8 research outputs found
Symmetry and Control of Spin-Scattering Processes in Two-Dimensional Transition Metal Dichalcogenides
Transition metal dichalcogenides (TMDs) combine interesting optical and
spintronic properties in an atomically-thin material, where the light
polarization can be used to control the spin and valley degrees-of-freedom for
the development of novel opto-spintronic devices. These promising properties
emerge due to their large spin-orbit coupling in combination with their crystal
symmetries. Here, we provide simple symmetry arguments in a group-theory
approach to unveil the symmetry-allowed spin scattering mechanisms, and
indicate how one can use these concepts towards an external control of the spin
lifetime. We perform this analysis for both monolayer (inversion asymmetric)
and bilayer (inversion symmetric) crystals, indicating the different mechanisms
that play a role in these systems. We show that, in monolayer TMDs, electrons
and holes transform fundamentally differently -- leading to distinct
spin-scattering processes. We find that one of the electronic states in the
conduction band is partially protected by time-reversal symmetry, indicating a
longer spin lifetime for that state. In bilayer and bulk TMDs, a hidden
spin-polarization can exist within each layer despite the presence of global
inversion symmetry. We show that this feature enables control of the interlayer
spin-flipping scattering processes via an out-of-plane electric field,
providing a mechanism for electrical control of the spin lifetime.Comment: 9 pages, 3 figure
Identification and tunable optical coherent control of transition-metal spins in silicon carbide
Color centers in wide-bandgap semiconductors are attractive systems for
quantum technologies since they can combine long-coherent electronic spin and
bright optical properties. Several suitable centers have been identified, most
famously the nitrogen-vacancy defect in diamond. However, integration in
communication technology is hindered by the fact that their optical transitions
lie outside telecom wavelength bands. Several transition-metal impurities in
silicon carbide do emit at and near telecom wavelengths, but knowledge about
their spin and optical properties is incomplete. We present all-optical
identification and coherent control of molybdenum-impurity spins in silicon
carbide with transitions at near-infrared wavelengths. Our results identify
spin for both the electronic ground and excited state, with highly
anisotropic spin properties that we apply for implementing optical control of
ground-state spin coherence. Our results show optical lifetimes of 60 ns
and inhomogeneous spin dephasing times of 0.3 s, establishing
relevance for quantum spin-photon interfacing.Comment: Updated version with minor correction, full Supplementary Information
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A quantum coherent spin in a two-dimensional material at room temperature
Quantum networks and sensing require solid-state spin-photon interfaces that
combine single-photon generation and long-lived spin coherence with scalable
device integration, ideally at ambient conditions. Despite rapid progress
reported across several candidate systems, those possessing quantum coherent
single spins at room temperature remain extremely rare. Here, we report quantum
coherent control under ambient conditions of a single-photon emitting defect
spin in a a two-dimensional material, hexagonal boron nitride. We identify that
the carbon-related defect has a spin-triplet electronic ground-state manifold.
We demonstrate that the spin coherence is governed predominantly by coupling to
only a few proximal nuclei and is prolonged by decoupling protocols. Our
results allow for a room-temperature spin qubit coupled to a multi-qubit
quantum register or quantum sensor with nanoscale sample proximity
Electromagnetically induced transparency in inhomogeneously broadened divacancy defect ensembles in SiC
Electromagnetically induced transparency (EIT) is a phenomenon that can provide strong and robust interfacing between optical signals and quantum coherence of electronic spins. In its archetypical form, mainly explored with atomic media, it uses a (near-)homogeneous ensemble of three-level systems, in which two low-energy spin-1/2 levels are coupled to a common optically excited state. We investigate the implementation of EIT with c-axis divacancy color centers in silicon carbide. While this material has attractive properties for quantum device technologies with near-IR optics, implementing EIT is complicated by the inhomogeneous broadening of the optical transitionsthroughout the ensemble and the presence of multiple ground-state levels. These may lead to darkening of the ensemble upon resonant optical excitation. Here, we show that EIT can be established with high visibility also in this material platform upon careful design of the measurement geometry. Comparison of our experimental results with a model based on the Lindblad equations indicates that we can create coherences between different sets of two levels all-optically in these systems, with potential impact for RF-free quantum sensing applications. Our work provides an understanding of EIT in multi-level systems with significant inhomogeneities, and our considerations are valid for awide array of defects in semiconductors
Electromagnetically induced transparency in inhomogeneously broadened divacancy defect ensembles in SiC
Electromagnetically induced transparency (EIT) is a phenomenon that can
provide strong and robust interfacing between optical signals and quantum
coherence of electronic spins. In its archetypical form, mainly explored with
atomic media, it uses a (near-)homogeneous ensemble of three-level systems, in
which two low-energy spin-1/2 levels are coupled to a common optically excited
state. We investigate the implementation of EIT with c-axis divacancy color
centers in silicon carbide. While this material has attractive properties for
quantum device technologies with near-IR optics, implementing EIT is
complicated by the inhomogeneous broadening of the optical transitions
throughout the ensemble and the presence of multiple ground-state levels. These
may lead to darkening of the ensemble upon resonant optical excitation. Here,
we show that EIT can be established with high visibility also in this material
platform upon careful design of the measurement geometry. Comparison of our
experimental results with a model based on the Lindblad equations indicates
that we can create coherences between different sets of two levels
all-optically in these systems, with potential impact for RF-free quantum
sensing applications. Our work provides an understanding of EIT in multi-level
systems with significant inhomogeneities, and our considerations are valid for
a wide array of defects in semiconductors.Comment: 9 pages, 5 figure
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A quantum coherent spin in hexagonal boron nitride at ambient conditions.
Solid-state spin-photon interfaces that combine single-photon generation and long-lived spin coherence with scalable device integration-ideally under ambient conditions-hold great promise for the implementation of quantum networks and sensors. Despite rapid progress reported across several candidate systems, those possessing quantum coherent single spins at room temperature remain extremely rare. Here we report quantum coherent control under ambient conditions of a single-photon-emitting defect spin in a layered van der Waals material, namely, hexagonal boron nitride. We identify that the carbon-related defect has a spin-triplet electronic ground-state manifold. We demonstrate that the spin coherence is predominantly governed by coupling to only a few proximal nuclei and is prolonged by decoupling protocols. Our results serve to introduce a new platform to realize a room-temperature spin qubit coupled to a multiqubit quantum register or quantum sensor with nanoscale sample proximity
Quantum communication networks with defects in silicon carbide
Quantum communication promises unprecedented communication capabilities enabled by the transmission of quantum states of light. However, current implementations face severe limitations in communication distance due to photon loss. Silicon carbide (SiC) defects have emerged as a promising quantum device platform, offering strong optical transitions, long spin coherence lifetimes and the opportunity for integration with semiconductor devices. Some defects with optical transitions in the telecom range have been identified, allowing to interface with fiber networks without the need for wavelength conversion. These unique properties make SiC an attractive platform for the implementation of quantum nodes for quantum communication networks. We provide an overview of the most prominent defects in SiC and their implementation in spin-photon interfaces. Furthermore, we model a memory-enhanced quantum communication protocol in order to extract the parameters required to surpass a direct point-to-point link performance. Based on these insights, we summarize the key steps required towards the deployment of SiC devices in large-scale quantum communication networks