Quantum Machine Learning Interviews

A glimpse into the knowledge prerequisites for quantum computing internships, lab positions, or careers

This post is Part 5 of the 5-part Machine Learning Research Interview Handbook series (you can see the rest of the series here).

This section is clearly an outlier compared to the other entries in this series. The math section is obviously a prerequisite for any kind of learning. It’s important to know how ML works outside of just neural networks. There are tons of topics to cover in deep learning. And obviously, you need to know how to build and scale a deep learning system outside of a Jupyter Notebook.

But quantum machine learning? That came out of nowhere! You may be asking “Matt, is this just another click-bait article with both quantum and ML in the title”?

To which I respond NO (well, not anymore at least). Yes, quantum computing is nearing the peak of the hype cycle at the moment, and by extension so is quantum machine learning. It is clearly not ready for widespread real-world practical use yet, but there is still a lot of value in putting together a list of the fundamentals. For one, there are plenty of marketing people raving about quantum computers with little understanding beyond quantum=MAGIC\text{quantum} = \text{MAGIC}. Many genuine research labs and companies in the space need to sift through crowds of professional BS-artists to find people who actually know what they’re talking about. As these organizations standardize their practices, many talented undergrads and grad students (and eventually, even just talented senior engineers who want to switch into a new field) will need to make sure they’re up to speed on all the important topics.

Credit to Randal Munroe of XKCD. Also, if you draw a diagonal line from lower left to upper right, that’s the ICP ‘Miracles’ axis.

With that in mind, I assembled this guide for use by both organizations and individuals. It’s a combination of pieces of information from reading material, papers, as well as questions friends of mine have received while interviewing for places like Strangeworks, Zapata Computing, Coldquanta, QC Ware, IBM, Rigetti Computing D-Wave Systems, Bleximo, 1QBit, Xanadu, Intel, Isara, Google, Microsoft, Atom Computing, ProteinQure. If that last name is any indication, quantum computing and quantum machine learning is being thrown at drug discovery a lot.

If any of this does reach practical usability status, there will likely be a flood of researchers scrambling to incorporate these techniques into their research (and likely long before any of them are intellectually prepared to do something with it). Deep learning progressed slowly as a field for years and decades with incremental progress, but around 2011 to 2012 many of these techniques became fast enough to actually use an the “deep learning revolution” exploded forth. As such, this is a list of important fundamentals and concepts for my own use as well, should I ever need it (Update April 08, 2020: Looks like I might need it sooner rather than later).

If you have any suggestions or feedback, please let me know. This resource will likely expand a lot in the coming months.

A curated list of awesome quantum machine learning algorithms,study materials,libraries and software (by language).


Table of Contents

High-level Overview

What is the motivation behind Quantum Machine Learning?

Machine Learning(ML) is just a term in recent days but the work effort start from 18th century.

What is Machine Learning ? , In Simple word the answer is making the computer or application to learn themselves . So its totally related with computing fields like computer science and IT ? ,The answer is not true . ML is a common platform which is mingled in all the aspects of the life from agriculture to mechanics . Computing is a key component to use ML easily and effectively . To be more clear ,Who is the mother of ML ?, As no option Mathematics is the mother of ML . The world tremendous invention complex numbers given birth to this field . Applying mathematics to the real life problem always gives a solution . From Neural Network to the complex DNA is running under some specific mathematical formulas and theorems.

As computing technology growing faster and faster mathematics entered into this field and makes the solution via computing to the real world . In the computing technology timeline once a certain achievements reached peoples interested to use advanced mathematical ideas such as complex numbers ,eigen etc and its the kick start for the ML field such as Artificial Neural Network ,DNA Computing etc.

Now the main question, why this field is getting boomed now a days ? , From the business perspective , 8-10 Years before during the kick start time for ML ,the big barrier is to merge mathematics into computing field . people knows well in computing has no idea on mathematics and research mathematician has no idea on what is computing . The education as well as the Job Opportunities is like that in that time . Even if a person tried to study both then the business value for making a product be not good.

Then the top product companies like Google ,IBM ,Microsoft decided to form a team with mathematician ,a physician and a computer science person to come up with various ideas in this field . Success of this team made some wonderful products and they started by providing cloud services using this product . Now we are in this stage.

So what’s next ? , As mathematics reached the level of time travel concepts but the computing is still running under classical mechanics . the companies understood, the computing field must have a change from classical to quantum, and they started working on the big Quantum computing field, and the market named this field as Quantum Information Science .The kick start is from Google and IBM with the Quantum Computing processor (D-Wave) for making Quantum Neural Network .The field of Quantum Computer Science and Quantum Information Science will do a big change in AI in the next 10 years. Waiting to see that…(google, ibm).

What is Quantum Mechanics?

In a single line study of an electron moved out of the atom then its classical mechanic ,vibrates inside the atom its quantum mechanics

What is Quantum Computing?

