Nitrogen-vacancy Center System Research Articles

A noise-robust quantum dynamics learning protocol based on Choi–Jamiolkowski isomorphism: theory and experiment

With the rapid development of quantum technology, the growing manipulated Hilbert space makes learning the dynamics of the quantum system a significant challenge. Machine learning technique has brought apparent advantages in some learning strategies, therefore, we introduce it to indirect learning in this paper. Based on Choi–Jamiolkowski isomorphism, we propose a protocol that learns the dynamics of an inaccessible quantum system using a quantum device at hand. For an n-qubit system, the learning task can be done iteratively, with operational complexity O(poly(n,L)/ϵ2) in each iteration, where L is the circuit depth and ε is the measurement error. Then we theoretically prove its noise resilience to global depolarization, state preparation and measurement noise, and unitary noise in gates implementation, where we find the learned dynamics stay invariant. Finally, we investigate the protocol experimentally on a nitrogen-vacancy center system with a natural noise source. The results show that the behavior of a relatively intractable nuclear spin can be learned through an easily accessible electron spin under different noise models, demonstrating the protocol’s feasibility.

Enhanced Energy Transfer between Nitrogen‐Vacancy Centers and 2D MoS2 Films Accurately Fabricated by Atomic Layer Deposition

AbstractEnergy transfer between 2D MoS2 films and fluorescent emitters is widely used in biological detection and imaging. In this paper, by regulating the thickness of the MoS2 film on the diamond surface through the number of atomic layer deposition (ALD) cycles, the energy transfer efficiency between the nitrogen vacancy (NV) center and the MoS2 film is improved and precisely controlled. When the number of ALD cycles is 8, the energy transfer efficiency between the 2D MoS2 film and the NV center is 86.35%. Furthermore, when the number of ALD cycles is more significant than 140, compared with 2D and 3D graphene structures, the energy transfer efficiency of the NV center is increased by 126.55% and 24.60%, respectively. Meantime, the fluorescence lifetime of the NV center is reduced in the presence of the MoS2 film, indicating that the MoS2 film provides a new, additional fluorescence decay channel for the NV center in the MoS2 film and the NV center system. Moreover, ALD can also effectively improve the tightness of the contact interface between the MoS2 film and the diamond. This paper provides a new method and experimental basis for regulating the photon emission behavior of emitters.

All Fiber Vector Magnetometer Based on Nitrogen-Vacancy Center.

Magnetometers based on nitrogen-vacancy (NV) centers in diamonds have promising applications in fields of living systems biology, condensed matter physics, and industry. This paper proposes a portable and flexible all-fiber NV center vector magnetometer by using fibers to substitute all conventional spatial optical elements, realizing laser excitation and fluorescence collection of micro-diamond with multi-mode fibers simultaneously and efficiently. An optical model is established to investigate multi-mode fiber interrogation of micro-diamond to estimate the optical performance of NV center system. A new analysis method is proposed to extract the magnitude and direction of the magnetic field, combining the morphology of the micro-diamond, thus realizing μm-scale vector magnetic field detection at the tip of the fiber probe. Experimental testing shows our fabricated magnetometer has a sensitivity of 0.73 nT/Hz1/2, demonstrating its feasibility and performance in comparison with conventional confocal NV center magnetometers. This research presents a robust and compact magnetic endoscopy and remote-magnetic measurement approach, which will substantially promote the practical application of magnetometers based on NV centers.

Robust Dynamical Decoupling for the Manipulation of a Spin Network Via a Single Spin

High-fidelity control of quantum systems is crucial for quantum information processing, but is often limited by perturbations from the environment and imperfections in the applied control fields. Here, we investigate the combination of dynamical decoupling (DD) and robust optimal control (ROC) to address this problem. In this combination, ROC is employed to find robust shaped pulses, wherein the directional derivatives of the controlled dynamics with respect to control errors are reduced to a desired order. Then, we incorporate ROC pulses into DD sequences, achieving a remarkable improvement of robustness against multiple error channels. We demonstrate this method in the example of manipulating nuclear spin bath via an electron spin in the nitrogen-vacancy center system. Simulation results indicate that ROC-based DD sequences outperform the state-of-the-art robust DD sequences. Our work has implications for robust quantum control on near-term noisy quantum devices.

Telecom photon interface of solid-state quantum nodes

Solid-state spins such as nitrogen-vacancy (NV) center are promising platforms for large-scale quantum networks. Despite the optical interface of NV center system, however, the significant attenuation of its zero-phonon-line photon in optical fiber prevents the network extended to long distances. Therefore a telecom-wavelength photon interface would be essential to reduce the photon loss in transporting quantum information. Here we propose an efficient scheme for coupling telecom photon to NV center ensembles mediated by rare-earth doped crystal. Specifically, we proposed protocols for high fidelity quantum state transfer and entanglement generation with parameters within reach of current technologies. Such an interface would bring new insights into future implementations of long-range quantum network with NV centers in diamond acting as quantum nodes.

Quantum beats and metrology in a rapidly rotating Nitrogen-Vacancy center

In this paper, we study the dynamical behavior and quantum metrology in a rotating Nitrogen-Vacancy(NV) center system which is subject to an external magnetic field. Based on the recently realized rapid rotation of nano-rotor [J. Ahn, et. al., Phys. Rev. Lett. 121, 033603 (2018) and R. Reimann, et. al., Phys. Rev. Lett. 121, 033602 (2018)], the frequency of the rotation is close to that of the intrinsic frequency of the NV center system, we predict the quantum beats phenomenon in the time domain and show that the quantum metrology can be enhanced by the superposition effect in our system.

Dynamical decoupling design for identifying weakly coupled nuclear spins in a bath

Identifying weakly coupled nuclear spins around single electron spins is a key step toward implementing quantum information processing using coupled electron-nuclei spin systems or sensing like single-spin nuclear magnetic resonance detection using diamond defect spins. Dynamical decoupling control of the center electron spin with periodic pulse sequences [e.g., the Carre-Purcell-Meiboom-Gill (CPMG) sequence] has been successfully used to identify single nuclear spins and to resolve structure of nuclear spin clusters. Here, we design a type of pulse sequence by replacing the repetition unit (a single $\ensuremath{\pi}$ pulse) of the CPMG sequence with a group of nonuniformly spaced $\ensuremath{\pi}$ pulses. Using the nitrogen-vacancy center system in diamond, we theoretically demonstrate that the designed pulse sequence improves the resolution of nuclear spin noise spectroscopy, and more information about the surrounding nuclear spins is extracted. The principle of dynamical decoupling design proposed in this paper is useful in many systems (e.g., defect spin qubit in solids, trapped ion, and superconducting qubit) for high-resolution noise spectroscopy.

Propagation of magnetically controllable lasers and magneto-optic dual switching using nitrogen-vacancy centers in diamond

We study coherent laser-induced optical behaviors in weak twin-light propagation through strained diamond nitrogen-vacancy (NV) centers via switching on and off an external magnetic field. By numerically solving the coupled Bloch-Maxwell equations for NV center and field simultaneously in space and time, we address dynamic control of pulse propagation and magneto-optic dual switching in such a laser-driven NV center system. The proposed scheme may have applications in the design of magneto-optic switching and magneto-optic storage devices.