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.
Purpose-led Publishing is a coalition of three not-for-profit publishers in the field of physical sciences: AIP Publishing, the American Physical Society and IOP Publishing.
Together, as publishers that will always put purpose above profit, we have defined a set of industry standards that underpin high-quality, ethical scholarly communications.
We are proudly declaring that science is our only shareholder.
ISSN: 2633-4356
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 About the journal section.
Free for readers. All article publication charges are currently paid by IOP Publishing.
Open all abstracts, in this tab
Christoph Becher et al 2023 Mater. Quantum. Technol. 3 012501
Yinan Fang et al 2023 Mater. Quantum. Technol. 3 012003
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.
Wei Liu et al 2022 Mater. Quantum. Technol. 2 032002
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.
Stefania Castelletto 2021 Mater. Quantum. Technol. 1 023001
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.
Søren Engelberth Hansen et al 2024 Mater. Quantum. Technol. 4 016201
The scalability of integrated photonics hinges on low-loss chip-scale components, which are important for classical applications and crucial in the quantum domain. An important component is the power splitter, which is an essential building block for interferometric devices. Here, we use inverse design by topology optimization to devise a generic design framework for developing power splitters in any material platform, although we focus the present work on silicon photonics. We report on the design, fabrication, and characterization of silicon power splitters and explore varying domain sizes and wavelength spans around a center wavelength of 1550 nm. This results in a set of power splitters tailored for ridge, suspended, and embedded silicon waveguides with an emphasis on compact size and wide bandwidths. The resulting designs have a footprint of and exhibit remarkable 0.5 dB bandwidths exceeding 300 nm for the ridge and suspended power splitters and 600 nm for the embedded power splitter. We fabricate the power splitters in suspended silicon circuits and characterize the resulting devices using a cutback method. The experiments confirm the low excess loss, and we measure a 0.5 dB bandwidth of at least 245 nm—limited by the wavelength range of our lasers.
Andrew M Edmonds et al 2021 Mater. Quantum. Technol. 1 025001
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 (NS) 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 [NS], 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.
Caterina Taballione et al 2021 Mater. Quantum. Technol. 1 035002
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.
Sanoj Raj et al 2024 Mater. Quantum. Technol. 4 015404
The transmission of strong laser light in nonlinear optical materials can generate output photons sources that carry quantum entanglement in multiple degrees of freedom, making this process a fundamentally important tool in optical quantum technology. However, the availability of efficient optical crystals for entangled light generation is severely limited in terms of diversity, thus reducing the prospects for the implementation of next-generation protocols in quantum sensing, communication and computing. To overcome this, we developed and implemented a multi-scale first-principles modeling technique for the computational discovery of novel nonlinear optical devices based on metal–organic framework (MOF) materials that can efficiently generate entangled light via spontaneous parametric down-conversion (SPDC). Using collinear degenerate type-I SPDC as a case study, we computationally screen a database of 114 373 synthesized MOF materials to establish correlations between the structure and chemical composition of MOFs with the brightness and coherence properties of entangled photon pairs. We identify a subset of 49 non-centrosymmetric mono-ligand MOF crystals with high chemical and optical stability that produce entangled photon pairs with intrinsic correlation times fs and pair generation rates in the range at 1064 nm. Conditions for optimal type-I phase matching are given for each MOF and relationships between pair brightness, crystal band gap and optical birefringence are discussed. Correlations between the optical properties of crystals and their constituent molecular ligands are also given. Our work paves the way for the computational design of MOF-based devices for optical quantum technology.
