Dressed for coherence
Solid-state qubits based on the electron spin of defects in silicon carbide or diamond provide a robust and versatile architecture for developing quantum technologies. The ...longer the lifetime of a spin, the more manipulations and quantum calculations can be performed, making for a more powerful quantum computational platform. Miao
et al.
show that by dressing the spins associated with the divacancy in silicon carbide with microwave photons, the lifetime can be extended by several orders of magnitude into milliseconds (see the Perspective by Hemmer). The technique effectively creates a quiet space for the qubit, thereby protecting it from magnetic, electric, and temperature fluctuations. This approach could be applicable to other architectures and provide a universal route to protecting qubits.
Science
, this issue p.
1493
; see also p.
1432
Spin qubits in silicon carbide can be protected from environmental fluctuations to substantially extend their lifetime.
Decoherence limits the physical realization of qubits, and its mitigation is critical for the development of quantum science and technology. We construct a robust qubit embedded in a decoherence-protected subspace, obtained by applying microwave dressing to a clock transition of the ground-state electron spin of a silicon carbide divacancy defect. The qubit is universally protected from magnetic, electric, and temperature fluctuations, which account for nearly all relevant decoherence channels in the solid state. This culminates in an increase of the qubit’s inhomogeneous dephasing time by more than four orders of magnitude (to >22 milliseconds), while its Hahn-echo coherence time approaches 64 milliseconds. Requiring few key platform-independent components, this result suggests that substantial coherence improvements can be achieved in a wide selection of quantum architectures.
Spin defects in silicon carbide have the advantage of exceptional electron spin coherence combined with a near-infrared spin-photon interface, all in a material amenable to modern semiconductor ...fabrication. Leveraging these advantages, we integrated highly coherent single neutral divacancy spins in commercially available p-i-n structures and fabricated diodes to modulate the local electrical environment of the defects. These devices enable deterministic charge-state control and broad Stark-shift tuning exceeding 850 gigahertz. We show that charge depletion results in a narrowing of the optical linewidths by more than 50-fold, approaching the lifetime limit. These results demonstrate a method for mitigating the ubiquitous problem of spectral diffusion in solid-state emitters by engineering the electrical environment while using classical semiconductor devices to control scalable, spin-based quantum systems.
Nuclear spins in the solid state are both a cause of decoherence and a valuable resource for spin qubits. In this work, we demonstrate control of isolated
Si nuclear spins in silicon carbide (SiC) to ...create an entangled state between an optically active divacancy spin and a strongly coupled nuclear register. We then show how isotopic engineering of SiC unlocks control of single weakly coupled nuclear spins and present an ab initio method to predict the optimal isotopic fraction that maximizes the number of usable nuclear memories. We bolster these results by reporting high-fidelity electron spin control (F = 99.984(1)%), alongside extended coherence times (Hahn-echo T
= 2.3 ms, dynamical decoupling T
> 14.5 ms), and a >40-fold increase in Ramsey spin dephasing time (T
*) from isotopic purification. Overall, this work underlines the importance of controlling the nuclear environment in solid-state systems and links single photon emitters with nuclear registers in an industrially scalable material.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Hybrid spin–mechanical systems provide a platform for integrating quantum registers and transducers. Efficient creation and control of such systems require a comprehensive understanding of the ...individual spin and mechanical components as well as their mutual interactions. Point defects in silicon carbide (SiC) offer long-lived, optically addressable spin registers in a wafer-scale material with low acoustic losses, making them natural candidates for integration with high-quality-factor mechanical resonators. Here, we show Gaussian focusing of a surface acoustic wave in SiC, characterized using a stroboscopic X-ray diffraction imaging technique, which delivers direct, strain amplitude information at nanoscale spatial resolution. Using ab initio calculations, we provide a more complete picture of spin–strain coupling for various defects in SiC with C3v symmetry. This reveals the importance of shear strain for future device engineering and enhanced spin–mechanical coupling. We demonstrate all-optical detection of acoustic paramagnetic resonance without microwave magnetic fields, relevant for sensing applications. Finally, we show mechanically driven Autler–Townes splittings and magnetically forbidden Rabi oscillations. These results offer a basis for full strain control of three-level spin systems.The authors use surface acoustic waves, focused in a Gaussian geometry, to manipulate the spin state of divacancy defects in silicon carbide via mechanical driving. They demonstrate that shear strain is important in controlling the spin transitions.