Semiconductor Quantum Dots for Integrated Quantum Photonics

Abstract

Quantum mechanics promises to have a strong impact on many aspects of research and technology, improving classical analogues via purely quantum effects. A large variety of tasks are currently under investigation, for example, the implementation of quantum computing, sensing, metrology, and communication. From a general perspective, in a similar way as classical computing benefited by the reduction of the device footprint, enabling the realization of highly complex chips, a range of quantum applications will sensibly improve thanks to the successful realization of on-chip quantum photonics. Conversely to bulky table-top experiments, it would be very advantageous to transfer all required functionalities on the same quantum photonic chip. The key elements for quantum photonic circuits are on-demand nonclassical light sources, a versatile photonic logic, the ability to store quantum information, and highly efficient detectors, directly integrated on-chip. Among several systems capable of the efficient generation of singleand indistinguishable photons, quantum dots are rapidly establishing as one of the most appealing candidates. This paper reviews the recent progress in the on-chip integration of quantum-dot-based nonclassical light sources as well as in the development of the main building blocks, either integrated monolithically or hybridly on a compact and scalable platform. IntroductionFrom the foundation of quantum mechanics in the early 20th century to explain fundamental physical observations, over the development of transistors and lasers in the 1950s and 1960s, the second quantum revolution is now in full swing. The driving force behind this continuing "quantum footrace" are quantum mechanical effects based on superposition and entanglement that can lead to profound changes. Especially in the field of quantum information science, dramatic improvements are expected in terms of increased computational speed and communication security if compared with classical counterparts.Talking about quantum supremacy, two problems-Grover's algorithm for the efficient search in large unsorted databases and Shor's algorithm for the prime factorization of large integers-are frequently mentioned. [1][2][3] Grover's quantum search algorithm can find an element of a search space M in O( √ M) operations compared to the best known classical algorithms approximately requiring O(M) steps. [4] Shor's algorithm can prime factorize large integers with N bits in polynomial speed compared to the exponential scaling of classical algorithms. Currently, several cryptography schemes in electronic communication systems rely on the difficulty of prime factorization as its security method. Consequently, a quantum computer could break the cryptographic keys quickly by calculating or searching exhaustively all key possibilities, which may allow an eavesdropper to intercept the communication channel. [5] However, quantum key distribution schemes can be alternatively used, which are based on the secure exchange of a cryptographic key between remote...

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