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Frontiers in Quantum Science and Technology

The recently emerged field of quantum technology is aiming to employ quantum coherence and entanglement for realization of next generation sensors, standards, imaging systems, secure communication and computers. Although applications of quantum technologies cover a broad spectrum and their development stage varies from early demonstrations to commercially available devices, many challenges have been identified. The first includes tailoring materials for quantum technologies, which is playing an essential role in technological applications of quantum science. Solid state systems allowing long coherence time are essential for quantum computation and quantum sensing. Ultrapure materials with tailored isotopic content are important for reaching long coherence time of spin qubits (Awschalom et al., 2013). The ability to place single dopants with high precision and form spin qubits at desired location is essential for both quantum computing and quantum sensing applications (McCallum et al., 2012; Smith et al., 2019). The performance of different types of qubits is usually benchmarked in terms of controllability and coherence time. Usually solid-state systems allow fast control, but exhibit fast decoherence owing to complex environment. It is therefore important to search for new types of qubits combining isolation from environment and access via fast coherent control and readout. Novel approaches combining different quantum systems into build hybrid quantum devices for optimal performance is a promising avenue. Examples of such hybrid approaches are spin systems coupled to superconducting qubits (Kubo et al., 2011) and hybrid nuclear–electronic qubits (Morley et al., 2013). Optimal protocols for quantum technologies requires extension of coherence time of qubits beyond the coherence time of the isolated quantum system. The efficient protection toolkit includes dynamical decoupling (Yang et al., 2011) and quantum error correction (Terhal, 2015) based techniques. Although general principles of qubits protection were developed and tested experimentally in different model environments, it is essential to adapt them to realistic environmental noise. In the field of quantum sensing, it is also essential to combine protections against noise with non-reduced sensing performance. Experimental imperfections can be addressed using optimal control tools (Glaser et al., 2015). The development of efficient quantum algorithms is another growing field belonging to quantum software area. On one hand, it is essential to find problems where a quantum computer can outperform classical computers. On the other hand, it is essential to develop an application scenario for a limited number of qubits (Montanaro, 2016). In addition, in order to develop new algorithms, future work must include discoveries of application scenarios of already known algorithms. Application of quantum Fourier transform for sensing is a promising example of such new applications (Vorobyov et al., 2021). Signal processing is another field of quantum software that is becoming essential in applications. Advanced signal analysis protocols, like quantum compressed sensing, can be employed to quantify entanglement in large quantum devices via efficient quantum tomography (Riofrío et al., 2017). Edited and reviewed by: Gui-Lu Long, Tsinghua University, China