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Silicon carbide has recently been developed as a platform for optically addressable spin defects. In particular, the neutral divacancy in the 4H polytype displays an optically addressable spin-1 ...ground state and near-infrared optical emission. Here, we present the Purcell enhancement of a single neutral divacancy coupled to a photonic crystal cavity. We utilize a combination of nanolithographic techniques and a dopant-selective photoelectrochemical etch to produce suspended cavities with quality factors exceeding 5000. Subsequent coupling to a single divacancy leads to a Purcell factor of ∼50, which manifests as increased photoluminescence into the zero-phonon line and a shortened excited-state lifetime. Additionally, we measure coherent control of the divacancy ground-state spin inside the cavity nanostructure and demonstrate extended coherence through dynamical decoupling. This spin-cavity system represents an advance toward scalable long-distance entanglement protocols using silicon carbide that require the interference of indistinguishable photons from spatially separated single qubits.
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Defects in silicon carbide (SiC) have emerged as a favorable platform for optically active spin-based quantum technologies. Spin qubits exist in specific charge states of these defects, where the ...ability to control these states can provide enhanced spin-dependent readout and long-term charge stability. We investigate this charge state control for two major spin qubits in 4H-SiC, the divacancy and silicon vacancy, obtaining bidirectional optical charge conversion between the bright and dark states of these defects. We measure increased photoluminescence from divacancy ensembles by up to three orders of magnitude using near-ultraviolet excitation, depending on the substrate, and without degrading the electron spin coherence time. This charge conversion remains stable for hours at cryogenic temperatures, allowing spatial and persistent patterning of the charge state populations. We develop a comprehensive model of the defects and optical processes involved, offering a strong basis to improve material design and to develop quantum applications in SiC.
Significance
Atomic defects in solid-state materials are promising candidates as quantum bits, or qubits. New materials are actively being investigated as hosts for new defect qubits; however, there ...are no unifying guidelines that can quantitatively predict qubit performance in a new material. One of the most critical property of qubits is their quantum coherence. While cluster correlation expansion (CCE) techniques are useful to simulate the coherence of electron spins in defects, they are computationally expensive to investigate broad classes of stable materials. Using CCE simulations, we reveal a general scaling relation between the electron spin coherence time and the properties of qubit host materials that enables rapid and quantitative exploration of new materials hosting spin defects.
Spin defect centers with long quantum coherence times (
T
2
) are key solid-state platforms for a variety of quantum applications. Cluster correlation expansion (CCE) techniques have emerged as a powerful tool to simulate the
T
2
of defect electron spins in these solid-state systems with good accuracy. Here, based on CCE, we uncover an algebraic expression for
T
2
generalized for host compounds with dilute nuclear spin baths under a magnetic field that enables a quantitative and comprehensive materials exploration with a near instantaneous estimate of the coherence time. We investigated more than 12,000 host compounds at natural isotopic abundance and found that silicon carbide (SiC), a prominent widegap semiconductor for quantum applications, possesses the longest coherence times among widegap nonchalcogenides. In addition, more than 700 chalcogenides are shown to possess a longer
T
2
than SiC. We suggest potential host compounds with promisingly long
T
2
up to 47 ms and pave the way to explore unprecedented functional materials for quantum applications.
