Coherent harmonic generation of magnons in spin textures.

Harmonic generation, a notable non-linear phenomenon, has promising applications in information processing. For spin-waves in ferromagnetic materials, great progress has been made in the generation higher harmonics, however probing the coherence of these higher harmonics is challenging. Here, using in-situ diamond sensors, we study the coherent harmonic generation of spin waves in a soft ferromagnet.

Velocity Scanning Tomography for Room-Temperature Quantum Simulation.

Quantum simulation offers an analog approach for exploring exotic quantum phenomena using controllable platforms, typically necessitating ultracold temperatures to maintain the quantum coherence. Superradiance lattices (SLs) have been harnessed to simulate coherent topological physics at room temperature, but the thermal motion of atoms remains a notable challenge in accurately measuring the physical quantities. To overcome this obstacle, we implement a velocity scanning tomography technique to discern the responses of atoms with different velocities, allowing cold-atom spectroscopic resolution within room-temperature SLs.

Quantum Coherence Control at Temperatures up to 1400 K.

Coherent quantum control at high temperatures is important for expanding the quantum world and is useful for applying quantum technologies to realistic environments. Quantum control of spins in diamond has been demonstrated near 1000 K, with the spins polarized and read out at room temperature and controlled at elevated temperatures by rapid heating and cooling. Further increase of the working temperature is challenging due to fast spin relaxation in comparison with the heating and cooling rates.

Braiding Lateral Morphotropic Grain Boundaries in Homogenetic Oxides.

Interfaces formed by correlated oxides offer a critical avenue for discovering emergent phenomena and quantum states. However, the fabrication of oxide interfaces with variable crystallographic orientations and strain states integrated along a film plane is extremely challenging by conventional layer-by-layer stacking or self-assembling. Here, the creation of morphotropic grain boundaries (GBs) in laterally interconnected cobaltite homostructures is reported.

Dynamical-invariant-based holonomic quantum gates: Theory and experiment.

Among existing approaches to holonomic quantum computing, the adiabatic holonomic quantum gates (HQGs) suffer errors due to decoherence, while the non-adiabatic HQGs either require additional Hilbert spaces or are difficult to scale. Here, we report a systematic, scalable approach based on dynamical invariants to realize HQGs without using additional Hilbert spaces. While presenting the theoretical framework of our approach, we design and experimentally evaluate single-qubit and two-qubits HQGs for the nuclear magnetic resonance system.

Room-Temperature Ferromagnetism at an Oxide-Nitride Interface.

Heterointerfaces have led to the discovery of novel electronic and magnetic states because of their strongly entangled electronic degrees of freedom. Single-phase chromium compounds always exhibit antiferromagnetism following the prediction of the Goodenough-Kanamori rules. So far, exchange coupling between chromium ions via heteroanions has not been explored and the associated quantum states are unknown.

Association of Nanodiamond Rotation Dynamics with Cell Activities by Translation-Rotation Tracking.

Correlated translation-orientation tracking of single particles can provide important information for understanding the dynamics of live systems and their interaction with the probes. However, full six-dimensional (6D) motion tracking has yet to be achieved. Here, we developed synchronized 3D translation and 3D rotation tracking of single diamond particles based on nitrogen-vacancy center sensing.

Observing Information Backflow from Controllable Non-Markovian Multichannels in Diamond.

The unavoidable interaction of a quantum open system with its environment leads to the dissipation of quantum coherence and correlations, making its dynamical behavior a key role in many quantum technologies. In this Letter, we demonstrate the engineering of multiple dissipative channels by controlling the adjacent nuclear spins of a nitrogen-vacancy center in diamond. With a controllable non-Markovian dynamics of this open system, we observe that the quantum Fisher information flows to and from the environment using different noisy channels.

Coherent quantum control of nitrogen-vacancy center spins near 1000 kelvin.

Quantum coherence control usually requires low temperature environments. Even for nitrogen-vacancy center spins in diamond, a remarkable exception, the coherence signal is limited to about 700 K due to the quench of the spin-dependent fluorescence at a higher temperature. Here we overcome this limit and demonstrate quantum coherence control of the electron spins of nitrogen-vacancy centers in nanodiamonds at temperatures near 1000 K.

Hybrid nanodiamond quantum sensors enabled by volume phase transitions of hydrogels.

Diamond nitrogen-vacancy (NV) center-based magnetometry provides a unique opportunity for quantum bio-sensing. However, NV centers are not sensitive to parameters such as temperature and pressure, and immune to many biochemical parameters such as pH and non-magnetic biomolecules. Here, we propose a scheme that can potentially enable the measurement of various biochemical parameters using diamond quantum sensing, by employing stimulus-responsive hydrogels as a spacing transducer in-between a nanodiamond (ND, with NV centers) and magnetic nanoparticles (MNPs).

Single-Shot Readout of a Nuclear Spin Weakly Coupled to a Nitrogen-Vacancy Center at Room Temperature.

Single-shot readout of qubits is required for scalable quantum computing. Nuclear spins are superb quantum memories due to their long coherence time, but are difficult to be read out in a single shot due to their weak interaction with probes. Here we demonstrate single-shot readout of a weakly coupled ^{13}C nuclear spin at room temperature, which is unresolvable in traditional protocols.

Demonstration of entanglement-enhanced phase estimation in solid.

Precise parameter estimation plays a central role in science and technology. The statistical error in estimation can be decreased by repeating measurement, leading to that the resultant uncertainty of the estimated parameter is proportional to the square root of the number of repetitions in accordance with the central limit theorem. Quantum parameter estimation, an emerging field of quantum technology, aims to use quantum resources to yield higher statistical precision than classical approaches.

Protection of centre spin coherence by dynamic nuclear spin polarization in diamond.

We experimentally investigate the protection of electron spin coherence of a nitrogen-vacancy (NV) centre in diamond by dynamic nuclear spin polarization (DNP). The electron spin decoherence of an NV centre is caused by the magnetic field fluctuation of the (13)C nuclear spin bath, which contributes large thermal fluctuation to the centre electron spin when it is in an equilibrium state at room temperature. To address this issue, we continuously transfer the angular momentum from electron spin to nuclear spins, and pump the nuclear spin bath to a polarized state under the Hartmann-Hahn condition.

Room-temperature quantum cloning machine with full coherent phase control in nanodiamond.

In contrast to the classical world, an unknown quantum state cannot be cloned ideally, as stated by the no-cloning theorem. However, it is expected that approximate or probabilistic quantum cloning will be necessary for different applications, and thus various quantum cloning machines have been designed. Phase quantum cloning is of particular interest because it can be used to attack the Bennett-Brassard 1984 (BB84) states used in quantum key distribution for secure communications.

Controllable effects of quantum fluctuations on spin free-induction decay at room temperature.

Fluctuations of local fields cause decoherence of quantum objects. Usually at high temperatures, thermal noises are much stronger than quantum fluctuations unless the thermal effects are suppressed by certain techniques such as spin echo. Here we report the discovery of strong quantum-fluctuation effects of nuclear spin baths on free-induction decay of single electron spins in solids at room temperature.