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"Lyon, Stephen"
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Observation of an environmentally insensitive solid-state spin defect in diamond
Certain defects in diamond are among the most promising physical implementations of qubits, the building blocks of quantum computers. However, identifying a defect with balanced properties is tricky: Nitrogen vacancy centers have a long lifetime but comparatively poor optical properties, whereas negatively charged silicon vacancy centers have the opposite characteristics. Rose
et al.
used careful materials engineering to stabilize the neutral charge state of silicon vacancy centers and found that they combine long coherence times with excellent optical properties.
Science
, this issue p.
60
The neutral charge state of silicon vacancy centers in diamond shows promising quantum information properties.
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. We report a color center that shows insensitivity to environmental decoherence caused by phonons and electric field noise: the neutral charge state of silicon vacancy (SiV
0
). Through careful materials engineering, we achieved >80% conversion of implanted silicon to SiV
0
. SiV
0
exhibits spin-lattice relaxation times approaching 1 minute and coherence times approaching 1 second. Its optical properties are very favorable, with ~90% of its emission into the zero-phonon line and near–transform-limited optical linewidths. These combined properties make SiV
0
a promising defect for quantum network applications.
Journal Article
All-electric control of donor nuclear spin qubits in silicon
Coplanar photonic bandgap resonators are used to implement an all-electrical method for controlling neutral
31
P and
75
As donor nuclear spins in silicon.
The electronic and nuclear spin degrees of freedom of donor impurities in silicon form ultra-coherent two-level systems
1
,
2
that are potentially useful for applications in quantum information
3
and are intrinsically compatible with industrial semiconductor processing. However, because of their smaller gyromagnetic ratios, nuclear spins are more difficult to manipulate than electron spins and are often considered too slow for quantum information processing. Moreover, although alternating current magnetic fields are the most natural choice to drive spin transitions and implement quantum gates, they are difficult to confine spatially to the level of a single donor, thus requiring alternative approaches. In recent years, schemes for all-electrical control of donor spin qubits have been proposed
4
,
5
but no experimental demonstrations have been reported yet. Here, we demonstrate a scalable all-electric method for controlling neutral
31
P and
75
As donor nuclear spins in silicon. Using coplanar photonic bandgap resonators, we drive Rabi oscillations on nuclear spins exclusively using electric fields by employing the donor-bound electron as a quantum transducer, much in the spirit of recent works with single-molecule magnets
6
. The electric field confinement leads to major advantages such as low power requirements, higher qubit densities and faster gate times. Additionally, this approach makes it possible to drive nuclear spin qubits either at their resonance frequency or at its first subharmonic, thus reducing device bandwidth requirements. Double quantum transitions
7
can be driven as well, providing easy access to the full computational manifold of our system and making it convenient to implement nuclear spin-based qudits using
75
As donors
8
.
Journal Article
Atomic clock transitions in silicon-based spin qubits
A major challenge in using spins in the solid state for quantum technologies is protecting them from sources of decoherence. This is particularly important in nanodevices where the proximity of material interfaces, and their associated defects, can play a limiting role. Spin decoherence can be addressed to varying degrees by improving material purity or isotopic composition
1
,
2
, for example, or active error correction methods such as dynamic decoupling
3
,
4
(or even combinations of the two
5
,
6
). However, a powerful method applied to trapped ions in the context of atomic clocks
7
,
8
is the use of particular spin transitions that are inherently robust to external perturbations. Here, we show that such ‘clock transitions’ can be observed for electron spins in the solid state, in particular using bismuth donors in silicon
9
,
10
. This leads to dramatic enhancements in the electron spin coherence time, exceeding seconds. We find that electron spin qubits based on clock transitions become less sensitive to the local magnetic environment, including the presence of
29
Si nuclear spins as found in natural silicon. We expect the use of such clock transitions will be of additional significance for donor spins in nanodevices
11
, mitigating the effects of magnetic or electric field noise arising from nearby interfaces and gates.
Clock transitions, typically observed in arrays of trapped atoms, can now be observed for electron spins in silicon doped with bismuth.
Journal Article
NLRP3 activation and mitosis are mutually exclusive events coordinated by NEK7, a new inflammasome component
NEK7 is a serine-threonine kinase linked to mitosis. Beutler and colleagues show that NEK7 is required for assembly of the NLRP3 inflammasome and restricts NLRP3 activation to interphase of the cell cycle.
The NLRP3 inflammasome responds to microbes and danger signals by processing and activating proinflammatory cytokines, including interleukin 1β (IL-1β) and IL-18. We found here that activation of the NLRP3 inflammasome was restricted to interphase of the cell cycle by NEK7, a serine-threonine kinase previously linked to mitosis. Activation of the NLRP3 inflammasome required NEK7, which bound to the leucine-rich repeat domain of NLRP3 in a kinase-independent manner downstream of the induction of mitochondrial reactive oxygen species (ROS). This interaction was necessary for the formation of a complex containing NLRP3 and the adaptor ASC, oligomerization of ASC and activation of caspase-1. NEK7 promoted the NLRP3-dependent cellular inflammatory response to intraperitoneal challenge with monosodium urate and the development of experimental autoimmune encephalitis in mice. Our findings suggest that NEK7 serves as a cellular switch that enforces mutual exclusivity of the inflammasome response and cell division.
