Materials for Quantum Technology - IOPscience

Materials for Quantum Technology - IOPscience
Materials for Quantum Technology
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Materials for Quantum Technology
is a multidisciplinary, open access journal devoted to publishing cutting-edge research on the development and application of materials for all quantum-enabled technologies and devices. For specific information about subject coverage see the
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The following article is
Open access
Bottom-up fabrication of scalable room-temperature diamond quantum computing and sensing technologies
Lachlan Oberg
et al
2025
Mater. Quantum. Technol.
033001
View article
, Bottom-up fabrication of scalable room-temperature diamond quantum computing and sensing technologies
PDF
, Bottom-up fabrication of scalable room-temperature diamond quantum computing and sensing technologies
The nitrogen-vacancy (NV) centre in diamond is a premier solid-state defect for quantum information processing and metrology. An integrated diamond quantum device harnesses the collective properties of multiple NV centres, enabling room-temperature quantum computing and sensing. While large-scale devices are poised to fill an important gap in the burgeoning quantum technology landscape, their practical realisation has not been achieved using current top-down fabrication techniques such as ion implantation. Consequently, this necessitates the development of a bottom-up fabrication technique, which is scalable, deterministic, and possesses atomic-scale precision. Informed by existing methods for fabricating phosphorous defect qubits in silicon, we envision a hydrogen depassivation lithography technique for atomically-precise manufacturing of nitrogen-vacancy centres in diamond. This perspective article outlines a viable multi-step procedure for realising scalable fabrication of diamond quantum devices and identifies the key challenges in its development.
The following article is
Open access
2023 roadmap for materials for quantum technologies
Christoph Becher
et al
2023
Mater. Quantum. Technol.
012501
View article
, 2023 roadmap for materials for quantum technologies
PDF
, 2023 roadmap for materials for quantum technologies
Quantum technologies are poised to move the foundational principles of quantum physics to the forefront of applications. This roadmap identifies some of the key challenges and provides insights on material innovations underlying a range of exciting quantum technology frontiers. Over the past decades, hardware platforms enabling different quantum technologies have reached varying levels of maturity. This has allowed for first proof-of-principle demonstrations of quantum supremacy, for example quantum computers surpassing their classical counterparts, quantum communication with reliable security guaranteed by laws of quantum mechanics, and quantum sensors uniting the advantages of high sensitivity, high spatial resolution, and small footprints. In all cases, however, advancing these technologies to the next level of applications in relevant environments requires further development and innovations in the underlying materials. From a wealth of hardware platforms, we select representative and promising material systems in currently investigated quantum technologies. These include both the inherent quantum bit systems and materials playing supportive or enabling roles, and cover trapped ions, neutral atom arrays, rare earth ion systems, donors in silicon, color centers and defects in wide-band gap materials, two-dimensional materials and superconducting materials for single-photon detectors. Advancing these materials frontiers will require innovations from a diverse community of scientific expertise, and hence this roadmap will be of interest to a broad spectrum of disciplines.
The following article is
Open access
A review of design concerns in superconducting quantum circuits
Eli M Levenson-Falk and Sadman Ahmed Shanto 2025
Mater. Quantum. Technol.
022003
View article
, A review of design concerns in superconducting quantum circuits
PDF
, A review of design concerns in superconducting quantum circuits
In this short review we describe the process of designing a superconducting circuit device for quantum information applications. We discuss the factors that must be considered to implement a desired effective Hamiltonian on a device. We describe the translation between a device’s physical layout, the circuit graph, and the effective Hamiltonian. We go over the process of electromagnetic simulation of a device layout to predict its behavior. We also discuss concerns such as connectivity, crosstalk suppression, and radiation shielding, and how they affect both on-chip design and enclosure structures. This paper provides an overview of the challenges in superconducting quantum circuit design and acts as a starter document for researchers working on any of these challenges.
The following article is
Open access
The properties of the nitrogen-vacancy center in milled chemical vapor deposition nanodiamonds
Alessandro Mameli
et al
2026
Mater. Quantum. Technol.
015202
View article
, The properties of the nitrogen-vacancy center in milled chemical vapor deposition nanodiamonds
PDF
, The properties of the nitrogen-vacancy center in milled chemical vapor deposition nanodiamonds
Fluorescent nanodiamonds (FNDs) containing negatively charged nitrogen-vacancy (NV
) centers are vital for many emerging quantum sensing applications from magnetometry to intracellular sensing in biology. However, developing a scalable fabrication method for FNDs hosting color centers with consistent bulk-like photoluminescence (PL) and spin coherence properties remains a highly desired but unrealized goal. Here, we investigate optimized ball milling of single-crystal diamonds produced via chemical vapor deposition (CVD) and containing 2 ppm of substitutional nitrogen and 0.3 ppm of NV
to achieve this goal. The NV charge state, PL lifetime, and spin properties of bulk CVD diamond samples are directly compared to milled CVD FNDs and commercial high-pressure high-temperature (HPHT) FNDs. We find that on average, the relative contribution of the NV
charge state to the total NV PL is lower and the NV PL lifetime is longer in CVD FNDs compared to HPHT FNDs, both likely due to the lower N
concentration in CVD FNDs. The CVD bulk and CVD FNDs on average show similar average
spin relaxation times of 3.2 ± 0.7 ms and 4.7 ± 1.6 ms, respectively, compared to 0.17 ± 0.01 ms for commercial HPHT FNDs. Our results demonstrate that ball milling of CVD diamonds enables the large-scale fabrication of NV ensembles in FNDs with bulk-like
spin relaxation properties.
