38 research outputs found
Nuclear Spin Quantum Memory in Silicon Carbide
Transition metal (TM) defects in silicon carbide (SiC) are a promising
platform for applications in quantum technology. Some TM defects, e.g.
vanadium, emit in one of the telecom bands, but the large ground state
hyperfine manifold poses a problem for applications which require pure quantum
states. We develop a driven, dissipative protocol to polarize the nuclear spin,
based on a rigorous theoretical model of the defect. We further show that
nuclear-spin polarization enables the use of well-known methods for
initialization and long-time coherent storage of quantum states. The proposed
nuclear-spin preparation protocol thus marks the first step towards an
all-optically controlled integrated platform for quantum technology with TM
defects in SiC.Comment: 12 Pages, 5 figure
Coupling spin 'clock states' to superconducting circuits
A central goal in quantum technologies is to maximize GT2, where G stands for
the rate at which each qubit can be coherently driven and T2 is the qubit's
phase coherence time. This is challenging, as increasing G (e.g. by coupling
the qubit more strongly to external stimuli) often leads to deleterious effects
on T2. Here, we study a physical situation in which both G and T2 can be
simultaneously optimized. We measure the coupling to microwave superconducting
coplanar waveguides of pure (i.e. non magnetically diluted) crystals of HoW10
magnetic clusters, which show level anticrossings, or spin clock transitions,
at equidistant magnetic fields. The absorption lines give a complete picture of
the magnetic energy level scheme and, in particular, confirm the existence of
such clock transitions. The quantitative analysis of the microwave transmission
allows monitoring the overlap between spin wave functions and gives information
about their coupling to the environment and to the propagating photons. The
formation of quantum superpositions of spin-up and spin-down states at the
clock transitions allows simultaneously maximizing the spin-photon coupling and
minimizing environmental spin perturbations. Using the same experimental
device, we also explore the coupling of these qubits to a 11.7 GHz cavity mode,
arising from a nonperfect microwave propagation at the chip boundaries and find
a collective spin to single photon coupling GN = 100 MHz. The engineering of
spin states in molecular systems offers a promising strategy to combine
sizeable photon-mediated interactions, thus scalability, with a sufficient
isolation from unwanted magnetic noise sources.Comment: 7 pages, 5 figure
Optimal coupling of Ho W<sub>10 molecular magnets to superconducting circuits near spin clock transitions
A central goal in quantum technologies is to maximize GT2, where G stands for the coupling of a qubit to control and readout signals and T2 is the qubit’s coherence time. This is challenging, as increasing G (e.g., by coupling the qubit more strongly to external stimuli) often leads to deleterious effects on T2. Here, we study the coupling of pure and magnetically diluted crystals of Ho W10 magnetic clusters to microwave superconducting coplanar waveguides. Absorption lines give a broadband picture of the magnetic energy level scheme and, in particular, confirm the existence of level anticrossings at equidistant magnetic fields determined by the combination of crystal field and hyperfine interactions. Such “spin clock transitions” are known to shield the electronic spins against magnetic field fluctuations. The analysis of the microwave transmission shows that the spin-photon coupling also becomes maximum at these transitions. The results show that engineering spin-clock states of molecular systems offers a promising strategy to combine sizable spin-photon interactions with a sufficient isolation from unwanted magnetic noise sources
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.Comment: 20 pages, 8 figure