+The goal of transfer learning is to transfer the model or knowledge
+obtained from a source task to the target task, in order to resolve
+the issues of insufficient training data in the target task. The
+rationality of doing so lies in that usually the source and target
+tasks have inter-correlations, and therefore either the features,
+samples, or models in the source task might provide useful information
+for us to better solve the target task. Transfer learning is a hot
+research topic in recent years, with many problems still waiting to be
+solved in this space.
+
+
+The conventional deep generative model has a potential problem: the
+model tends to generate extreme instances to maximize the
+probabilistic likelihood, which will hurt its performance. Adversarial
+learning utilizes the adversarial behaviors (e.g., generating
+adversarial instances or training an adversarial model) to enhance the
+robustness of the model and improve the quality of the generated
+data. In recent years, one of the most promising unsupervised learning
+technologies, generative adversarial networks (GAN), has already been
+successfully applied to image, speech, and text.
+
+
+Dual learning is a new learning paradigm, the basic idea of which is
+to use the primal-dual structure between machine learning tasks to
+obtain effective feedback/regularization, and guide and strengthen the
+learning process, thus reducing the requirement of large-scale labeled
+data for deep learning. The idea of dual learning has been applied to
+many problems in machine learning, including machine translation,
+image style conversion, question answering and generation, image
+classification and generation, text classification and generation,
+image-to-text, and text-to-image.
+
+
+Distributed computation will speed up machine learning algorithms,
+significantly improve their efficiency, and thus enlarge their
+application. When distributed meets machine learning, more than just
+implementing the machine learning algorithms in parallel is required.
+
+
+Meta learning is an emerging research direction in machine
+learning. Roughly speaking, meta learning concerns learning how to
+learn, and focuses on the understanding and adaptation of the learning
+itself, instead of just completing a specific learning task. That is,
+a meta learner needs to be able to evaluate its own learning methods
+and adjust its own learning methods according to specific learning
+tasks.
+
+
+While there has been much progress in machine learning, there are also challenges.
+
+
+For example, the mainstream machine learning technologies are
+black-box approaches, making us concerned about their potential
+risks. To tackle this challenge, we may want to make machine learning
+more explainable and controllable. As another example, the
+computational complexity of machine learning algorithms is usually
+very high and we may want to invent lightweight algorithms or
+implementations. Furthermore, in many domains such as physics,
+chemistry, biology, and social sciences, people usually seek elegantly
+simple equations (e.g., the Schrödinger equation) to uncover the
+underlying laws behind various phenomena. In the field of machine
+learning, can we reveal simple laws instead of designing more complex
+models for data fitting? Although there are many challenges, we are
+still very optimistic about the future of machine learning. As we look
+forward to the future, here are what we think the research hotspots in
+the next ten years will be.
+
+
+Machine learning, especially deep learning, evolves rapidly. The
+ability gap between machine and human on many complex cognitive tasks
+becomes narrower and narrower. However, we are still in the very early
+stage in terms of explaining why those effective models work and how
+they work.
+
+
+What is missing: the gap between correlation and causation Most
+machine learning techniques, especially the statistical ones, depend
+highly on data correlation to make predictions and analyses. In
+contrast, rational humans tend to reply on clear and trustworthy
+causality relations obtained via logical reasoning on real and clear
+facts. It is one of the core goals of explainable machine learning to
+transition from solving problems by data correlation to solving
+problems by logical reasoning.
+
+
+Quantum machine learning is an emerging interdisciplinary research
+area at the intersection of quantum computing and machine learning.
+
+
+Quantum computers use effects such as quantum coherence and quantum
+entanglement to process information, which is fundamentally different
+from classical computers. Quantum algorithms have surpassed the best
+classical algorithms in several problems (e.g., searching for an
+unsorted database, inverting a sparse matrix), which we call quantum
+acceleration.
+
+
+When quantum computing meets machine learning, it can be a mutually
+beneficial and reinforcing process, as it allows us to take advantage
+of quantum computing to improve the performance of classical machine
+learning algorithms. In addition, we can also use the machine learning
+algorithms (on classic computers) to analyze and improve quantum
+computing systems.
+
+
Quantum machine learning algorithms based on linear algebra
+
+
+Many quantum machine learning algorithms are based on variants of
+quantum algorithms for solving linear equations, which can efficiently
+solve N-variable linear equations with complexity of O(log2 N) under
+certain conditions. The quantum matrix inversion algorithm can
+accelerate many machine learning methods, such as least square linear
+regression, least square version of support vector machine, Gaussian
+process, and more. The training of these algorithms can be simplified
+to solve linear equations. The key bottleneck of this type of quantum
+machine learning algorithms is data input—that is, how to initialize
+the quantum system with the entire data set. Although efficient
+data-input algorithms exist for certain situations, how to efficiently
+input data into a quantum system is as yet unknown for most cases.
+
+
+In quantum reinforcement learning, a quantum agent interacts with the
+classical environment to obtain rewards from the environment, so as to
+adjust and improve its behavioral strategies. In some cases, it
+achieves quantum acceleration by the quantum processing capabilities
+of the agent or the possibility of exploring the environment through
+quantum superposition. Such algorithms have been proposed in
+superconducting circuits and systems of trapped ions.
+
+
+Dedicated quantum information processors, such as quantum annealers
+and programmable photonic circuits, are well suited for building deep
+quantum networks. The simplest deep quantum network is the Boltzmann
+machine. The classical Boltzmann machine consists of bits with tunable
+interactions and is trained by adjusting the interaction of these bits
+so that the distribution of its expression conforms to the statistics
+of the data. To quantize the Boltzmann machine, the neural network can
+simply be represented as a set of interacting quantum spins that
+correspond to an adjustable Ising model. Then, by initializing the
+input neurons in the Boltzmann machine to a fixed state and allowing
+the system to heat up, we can read out the output qubits to get the
+result.
+
+
+Machine learning aims to imitate how humans
+learn. While we have developed successful machine learning algorithms,
+until now we have ignored one important fact: humans are social. Each
+of us is one part of the total society and it is difficult for us to
+live, learn, and improve ourselves, alone and isolated. Therefore, we
+should design machines with social properties. Can we let machines
+evolve by imitating human society so as to achieve more effective,
+intelligent, interpretable “social machine learning”?
+
+
+Early computer scientist Alan Kay said, The best way to predict the
+future is to create it. Therefore, all machine learning
+practitioners, whether scholars or engineers, professors or students,
+need to work together to advance these important research
+topics. Together, we will not just predict the future, but create it.
+
+