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Nanoscale solid-state spin systems in emerging quantum technologies

Periodic Reporting for period 2 - Spin-NANO (Nanoscale solid-state spin systems in emerging quantum technologies)

Reporting period: 2018-01-01 to 2019-12-31

The Spin-NANO project is designed to tackle new challenges in materials, science, and device engineering for implementation of nano-scale condensed matter systems in emerging quantum technologies. The innovative science is directed at tackling developments in quantum computing, quantum communications and networks, and nano-sensing. It is expected that the emerging quantum technologies will bring a plethora of applications from ultra-secure communications and fast computing to new ultra-high precision metrology. The Spin-NANO network provides advanced training for excellent researchers and engineers who upon graduation from the PhD programme will be ready to make significant contribution to this growing technological field and will develop the field of quantum technologies to the level of real-world applications.

The goals of the network are to explore the quantum degrees of freedom (for example the electron spin) accessible in nano-scale structures such as single atom impurity centres in diamond, nano-structures in ubiquitous semiconductors such as silicon and germanium, as well as in atomically thin graphene-like semiconductors transition metal dichalcogenides. The spin can be used as a bit of quantum information, qubit. Such spin qubits receive special attention in this project, as they can be addressed optically and electrically, opening the way for a range of quantum technology applications.

The project pursues the following goals:
1. The technological and scientific goal is to fabricate and explore various nano-scale condensed matter systems suitable for realisation of qubits, and demonstrate first prototypes of functional qubit devices.
2. The educational goal is to provide a wide-ranging multidisciplinary training programme to create a new generation of European researchers who will be capable to develop Quantum Technologies to the level of real-world applications.
"Spin-NANO has achieved significant progress towards its scientific objectives and also in providing training in research and complementary skills to the cohort of 15 Early Stage Researchers (ESRs).

Our scientific programme was divided in four work-packages encompassing research and development effort in: WP1, electrically controlled qubits; WP2, qubits with a photon interface; WP3, exploration of new nano-scale materials potentially suitable for quantum technologies; WP4, experimental hardware for materials with photonic interface.

In WP1, very significant progress has been achieved in the use of silicon-germanium nanostructures (called ‘quantum dots’), where we demonstrated a programmable two-qubit quantum processor in silicon and used it to perform search algorithms.

In WP2, a complementary approach using photons to achieve and detect quantum entanglement between the spin states in the nano-scale impurities in diamond separated by the record 2 meters was applied.

In WP3 significant developments have been achieved in understanding and control of electronic and optical properties of atomically thin semiconducting transition metal dichalcogenides (TMDs). Large effort has been directed to studies of so-called van der Waals heterostructures, artificial structures combining more than one atomically thin material stacked on top of one another and held together by van der Waals interactions. This approach has enabled new high quality structures to be realised and studied using both optical spectroscopy and electron transport methods following a breakthrough in fabrication. We showed that the optical and electronic properties of TMDs improve dramatically when the atomic layer is ‘encapsulated’ in thin high quality hexagonal boron nitride (hBN) nanolayer sheets. This approach is now used as a ‘golden standard’ in this very large field of research. We applied this approach to realise: an ‘atomically thin mirror’ made from a highly reflective monolayer of a TMD MoSe2; one of the first electronic quantum devices using TMDs interfaced with graphene, opening the way to development of qubits based on atomically thin materials. As part of this effort we also developed a new method for optical imaging of the coupling between the two TMD monolayers. Finally, we discovered in experiment that TMDs can be used to deterministically create single photon emitters (key for quantum networks) by straining the monolayers placed on patterned surfaces, for which we have additionally developed theoretical understanding.

In WP4, we addressed an important issue in the photon-based entanglement experiments, namely the efficiency with which the photons can be extracted from the impurities in diamond. To this end we developed a special optical microcavity incorporating diamond membranes, worked to provide a practical technical solution to highly stable optical microcavities, and investigated how the quality of the dielectric mirrors in such microcavities can be improved.

In addition to excellent research training, ESRs received training in complementary skills through network-wide training provided by Think Ahead (led by Sandrine Soubes, Spin-NANO’s Researcher Development Manager). The first workshop that took place (Delft June 2017) was dedicated to the topic of “Becoming excellent and impactful communicators”, the second workshop (Sheffield Jan 2018) addressed the topic of “Collaborations across borders” and addressed collaboration, outreach and public engagement. The final workshop (Cambridge Jan 2019) - ""Researchers of the future"" - considered creativity, innovation, enterprise, industry, entrepreneurship and globalisation. In between the workshops ESRs were given tasks to follow on the training. In particular, they created YouTube videos explaining their research to non-specialists - 8 videos on the Spin-NANO Youtube channel have over 7000 views. ESRs also successfully developed a Spin-NANO blog, covering the scientific topics explained at the non-specialist level: https://spinnanoblog.wordpress.com/.

During the project the network organised 7 meetings - Kick-off meeting Munich Jan 2016 (including Gender Training workshop), Summer School on Quantum information in condensed matter physics (Copenhagen Jul 2016), two Project meetings with industry (Delft Jun 2017 and Cambridge Jan 2019), Mid Term Review Meeting (Sheffield Jan 2018), Spin-based Quantum Information Processing Conference (Konstanz Sep 2018) and a Meeting on Nano physics (Toulouse Mar 2019)."
The consortium published 41 papers co-authored by the ESRs, all proceeding far beyond the state of the art in the respective research fields and including 1 Nature, 6 Nature Communications, 6 Nano Letters, 1 Advanced Materials, 5 PRL, 3 Physical Review X. We have substantially contributed to the following developments in: qubits in SiGe-based devices; realisation of a quantum network based on impurities in diamond; progress in optical manipulation of quantum degrees of freedom in TMD structures; improvement of light-matter coupling in nano-structures placed inside optical microcavities. The Spin-NANO network have trained 15 Early Stage Researchers who will contribute to the development of research topic in Quantum Technologies to the level of real-world applications. EU is investing very significantly in this area, currently mostly at the level of research. However, the scientific findings will need to be turned into applications, the task that will be carried out by researchers trained within Spin-NANO and similar training initiatives.