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SiC quantum spintronics: towards quantum devices in a technological material

Scientific meeting

Location

Kavli Royal Society Centre, Chicheley Hall, Newport Pagnell, Buckinghamshire, MK16 9JJ

Overview

Theo Murphy international scientific meeting organised by Dr Cristian Bonato, Professor Jörg Wrachtrup and Sang-Yun Lee.

SiC quantum device. Credit: Matthias Widmann, University of Stuttgart

Recent research has shown that spin-active colour centres in silicon carbide (SiC) are a promising system for quantum technology. In contrast to similar platforms, such as diamond, SiC is an industrially-mature material for micro-electronics, opening exciting prospects for integrated quantum devices. This symposium will interface leading academic and industrial researchers to discuss the potential of SiC-based quantum devices.

More information on the schedule of talks will be available soon. Recorded audio of the presentations will be available on this page after the meeting has taken place.

Attending this event

This is a residential conference, which allows for increased discussion and networking.

  • Free to attend
  • Advance registration essential
  • Catering and accommodation available to purchase during registration

Enquiries: contact the Scientific Programmes team

Event organisers

Select an organiser for more information

Schedule of talks

05 November

09:00-12:30

Session 1

4 talks Show detail Hide detail

Chairs

Dr Sang-Yun Lee, Korea Institute of Science and Technology, South Korea

09:00-09:10 Welcome by the Royal Society and Dr Cristian Bonato

09:10-09:40 Quantum spintronics with SiC defects

Professor Jörg Wrachtrup, University of Stuttgart, Germany

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09:40-09:55 Discussion

09:55-10:25 Coherent control of spin qudit modes associated with defects in SiC

Professor Georgy Astakov, Institute of Ion Beam Physics and Materials Research, Germany

Abstract

Quantum bit or qubit is a two-level system, which builds the foundation for quantum computation, simulation, communication and sensing. Quantum states of higher dimension, ie, qutrits (D = 3) and especially qudits (D = 4 or higher), offer significant advantages. Particularly, they can provide noise-resistant quantum cryptography, simplify quantum logic and improve quantum metrology. Flying and solid-state qudits have been implemented on the basis of photonic chips and superconducting circuits, respectively. However, there is still a lack of room-temperature qudits with long coherence time and high spectral resolution. The silicon vacancy centers in silicon carbide (SiC) with spin S = 3/2 are quite promising in this respect. Here, Dr Astakhov reports a two-frequency protocol to excite and image multiple qudit modes in a SiC spin ensemble under ambient conditions. Strikingly, their spectral width is about one order of magnitude narrower than the inhomogeneous broadening of the corresponding spin resonance. By applying Ramsey interferometry to these spin qudits, a spectral selectivity of 600 kHz and a spectral resolution of 30 kHz are achieved. As a practical consequence, Dr Astakhov's team demonstrates absolute DC magnetometry insensitive to thermal noise and strain fluctuations.

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10:25-10:40 Discussion

10:40-11:00 Coffee

11:00-11:30 Optical Properties of Single Silicon Vacancies in 4H-SiC

Dr Samuel G Carter, US Naval Research Laboratory, USA

Abstract

Defects in wide bandgap materials have generated substantial interest as promising systems for quantum information and quantum sensing. SiC is an attractive material in terms of mature growth and fabrication technology and also has a low natural abundance of nuclear spins, which reduces spin dephasing. One promising defect system is the silicon monovacancy in SiC (VSi), which has a spin-3/2 ground state that can be optically polarized and maintain long spin coherence times even at room temperature. While significant work has been performed to study the spin properties of VSi for ensembles and even single defects, the optical properties and their connection to the spin system are less developed. In this presentation, Dr Samuel Carter will report on optical spectroscopy of single VSi defects, primarily V2 defects, at low temperatures. Using laser excitation spectroscopy, the zero phonon line (ZPL) transitions corresponding to the m_s=±1⁄2 and m_s=±3⁄2 spin states are resolved, with a linewidth down to 70 MHz. The spin polarization dynamics are measured for resonant and non-resonant optical excitation, and the results agree well with a theoretical model of the spin states and intersystem crossing. These results are essential to understanding the optical and spin physics of the defect and for developing a spin-photon interface. Dr Carter will also discuss results on producing VSi at precise locations using ion implantation and efforts to fabricate photonic crystal cavities to enhance defect emission.