A way of parallel execution of multiple processess in a same time using qubit ,It reduces the computation time and size of the processor probably in neuro size

What are some differences between Quantum Computing vs Classical Computing?

  • LINK - Basic outline


Quantum Computing

Atom Structure

Electron Orbiting around the nucleous in an eliptical format

  • YOUTUBE - A nice animation video about the basic atom structure


Photon Wave

Light nornmally called as wave transmitted as photons as similar as atoms in solid particles

  • YOUTUBE - A nice animation video about the basic photon 1
  • YOUTUBE - A nice animation video about the basic photon 2

Photon wave

Electron Fluctuation or spin

When a laser light collide with solid particles the electrons of the atom will get spin between the orbitary layers of the atom


  • YOUTUBE - A nice animation video about the basic Electron Spin 1
  • YOUTUBE - A nice animation video about the basic Electron Spin 2
  • YOUTUBE - A nice animation video about the basic Electron Spin 3


Put a point on the spinning electron ,if the point is in the top then state 1 and its in bottom state 0


  • YOUTUBE - A nice animation video about the Quantum States


During the spin of the electron the point may be in the middle of upper and lower position, So an effective decision needs to take on the point location either 0 or 1 . Better option to analyse it along with other electrons using probability and is called superposition


  • YOUTUBE - A nice animation video about the Quantum Superposition

SuperPosition specific for machine learning(Quantum Walks)

As due to computational complexity ,quantum computing only consider superposition between limited electrons ,In case to merge more than one set quantum walk be the idea

SuperPosition specific for machine learning

  • YOUTUBE - A nice video about the Quantum Walks

Classical Bits

If electron moved from one one atom to other ,from ground state to excited state a bit value 1 is used else bit value 0 used

Classical Bits


The superposition value of states of a set of electrons is Qubit


  • YOUTUBE - A nice video about the Quantum Bits 1
  • YOUTUBE - A nice video about the Bits and Qubits 2

Basic Gates in Quantum Computing

As like NOT, OR and AND , Basic Gates like NOT, Hadamard gate , SWAP, Phase shift etc can be made with quantum gates

Basic Gates in Quantum Computing

  • YOUTUBE - A nice video about the Quantum Gates

Quantum Diode

Quantum Diodes using a different idea from normal diode, A bunch of laser photons trigger the electron to spin and the quantum magnetic flux will capture the information

Diodes in Quantum Computing1
Diodes in Quantum Computing2
Diodes in Quantum Computing3

  • YOUTUBE - A nice video about the Quantum Diode

Quantum Transistors

A transistor default have Source ,drain and gate ,Here source is photon wave ,drain is flux and gate is classical to quantum bits

Quantum Transistors1
Quantum Transistors2

  • QUORA -Discussion about the Quantum Transistor
  • YOUTUBE - Well Explained

Quantum Processor

A nano integration circuit performing the quantum gates operation sorrounded by cooling units to reduce the tremendous amount of heat

Quantum Processor1
Quantum Processor2
Quantum Processor3

Quantum Registery QRAM

Comapring the normal ram ,its ultrafast and very small in size ,the address location can be access using qubits superposition value ,for a very large memory set coherent superposition(address of address) be used


  • PDF - very Well Explained

Quantum-computing-ML Bridge

Complex Numbers

Normally Waves Interference is in n dimensional structure , to find a polynomial equation n order curves ,better option is complex number

Complex Numbers1
Complex Numbers2
Complex Numbers3

  • YOUTUBE - Wonderful Series very super Explained


Vectors have a direction in 2D vector space ,If on a n dimensional vector space ,vectors direction can be specify with the tensor ,The best solution to find the superposition of a n vector electrons spin space is representing vectors as tensors and doing tensor calculus


  • YOUTUBE - Wonderful super Explained tensors basics
  • YOUTUBE - Quantum tensors basics

Tensors Network

As like connecting multiple vectors ,multple tensors form a network ,solving such a network reduce the complexity of processing qubits

Tensors Network1
Tensors Network2
Tensors Network3

  • YOUTUBE - Tensors Network Some ideas specifically for quantum algorithms

Quantum Machine Learning Algorithms

How does Quantum K-Nearest Neighbour work?

info : Here the centroid(euclidean distance) can be detected using the swap gates test between two states of the qubit , As KNN is regerssive loss can be tally using the average

How does Quantum K-Means work?

info : Two Approaches possible ,1. FFT and iFFT to make an oracle and calculate the means of superposition 2. Adiobtic Hamiltonian generation and solve the hamiltonian to determine the cluster

  • PDF1 - Applying Quantum Kmeans on Images in a nice way
  • PDF2 - Theory
  • PDF3 - Explaining well the K-means clustering using hamiltonian
  • Matlab - Yet to come soon
  • Python - Yet to come soon

How does Quantum Fuzzy C-Means work?

info : As similar to kmeans fcm also using the oracle dialect ,but instead of means,here oracle optimization followed by a rotation gate is giving a good result