The following article is
Open access
Exploring Wigner crystals in two-dimensional and moiré systems: from spectroscopy to theoretical modeling
Yifan Ke and Wei Hu 2025
Mater. Quantum. Technol.
022001
View article
, Exploring Wigner crystals in two-dimensional and moiré systems: from spectroscopy to theoretical modeling
PDF
, Exploring Wigner crystals in two-dimensional and moiré systems: from spectroscopy to theoretical modeling
Electron correlation effects have long been a central issue in condensed matter physics, particularly with the successful development of various two-dimensional materials. Notably, recent research interest has centered on the ordered states of twisted moiré lattices, where doped low-density electrons exhibit crystallized behavior as predicted by Eugene Wigner nearly a century ago. Such correlation effects are often highly sensitive to external perturbations, including electrostatic fields or material strains. Consequently, significant challenges remain in both experimental and theoretical investigations of these correlated states. Preparing a pure moiré lattice without distortion is particularly difficult, and the computational cost of theoretical modeling for such systems grows rapidly with decreasing angles due to the increasing size of the system. In this review, we introduce recent theoretical and experimental progress regarding Wigner crystal states induced by magnetic fields and generalized Wigner crystals or Wigner molecules emerging in moiré materials, followed by a discussion of future directions in this area.
The following article is
Open access
Characterisation of CVD diamond with high concentrations of nitrogen for magnetic-field sensing applications
Andrew M Edmonds
et al
2021
Mater. Quantum. Technol.
025001
View article
, Characterisation of CVD diamond with high concentrations of nitrogen for magnetic-field sensing applications
PDF
, Characterisation of CVD diamond with high concentrations of nitrogen for magnetic-field sensing applications
Ensembles of nitrogen-vacancy (NV) centres in diamond are a leading platform for practical quantum sensors. Reproducible and scalable fabrication of NV-ensembles with desired properties is crucial, as is an understanding of how those properties influence performance. This work addresses these issues by characterising nitrogen-doped diamond produced by the chemical vapour deposition (CVD) method across a range of synthesis conditions. This is shown to produce material with widely differing absorption characteristics, which is linked to the level of defects other than substitutional nitrogen (N
) and NV. In such material, the achievable concentration of NV
([NV
]) is found to be influenced by the as-grown properties. At the 10–20 ppm level for [N
], the production of CVD-grown material with strain levels sufficient not to limit achievable device sensitivity is demonstrated and a favourable product of [NV
] and
is obtained. Additionally, reproducible properties over a batch of 23 samples from a single synthesis run are achieved, which appears promising for the scalability efforts underway in this area of research.
The following article is
Open access
Low-loss
-tantalum coplanar waveguide resonators on silicon wafers: fabrication, characterization and surface modification
D P Lozano
et al
2024
Mater. Quantum. Technol.
025801
View article
, Low-loss α-tantalum coplanar waveguide resonators on silicon wafers: fabrication, characterization and surface modification
PDF
, Low-loss α-tantalum coplanar waveguide resonators on silicon wafers: fabrication, characterization and surface modification
The performance of state-of-the-art superconducting quantum devices is currently limited by microwave dielectric loss at different interfaces.
-tantalum is a superconductor that has proven effective in reducing dielectric loss and improving device performance due to its thin low-loss oxide. Here, we demonstrate the fabrication of high-quality factor
-tantalum coplanar-waveguide resonators directly on pristine 300 mm silicon wafers over a variety of metal deposition conditions and perform a comprehensive material and electrical characterization study. Additionally, we apply a surface treatment based on hydrofluoric acid that allows us to modify different resonators surfaces, leading to a reduction in two-level system loss in the devices by a factor of three. This loss reduction can be entirely attributed to the removal of surface oxides. Our study indicates that large scale manufacturing of low-loss superconducting circuits should indeed be feasible and suggests a viable avenue to materials-driven advancements in superconducting circuit performance.
The following article is
Open access
Recent advances in hole-spin qubits
Yinan Fang
et al
2023
Mater. Quantum. Technol.
