1,676 research outputs found
Tunable Nb superconducting resonators based upon a Ne-FIB-fabricated constriction nanoSQUID
Hybrid superconducting--spin systems offer the potential to combine highly
coherent atomic quantum systems with the scalability of superconducting
circuits. To fully exploit this potential requires a high quality-factor
microwave resonator, tunable in frequency and able to operate at magnetic
fields optimal for the spin system. Such magnetic fields typically rule out
conventional Al-based Josephson junction devices that have previously been used
for tunable high- microwave resonators. The larger critical field of niobium
(Nb) allows microwave resonators with large field resilience to be fabricated.
Here, we demonstrate how constriction-type weak links, patterned in parallel
into the central conductor of a Nb coplanar resonator using a neon focused ion
beam (FIB), can be used to implement a frequency-tunable resonator. We study
transmission through two such devices and show how they realise high quality
factor, tunable, field resilient devices which hold promise for future
applications coupling to spin systems
Coherent spin dynamics of rare-earth doped crystals in the high-cooperativity regime
Rare-earth doped crystals have long coherence times and the potential to
provide quantum interfaces between microwave and optical photons. Such
applications benefit from a high cooperativity between the spin ensemble and a
microwave cavity -- this motivates an increase in the rare earth ion
concentration which in turn impacts the spin coherence lifetime. We measure
spin dynamics of two rare-earth spin species, Nd and Yb doped into
YSiO, coupled to a planar microwave resonator in the high
cooperativity regime, in the temperature range 1.2 K to 14 mK. We identify
relevant decoherence mechanisms including instantaneous diffusion arising from
resonant spins and temperature-dependent spectral diffusion from impurity
electron and nuclear spins in the environment. We explore two methods to
mitigate the effects of spectral diffusion in the Yb system in the
low-temperature limit, first, using magnetic fields of up to 1 T to suppress
impurity spin dynamics and, second, using transitions with low effective
g-factors to reduce sensitivity to such dynamics. Finally, we demonstrate how
the `clock transition' present in the Yb system at zero field can be
used to increase coherence times up to ms.Comment: 8 pages, 5 figure
Random-access quantum memory using chirped pulse phase encoding
Quantum memories capable of faithfully storing and recalling quantum states
on-demand are powerful ingredients in bulding quantum networks
[arXiv:0806.4195] and quantum information processors [arXiv:1109.3743]. As in
conventional computing, key attributes of such memories are high storage
density and, crucially, random access, or the ability to read from or write to
an arbitrarily chosen register. However, achieving such random access with
quantum memories [arXiv:1904.09643] in a dense, hardware-efficient manner
remains a challenge, for example requiring dedicated cavities per qubit
[arXiv:1109.3743] or pulsed field gradients [arXiv:0908.0101]. Here we
introduce a protocol using chirped pulses to encode qubits within an ensemble
of quantum two-level systems, offering both random access and naturally
supporting dynamical decoupling to enhance the memory lifetime. We demonstrate
the protocol in the microwave regime using donor spins in silicon coupled to a
superconducting cavity, storing up to four multi-photon microwave pulses and
retrieving them on-demand up to 2~ms later. A further advantage is the natural
suppression of superradiant echo emission, which we show is critical when
approaching unit cooperativity. This approach offers the potential for
microwave random access quantum memories with lifetimes exceeding seconds
[arXiv:1301.6567, arXiv:2005.09275], while the chirped pulse phase encoding
could also be applied in the optical regime to enhance quantum repeaters and
networks
Probing spin dynamics of ultra-thin van der Waals magnets via photon-magnon coupling
Layered van der Waals (vdW) magnets can maintain a magnetic order even down to the single-layer regime and hold promise for integrated spintronic devices. While the magnetic ground state of vdW magnets was extensively studied, key parameters of spin dynamics, like the Gilbert damping, crucial for designing ultra-fast spintronic devices, remains largely unexplored. Despite recent studies by optical excitation and detection, achieving spin wave control with microwaves is highly desirable, as modern integrated information technologies predominantly are operated with these. The intrinsically small numbers of spins, however, poses a major challenge to this. Here, we present a hybrid approach to detect spin dynamics mediated by photon-magnon coupling between high-Q superconducting resonators and ultra-thin flakes of Cr2Ge2Te6 (CGT) as thin as 11 nm. We test and benchmark our technique with 23 individual CGT flakes and extract an upper limit for the Gilbert damping parameter. These results are crucial in designing on-chip integrated circuits using vdW magnets and offer prospects for probing spin dynamics of monolayer vdW magnets
AMR, stability and higher accuracy
Efforts to achieve better accuracy in numerical relativity have so far
focused either on implementing second order accurate adaptive mesh refinement
or on defining higher order accurate differences and update schemes. Here, we
argue for the combination, that is a higher order accurate adaptive scheme.
This combines the power that adaptive gridding techniques provide to resolve
fine scales (in addition to a more efficient use of resources) together with
the higher accuracy furnished by higher order schemes when the solution is
adequately resolved. To define a convenient higher order adaptive mesh
refinement scheme, we discuss a few different modifications of the standard,
second order accurate approach of Berger and Oliger. Applying each of these
methods to a simple model problem, we find these options have unstable modes.
However, a novel approach to dealing with the grid boundaries introduced by the
adaptivity appears stable and quite promising for the use of high order
operators within an adaptive framework
Mapping the Origins of Luminescence in ZnO Nanowires by STEM-CL
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpclett.8b03286.In semiconductor nanowires, understanding both the sources of luminescence (excitonic recombination, defects, etc.) and the distribution of luminescent centers (be they uniformly distributed, or concentrated at structural defects or at the surface) is important for synthesis and applications. We develop scanning transmission electron microscopy−cathodoluminescence (STEM-CL) measurements, allowing the structure and cathodoluminescence (CL) of single ZnO nanowires to be mapped at high resolution. Using a CL pixel resolution of 10 nm, variations of the CL spectra within such nanowires in the direction perpendicular to the nanowire growth axis are identified for the first time. By comparing the local CL spectra with the bulk photoluminescence spectra, the CL spectral features are assigned to internal and surface defect structures. Hyperspectral CL maps are deconvolved to enable characteristic spectral features to be spatially correlated with structural features within single nanowires. We have used these maps to show that the spatial distribution of these defects correlates well with regions that show an increased rate of nonradiative transitions
Integration of selectively grown topological insulator nanoribbons in superconducting quantum circuits
We report on the precise integration of nm-scale topological insulator
Josephson junctions into mm-scale superconducting quantum circuits via
selective area epitaxy and local stencil lithography. By studying dielectric
losses of superconducting microwave resonators fabricated on top of our
selective area growth mask, we verify the compatibility of this in situ
technique with microwave applications. We probe the microwave response of
on-chip microwave cavities coupled to topological insulator-shunted
superconducting qubit devices and observe a power dependence that indicates
nonlinear qubit behaviour. Our method enables integration of complex networks
of topological insulator nanostructures into superconducting circuits, paving
the way for both novel voltage-controlled Josephson and topological qubits.Comment: 11 pages, 6 figure
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