This work was supported by the Office of Naval Research and the Office of the Secretary of Defense Quantum Sciences and Engineering Program.

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11:30-11:45 Discussion

11:45-12:15 Quantum control of spins in silicon carbide with photons and phonons

Professor David Awschalom, University of Chicago, USA

Abstract

There is a growing interest in exploiting the quantum properties of electronic and nuclear spins for the manipulation and storage of quantum information. Here Professor Awschalom and his team focus on recent developments in controlling and connecting spins in silicon carbide (SiC) using photons and phonons. They find that defect-based electronic states in SiC can be isolated and optically probed at the single spin level with surprisingly long spin coherence times and high-fidelity control within a wafer-scale material operating at near-telecom wavelengths. Moreover, a detailed study of the defect spin-photon interface yields efficient quantum control in various polytypes along with near-unity electronic and nuclear polarization, highlighting the potential of SiC for photon-mediated entanglement. In addition, they use Gaussian surface acoustic wave (SAW) resonators to exploit both the piezoelectric and isotropic phonon properties of SiC to create Autler-Townes splittings, mechanically drive coherent Rabi oscillations, and explore spin-strain coupling contributions from all mechanical degrees of freedom, including shear. The spatial confinement of phonons is mapped using a nanoscale diffraction imaging technique with a synchrotron to focus x-rays and provide 25 nm spatial resolution. This work expands the versatility of optically and mechanically driven spins in a material with developed device and fabrication capabilities, and shows promise towards integrating quantum states with nanomechanical systems for both control and communication.

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12:15-12:30 Discussion

12:30-13:30 Lunch

13:30-17:00

Session 2

4 talks Show detail Hide detail

Chairs

Dr Cristian Bonato, Heriot-Watt University, UK

13:30-14:00 Integrated optics in silicon carbide

Dr Alberto Politi, University of Southampton, UK

Abstract

The excellent physical properties of silicon carbide offer a wide range of potential applications for optics, from photonic devices spanning a wide wavelength range to non-linear and quantum optics. This talk will discuss the recent advances on the integration of optical components in silicon carbide, particularly focusing on the 3C polytype. A complete photonic platform that includes grating couplers, waveguides and ring resonators has been developed, offering a platform for classical and non-linear optics. The demonstration of photonic crystal cavities that show high field confinement will be presented. Their integration with colour centres can expand applications to the quantum technology domain. Finally, the extension to longer wavelength ranges will be discussed. Sub-wavelength confined cavities and strong nonlinearities can be achieved in the mid-infrared band by harnessing the unique phononic properties of SiC.

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14:00-14:15 Discussion

14:15-14:45 Optimizing Spin and Optical Defect Signatures in SiC Nanocavities

Professor Evelyn Hu, Harvard, USA

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14:45-15:00 Discussion

15:00-15:30 Tea

15:30-16:00 Silicon carbide color center photonics

Dr Marina Radulaski, Stanford University, USA

Abstract

Silicon carbide color centers are promising systems for quantum communication, spintronics and sensing. Their integration with photonic devices is a path to scalability, higher efficiency and new regimes of operation. Advanced material processing is the main challenge in the realization of the designed devices. So far, high quality color centers have been available only in bulk substrates, which impedes the development of freestanding nanophotonic structures, such as photonic crystal cavities. This talk will report on the progress in the development of nanofabrication processes in bulk silicon carbide, and hybrid silicon carbide-diamond platform, where color centers are hosted in nanodiamonds. The realized systems provide a scalable interface for addressing individual SiC color centers and demonstrate SiC-assisted Purcell enhancement of diamond color center emission.

Furthermore, theoretical insights into cavity quantum electrodynamics of color centers will be discussed. The small inhomogeneous broadening of color center ensembles is leveraged to potentially achieve collective coupling to a common cavity. Such regime not only exhibits arbitrarily high light-matter interaction, but also holds novel quantum light generating mechanisms. In addition to the conventional photon blockade that results in a steam of individual photons, multi-emitter-cavity systems can facilitate the so-called subradiant photon blockade with higher purity of single-photons. Finally, they also offer three-photon generating channels.

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16:00-16:15 Discussion

16:15-16:45 High-performance microcavity arrays for solid-state qubits

Dr Michael Trupke, University of Vienna, Austria

Abstract

Numerous applications in quantum technology, including photon generation, nanoparticle manipulation, and optical readout of qubits, require enhanced interactions between light and matter. Such an enhancement can be achieved with the use of microcavities, in which strong spatial confinement and high-reflectivity mirrors can drastically increase the desired interaction strength. For several of the intended applications, such as quantum computation and communication, it will furthermore be beneficial to create large numbers of efficient light-matter interfaces.