012003
View article
, Recent advances in hole-spin qubits
PDF
, Recent advances in hole-spin qubits
In recent years, hole-spin qubits based on semiconductor quantum dots have advanced at a rapid pace. We first review the main potential advantages of these hole-spin qubits with respect to their electron-spin counterparts and give a general theoretical framework describing them. The basic features of spin–orbit coupling and hyperfine interaction in the valence band are discussed, together with consequences on coherence and spin manipulation. In the second part of the article, we provide a survey of experimental realizations, which spans a relatively broad spectrum of devices based on GaAs, Si and Si/Ge heterostructures. We conclude with a brief outlook.
The following article is
Open access
Spectroscopy and coherent control of two-level system defect ensembles using a broadband 3D waveguide
Qianxu Wang
et al
2025
Mater. Quantum. Technol.
045201
View article
, Spectroscopy and coherent control of two-level system defect ensembles using a broadband 3D waveguide
PDF
, Spectroscopy and coherent control of two-level system defect ensembles using a broadband 3D waveguide
Defects in solid-state materials play a central role in determining coherence, stability, and performance in quantum technologies. Although narrowband techniques can probe specific resonances with high precision, a broadband spectroscopic approach captures the full spectrum of defect properties and dynamics. Two-level system (TLS) defects in amorphous dielectrics are a particularly important example because they are major sources of decoherence and energy loss in superconducting quantum devices. However, accessing and characterizing their collective dynamics remains far more challenging than probing individual TLS defects. Building on our previously developed Broadband Cryogenic Transient Dielectric Spectroscopy (BCTDS) technique, we study the coherent control and time-resolved dynamics of TLS defect ensembles over a wide frequency range of 3–5 GHz without requiring full device fabrication. Unlike conventional approaches limited to narrow spectral windows and fully fabricated devices, BCTDS enables modular, device-independent measurements that reveal quantum interference effects, memory-dependent dynamics, and dressed-state evolution within the TLS defect bath. The spectral response reveals distinct V-shaped structures corresponding to the bare eigenmode frequencies. Using these features, we extract a TLS defect spectral density of 84 GHz
−1
for a silicon sample, across a 4.1–4.6 GHz span. Furthermore, we systematically investigate amplitude- and phase-controlled interference fringes for multiple temperatures and inter-pulse delays, providing direct evidence of coherent dynamics and control. A driven minimal spin model with dipole–dipole interactions that qualitatively capture the observed behavior is presented. Our results establish BCTDS as a versatile platform for broadband defect spectroscopy, offering new capabilities for diagnosing and mitigating sources of decoherence, engineering many-body dynamics, and exploring non-equilibrium phenomena in disordered quantum systems.
The following article is
Open access
XPS analysis of molecular contamination and sp
amorphous carbon on oxidized (100) diamond
Ricardo Vidrio
et al
2024
Mater. Quantum. Technol.
025201
View article
, XPS analysis of molecular contamination and sp2 amorphous carbon on oxidized (100) diamond
PDF
, XPS analysis of molecular contamination and sp2 amorphous carbon on oxidized (100) diamond
The efficacy of oxygen (O) surface terminations on diamond is an important factor for the performance and stability for diamond-based quantum sensors and electronics. Given the wide breadth of O-termination techniques, it can be difficult to discern which method would yield the highest and most consistent O coverage. Furthermore, the interpretation of surface characterization techniques is complicated by surface morphology and purity, which if not accounted for will yield inconsistent determination of the oxygen coverage. We present a comprehensive approach to consistently prepare and analyze oxygen termination of surfaces on (100) single-crystalline diamond. We report on x-ray photoelectron spectroscopy (XPS) characterization of diamond surfaces treated with six oxidation methods that include various wet chemical oxidation techniques, photochemical oxidation with UV illumination, and steam oxidation using atomic layer deposition (ALD). Our analysis entails a rigorous XPS peak-fitting procedure for measuring the functionalization of O-terminated diamond. The findings herein have provided molecular-level insights on oxidized surfaces in (100) diamond, including the demonstration of clear correlation between the measured oxygen atomic percentage and the presence of molecular contaminants containing nitrogen, silicon, and sulfur. We also provide a comparison of the sp
carbon content with the O1s atomic percentage and discern a correlation with the diamond samples treated with dry oxidation which eventually tapers off at a max O1s atomic percentage value of 7.09 ± 0.40%. Given these results, we conclude that the dry oxidation methods yield some of the highest oxygen amounts, with the ALD water vapor technique proving to be the cleanest technique out of all the oxidation methods explored in this work.
The following article is
Open access
Theory of single-photon emission from neutral and charged excitons in a polarization-selective cavity
Luca Vannucci and Niels Gregersen 2026
Mater. Quantum. Technol.
