arXiv subjects

Nathalie P. de Leon

Publications and source records attributed to Nathalie P. de Leon.

48 records · Page 3Linked to original sources

arXiv2021

Probing spin dynamics on diamond surfaces using a single quantum sensor

Understanding the dynamics of a quantum bit's environment is essential for the realization of practical systems for quantum information processing and metrology. We use single nitrogen-vacancy (NV) centers in diamond to study the dynamics of a disordered spin ensemble at the diamond surface. Specifically, we tune the density of "dark" surface spins to interrogate their contribution to the decoherence of shallow NV center spin qubits. When the average surface spin spacing exceeds the NV center depth, we find that the surface spin contribution to the NV center free induction decay can be described by a stretched exponential with variable power n. We show that these observations are consistent with a model in which the spatial positions of the surface spins are fixed for each measurement, but some of them reconfigure between measurements. In particular, we observe a depth-dependent critical time associated with a dynamical transition from Gaussian (n=2) decay to n=2/3, and show that this transition arises from the competition between the small decay contributions of many distant spins and strong coupling to a few proximal spins at the surface. These observations demonstrate the potential of a local sensor for understanding complex systems and elucidate pathways for improving and controlling spin qubits at the surface.

quant-ph↗

arXiv2020

Optically detected magnetic resonance in neutral silicon vacancy centers in diamond via bound exciton states

Neutral silicon vacancy (SiV0) centers in diamond are promising candidates for quantum networks because of their excellent optical properties and long spin coherence times. However, spin-dependent fluorescence in such defects has been elusive due to poor understanding of the excited state fine structure and limited off-resonant spin polarization. Here we report the realization of optically detected magnetic resonance and coherent control of SiV0 centers at cryogenic temperatures, enabled by efficient optical spin polarization via previously unreported higher-lying excited states. We assign these states as bound exciton states using group theory and density functional theory. These bound exciton states enable new control schemes for SiV0 as well as other emerging defect systems.

cond-mat.mes-hall↗

arXiv2020

Hybrid III-V diamond photonic platform for quantum nodes based on neutral silicon vacancy centers in diamond

Integrating atomic quantum memories based on color centers in diamond with on-chip photonic devices would enable entanglement distribution over long distances. However, efforts towards integration have been challenging because color centers can be highly sensitive to their environment, and their properties degrade in nanofabricated structures. Here, we describe a heterogeneously integrated, on-chip, III-V diamond platform designed for neutral silicon vacancy (SiV0) centers in diamond that circumvents the need for etching the diamond substrate. Through evanescent coupling to SiV0 centers near the surface of diamond, the platform will enable Purcell enhancement of SiV0 emission and efficient frequency conversion to the telecommunication C-band. The proposed structures can be realized with readily available fabrication techniques.

quant-ph↗

arXiv2020

Identifying candidate hosts for quantum defects via data mining

Atom-like defects in solid-state hosts are promising candidates for the development of quantum information systems, but despite their importance, the host substrate/defect combinations currently under study have almost exclusively been found serendipitously. Here we systematically evaluate the suitability of host materials by applying a combined four-stage data mining and manual screening process to all entries in the Materials Project database, with literature-based experimental confirmation of band gap values. We identify 580 viable host substrates for quantum defect introduction and use in quantum information systems. While this constitutes a significant increase in the number of known and potentially viable material systems, it nonetheless represents a significant (99.54%) reduction from the total number of known inorganic phases, and the application of additional selection criteria for specific applications will reduce their number even further. The screening principles outlined may easily be applied to previously unrealized phases and other technologically important materials systems.

cond-mat.mtrl-sci↗

arXiv2020

Charge State Dynamics and Optically Detected Electron Spin Resonance Contrast of Shallow Nitrogen-Vacancy Centers in Diamond

Nitrogen-vacancy (NV) centers in diamond can be used for nanoscale sensing with atomic resolution and sensitivity; however, it has been observed that their properties degrade as they approach the diamond surface. Here we report that in addition to degraded spin coherence, NV centers within nanometers of the surface can also exhibit decreased fluorescence contrast for optically detected electron spin resonance (OD-ESR). We demonstrate that this decreased OD-ESR contrast arises from charge state dynamics of the NV center, and that it is strongly surface-dependent, indicating that surface engineering will be critical for nanoscale sensing applications based on color centers in diamond.

quant-ph↗

arXiv2020

New material platform for superconducting transmon qubits with coherence times exceeding 0.3 milliseconds

The superconducting transmon qubit is a leading platform for quantum computing and quantum science. Building large, useful quantum systems based on transmon qubits will require significant improvements in qubit relaxation and coherence times, which are orders of magnitude shorter than limits imposed by bulk properties of the constituent materials. This indicates that relaxation likely originates from uncontrolled surfaces, interfaces, and contaminants. Previous efforts to improve qubit lifetimes have focused primarily on designs that minimize contributions from surfaces. However, significant improvements in the lifetime of two-dimensional transmon qubits have remained elusive for several years. Here, we fabricate two-dimensional transmon qubits that have both lifetimes and coherence times with dynamical decoupling exceeding 0.3 milliseconds by replacing niobium with tantalum in the device. We have observed increased lifetimes for seventeen devices, indicating that these material improvements are robust, paving the way for higher gate fidelities in multi-qubit processors.

