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Guide to Quantum Machine Learning

Navdeep Singh Gill | 26 May 2023

Quantum Machine Learning

What is Quantum ML? 

Quantum machine learning (Quantum ML) is a field of study that combines quantum computing principles with machine learning techniques. It aims to improve the performance of machine learning algorithms by utilizing the unique properties of quantum systems, such as superposition and entanglement. Two examples of quantum machine learning are using quantum computers to perform optimization tasks difficult for classical computers or using quantum algorithms to analyze large data sets more efficiently. However, it is still an active research area, with many proposed approaches still in the theoretical stage.    

What is Quantum Data? 

Quantum data is any data source that occurs in a natural or artificial quantum system. This could be data generated by a quantum computer, such as the samples gathered from the Sycamore processor for Google's demonstration of quantum supremacy. Quantum data exhibit superposition and entanglement, resulting in joint probability distributions that could require an exponential amount of classical computational resources to represent or store. The quantum supremacy experiment demonstrated that it is possible to sample from a highly complex joint probability distribution of 253 Hilbert space. 

NISQ processors generate noisy quantum data that is typically entangled just before the measurement. Models can be created using heuristic machine learning techniques that maximize the extraction of useful classical information from noisy entangled data. The TensorFlow Quantum (TFQ) library provides primitives for developing models that disentangle and generalize correlations in quantum data, allowing for improving existing quantum algorithms and discovering new quantum algorithms. 

 Benefits of Quantum Machine Learning 

Quantum machine learning (QML) combines the power of quantum computing with machine learning techniques to solve problems that would be infeasible or impractical to solve using traditional methods. Some of the potential advantages of QML include: 

  • Speedup: For certain tasks, such as large-scale data classification and feature selection, quantum algorithms, such as the quantum version of support vector machines, can provide exponential speedups over classical algorithms. 
  • Improved optimization: Quantum computing can be used to find global optima more efficiently than classical methods for multidimensional, non-convex cost functions, which can be helpful for model training and tuning hyperparameters. 
  • Enhanced representation: Quantum states can provide a richer set of features for representing data than classical states, leading to improved performance for tasks such as image and speech recognition. 
  • Increased security: Quantum-based methods can enhance machine learning security against adversarial attacks, including transmitting quantum keys. 

More benefits are  : 

  • Improvements in run-time: obtaining faster results. 
  • Learning capacity improvements: increase of the capacity of associative or content-addressable memories. 
  • Learning efficiency improvements: less training information or simpler models needed to produce the same results or more complex relations can be learned from the same data. 

Key differences between Classical and Quantum Machine Learning algorithms 

Classical machine learning algorithms are based on mathematical optimization and probability theory and are used to train models that can make predictions or decisions based on input data. Examples include decision trees, support vector machines, and neural networks. These algorithms work by searching for patterns in the data and using these patterns to make predictions. 

Quantum machine learning algorithms, on the other hand, are based on quantum mechanics and are used to train models that can make predictions or decisions based on quantum states. These algorithms take advantage of the unique properties of quantum mechanics, such as superposition and entanglement, to perform impossible calculations with classical algorithms. Examples of quantum machine learning algorithms include quantum neural networks, quantum support vector machines, and quantum principal component analysis. 

Overall, the main difference between classical and quantum machine learning algorithms is the underlying mathematical framework they are based on and the types of calculations they can perform. While classical algorithms are based on classical physics and are limited by the computational resources available, quantum algorithms are based on quantum physics and can potentially perform certain calculations exponentially faster than classical algorithms. 

Challenges and Limitations of Quantum ML : 

Quantum machine learning (QML) is a relatively new field that combines the power of quantum computing with machine learning capabilities. However, several obstacles and limitations are currently impeding the development and practical application of QML. 

  • Lack of large-scale quantum computers:
The main challenge for QML is the need for large-scale quantum computers. Current quantum computers are in their early stages of development and have a limited number of qubits (quantum bits) that they can handle. As a result, most QML algorithms can only be executed on small-scale quantum computers, limiting their practical applications. 
  • Lack of understanding of quantum algorithms:
QML is based on quantum algorithms, which still need to be discovered. This makes it difficult to design and develop efficient QML algorithms that take full advantage of quantum computing's unique properties. 
Noisy quantum devices:
Quantum devices are extremely sensitive to noise and errors, which can lead to errors in QML algorithm results. The "noise problem" is one of the most significant limitations of quantum computing in general. 
  • Limited availability of quantum software and libraries:

There currently needs to be more quantum software and libraries for QML; implementing QML algorithms is difficult for researchers and practitioners. 

  • Lack of standardization:

QML is still in its early stages, and there currently needs to be more standardization in terms of the algorithms and techniques used. This makes comparing and evaluating different QML approaches difficult. 

Despite these obstacles and limitations, the field of QML remains an active area of research, with numerous ongoing efforts to overcome them. QML is likely to become a more practical and powerful tool for solving complex problems in the future as larger-scale quantum computers are developed and our understanding of quantum algorithms grows.  

Industrial Use-cases of Quantum ML 

Various industries, including finance, healthcare, and energy, can benefit from quantum computing. Some specific use cases of quantum computing in the enterprise include 

  • Drug Discovery:
    Molecular simulations with quantum computing can speed up the discovery of new drugs. 
  • Financial modeling:
    Using quantum computing to solve complex financial models and optimize portfolios is possible. 
  • Supply Chain Optimization: Quantum computing can be used to optimize logistics and transportation in supply chain management. 
  • Cybersecurity: Using quantum computing, new, more secure encryption technologies can be developed and used to break prevalent encryptions. 
  • Energy:
    By optimizing the design and operation of energy systems like power grids and batteries, quantum computing can help reduce environmental impact. 
  • Machine Learning:
    Quantum computing can be used to train and run machine learning models on massive amounts of data. 


 The availability of data profoundly changes the question when assessing the capabilities of quantum computers to aid in machine learning. In our work, we create a practical set of tools for investigating these concerns, which we then use to create a new projected quantum kernel method that has several advantages over prior approaches. We progress towards the largest numerical demonstration of potential learning advantages for quantum embeddings to date, 30 qubits. While a comprehensive computational advantage in a real-world application needs to be observed, this research lays the groundwork for the future. We invite any interested readers to read the paper as well as the accompanying TensorFlow-Quantum tutorials, which make it simple to build on this work.

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