025001
View article
, Theory of single-photon emission from neutral and charged excitons in a polarization-selective cavity
PDF
, Theory of single-photon emission from neutral and charged excitons in a polarization-selective cavity
Single-photon sources based on neutral or charged excitons in a semiconductor quantum dot are attractive resources for photonic quantum computers and simulators. To obtain indistinguishable photons, the source is pumped on resonance with polarized laser pulses, and the output is collected in orthogonal polarization. However, for sources featuring vertical emission of light, 50% of the emitted photons are unavoidably lost in this way. Here, we theoretically study the quantum dynamics of an exciton embedded in an asymmetric vertical cavity that favors emission in a specific polarization. We identify the configuration for optimal state initialization and demonstrate a path toward near-unity polarized efficiency. We also derive simple analytical formulas for the photon output in each polarization as a function of the Purcell-enhanced emission rates, which shed light on the physical mechanism behind our results.
The following article is
Open access
In-vacuum surface flashover of SiN, AlN, and etched SiO
thin films at micrometre scales
Vijay Kumar
et al
2026
Mater. Quantum. Technol.
025501
View article
, In-vacuum surface flashover of SiN, AlN, and etched SiO2 thin films at micrometre scales
PDF
, In-vacuum surface flashover of SiN, AlN, and etched SiO2 thin films at micrometre scales
We investigate the surface flashover voltage threshold for SiO
, SiN, and AlN thin films over micrometre scale lengths. Furthermore, we test the effects of different etching chemistries on SiO
layers. We find that there is little significant difference between untreated SiO
samples and those that have been etched with hydrogen fluoride or Transene AlPad Etch 639. SiN and AlN samples performed significantly better than all SiO
samples giving a 45% increase in surface flashover voltage at a distance of 5
m with the difference increasing with electrode spacing.
The following article is
Open access
Charge state entropy and heat capacity of quantised states in a dopant atom quantum dot single-electron transistor
Jun Hwan Kim
et al
2026
Mater. Quantum. Technol.
016203
View article
, Charge state entropy and heat capacity of quantised states in a dopant atom quantum dot single-electron transistor
PDF
, Charge state entropy and heat capacity of quantised states in a dopant atom quantum dot single-electron transistor
The dependence of the entropy and heat capacity on applied drain and source bias and temperature in a few-nanometre-scale dopant atom quantum dot (QD) single-electron transistor (SET) has been investigated theoretically. In this system, the quantisation energy is comparable to the Coulomb charging energy. To make this study relevant, we choose energy scales matching experimental work on dopant atom QD SETs capable of room-temperature operation. The entropy of both a single QD, and double QDs, is investigated, where the latter provides additional information for a simple multiple QD system. Energy state diagrams are used to explain resonant tunnelling features in the Coulomb diamond plot and the Gibbs entropy
. For well-defined states within Coulomb diamonds, if spin is neglected,
S →
0 at low temperature. In contrast, at finite drain bias, electron transport via higher energy quantised states increases their occupation probability, significantly perturbing
. Within regions of constant average current, the entropy reaches a maximum
, for
‘effective’ states. The single-electron heat capacity is extracted, using
vs. temperature plots. A Schottky anomalous heat capacity-like peak occurs, linking single-particle dynamics to macroscopic, many-particle behaviour.
The following article is
Open access
The properties of the nitrogen-vacancy center in milled chemical vapor deposition nanodiamonds
Alessandro Mameli
et al
2026
Mater. Quantum. Technol.
015202
View article
, The properties of the nitrogen-vacancy center in milled chemical vapor deposition nanodiamonds
PDF
, The properties of the nitrogen-vacancy center in milled chemical vapor deposition nanodiamonds
Fluorescent nanodiamonds (FNDs) containing negatively charged nitrogen-vacancy (NV
) centers are vital for many emerging quantum sensing applications from magnetometry to intracellular sensing in biology. However, developing a scalable fabrication method for FNDs hosting color centers with consistent bulk-like photoluminescence (PL) and spin coherence properties remains a highly desired but unrealized goal. Here, we investigate optimized ball milling of single-crystal diamonds produced via chemical vapor deposition (CVD) and containing 2 ppm of substitutional nitrogen and 0.3 ppm of NV
to achieve this goal. The NV charge state, PL lifetime, and spin properties of bulk CVD diamond samples are directly compared to milled CVD FNDs and commercial high-pressure high-temperature (HPHT) FNDs. We find that on average, the relative contribution of the NV
charge state to the total NV PL is lower and the NV PL lifetime is longer in CVD FNDs compared to HPHT FNDs, both likely due to the lower N
concentration in CVD FNDs. The CVD bulk and CVD FNDs on average show similar average
spin relaxation times of 3.2 ± 0.7 ms and 4.7 ± 1.6 ms, respectively, compared to 0.17 ± 0.01 ms for commercial HPHT FNDs. Our results demonstrate that ball milling of CVD diamonds enables the large-scale fabrication of NV ensembles in FNDs with bulk-like
spin relaxation properties.
The following article is
Open access
Impact of irradiation conditions on the magnetic field sensitivity of spin defects in hBN nano flakes
Saksham Mahajan
et al
2026
Mater. Quantum. Technol.