Chia-Tse Tai and Jiun-Yun Li 2024 Mater. Quantum. Technol. 4 012001
Silicon has been a core material for digital computing owing to its high mobility, stability oxide interface, mature manufacturing technologies for more than half a century. While Moore's law seems to further advance via various technologies to extend its expiration date, some intractable problems that requires processing times growing exponentially cannot be solved in a reasonable scale of time. Meanwhile, quantum computing is a promising tool to perform calculations much more efficiently than classical computing for certain types of problems. To realize a practical quantum computer, quantum dots on group-IV semiconductor heterostructures are promising due to the long decoherence time, scalability, and compatibility with the Si very-large-scale integrated technology. In this review, we start with the advancement of group-IV undoped heterostructures since 2000 and review carrier transport properties in these undoped heterostructure. We also review the hole effective masses, spin-orbit coupling, and effective g-factors in the Ge-based heterostructures and conclude with a brief summary.
Open all abstracts, in this tab
Dominic Scognamiglio et al 2024 Mater. Quantum. Technol. 4 025402
Quantum communication has been at the forefront of modern research for decades, however it is severely hampered in underwater applications, where the properties of water absorb nearly all useful optical wavelengths and prevent them from propagating more than, in most cases, a few metres. This research reports on-demand quantum light sources, suitable for underwater optical communication. The single photon emitters, which can be engineered using an electron beam, are based on impurities in hexagonal boron nitride. They have a zero phonon line at ∼436 nm, near the minimum value of water absorption and are shown to suffer negligible transmission and purity loss when travelling through water channels. These emitters are also shown to possess exceptional underwater transmission properties compared to emitters at other optical wavelengths and are utilised in a completely secure quantum key distribution experiment with rates of kbits s−1.
J T Patton et al 2024 Mater. Quantum. Technol. 4 025401
Integrated photonics has been a promising platform for analog quantum simulation of condensed matter phenomena in strongly correlated systems. To that end, we explore the implementation of all-photonic quantum simulators in coupled cavity arrays with integrated ensembles of spectrally disordered emitters. Our model is reflective of color center ensembles integrated into photonic crystal cavity arrays. Using the Quantum Master equation and the Effective Hamiltonian approaches, we study energy band formation and wavefunction properties in the open quantum Tavis–Cummings–Hubbard framework. We find conditions for polariton creation and (de)localization under experimentally relevant values of disorder in emitter frequencies, cavity resonance frequencies, and emitter-cavity coupling rates. To quantify these properties, we introduce two metrics, the polaritonic and nodal participation ratios, that characterize the light-matter hybridization and the node delocalization of the wavefunction, respectively. These new metrics combined with the Effective Hamiltonian approach prove to be a powerful toolbox for cavity quantum electrodynamical engineering of solid-state systems.
Sanoj Raj et al 2024 Mater. Quantum. Technol. 4 015404
The transmission of strong laser light in nonlinear optical materials can generate output photons sources that carry quantum entanglement in multiple degrees of freedom, making this process a fundamentally important tool in optical quantum technology. However, the availability of efficient optical crystals for entangled light generation is severely limited in terms of diversity, thus reducing the prospects for the implementation of next-generation protocols in quantum sensing, communication and computing. To overcome this, we developed and implemented a multi-scale first-principles modeling technique for the computational discovery of novel nonlinear optical devices based on metal–organic framework (MOF) materials that can efficiently generate entangled light via spontaneous parametric down-conversion (SPDC). Using collinear degenerate type-I SPDC as a case study, we computationally screen a database of 114 373 synthesized MOF materials to establish correlations between the structure and chemical composition of MOFs with the brightness and coherence properties of entangled photon pairs. We identify a subset of 49 non-centrosymmetric mono-ligand MOF crystals with high chemical and optical stability that produce entangled photon pairs with intrinsic correlation times fs and pair generation rates in the range at 1064 nm. Conditions for optimal type-I phase matching are given for each MOF and relationships between pair brightness, crystal band gap and optical birefringence are discussed. Correlations between the optical properties of crystals and their constituent molecular ligands are also given. Our work paves the way for the computational design of MOF-based devices for optical quantum technology.
