16 research outputs found
Atomic Layer Deposition Nucleation Dependence on Diamond Surface Termination
Surface termination and interfacial interactions are critical for advanced
solid-state quantum applications. In this paper, we demonstrate that atomic
layer deposition (ALD) can both provide valuable insight on the chemical
environment of the surface, having sufficient sensitivity to distinguish
between the common diamond (001) surface termination types and passivate these
interfaces as desired. We selected diamond substrates exhibiting both smooth
and anomalously rough surfaces to probe the effect of morphology on ALD
nucleation. We use high resolution in situ spectroscopic ellipsometry to
monitor the surface reaction with sub-angstrom resolution, to evaluate the
nucleation of an ALD Al2O3 process as a function of different ex and in situ
treatments to the diamond surface. In situ water dosing and high vacuum
annealing provided the most favorable environment for nucleation of
dimethylaluminum isopropoxide and water ALD. Hydrogen termination passivated
both smooth and rough surfaces while triacid cleaning passivated the smooth
surface only, with striking effectiveness.Comment: 31 pages, 14 figure
Quantifying the limits of controllability for the nitrogen-vacancy electron spin defect
Solid-state electron spin qubits, like the nitrogen-vacancy center in
diamond, rely on control sequences of population inversion to enhance
sensitivity and improve device coherence. But even for this paradigmatic
system, the fundamental limits of population inversion and potential impacts on
applications like quantum sensing have not been assessed quantitatively. Here,
we perform high accuracy simulations beyond the rotating wave approximation,
including explicit unitary simulation of neighboring nuclear spins. Using
quantum optimal control, we identify analytical pulses for the control of a
qubit subspace within the spin-1 ground state and quantify the relationship
between pulse complexity, control duration, and fidelity. We find exponentially
increasing amplitude and bandwidth requirements with reduced control duration
and further quantify the emergence of non-Markovian effects for multipulse
sequences using sub-nanosecond population inversion. From this, we determine
that the reduced fidelity and non-Markovianity is due to coherent interactions
of the electron spin with the nuclear spin environment. Ultimately, we identify
a potentially realizable regime of nanosecond control duration for
high-fidelity multipulse sequences. These results provide key insights into the
fundamental limits of quantum information processing using electron spin
defects in diamond.Comment: 9 pages, 5 figure
Scanning X-ray Diffraction Microscopy for Diamond Quantum Sensing
Understanding nano- and micro-scale crystal strain in CVD diamond is crucial
to the advancement of diamond quantum technologies. In particular, the presence
of such strain and its characterization present a challenge to diamond-based
quantum sensing and information applications -- as well as for future dark
matter detectors where directional information of incoming particles is encoded
in crystal strain. Here, we exploit nanofocused scanning X-ray diffraction
microscopy to quantitatively measure crystal deformation from growth defects in
CVD diamond with high spatial and strain resolution. Combining information from
multiple Bragg angles allows stereoscopic three-dimensional reconstruction of
strained volumes; the diffraction results are validated via comparison to
optical measurements of the strain tensor based on spin-state-dependent
spectroscopy of ensembles of nitrogen vacancy (NV) centers in the diamond. Our
results open a path towards directional detection of dark matter via X-ray
measurement of crystal strain, and provide a new tool for diamond growth
analysis and improvement of defect-based sensing.Comment: 15 pages, 17 figures (incl. Supplemental Material
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High-Q cavity interface for color centers in thin film diamond
Quantum information technology offers the potential to realize unprecedented computational resources via secure channels distributing entanglement between quantum computers. Diamond, as a host to optically-accessible spin qubits, is a leading platform to realize quantum memory nodes needed to extend such quantum links. Photonic crystal (PhC) cavities enhance light-matter interaction and are essential for an efficient interface between spins and photons that are used to store and communicate quantum information respectively. Here, we demonstrate one- and two-dimensional PhC cavities fabricated in thin-film diamonds, featuring quality factors (Q) of 1.8 × 105 and 1.6 × 105, respectively, the highest Qs for visible PhC cavities realized in any material. Importantly, our fabrication process is simple and high-yield, based on conventional planar fabrication techniques, in contrast to the previous with complex undercut processes. We also demonstrate fiber-coupled 1D PhC cavities with high photon extraction efficiency, and optical coupling between a single SiV center and such a cavity at 4 K achieving a Purcell factor of 18. The demonstrated photonic platform may fundamentally improve the performance and scalability of quantum nodes and expedite the development of related technologies
Guiding Diamond Spin Qubit Growth with Computational Methods
The nitrogen vacancy (NV) center in diamond, a well-studied, optically active