016202
View article
, Impact of irradiation conditions on the magnetic field sensitivity of spin defects in hBN nano flakes
PDF
, Impact of irradiation conditions on the magnetic field sensitivity of spin defects in hBN nano flakes
We study
centres generated by 25 keV helium focused ion beam (FIB) irradiation in thin (∼70 nm) hexagonal boron nitride (hBN) nanoflakes, to investigate the effect of implantation conditions on the key parameters that influence the magnetic field sensitivity of
quantum sensors. Using a combination of photoluminescence, optically detected magnetic resonance, and Raman spectroscopy we examine the competing factors of maximising signal intensity through larger
concentration against the degradation in spin coherence and lattice quality at high ion fluences. Both the
spin properties and hBN lattice parameters are largely preserved up to an ion fluence of 10
14
ions cm
−2
, and beyond this significant degradation occurs in both. Our measurements give an inferred AC magnetic field sensitivity of
at the optimal implantation dose. Using the patterned implantation enabled by the FIB, the
centres and the associated lattice damage are well localised to the implanted regions. This work demonstrates how careful selection of fabrication parameters optimises the properties of
centres in hBN, supporting their application as quantum sensors based in 2D materials.
The following article is
Open access
Next-generation tunnel FETs: exploring material perspectives and areal tunneling configurations
C R Allemang
et al
2025
Mater. Quantum. Technol.
042002
View article
, Next-generation tunnel FETs: exploring material perspectives and areal tunneling configurations
PDF
, Next-generation tunnel FETs: exploring material perspectives and areal tunneling configurations
The end of Dennard scaling, which facilitated proportional increases in computing power without added energy costs until the mid-2000s, has underscored the urgent need for innovative semiconductor devices that can enhance energy efficiency. Tunnel field-effect transistors (TFETs) have emerged as promising candidates to surpass the energy efficiency of conventional metal oxide semiconductor field-effect transistors (MOSFETs). Unlike MOSFETs, which rely on thermionic emission to overcome the source-channel potential barrier, TFETs operate through quantum tunneling, potentially enabling sub-60 mV dec
−1
subthreshold swing (SS) for low-voltage operation. However, lateral TFETs have faced challenges in achieving adequate on-state current (
ON
) and a broad SS operation window, limiting their practical utility. This review article advocates for areal TFETs, which utilize face-to-face tunnel junctions that ideally offer step-function current turn-on characteristics and allow
ON
to scale with device area rather than width. We highlight recent advancements in integrating 2D materials into tunneling structures, which could facilitate efficient band-to-band tunneling through atomically thin layers, while addressing challenges of gate field screening. We then discuss the nearer-term prospects of epitaxial areal TFETs comprising III–V compound semiconductors and group-IV semiconductors based on recent experimental progress. The review examines both quantum mechanical and semiclassical modeling approaches for TFETs, including techniques to reduce the computational complexity. The article delves into ongoing challenges in material synthesis, interface engineering, device fabrication, and integration pathways, concluding with recommendations for future research directions to overcome the fundamental power density limitations of conventional transistor technology.
The following article is
Open access
Multi-emitter solid state quantum optics
Joel Q Grim
et al
2025
Mater. Quantum. Technol.
042001
View article
, Multi-emitter solid state quantum optics
PDF
, Multi-emitter solid state quantum optics
Photonic quantum science—which harnesses light-matter interactions down to the single photon level—provides advanced light sources for quantum sensing, communication, and computing. Integrating solid-state light sources on a photonic chip provides a means of creating scalable on-chip quantum networks with sophisticated optoelectronic circuitry. Extending beyond single emitters to multi-emitter systems is a frontier that offers substantial opportunities for fundamental scientific advances as well as applications that require multi-emitter quantum states. A key challenge in this endeavor is the spectral inhomogeneity of solid-state emitters, which results in non-identical emitters that cannot be interfaced with one another. This review describes recent advances in tailoring the emission properties of individual emitters and the multi-emitter demonstrations that are enabled by this control for a variety of prominent materials, as well as prospects for further development.
The following article is
Open access
A review of site-controlled compound semiconductor quantum dots for single photon emitters
Yaonan Hou 2025
Mater. Quantum. Technol.
032001
View article
, A review of site-controlled compound semiconductor quantum dots for single photon emitters
PDF
, A review of site-controlled compound semiconductor quantum dots for single photon emitters
Single photon emitters (SPEs) serve as the fundamental building blocks of photonic networks for applications in quantum information science and technology. This review paper focuses specifically on the rapidly growing area of site-controlled and deterministically fabricated compound semiconductor quantum dots (QDs), which holds great potential for scalability given their high quantum efficiency, flexible coherence tunability and compatibility with silicon photonics. In this paper, the state-of-the-art growth and fabrication approaches, integration with photonic structures have been reviewed. Meanwhile, the emission properties from QD-based SPEs, including brightness, purity and coherence tunability, have been discussed. This review also provides an outlook of future developments of site-controlled QDs, offering insights into the progress toward scalable quantum photonic systems.