G Landry and C Bradac 2024 Mater. Quantum. Technol. 4 015403
Single photon emitters are core building blocks of quantum technologies, with established and emerging applications ranging from quantum computing and communication to metrology and sensing. Regardless of their nature, quantum emitters universally display fluorescence intermittency or photoblinking: interaction with the environment can cause the emitters to undergo quantum jumps between on and off states that correlate with higher and lower photoemission events, respectively. Understanding and quantifying the mechanism and dynamics of photoblinking is important for both fundamental and practical reasons. However, the analysis of blinking time traces is often afflicted by data scarcity. Blinking emitters can photo-bleach and cease to fluoresce over time scales that are too short for their photodynamics to be captured by traditional statistical methods. Here, we demonstrate two approaches based on machine learning that directly address this problem. We present a multi-feature regression algorithm and a genetic algorithm that allow for the extraction of blinking on/off switching rates with ⩾85% accuracy, and with ⩾10× less data and ⩾20× higher precision than traditional methods based on statistical inference. Our algorithms effectively extend the range of surveyable blinking systems and trapping dynamics to those that would otherwise be considered too short-lived to be investigated. They are therefore a powerful tool to help gain a better understanding of the physical mechanism of photoblinking, with practical benefits for applications based on quantum emitters that rely on either mitigating or harnessing the phenomenon.
Lior Shani et al 2024 Mater. Quantum. Technol. 4 015101
Quantum devices based on InSb nanowires (NWs) are a prime candidate system for realizing and exploring topologically-protected quantum states and for electrically-controlled spin-based qubits. The influence of disorder on achieving reliable quantum transport regimes has been studied theoretically, highlighting the importance of optimizing both growth and nanofabrication. In this work, we consider both aspects. We developed InSb NW with thin diameters, as well as a novel gating approach, involving few-layer graphene and atomic layer deposition-grown AlOx. Low-temperature electronic transport measurements of these devices reveal conductance plateaus and Fabry–Pérot interference, evidencing phase-coherent transport in the regime of few quantum modes. The approaches developed in this work could help mitigate the role of material and fabrication-induced disorder in semiconductor-based quantum devices.
Open all abstracts, in this tab
Chia-Tse Tai and Jiun-Yun Li 2024 Mater. Quantum. Technol. 4 012001
Silicon has been a core material for digital computing owing to its high mobility, stability oxide interface, mature manufacturing technologies for more than half a century. While Moore's law seems to further advance via various technologies to extend its expiration date, some intractable problems that requires processing times growing exponentially cannot be solved in a reasonable scale of time. Meanwhile, quantum computing is a promising tool to perform calculations much more efficiently than classical computing for certain types of problems. To realize a practical quantum computer, quantum dots on group-IV semiconductor heterostructures are promising due to the long decoherence time, scalability, and compatibility with the Si very-large-scale integrated technology. In this review, we start with the advancement of group-IV undoped heterostructures since 2000 and review carrier transport properties in these undoped heterostructure. We also review the hole effective masses, spin-orbit coupling, and effective g-factors in the Ge-based heterostructures and conclude with a brief summary.
F Bussolotti et al 2023 Mater. Quantum. Technol. 3 032001
In this review, we present a perspective on the use of angle-resolved photoemission spectroscopy (ARPES) and spin-resolved ARPES (SARPES) for the study of the electronic properties of semiconducting transition metal dichalcogenides (TMDCs), a prime example of two-dimensional (2D) materials for valleytronics applications. In the introductory part, we briefly describe the structural and electronic properties of semiconducting TMDCs and the main valleytronics related physical effects. After a short presentation of theoretical methods utilized in the band structure and spin texture calculation of semiconducting TMDCs, we illustrate the basic principles and methodology of photoemission techniques and then provide a detailed survey on the electronic band structure studies of these materials. In particular, by selecting and comparing seminal results in the field, we highlight the critical role played by the sample preparation strategy on the amount and quality of information that can be extracted in the ARPES investigations of TMDCs. This is followed by a detailed discussion on the impact of interface potential landscape and doping on their electronic properties, considering the importance of their contact with metal electrode and/or dielectric substrate in determining the electrical transport in real devices' architecture. Finally, we summarize key SARPES findings on the spin texture of TMDCs and conclude by pointing out current open issues and potential directions for future photoemission-based studies on these 2D systems.