spin defect, is the prototypical system in many state of the art quantum
sensing and communication applications. In addition to the enticing properties
intrinsic to the NV center, its diamond host's nuclear and electronic spin
baths can be leveraged as resources for quantum information, rather than
considered solely as sources of decoherence. However, current synthesis
approaches result in stochastic defect spin positions, reducing the
technology's potential for deterministic control and yield of NV-spin bath
systems, as well as scalability and integration with other technologies. Here,
we demonstrate the use of theoretical calculations of electronic central spin
decoherence as an integral part of an NV-spin bath synthesis workflow,
providing a path forward for the quantitative design of NV center-based quantum
sensing systems. We use computationally generated coherence data to
characterize the properties of single NV center qubits across relevant growth
parameters to find general trends in coherence time distributions dependent on
spin bath dimensionality and density. We then build a maximum likelihood
estimator with our theoretical model, enabling the characterization of a test
sample through NV T2* measurements. Finally, we explore the impact of
dimensionality on the yield of strongly coupled electron spin systems. The
methods presented herein are general and applicable to other qubit platforms
that can be appropriately simulated.Comment: 12 pages, 6 figure
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Magnon-mediated qubit coupling determined via dissipation measurements
Controlled interaction between localized and delocalized solid-state spin systems offers a compelling platform for on-chip quantum information processing with quantum spintronics. Hybrid quantum systems (HQSs) of localized nitrogen-vacancy (NV) centers in diamond and delocalized magnon modes in ferrimagnets—systems with naturally commensurate energies—have recently attracted significant attention, especially for interconnecting isolated spin qubits at length-scales far beyond those set by the dipolar coupling. However, despite extensive theoretical efforts, there is a lack of experimental characterization of the magnon-mediated interaction between NV centers, which is necessary to develop such hybrid quantum architectures. Here, we experimentally determine the magnon-mediated NV–NV coupling from the magnon-induced self-energy of NV centers. Our results are quantitatively consistent with a model in which the NV center is coupled to magnons by dipolar interactions. This work provides a versatile tool to characterize HQSs in the absence of strong coupling, informing future efforts to engineer entangled solid-state systems
Deterministic nanoscale quantum spin-defect implantation and diffraction strain imaging
Local crystallographic features negatively affect quantum spin defects by changing the local electrostatic environment, often resulting in degraded or varied qubit optical and coherence properties. Few tools exist that enable the deterministic synthesis and study of such intricate systems on the nano-scale, making defect-to-defect strain environment quantification difficult. In this paper, we highlight state-of-the-art capabilities from the U.S. Department of Energy's Nanoscale Science Research Centers that directly address these shortcomings. Specifically, we demonstrate how complementary capabilities of nano-implantation and nano-diffraction can be used to demonstrate the quantum relevant, spatially deterministic creation of neutral divacancy centers in 4H silicon carbide, while investigating and characterizing these systems on the scale with strain sensitivities on the order of relevant to defect formation dynamics. This work lays the foundation for ongoing studies into the dynamics and deterministic formation of low strain homogeneous quantum relevant spin defects in the solid state
Microwave-based quantum control and coherence protection of tin-vacancy spin qubits in a strain-tuned diamond membrane heterostructure
Robust spin-photon interfaces in solids are essential components in quantum
networking and sensing technologies. Ideally, these interfaces combine a
long-lived spin memory, coherent optical transitions, fast and high-fidelity
spin manipulation, and straightforward device integration and scaling. The
tin-vacancy center (SnV) in diamond is a promising spin-photon interface with
desirable optical and spin properties at 1.7 K. However, the SnV spin lacks
efficient microwave control and its spin coherence degrades with higher
temperature. In this work, we introduce a new platform that overcomes these
challenges - SnV centers in uniformly strained thin diamond membranes. The
controlled generation of crystal strain introduces orbital mixing that allows
microwave control of the spin state with 99.36(9) % gate fidelity and spin
coherence protection beyond a millisecond. Moreover, the presence of crystal
strain suppresses temperature dependent dephasing processes, leading to a
considerable improvement of the coherence time up to 223(10) s at 4 K, a
widely accessible temperature in common cryogenic systems. Critically, the
coherence of optical transitions is unaffected by the elevated temperature,
exhibiting nearly lifetime-limited optical linewidths. Combined with the
compatibility of diamond membranes with device integration, the demonstrated
platform is an ideal spin-photon interface for future quantum technologies