The following article is
Open access
A review of design concerns in superconducting quantum circuits
Eli M Levenson-Falk and Sadman Ahmed Shanto 2025
Mater. Quantum. Technol.
022003
View article
, A review of design concerns in superconducting quantum circuits
PDF
, A review of design concerns in superconducting quantum circuits
In this short review we describe the process of designing a superconducting circuit device for quantum information applications. We discuss the factors that must be considered to implement a desired effective Hamiltonian on a device. We describe the translation between a device’s physical layout, the circuit graph, and the effective Hamiltonian. We go over the process of electromagnetic simulation of a device layout to predict its behavior. We also discuss concerns such as connectivity, crosstalk suppression, and radiation shielding, and how they affect both on-chip design and enclosure structures. This paper provides an overview of the challenges in superconducting quantum circuit design and acts as a starter document for researchers working on any of these challenges.
The following article is
Open access
Buried-stressor technology for the epitaxial growth and device integration of site-controlled quantum dots
Kartik Gaur
et al
2025
Mater. Quantum. Technol.
022002
View article
, Buried-stressor technology for the epitaxial growth and device integration of site-controlled quantum dots
PDF
, Buried-stressor technology for the epitaxial growth and device integration of site-controlled quantum dots
Semiconductor quantum dots (QDs) are high-quality nanocrystals that provide three-dimensional carrier confinement on the scale of the de Broglie wavelength. This makes them ideal candidates as light emitters, especially in the emerging field of photonic quantum technologies, where they can act as quantum light sources. However, their self-assembled epitaxial growth leads to randomness in position and emission wavelength, which hinders their scalable integration into photonic quantum devices. This review summarizes and highlights advances in the site-controlled growth of high-quality epitaxial QDs, with a particular focus on the buried stressor concept. Compared to other QD positioning techniques based for instance on nanohole arrays, nanowire arrays, and arrays of inverted pyramids as dot nucleation centers, the buried stressor growth method is distinguished by its ability to achieve not only spatial accuracy and precision, but also control of the local QD density in combination in an industry-compatible process flow. Therefore, the buried stressor growth technique is highly suitable for the development of both QD-based quantum light sources and microlasers. The buried stressor site-controlled QD growth technique involves the sub-surface embedding of a nano-engineered stressor material, which generates localized strain fields at the growth surface that control the nucleation of QDs. We provide an in-depth review of the underlying mechanisms and technological implementations, and discuss the differences and comparative advantages of the buried stressor method over other techniques for site-controlled growth of QDs. We also address persistent challenges, such as scalability and integration with existing semiconductor technologies, and outline potential future research directions.
The following article is
Open access
Reproducibility and variability in commercial SiC MOSFETs at deep-cryogenictemperatures
Powell et al
View accepted manuscript
, Reproducibility and variability in commercial SiC MOSFETs at deep-cryogenictemperatures
PDF
, Reproducibility and variability in commercial SiC MOSFETs at deep-cryogenictemperatures
Silicon carbide is a wide-bandgap semiconductor with an emerging CMOS technology platform and it is widely deployed in high power and harsh environment electronics. This material is also attracting interest for quantum technologies through its crystal defects, which can act as spin-based qubits or single-photon sources. In this work, we assess the cryogenic performance of commercial power MOSFETs to evaluate their suitability for CMOS-compatible quantum electronics. We per- form a statistical study of threshold voltage and subthreshold swing from 300 K down to 650 mK, focusing on reproducibility and variability. Our results show significant performance degradation at low temperatures, including large gate hysteresis, threshold voltage shifts, and subthreshold swing deterioration. These effects suggest instability in electrostatic control, likely due to carrier freeze- out and high interface trap density, which may pose challenges for the reliable use of this transistor technology towards the realisation of quantum devices or cryo-CMOS electronics.
The following article is
Open access
Recent advances in hole-spin qubits
Yinan Fang
et al
2023
Mater. Quantum. Technol.
012003
View article
, Recent advances in hole-spin qubits
PDF
, Recent advances in hole-spin qubits
In recent years, hole-spin qubits based on semiconductor quantum dots have advanced at a rapid pace. We first review the main potential advantages of these hole-spin qubits with respect to their electron-spin counterparts and give a general theoretical framework describing them. The basic features of spin–orbit coupling and hyperfine interaction in the valence band are discussed, together with consequences on coherence and spin manipulation. In the second part of the article, we provide a survey of experimental realizations, which spans a relatively broad spectrum of devices based on GaAs, Si and Si/Ge heterostructures. We conclude with a brief outlook.
The following article is
Open access
Spin-active defects in hexagonal boron nitride
Wei Liu
et al
2022
Mater. Quantum. Technol.