In this presentation, results from the University of Vienna in creating high-performance microcavity arrays will be discussed. The microcavities are micro-machined using highly precise lithographic methods, which enable the creation of large arrays of devices. By tailored optimization of the mirror morphology and surface quality, these microcavities have now reached a mirror reflectivity which approaches that of the best available macroscopic substrates. Lithographically defined alignment structures were furthermore used to robustly align arrays of micromirrors to each other while preserving their high performance values. As each microcavity needs to resonant with the desired optical transition, tuning of the microcavities using integrated micro-electromechanical actuators will also be described. Finally, efforts towards the integration of optically active defects in diamond and silicon carbide will be presented.

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16:45-17:00 Discussion

17:00-18:00

Poster session

06 November

09:00-12:30

Session 3

4 talks Show detail Hide detail

Chairs

Dr Marina Radulaski, Stanford University, USA

09:00-09:30 Intrinsic defects in silicon carbide: engineering and charge state control

Professor Nguyen Tien Son, Linköping University, Sweden

Abstract

Silicon carbide (SiC) has recently shown to be a promising material that hosts colour centers with excellent optical and spin properties suitable for different applications in quantum technology. Among these, intrinsic defects, such as the Si vacancy and the divacancy, can be created irradiation of high-energy particles with well-controlled concentrations down to the levels that allow to isolate single emitters. However, controlling their charge states for achieving bright and stable single emitters is still a challenge. This requires controlling the charge compensation processes between residual impurities, such as the shallow N donor and shallow acceptors (Al and B), and other intrinsic defects induced by irradiation in order to tune the Fermi level. 

In this talk, an overview on defects created by electron irradiation in SiC and charge compensation processes in irradiated low-doped and undoped n-type and p-type epitaxial layers grown by chemical vapour deposition and commercial high-purity semi-insulating materials is given. Based on the data from electron paramagnetic resonance, deep level transient spectroscopy, photoluminescence and theoretical calculations, the charge state control of the Si vacancy and the divacancy and the role of the carbon vacancy in tuning the Fermi level are discussed. 

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09:30-09:45 Discussion

09:45-10:15 Identification and tunable optical coherent control of transition-metal spins in silicon carbide

Professor Caspar H van der Wal, University of Groningen, The Netherlands

Abstract

Colour 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 S=1/2 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 about 60 ns and inhomogeneous spin dephasing times of about 1 microsecond, establishing relevance for quantum spin-photon interfacing.

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10:15-10:30 Discussion

10:30-11:00 Coffee

11:00-11:30 Ab initio study of SiC qubits for hyperpolarization, quantum sensing and communication

Professor Adam Gali, Hungarian Academy of Sciences, Hungary

Abstract

Paramagnetic and luminescent point defects in silicon carbide (SiC) are very promising for integrating semiconductor technology and quantum technology into a single platform. In particular, divacancy defects akin to nitrogen-vacancy center in diamond show similar electronic structure but the former are more sensitive to strain and electric fields that enables to employ them for quantum sensing protocols. First principles calculations show that divacancies in SiC can be also used to polarize the surrounding nuclear spins at arbitrary direction by controlling a small, constant magnetic field. First principles calculations also revealed interesting features on the silicon-vacancy quantum bits. Silicon-vacancy quantum bits have a special electronic structure that makes the optical emission almost intact to electrical stray fields and makes it a prominent candidate for quantum communication in the near infrared region with conversion to the telecom wavelengths. Finally, a transition metal defect will be discussed, vanadium, that was originally used to compensate electrically active impurities in SiC. Vanadium has optical transition in the O-band of telecom communication and an electron spin that can be detected by traditional electron spin resonance techniques which implies favourable spin coherence times. First principles calculations indicate that the Debye-Waller factor of the optical transition is around 0.5 that makes this centre a promising candidate for quantum communication in the telecom wavelengths applied in the every-day classical communication.

