work, a minimally calibrated two-qubit iSwap-like gate, tuned via straightforward parameter optimization (flux pulse amplitude and duration) is used, to prepare Bell states and GHZ state experimentally in systems of two and three transmon qubits. Integration of this gate into a variational quantum algorithm (VQA) bypasses the need for intricate calibration while maintaining high fidelity. The proposed methodology employs variational quantum algorithms (VQAs) to create the target quantum state through imperfect multiqubit operations. Furthermore, a violation of the Clauser–Horne–Shimony–Holt (CHSH) inequality for Bell states is experimentally demonstrated, confirming their high fidelity of preparation.

Atomic magnetometers serve as a type of quantum sensing instrument, offering extensive applications in the field of extremely weak magnetic field measurement. Miniaturized zero-field atomic magnetometers typically use continuous high-frequency magnetic fields to modulate atomic spin precession for multi-axis measurements. However, this modulation induces additional spin-exchange relaxation, which significantly broadens the resonance linewidth. In this study, the pulsed magnetic field modulation is introduced instead of continuous modulation to reduce the effective duration of the magnetic field. This operation significantly diminishes perturbations of steady-state spin distribution in Zeeman sublevels caused by Larmor precession during each modulation cycle, thus effectively mitigating decoherence effects. The relationship between spin-exchange relaxation rate and pulsed field parameters is studied based on the generalized hyperfine Bloch equation, and a spin dynamics model under the pulsed modulation is developed. Agreement between experimental and theoretical results validates the suppression effect of spin-exchange relaxation and the accuracy of this model. Experimental results indicate that the pulsed modulation scheme results in a 30% reduction in the spin-exchange relaxation rate and achieves dual-axis sensitivities of 1.5 and 2.5 fT Hz^−1/2, respectively, representing improvements of 25% and 20% over conventional continuous modulation methods.

To improve the performance of room-temperature terahertz detectors, particularly regarding sensitivity and noise characteristics, an innovative detector incorporating a sawtooth array fabricated through femtosecond-laser direct writing is developed. This device integrates e localized surface plasma effect with the unique properties of a Weyl semimetal within a subwavelength structural framework. The application of a magnetic field combined with laser excitation further enhances carrier mobility, resulting in improved device performance and faster response times. At a frequency of 0.1 THz, the responsivity increases from 1.134 × 10⁵ to 1.192 × 10⁵ V/W, the noise-equivalent power decreases from 0.436 to 0.414 pW Hz^−1/2, and the response time is reduced from 210 to 49 ms. Additionally, terahertz time-domain spectroscopy reveals a distinct absorption feature at 0.1 THz, aligning with critical requirements for 6G communication systems. This design presents both a novel conceptual approach and a technological platform for the advancement of high-performance terahertz detection technologies.

A model of the Heisenberg spin chain quantum battery that is charged by noise is built, and the energy can be extracted. In a phase-flip noisy environment, it is found that there are sudden changes in steady-state energy and ergotropy with the variation of the nearest neighbor interaction strength on the $��x�y�$ plane. These sudden changes are associated with quantum phase transition (QPT), which has been shown through the crossover of the ground state energy level and the first excited state energy level, as well as the order parameters. In a thermal bath, the changes are investigated in steady-state energy and ergotropy with the variation of the nearest neighbor interaction strength on the $��x�y�$ plane. The components of Hamiltonian of the battery in the $�x$, $�y$, and $�z$ directions are used to explain the steady-state energy continuity at the QPT points. In addition, the effect of mean occupation number of the thermal bath on the steady-state energy and ergotropy is also considered. For the general Heisenberg spin chain and $�N$-qubit batteries, it is proved that the noise can also be used to charge the battery, and the ergotropy is non-zero.

The measurements of photoluminescence quantum yield are a standard characterization method of both traditional and novel fluorophores. Here, a detailed protocol is summarized for the measurements of quantum yield in colloidal samples of nanoparticles. Furthermore, based on a detailed discussion of the non-standard statistics of the experimental uncertainty connected with quantum yield measurements, a simple-to-apply method is put forward that allows proper sampling of the histogram of QY values. This histogram-sampling method serves as a robust reliability test of the measurement. Despite focusing on colloidal samples here, the histogram-sampling method itself and its implications are readily generalized to any other form of sample in QY measurements.

Noise remains one of the most significant challenges in the development of reliable and scalable quantum processors. While quantum error correction and mitigation techniques offer potential solutions, they are often limited by the substantial overhead required. To address this, tailored approaches that exploit specific hardware characteristics have emerged. In quantum computing architectures utilizing cat-qubits, the inherent exponential suppression of bit-flip errors can significantly reduce the qubit count needed for effective error correction. In this work, how the unique noise bias of cat-qubits can be harnessed to enhance error mitigation efficiency is explored. Specifically, it is demonstrated that the sampling cost associated with probabilistic error cancellation (PEC) methods can be exponentially reduced with the depth of the circuit when gates act on cat-qubits and preserve the noise bias. Similar results also hold for Clifford circuits and Pauli channels. The error mitigation scheme is benchmarked across various quantum machine learning circuits, showcasing its practical advantages for near-term applications on cat-qubit architectures.

A discrete ‘Quantum Memory Matrix’ lattice (central orange cell) symbolizes Planck-scale quantum memory units imprinting and retrieving local quantum fields. The circuit diagram below, featuring controlled-Ry, Ry, and CSWAP gates, illustrates the fully unitary QMM imprint–retrieval primitive that underpins enhanced error suppression and hybrid quantum-classical learning on NISQ devices. More in article number 2500262, Florian Neukart and co-workers.

The cover picture shows a controlled SWAP test quantum circuit with several state copies, and bitstrings (e.g., 0000, 1001, 1111) as measurement results. These bitstrings correspond to probabilities to simultaneously estimate traces of the 2nd to nth power traces of reduced density matrices via a single circuit, applied to entanglement measure computation. More in article number 2500376, Ming Li and co-workers.