Journal Article
Embracing the quantum limit in silicon computing
Quantum computers hold the promise of massive performance enhancements across a range of applications, from cryptography and databases to revolutionary scientific simulation tools. Such computers would make use of the same quantum mechanical phenomena that pose limitations on the continued shrinking of conventional information processing devices. Many of the key requirements for quantum computing differ markedly from those of conventional computers. However, silicon, which plays a central part in conventional information processing, has many properties that make it a superb platform around which to build a quantum computer.
Journal Article
Comparison of predicted and actual consequences of missense mutations
Each person’s genome sequence has thousands of missense variants. Practical interpretation of their functional significance must rely on computational inferences in the absence of exhaustive experimental measurements. Here we analyzed the efficacy of these inferences in 33 de novo missense mutations revealed by sequencing in first-generation progeny ofN-ethyl-N-nitrosourea–treated mice, involving 23 essential immune system genes. Poly-Phen2, SIFT, MutationAssessor, Panther, CADD, and Condel were used to predict each mutation’s functional importance, whereas the actual effect was measured by breeding and testing homozygotes for the expected in vivo loss-of-function phenotype. Only 20% of mutations predicted to be deleterious by PolyPhen2 (and 15% by CADD) showed a discernible phenotype in individual homozygotes. Half of all possible missense mutations in the same 23 immune genes were predicted to be deleterious, and most of these appear to become subject to purifying selection because few persist between separate mouse substrains, rodents, or primates. Because defects in immune genes could be phenotypically masked in vivo by compensation and environment, we compared inferences by the same tools with the in vitro phenotype of all 2,314 possible missense variants inTP53; 42% of mutations predicted by PolyPhen2 to be deleterious (and 45% by CADD) had little measurable consequence forTP53-promoted transcription. We conclude that for de novo or low-frequency missense mutations found by genome sequencing, half those inferred as deleterious correspond to nearly neutral mutations that have little impact on the clinical phenotype of individual cases but will nevertheless become subject to purifying selection.
Journal Article
Chemical Profiles of the Oxides on Tantalum in State of the Art Superconducting Circuits
Over the past decades, superconducting qubits have emerged as one of the leading hardware platforms for realizing a quantum processor. Consequently, researchers have made significant effort to understand the loss channels that limit the coherence times of superconducting qubits. A major source of loss has been attributed to two level systems that are present at the material interfaces. It is recently shown that replacing the metal in the capacitor of a transmon with tantalum yields record relaxation and coherence times for superconducting qubits, motivating a detailed study of the tantalum surface. In this work, the chemical profile of the surface of tantalum films grown on c‐plane sapphire using variable energy X‐ray photoelectron spectroscopy (VEXPS) is studied. The different oxidation states of tantalum that are present in the native oxide resulting from exposure to air are identified, and their distribution through the depth of the film is measured. Furthermore, it is shown how the volume and depth distribution of these tantalum oxidation states can be altered by various chemical treatments. Correlating these measurements with detailed measurements of quantum devices may elucidate the underlying microscopic sources of loss.
Tantalum superconducting qubits are a leading candidate for large‐scale quantum computing. These devices are currently limited by two‐level‐systems at material surfaces and interfaces whose microscopic origin is unknown. This study uses variable energy X‐ray photoelectron spectroscopy to determine the chemical profile of the tantalum oxide along its depth, which allows comparison with device measurements to elucidate microscopic loss mechanisms.
Journal Article
Probability of phenotypically detectable protein damage by ENU-induced mutations in the Mutagenetix database
Computational inference of mutation effects is necessary for genetic studies in which many mutations must be considered as etiologic candidates. Programs such as PolyPhen-2 predict the relative severity of damage caused by missense mutations, but not the actual probability that a mutation will reduce/eliminate protein function. Based on genotype and phenotype data for 116,330 ENU-induced mutations in the Mutagenetix database, we calculate that putative null mutations, and PolyPhen-2-classified “probably damaging”, “possibly damaging”, or “probably benign” mutations have, respectively, 61%, 17%, 9.8%, and 4.5% probabilities of causing phenotypically detectable damage in the homozygous state. We use these probabilities in the estimation of genome saturation and the probability that individual proteins have been adequately tested for function in specific genetic screens. We estimate the proportion of essential autosomal genes in
Mus musculus
(C57BL/6J) and show that viable mutations in essential genes are more likely to induce phenotype than mutations in non-essential genes.
Programs such as PolyPhen-2 predict the relative severity of damage by missense mutations. Here, Wang et al estimate probabilities that putative null or missense alleles would reduce protein function to cause detectable phenotype by analyzing data from ENU-induced mouse mutations.
Journal Article