Yinan Fang et al 2023 Mater. Quantum. Technol. 3 012003
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.
Kavya Ravindran et al 2023 Mater. Quantum. Technol. 3 012002
Topological phenomena at the oxide interfaces attract the scientific community for the fertile ground of exotic physical properties and highly favorable applications in the area of high-density low-energy nonvolatile memory and spintronic devices. Synthesis of atomically controlled ultrathin high-quality films with superior interfaces and their characterization by high resolution experimental set up along with high output theoretical calculations matching with the experimental results make this field possible to explain some of the promising quantum phenomena and exotic phases. In this review, we highlight some of the interesting interface aspects in ferroic thin films and heterostructures including the topological Hall effect in magnetic skyrmions, strain dependent interlayer magnetic interactions, interlayer coupling mediated electron conduction, switching of noncollinear spin texture etc. Finally, a brief overview followed by the relevant aspects and future direction for understanding, improving, and optimizing the topological phenomena for next generation applications are discussed.
Dylan G Stone and Carlo Bradac 2023 Mater. Quantum. Technol. 3 012001
In recent years, machine and quantum learning have gained considerable momentum sustained by growth in computational power and data availability and have shown exceptional aptness for solving recognition- and classification-type problems, as well as problems that require complex, strategic planning. In this work, we discuss and analyze the role machine and quantum learning are playing in the development of diamond-based quantum technologies. This matters as diamond and its optically addressable spin defects are becoming prime hardware candidates for solid state-based applications in quantum information, computing and metrology. Through a selected number of demonstrations, we show that machine and quantum learning are leading to both practical and fundamental improvements in measurement speed and accuracy. This is crucial for quantum applications, especially for those where coherence time and signal-to-noise ratio are scarce resources. We summarize some of the most prominent machine and quantum learning approaches that have been conducive to the presented advances and discuss their potential, as well as their limits, for proposed and future quantum applications.
Open all abstracts, in this tab
Vidrio et al
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 sp2 carbon content with the O(1s) atomic percentage and discern a correlation with the diamond samples treated with dry oxidation which eventually tapers off at a max O(1s) 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.
Huebener et al
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 transition is predicted by the coupling of the matter to mere vacuum fluctuations of the cavity, as a realizations of cavity materials engineering in the dark.
Lozano et al
The performance of state-of-the-art superconducting quantum devices is currently limited by microwave dielectric loss at different interfaces. α-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 α-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 (TLS) 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.
Wahl et al
In order to study the structural formation yield of germanium-vacancy (GeV) centers from implanted Ge in diamond, we have investigated its lattice location by using the β− emission channeling technique from the radioactive isotope 75Ge (t1/2=83 min) produced at the ISOLDE/CERN facility. 75Ge was introduced via recoil implantation following 30 keV ion implantation of the precursor isotope 75Ga (126 s) with fluences around 2×1012 - 5×1013 cm−2. While for room temperature implantation fractions around 20% were observed in split-vacancy configuration and 45% substitutional Ge, following implantation or annealing up to 900°C, the split-vacancy fraction dropped to 6-9% and the substitutional fraction reached 85-96%. GeV complexes thus show a lower structural formation yield than other impurities, with substitutional Ge being the dominant configuration. Moreover, annealing or high-temperature implantation seem to favour the formation of substitutional Ge over GeV. Our results strongly suggest that GeV complexes are thermally unstable, and transformed to substitutional Ge by capture of mobile carbon interstitials, which is likely to contribute to the difficulties in achieving high formation yields of these optically active centers.