How does Quantum Support Vector Machine work?

info : A little different from above as here kernel preparation is via classical and the whole training be in oracles and oracle will do the classification, As SVM is linear ,An optimal Error(Optimum of the Least Squares Dual Formulation) Based regression is needed to improve the performance

  • PDF1 - Nice Explanation but little hard to understand :)
  • PDF2 - Nice Application of QSVM
  • Matlab - Yet to come soon
  • Python - Yet to come soon

How does Quantum Genetic Algorithm work?

info : One of the best algorithm suited for Quantum Field ,Here the chromosomes act as qubit vectors ,the crossover part carrying by an evaluation and the mutation part carrying by the rotation of gates

Flow Chart

  • PDF1 - Very Beautiful Article , well explained and superp
  • PDF2 - A big theory :)
  • PDF3 - Super Comparison
  • Matlab - Simulation
  • Python1 - Simulation
  • Python2 - Yet to come

How does Quantum Hidden Morkov Models work?

info : As HMM is already state based ,Here the quantum states acts as normal for the markov chain and the shift between states is using quantum operation based on probability distribution

Flow Chart

  • PDF1 - Nice idea and explanation
  • PDF2 - Nice but a different concept little
  • Matlab - Yet to come
  • Python1 - Yet to come
  • Python2 - Yet to come

How does Quantum state classification with Bayesian methods work?

info : Quantum Bayesian Network having the same states concept using quantum states,But here the states classification to make the training data as reusable is based on the density of the states(Interference)

Bayesian Network Sample1

Bayesian Network Sample2

Bayesian Network Sample3

How does Quantum Ant Colony Optimization work?

info : A good algorithm to process multi dimensional equations, ACO is best suited for Sales man issue , QACO is best suited for Sales man in three or more dimension, Here the quantum rotation circuit is doing the peromene update and qubits based colony communicating all around the colony in complex space

Ant Colony Optimization 1

How does Quantum Cellular Automata work?

info : One of the very complex algorithm with various types specifically used for polynomial equations and to design the optimistic gates for a problem, Here the lattice is formed using the quatum states and time calculation is based on the change of the state between two qubits ,Best suited for nano electronics

Quantum Cellular Automata

Quantum Neural Networks


Its really one of the hardest topic , To understand easily ,Normal Neural Network is doing parallel procss ,QNN is doing parallel of parallel processess ,In theory combination of various activation functions is possible in QNN ,In Normal NN more than one activation function reduce the performance and increase the complexity

How does Quantum perceptrons work?

info : Perceptron(layer) is the basic unit in Neural Network ,The quantum version of perceptron must satisfy both linear and non linear problems , Quantum Concepts is combination of linear(calculus of superposition) and nonlinear(State approximation using probability) ,To make a perceptron in quantum world ,Transformation(activation function) of non linearity to certain limit is needed ,which is carrying by phase estimation algorithm

Quantum Perceptron 1

Quantum Perceptron 2

Quantum Perceptron 3
Quantum Perceptron 4
Quantum Perceptron 5

Quantum Statistical Data Analysis work?

one line: An under research concept ,It can be seen in multiple ways, one best way if you want to apply n derivative for a problem in current classical theory its difficult to compute as its serialization problem instead if you do parallelization of differentiation you must estimate via probability the value in all flows ,Quantum Probability Helps to achieve this ,as the loss calculation is very less . the other way comparatively booming is Quantum Bayesianism, its a solution to solve most of the uncertainity problem in statistics to combine time and space in highly advanced physical research


Quantum Computing for Natural Language Processing?

How would you go about explaining Shakespeare’s Romeo and Juliet to a small and noisy quantum computer? (our model does get “Romeo who loves Juliet dies”)


Problem overview



Tradeoffs between various Quantum Computing Programming Languages?

GitHub - aws/amazon-braket-examples: Example notebooks that show how to apply quantum computing in Amazon Braket.


References and Resources

In the ML community, and especially in the quantum computing community, it’s important to give credit where credit is due, and not just slap our name on someone else’s hard work cough. Here is a list of the references and resources I used for various equations, concepts, explanations, examples, and inspiration for visualizations:

Cited as:

  title   = "Quantum Machine Learning Interviews",
  author  = "McAteer, Matthew",
  journal = "matthewmcateer.me",
  year    = "2020",
  url     = "https://matthewmcateer.me/blog/ml-research-interview-quantum-ml/"

If you notice mistakes and errors in this post, don’t hesitate to contact me at [contact at matthewmcateer dot me] and I will be very happy to correct them right away! Alternatily, you can follow me on Twitter and reach out to me there.

See you in the next post 😄

I write about AI, Biotech, and a bunch of other topics. Subscribe to get new posts by email!

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

At least this isn't a full-screen popup

That'd be more annoying. Anyways, subscribe to my newsletter to get new posts by email! I write about AI, Biotech, and a bunch of other topics.

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.