quant-ph↗

arXiv2019

Narrow optical linewidths in erbium implanted in TiO$_2$

Atomic and atom-like defects in the solid-state are widely explored for quantum computers, networks and sensors. Rare earth ions are an attractive class of atomic defects that feature narrow spin and optical transitions that are isolated from the host crystal, allowing incorporation into a wide range of materials. However, the realization of long electronic spin coherence times is hampered by magnetic noise from abundant nuclear spins in the most widely studied host crystals. Here, we demonstrate that Er$^{3+}$ ions can be introduced via ion implantation into TiO$_2$, a host crystal that has not been studied extensively for rare earth ions and has a low natural abundance of nuclear spins. We observe efficient incorporation of the implanted Er$^{3+}$ into the Ti$^{4+}$ site (40% yield), and measure narrow inhomogeneous spin and optical linewidths (20 and 460 MHz, respectively) that are comparable to bulk-doped crystalline hosts for Er$^{3+}$. This work demonstrates that ion implantation is a viable path to studying rare earth ions in new hosts, and is a significant step towards realizing individually addressed rare earth ions with long spin coherence times for quantum technologies.

physics.app-ph↗

arXiv2018

Origins of diamond surface noise probed by correlating single spin measurements with surface spectroscopy

The nitrogen vacancy (NV) center in diamond exhibits spin-dependent fluorescence and long spin coherence times under ambient conditions, enabling applications in quantum information processing and sensing. NV centers near the surface can have strong interactions with external materials and spins, enabling new forms of nanoscale spectroscopy. However, NV spin coherence degrades within 100 nanometers of the surface, suggesting that diamond surfaces are plagued with ubiquitous defects. Prior work on characterizing near-surface noise has primarily relied on using NV centers themselves as probes; while this has the advantage of exquisite sensitivity, it provides only indirect information about the origin of the noise. Here we demonstrate that surface spectroscopy methods and single spin measurements can be used as complementary diagnostics to understand sources of noise. We find that surface morphology is crucial for realizing reproducible chemical termination, and use these insights to achieve a highly ordered, oxygen-terminated surface with suppressed noise. We observe NV centers within 10 nm of the surface with coherence times extended by an order of magnitude.

cond-mat.mtrl-sci↗

arXiv2018

Evidence for Primal sp2 Defects at the Diamond Surface: Candidates for Electron Trapping and Noise Sources

Diamond materials are central to an increasing range of advanced technological demonstrations, from high power electronics, to nano-scale quantum bio-imaging with unprecedented sensitivity. However, the full exploitation of diamond for these applications is often limited by the uncontrolled nature of the diamond material surface, which suffers from Fermi-level pinning and hosts a significant density of electro-magnetic noise sources. These issues occur despite the oxide-free and air-stable nature of the diamond crystal surface, which should be an ideal candidate for functionalization and chemical-engineering. In this work we reveal a family of previously unidentified and near-ubiquitous primal surface defects which we assign to differently reconstructed surface vacancies. The density of these defects is quantified with X-ray absorption spectroscopy, their energy structures are elucidated by ab initio calculations, and their effect on near-surface quantum probes is measured directly. Subsequent ab-initio calculation of band-bending from these defects suggest they are the source of Fermi-level pinning at most diamond surfaces. Finally, an investigation is conducted on a broad range of post-growth surface treatments and concludes that none of them can reproducibly reduce this defect density below the Fermi-pinning threshold, making this defect a prime candidate as the source for decoherence-limiting noise in near-surface quantum probes.

cond-mat.mes-hall↗

arXiv2017

Strongly Anisotropic Spin Relaxation in the Neutral Silicon Vacancy Center in Diamond

Color centers in diamond are a promising platform for quantum technologies, and understanding their interactions with the environment is crucial for these applications. We report a study of spin- lattice relaxation (T1) of the neutral charge state of the silicon vacancy center in diamond. Above 20 K, T1 decreases rapidly with a temperature dependence characteristic of an Orbach process, and is strongly anisotropic with respect to magnetic field orientation. As the angle of the magnetic field is rotated relative to the symmetry axis of the defect, T1 is reduced by over three orders of magnitude. The electron spin coherence time (T2) follows the same temperature dependence but is drastically shorter than T1. We propose that these observations result from phonon-mediated transitions to a low lying excited state that are spin conserving when the magnetic field is aligned with the defect axis, and we discuss likely candidates for this excited state.

quant-ph↗

arXiv2017

Observation of an environmentally insensitive solid state spin defect in diamond

Engineering coherent systems is a central goal of quantum science. Color centers in diamond are a promising approach, with the potential to combine the coherence of atoms with the scalability of a solid state platform. However, the solid environment can adversely impact coherence. For example, phonon- mediated spin relaxation can induce spin decoherence, and electric field noise can change the optical transition frequency over time. We report a novel color center with insensitivity to both of these sources of environmental decoherence: the neutral charge state of silicon vacancy (SiV0). Through careful material engineering, we achieve over 80% conversion of implanted silicon to SiV0. SiV0 exhibits excellent spin properties, with spin-lattice relaxation times (T1) approaching one minute and coherence times (T2) approaching one second, as well as excellent optical properties, with approximately 90% of its emission into the zero-phonon line and near-transform limited optical linewidths. These combined properties make SiV0 a promising defect for quantum networks.

cond-mat.mtrl-sci↗

arXiv2012

Tailoring Light-Matter Interaction with a Nanoscale Plasmon Resonator

We propose and demonstrate a new approach for achieving strong light-matter interactions with quantum emitters. Our approach makes use of a plasmon resonator composed of defect-free, highly crystalline silver nanowires surrounded by patterned dielectric distributed Bragg reflectors (DBRs). These resonators have an effective mode volume (Veff) two orders of magnitude below the diffraction limit and quality factor (Q) approaching 100, enabling enhancement of spontaneous emission rates by a factor exceeding 75 at the cavity resonance. We also show that these resonators can be used to convert a broadband quantum emitter to a narrowband single-photon source with color-selective emission enhancement.

cond-mat.mes-hall↗