Quantum Dynamics in Nanoscale Devices

Aiichiro Nakano, Rajiv K. Kalia, Priya D. Vashishta

Oleg V. Prezhdo

Mario Agio

Jan Hendrik Rueschkamp, Shantam Ravan, Daniel Fernandez +6 more

Magnetic field fluctuations on nanometer length scales manifest in a diverse range of phenomena -- electron and spin dynamics in materials and devices, quantum many-body systems, and molecular chemistry. Measuring these phenomena requires sensors with a challenging combination of broad spectral bandwidth, high sensitivity, and nanoscale spatial resolution. Nitrogen-vacancy (NV) centers, atom-like quantum sensors in diamond, possess the requisite sensitivity and nanoscale sensing volume, but are typically limited in bandwidth by the practical speed of the applied quantum control sequence. Here, we overcome this limitation by exposing the NV qubit to a microwave dressing field during a dynamical decoupling sequence, which both amplifies and frequency-mixes target signals at arbitrary frequencies into the detection band of the dynamical decoupling protocol. We demonstrate this approach by using NV centers to detect both coherent and noisy nanoscale spin wave dynamics in a magnetic yttrium-iron-garnet (YIG) thin film over a broad frequency range. Our technique generalizes to other qubit platforms, providing a versatile framework for nanoscale spectroscopy across diverse physical and chemical systems.

Anthony G. Gianfrancesco, Andrei Victor Ilyashenko, C.R. Boucher +1 more

Shoaib Mahmud, Wei Zhang, Pronoy Das +3 more

Superparamagnetism in nanoscale magnetic layers is a critical property for a wide range of spintronic-based sensor and computing applications. While conventional magnetization measurements can detect superparamagnetic signatures, they often require the application of high perturbative fields and are difficult to implement for magnetic layers integrated within functional devices. In this study, we non-invasively investigate the superparamagnetic spin dynamics of a nanoscale CoFeB layer of thickness 1.1 nm, deposited on a diamond substrate, by probing its low-frequency near-field electromagnetic (EM) fluctuations using nitrogen-vacancy (NV) centers-based quantum dephasometry. Our measurements reveal an unconventional, non-monotonic temperature dependence of the dephasing time of NV centers, which we attribute to EM fluctuations produced by thermally driven superparamagnetic domain flipping in CoFeB. Our findings are further supported by the theoretical interpretation of the dephasing dynamics of NV centers and the complementary SQUID-based magnetization characterizations of the CoFeB layer. Additionally, exploiting the technique of NV dephasometry, we extract the spectral density of the EM fluctuations in CoFeB, which is used to isolate different components of the EM fluctuations acting on NV centers. We also measure the CoFeB-to-NV distance-dependent coherence times of NV centers to investigate the effect of the dimensionality of the CoFeB layer on the generated near-field EM fluctuations. These results provide critical insight into the magnetization dynamics and near-field EM environment of nanoscale magnetic layers. It also has significant implications for the development of hybrid quantum spintronic devices and applications involving nanoscale opto-magnetic materials.