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11:30-11:45 Discussion

11:45-12:15 Electronic structure, spin control, and spin-photon interfaces of the silicon vacancy in SiC

Professor Sophia Economou, Virginia Tech, USA

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12:15-12:30 Discussion

12:30-13:30 Lunch

13:30-17:00

Session 4

5 talks Show detail Hide detail

Chairs

Professor Jörg Wrachtrup, University of Stuttgart, Germany

13:30-14:00 Laser fabrication of colour centres in silicon carbide and diamond

Dr Stefania Castelletto, RMIT University, Australia

Abstract

Optically active colour centres in silicon carbide and diamond have attracted considerable attention in the past few years as candidates for quantum applications, single photon sources, nanomagnetic resonance imaging and spintronics devices. The control of defects position and their placement at a desired location in a chip, necessary to integrate them within optical and electronic devices, is still a challenge. Recently, laser writing emerged as a new tool to generate vacancies in crystals as a starting point for the formation of colour centres. In this work, a laser writing method has been used to produce colour centres in 4H and 6H bulk silicon carbide and diamond by using a femtosecond laser with repetition rate of 200kHz. Array of colour centres were fabricated by different pulse laser energies in sites of square grids at varied depths (from surface level to 10µm below surface). We optically characterized the fabricated colour centres using confocal imaging and spectroscopy. We show that the technique can produce specifically the silicon vacancy colour centres with a relevant emission in the 900nm and other emitters in the visible range. This method can be adopted to engineer colour centres in silicon carbide for the above-mentioned applications in addition to display fabrication and light emitting diodes.

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14:00-14:15 Discussion

14:15-14:45 CVD growth of ultra-high purity SiC: Challenges and solutions

Dr Jawad Ul-Hassan, Linköping University, Sweden

Abstract

Epitaxial growth is required to obtain high quality and high purity layers of 4H-SiC with controlled doping concentration. Such layers are usually grown using horizontal hot-wall CVD reactor, developed at Linköping university in 90’s, which today is a standard reactor design being used worldwide. Off-cut substrates are used to replicate substrate’s polytype in the epilayer and smooth surface. High quality large area (150 mm diameter) substrates are commercially available and off-cut epitaxial growth is already mastered to produce thick layers suitable for electronic devices. However, epitaxial growth process is not matured enough to produce ultra-high purity epilayers with extremely low doping and complex layer structure with controlled n- and p-type doping which is one of the basic requirements for spintronics applications. This is mainly due to high temperature growth (>1600 C) which leads to the formation of high density intrinsic defects and also limits the control over residual doping and surface morphology. At Linköping University, Dr Ul-Hassan has unique possibility to grow epilayers at extremely fast growth rate (>100 m/h) which enables significantly low background doping, growth of isotopically enriched 4H-28Si12C epilayers with high thermal conductivity and no nuclear spin, and growth on on-axis substrates which leads to ultra-high purity and low defect density epilayers. In this talk, Dr Ul-Hassan will present the current status of SiC epitaxial growth and discuss different challenges and possible solutions to obtain ultra-high purity epilayers with controlled low doping using standard and non-standard growth processes on different off-cut substrates.

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14:45-15:00 Discussion

15:00-15:30 Tea

15:30-16:00 Perspective on SiC devices

Dr Cristian Bonato, Heriot-Watt University, UK

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16:00-16:15 Discussion

16:15-16:30 Growth of silicon carbide for new applications

Dr Björn Magnussonk, Norstel AB, Sweden

Abstract

The growth of silicon carbide crystals is today made with three different technologies: sublimation, HTCVD and liquid phase. Sublimation is the dominating process and it produce high quality n-type conducting substrates. CVD is used for epitaxial growth and can be both n-type and p-type doped depending on need. The key properties in the n-type substrates is developed and specified to fit power device (diodes and transistors) application and for the semi-insulating substrates it is to fit for nitride epitaxy targeting high frequency HEMT devices. For applications in the quantum spintronics field it is new requirements on the substrate and the epitaxy. The talk will describe the different methods for growth of crystals and epitaxy together with the benefit or disadvantage they have for applications in the quantum spintronics. The possibility of post-growth processing to change the properties of the substrates and epitaxy will also be discussed.

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16:15-17:00 Closing summary

Professor Jörg Wrachtrup, University of Stuttgart, Germany

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SiC quantum spintronics: towards quantum devices in a technological material

Theo Murphy international scientific meeting organised by Dr Cristian Bonato, Professor Jörg Wrachtrup and Sang-Yun Lee

Kavli Royal Society Centre, Chicheley Hall Newport Pagnell Buckinghamshire MK16 9JJ