032002
View article
, Spin-active defects in hexagonal boron nitride
PDF
, Spin-active defects in hexagonal boron nitride
Quantum technology grown out of quantum information theory, including quantum communication, quantum computation and quantum sensing, not only provides powerful research tools for numerous fields, but also is expected to go to civilian use in the future. Solid-state spin-active defects are one of promising platforms for quantum technology, and the host materials include three-dimensional diamond and silicon carbide, and the emerging two-dimensional hexagonal boron nitride (hBN) and transition-metal dichalcogenides. In this review, we will focus on the spin defects in hBN, and summarize theoretical and experimental progresses made in understanding properties of these spin defects. In particular, the combination of theoretical prediction and experimental verification is highlighted. We also discuss the future advantages and challenges of solid-state spins in hBN on the path towards quantum information applications.
The following article is
Open access
2023 roadmap for materials for quantum technologies
Christoph Becher
et al
2023
Mater. Quantum. Technol.
012501
View article
, 2023 roadmap for materials for quantum technologies
PDF
, 2023 roadmap for materials for quantum technologies
Quantum technologies are poised to move the foundational principles of quantum physics to the forefront of applications. This roadmap identifies some of the key challenges and provides insights on material innovations underlying a range of exciting quantum technology frontiers. Over the past decades, hardware platforms enabling different quantum technologies have reached varying levels of maturity. This has allowed for first proof-of-principle demonstrations of quantum supremacy, for example quantum computers surpassing their classical counterparts, quantum communication with reliable security guaranteed by laws of quantum mechanics, and quantum sensors uniting the advantages of high sensitivity, high spatial resolution, and small footprints. In all cases, however, advancing these technologies to the next level of applications in relevant environments requires further development and innovations in the underlying materials. From a wealth of hardware platforms, we select representative and promising material systems in currently investigated quantum technologies. These include both the inherent quantum bit systems and materials playing supportive or enabling roles, and cover trapped ions, neutral atom arrays, rare earth ion systems, donors in silicon, color centers and defects in wide-band gap materials, two-dimensional materials and superconducting materials for single-photon detectors. Advancing these materials frontiers will require innovations from a diverse community of scientific expertise, and hence this roadmap will be of interest to a broad spectrum of disciplines.
The following article is
Open access
A universal fully reconfigurable 12-mode quantum photonic processor
Caterina Taballione
et al
2021
Mater. Quantum. Technol.
035002
View article
, A universal fully reconfigurable 12-mode quantum photonic processor
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, A universal fully reconfigurable 12-mode quantum photonic processor
Photonic processors are pivotal for both quantum and classical information processing tasks using light. In particular, linear optical quantum information processing requires both large-scale and low-loss programmable photonic processors. In this paper, we report the demonstration of the largest universal quantum photonic processor to date: a low-loss 12-mode fully tunable linear interferometer with all-to-all mode coupling based on stoichiometric silicon nitride waveguides.
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Open access
Silicon carbide single-photon sources: challenges and prospects
Stefania Castelletto 2021
Mater. Quantum. Technol.
023001
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, Silicon carbide single-photon sources: challenges and prospects
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, Silicon carbide single-photon sources: challenges and prospects
The search for an ideal single-photon source (SPS) with superior emission properties is still at the core of many research efforts in optical quantum technologies and the criteria identifying a perfect SPS are now well outlined in various roadmaps established to develop future quantum communication networks. While many efforts have been placed into optimizing quantum dots in hybrid nanophotonic structures, these sources are limited by low-temperature operation and characterized by not yet facile and scalable engineering processes. Alternative material platforms have emerged to address room temperature operation and more achievable scalability and control. One of these platforms is silicon carbide (SiC). In this perspective, we first provide a very broad timelined introduction on last 30 years’ efforts developing SPSs, and then we provide a general outline of recent improvements in uncovering and evolving room-temperature SPSs in SiC viewed in a broader context. We will focus on some specific color centers or intra-bandgap defects and discuss challenges in their further expected development into scalable and robust integrated photonic platforms for nonlinear integrated photonics and spin–photon entanglement generation and distribution. A general comparison with other emerging platforms for SPS is also provided to identify comparative achievements, prospects, and challenges.
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Open access
Quantum materials engineering by structured cavity vacuum fluctuations
Hannes Hübener
et al
2024
Mater. Quantum. Technol.
023002
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, Quantum materials engineering by structured cavity vacuum fluctuations
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, Quantum materials engineering by structured cavity vacuum fluctuations
A paradigm shift in the research of optical cavities is taking place, focusing on the properties of materials inside cavities. The possibility to affect changes of material groundstates with or without actual photon population inside cavities is an avenue that promises a novel view of materials science and provides a new knob to control quantum phenomena in materials. Here, we present three theoretical scenarios where such groundstate quantum phase transitions are predicted by the coupling of the matter to mere vacuum fluctuations of the cavity, as a realizations of cavity materials engineering in the dark.
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Open access
Quantum dot technology for quantum repeaters: from entangled photon generation toward the integration with quantum memories
Julia Neuwirth
et al
2021
Mater. Quantum. Technol.
