Однородные и неоднородные ширины линий в оптических спектрах кристалла Y-=SUB=-2-=/SUB=-SiO-=SUB=-5-=/SUB=- : -=SUP=-171-=/SUP=-Yb-=SUP=-3+-=/SUP=-

Rare earth ions are actively investigated as optically addressable spin systems for quantum technologies thanks to their long optical and spin coherence lifetimes. 171Yb3+, which has 1/2 electron and nuclear spins, recently raised interest for its simple hyperfine structure that moreover can result in long coherence lifetimes at zero magnetic field, an unusual property for paramagnetic rare earth ions. Here, we report on the optical inhomogeneous and homogeneous linewidths in 171Yb3+:Y2SiO5 (site 2) for different doping concentrations. While inhomogeneous linewidth is not correlated to 171Yb3+ concentration, the homogeneous one strongly decreases between 10 and 2 ppm doping level, reaching 255 Hz at 3 K. This is attributed to a slowing down of 171Yb3+ ground state spin flip-flops.

Ground State, Magnetization Process and Bipartite Quantum Entanglement of a Spin-1/2 Ising–Heisenberg Model on Planar Lattices of Interconnected Trigonal Bipyramids

The ground state, magnetization scenario and the local bipartite quantum entanglement of a mixed spin-1/2 Ising–Heisenberg model in a magnetic field on planar lattices formed by identical corner-sharing bipyramidal plaquettes is examined by combining the exact analytical concept of generalized decoration-iteration mapping transformations with Monte Carlo simulations utilizing the Metropolis algorithm. The ground-state phase diagram of the model involves six different phases, namely, the standard ferrimagnetic phase, fully saturated phase, two unique quantum ferrimagnetic phases, and two macroscopically degenerate quantum ferrimagnetic phases with two chiral degrees of freedom of the Heisenberg triangular clusters. The diversity of ground-state spin arrangement is manifested themselves in seven different magnetization scenarios with one, two or three fractional plateaus whose values are determined by the number of corner-sharing plaquettes. The low-temperature values of the concurrence demonstrate that the bipartite quantum entanglement of the Heisenberg spins in quantum ferrimagnetic phases is field independent, but twice as strong if the Heisenberg spin arrangement is unique as it is two-fold degenerate.

STDP implementation using multi-state spin-orbit torque synapse

The abundance of data to be processed calls for new computing paradigms, which could accommodate, and directly map artificial neural network (ANN) architectures at the hardware level. Neuromorphic computing has emerged as a potential solution, proposing the implementation of artificial neurons and synapses on physical substrates. Conventionally, neuromorphic platforms are deployed in complementary metal-oxide–semiconductor (CMOS) technology. However, such implementations still cannot compete with the highly energy-efficient performance of the brain. This calls for novel ultra-low-power nano-scale devices with the possibility of upscaling for the implementation of complex networks. In this paper, a multi-state spin-orbit torque (SOT) synapse based on the three-terminal perpendicular-anisotropy magnetic tunnel junction (P-MTJ) is proposed. In this implementation, P-MTJs use common heavy metals (HMs) but with different cross-section areas, thereby creating multiple states that can be harnessed to implement synapses. The proposed multi-state SOT synapse can solve the state-limited issue of spin-based synapses. Moreover, it is shown that the proposed multi-state SOT synapse can be programmed to reproduce the spike-timing-dependent plasticity (STDP) learning algorithm.

All-optical noise spectroscopy of a solid-state spin

Noise spectroscopy elucidates the fundamental noise sources in spin systems, which is essential for developing spin qubits with long coherence times for quantum information processing, communication, and sensing. But noise spectroscopy typically relies on microwave coherent spin control to extract the noise spectrum, which becomes infeasible when there are high-frequency noise components stronger than the available microwave power. Here, we demonstrate an alternative all-optical approach to performing noise spectroscopy. Our approach utilises coherent Raman rotations of the spin state with controlled timing and phase to implement Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. Analysing the spin dynamics under these sequences enables us to extract the noise spectrum of a dense ensemble of nuclear spins interacting with a single spin in a quantum dot, which has thus far only been modelled theoretically. By providing large spectral bandwidths of over 100 MHz, our Raman-based approach could serve as an important tool to study spin dynamics and decoherence mechanisms for a broad range of solid-state spin qubits.

Magnetic properties of 1D spin systems with compositional disorder of three-spin structural units

The exact diagonalization (ED) approach and Quantum Monte-Carlo (QMC) method were used for the study of the lowest energy states and low-temperature magnetic properties of some disordered 1D Heisenberg spin-1/2 systems formed by two types of three-spin structural units. For the system with a singlet ground state and the random distribution of structural units along the chain system, a significant decrease of the size of the intermediate magnetization plateau in comparison to the corresponding uniform spin system was found. For the “polyallyl” spin chain with a macroscopic value of the ground state spin, a transition to the singlet ground state due to the effect of compositional disorder was observed.

A phononic interface between a superconducting quantum processor and quantum networked spin memories

We introduce a method for high-fidelity quantum state transduction between a superconducting microwave qubit and the ground state spin system of a solid-state artificial atom, mediated via an acoustic bus connected by piezoelectric transducers. Applied to present-day experimental parameters for superconducting circuit qubits and diamond silicon-vacancy centers in an optimized phononic cavity, we estimate quantum state transduction with fidelity exceeding 99% at a MHz-scale bandwidth. By combining the complementary strengths of superconducting circuit quantum computing and artificial atoms, the hybrid architecture provides high-fidelity qubit gates with long-lived quantum memory, high-fidelity measurement, large qubit number, reconfigurable qubit connectivity, and high-fidelity state and gate teleportation through optical quantum networks.

Beating the standard quantum limit under ambient conditions with solid-state spins

The use of entangled sensors improves the precision limit from the standard quantum limit (SQL) to the Heisenberg limit. Most previous experiments beating the SQL are performed on the sensors that are well isolated under extreme conditions. Here, we demonstrate a sub-SQL interferometer at ambient conditions by using a multispin system, namely, the nitrogen-vacancy (NV) defect in diamond. We achieve two-spin interference with a phase sensitivity of 1.79 ± 0.06 dB beyond the SQL and three-spin interference with a phase sensitivity of 2.77 ± 0.10 dB. Besides, a magnetic sensitivity of 0.87 ± 0.09 dB beyond the SQL is achieved by two-spin interference for detecting a real magnetic field. Particularly, the deterministic and joint initialization of NV negative state, NV electron spin, and two nuclear spins is realized at room temperature. The techniques used here are of fundamental importance for quantum sensing and computing, and naturally applicable to other solid-state spin systems.