Even as transformative service initiatives promote greater well-being, they may also create unintentionally negative consequences. Research investigates boundary conditions and boomerang effects that ...wash out or reverse the intended effects of service initiatives. However, such research generally advances greater depth of insight about unintended consequences in a particular stream rather than bridging this knowledge across service domains. Thus, service research lacks integrative frameworks, theory, and empirical insight to advance more generalizable knowledge about unintended consequences. The purpose of this editorial is to clarify the importance of investigating unintended consequences across service contexts and propose pathways as a catalyst for research. Using theory on unintended consequences, we delineate the types of unintended consequences and discuss the underlying mechanisms. We identify themes that span papers in the special issue and illuminate negative spillover consequences. The editorial concludes with an overview of future research avenues with potential to accelerate important transformative service research.
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Summary Background Systemic sclerosis is a rare disabling autoimmune disease with few treatment options. The efficacy and safety of tocilizumab, an interleukin 6 receptor-α inhibitor, was assessed in ...the faSScinate phase 2 trial in patients with systemic sclerosis. Methods We did this double-blind, placebo-controlled study at 35 hospitals in Canada, France, Germany, the UK, and the USA. We enrolled adults with progressive systemic sclerosis of 5 or fewer years' duration from first non-Raynaud's sign or symptom. Patients were randomly assigned (1:1) to weekly subcutaneous tocilizumab 162 mg or placebo. The primary endpoint was the difference in mean change from baseline in modified Rodnan skin score at 24 weeks. This study is registered with ClinicalTrials.gov , number NCT01532869. Findings We enrolled 87 patients: 43 assigned to tocilizumab and 44 assigned to placebo. The least squares mean change in modified Rodnan skin score at 24 weeks was −3·92 in the tocilizumab group and −1·22 in the placebo group (difference −2·70, 95% CI −5·85 to 0·45; p=0·0915). The least squares mean change at 48 weeks was −6·33 in the tocilizumab group and −2·77 in the placebo group (treatment difference −3·55, 95% CI −7·23 to 0·12; p=0·0579). In one of several exploratory analyses, fewer patients in the tocilizumab group than in the placebo group had a decline in percent predicted forced vital capacity at 48 weeks (p=0·0373). However, we detected no significant difference in disability, fatigue, itching, or patient or clinician global disease severity. 42 (98%) of 43 patients in the tocilizumab group versus 40 (91%) of 44 in the placebo group had adverse events. 14 (33%) versus 15 (34%) had serious adverse events. Serious infections were more common in the tocilizumab group (seven 16% of 43 patients) than in the placebo group (two 5% of 44). One patient died in relation to tocilizumab treatment. Interpretation Tocilizumab was not associated with a significant reduction in skin thickening. However, the difference was greater in the tocilizumab group than in the placebo group and we found some evidence of less decline in forced vital capacity. The efficacy and safety of tocilizumab should be investigated in a phase 3 trial before definitive conclusions can be made about its risks and benefits. Funding F Hoffmann-La Roche, Genentech.
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Defects with associated electron and nuclear spins in solid-state materials have a long history relevant to quantum information science that goes back to the first spin echo experiments with silicon ...dopants in the 1950s. Since the turn of the century, the field has rapidly spread to a vast array of defects and host crystals applicable to quantum communication, sensing and computing. From simple spin resonance to long-distance remote entanglement, the complexity of working with spin defects is fast increasing, and requires an in-depth understanding of the defects’ spin, optical, charge and material properties in this modern context. This is especially critical for discovering new relevant systems for specific quantum applications. In this Review, we expand upon all the key components of solid-state spin defects, with an emphasis on the properties of defects and of the host material, on engineering opportunities and on other pathways for improvement. This Review aims to be as defect and material agnostic as possible, with some emphasis on optical emitters, providing broad guidelines for the field of solid-state spin defects for quantum information.Defect-based spin qubits offer a versatile platform for creating solid-state quantum devices. This Review is a guide for understanding the properties and applications of current spin defects, and provides a framework for designing, engineering and discovering new qubit candidates
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