043001
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, Quantum dot technology for quantum repeaters: from entangled photon generation toward the integration with quantum memories
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, Quantum dot technology for quantum repeaters: from entangled photon generation toward the integration with quantum memories
The realization of a functional quantum repeater is one of the major research goals in long-distance quantum communication. Among the different approaches that are being followed, the one relying on quantum memories interfaced with deterministic quantum emitters is considered as one of the most promising solutions. In this work, we focus on the hardware to implement memory-based quantum-repeater schemes that rely on semiconductor quantum dots (QDs) for the generation of polarization entangled photons. Going through the most relevant figures of merit related to efficiency of the photon source, we select significant developments in fabrication, processing and tuning techniques aimed at combining high degree of entanglement with on-demand pair generation, with a special focus on the progress achieved in the representative case of the GaAs system. We proceed to offer a perspective on integration with quantum memories, both highlighting preliminary works on natural–artificial atomic interfaces and commenting a wide choice of currently available and potentially viable memory solutions in terms of wavelength, bandwidth and noise-requirements. To complete the overview, we also present recent implementations of entanglement-based quantum communication protocols with QDs and highlight the next challenges ahead for the implementation of practical quantum networks.
The following article is
Open access
Characterisation of CVD diamond with high concentrations of nitrogen for magnetic-field sensing applications
Andrew M Edmonds
et al
2021
Mater. Quantum. Technol.
025001
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, Characterisation of CVD diamond with high concentrations of nitrogen for magnetic-field sensing applications
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, Characterisation of CVD diamond with high concentrations of nitrogen for magnetic-field sensing applications
Ensembles of nitrogen-vacancy (NV) centres in diamond are a leading platform for practical quantum sensors. Reproducible and scalable fabrication of NV-ensembles with desired properties is crucial, as is an understanding of how those properties influence performance. This work addresses these issues by characterising nitrogen-doped diamond produced by the chemical vapour deposition (CVD) method across a range of synthesis conditions. This is shown to produce material with widely differing absorption characteristics, which is linked to the level of defects other than substitutional nitrogen (N
) and NV. In such material, the achievable concentration of NV
([NV
]) is found to be influenced by the as-grown properties. At the 10–20 ppm level for [N
], the production of CVD-grown material with strain levels sufficient not to limit achievable device sensitivity is demonstrated and a favourable product of [NV
] and
is obtained. Additionally, reproducible properties over a batch of 23 samples from a single synthesis run are achieved, which appears promising for the scalability efforts underway in this area of research.
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Open access
Low percolation density and charge noise with holes in germanium
Mario Lodari
et al
2021
Mater. Quantum. Technol.
011002
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, Low percolation density and charge noise with holes in germanium
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, Low percolation density and charge noise with holes in germanium
We engineer planar Ge/SiGe heterostructures for low disorder and quiet hole quantum dot operation by positioning the strained Ge channel 55 nm below the semiconductor/dielectric interface. In heterostructure field effect transistors, we measure a percolation density for two-dimensional hole transport of 2.1 × 10
10
cm
−2
, indicative of a very low disorder potential landscape experienced by holes in the buried Ge channel. These Ge heterostructures support quiet operation of hole quantum dots and we measure an average charge noise level of
at 1 Hz, with the lowest level below our detection limit
. These results establish planar Ge as a promising platform for scaled two-dimensional spin qubit arrays.
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Open access
Probing coherence properties of shallow implanted NV ensembles under different oxygen terminations
Jens Fuhrmann
et al
2024
Mater. Quantum. Technol.
041001
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, Probing coherence properties of shallow implanted NV ensembles under different oxygen terminations
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, Probing coherence properties of shallow implanted NV ensembles under different oxygen terminations
Nitrogen vacancy (NV) color centers in diamond have shown great potential for various applications in quantum technology due to their long coherence times, high sensitivity to magnetic fields and atomic scale resolution. However, one major challenge in utilizing near surface NV centers is the decoherence caused by spins and charges fluctuating on the surface, which affects the spin properties of the sensors. To reduce the induced noise, various oxygen surface treatments such as low power oxygen plasma treatment and annealing under oxygen atmosphere have been explored to terminate the diamond surface and reduce its impact on NV coherence. We showed that the NV center’s coherence time can be enhanced up to a factor of 3 over a large spectral range of noise. Double electron–electron resonance measurements revealed an extra source of decoherence, scaling similarly as the P1 spin bath. The improvement in coherence times is accompanied with an increase in measured ketone/ether content and reduction of sp
signal in x-ray photoelectron spectroscopy measurements. Finally we compared the performance of different NV ensembles and surface treatments for sensing external proton spins. The oxygen annealing is an effective procedure of enhancing the spin coherence times and reducing broad band spin noise experienced by shallow implanted ensemble NV centers in diamond.
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2020-present
Materials for Quantum Technology
doi: 10.1088/2633-4356
Online ISSN: 2633-4356