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Quantum computing, the sci fi frontier of computing

Quantum computing, the sci fi frontier of computing

08 April 2020

Sonya Weiser

In my last blog post I mentioned quantum computing, which will at some point in the future provide massive computational power.

So this month I'm going to tell you a little more about quantum computing and what it will mean for technology of the future.

What is quantum computing?

IBM Q Quantum computer

Quantum computing feels like the science fiction frontier of information technology, where amazing things can be done with computers that are almost beyond the imagination of today's world of technology.

This new technology will be based on qubits – short for quantum bits – instead of classical bits used in today's computers.

Classical bits in a conventional computer always only have one certain value, which is represented as 0 or 1. Researchers have been experimenting with quantum physics for many years, trying to harness the power of the uncertainty of quantum states in qubits.

Classical bits with 0 and 1 values can only be processed bit by bit, one after the other. Qubits however can store and process several values in parallel in one step, due to their superposition, entanglement and interference properties, which I'll go into in more detail later in this blog.

Here's a quick list showing the number of qubits vs the number of classical bits required for processing information:

2 qubits are equivalent to512 bits
3 qubits are equivalent to 1024 bits
10 qubits are equivalent to 16 kilobytes
16 qubits are equivalent to 1 megabyte
20 qubits are equivalent to 17 megabytes
30 qubits are equivalent to 17 gigabytes
35 qubits are equivalent to 550 gigabytes
100 qubits are equivalent to more than all the atoms of planet earth, and
280 qubits are equivalent to more than all the atoms in the known universe.

However, to truly unleash the power of quantum computers, the error rate must be kept low. The number of qubits timed by the error rate is referred to as the volume of qubits.

At the IBM Think Summit in May 2019 I heard they've released access to their 53 qubit quantum computer through a cloud-based interface, called Q Experience (available at https://quantum-computing.ibm.com/). This (and other offerings by IBM's competitors) opens up experimentation with quantum computer programming to anyone, not just the quantum physicists inside organisations with the funds to create these computers of the future. The real power of quantum computers will be in their use, once we go beyond theoretical case studies.

What will quantum computers be used for?

Applications for quantum computing include anything where we need the ability to simulate nature, such as chemistry, materials, and deep learning artificial intelligence. Problems that are intractable for classical computers will be able to be tackled by quantum computing.

Cyber Security

Quantum turns traditional computing on its head for difficult calculations, providing the massive computational power needed to crack cryptography algorithms. These algorithms rely on factoring, which cannot be reverse engineered using classical computers but will be a simple exercise for quantum computers.

The cyber security arms race will need to harness the power of quantum computers to negate the future threat to cryptography when quantum computers become available for general use.

Risk Analysis

Financial risk analysis is another area which is currently much too complex to be understood and predicted by classical computers. The power of quantum computing can be turned to complex equations such as risk calculations for fund managers. The ability to have a computer detecting potential risks within seconds of market changes would provide a game-changing advantage to fund managers using electronic trading.

Artificial Intelligence

Artificial intelligence, in particular deep learning, will benefit from the massive computational power of quantum computers and have the potential to mimic human thought processes.

Dr Dario Gil, IBM Head of Research, uses the example of classifying complex data, which is an intractable problem for today's classical computers.

When a traditional one-dimensional line is used to represent classifications, you can see that purple dots are not easily distinguished by a single straight line from blue dots.

But if this data is represented using a second dimension, which is much more complex to process but is achievable using the quantum property of entanglement, the data can be seen as being on a curve and it is now possible to use a single straight line to different the purple dots from the blue dots and successfully segment the data.

IBM have experimented using this theory to classify data and the results showed that increasing the amount of entanglement in the system reduced the classification error rates.

Why isn't quantum computing commonplace yet?

Quantum computers can't be used to run classical computers' programs. For example, we cannot recompile an existing C++ program to run on a quantum computer, because they have different operators from classical computers. Quantum computing requires different algorithms to take advantage of the power of qubits.

The nature of quantum physics also creates challenges with keeping qubits stable and error rates low. Experimentation is ongoing to find the best hardware for creating a stable system of qubits that can be scaled up to meaningful volumes.

At the IBM 2019 Think Summit I saw the very pretty IBM Q quantum computer (pictured above). The qubits its technology create are vulnerable to interference from outside the computer unless kept super cool, so the structure is designed to provide super cooling to keep its qubits stable. Competitors are using other hardware designs to develop quantum computers.

Superposition, entanglement and interference

The three quantum physics properties of superposition, entanglement and interference are used in quantum computing to manipulate the state of a qubit. Quantum entanglement and interference properties are used for quantum calculations.


quantum superposition

Superposition refers to the combination of states which a qubit can have, as referenced in the Schrödinger's cat thought experiment. In 1935 physicist Erwin Schrödinger proposed a thought experiment with a quantum cat, in which the cat is enclosed in a box together with a radioactive sample, a detector and a lethal amount of poison. If the radioactive material decays, the detector triggers an alarm and the poison is released. The special feature is that according to the rules of quantum mechanics, unlike everyday experience, it is not clear whether the cat is dead or alive. It would be both dead and alive at the same time until an experimenter looks in the box. A single state would only be obtained starting from the time of this observation.

Or, an analogy for the musicians amongst us is playing two musical notes at once; what you hear is a superposition of the two notes.

Another more visual analogy is a spinning coin, which could be understood to be in a superposition state of heads or tails until it stops spinning.


Entanglement is a little counter-intuitive, this phenomenon describes behaviour never seen outside quantum physics. Entangled quantum particles behave together as a system in ways that cannot be explained using classical logic. The states of entangled qubits cannot be described independently of each other.

Using the analogy of spinning coins again, when two coins are spun at the same time, in a classical world they are independent of each other. In the quantum world however, these two coins can influence each other. Their entanglement can cause correlations, for example if one coin finishes as heads the other coin will always come up heads too.


Quantum states can undergo interference due to a phenomenon known as phase and can be understood similarly to wave interference. When two waves are in phase, their amplitudes add and provide constructive interference. When two waves are out of phase however, their amplitudes cancel each other out, this is destructive interference.

Interference is used in quantum computers to manipulate the states of qubits for calculations, cancelling out all but the states containing the solution.

Want to have a chat about this?

If you'd like to talk further with me about quantum computers, or anything else technology related for that matter, get in contact with me today, I'm always happy to meet and have a chat over a coffee. I can't promise to have all the answers, but it's fun to dream together about the future of computers!

Further reading:

IBM Think Summit 2019 video, Dr Dario Gil, IBM Head of Research, available at: https://www.ibm.com/events/think/watch/playlist/468130/replay/120138441/

What is quantum computing? Available at: https://www.ibm.com/quantum-computing/learn/what-is-quantum-computing

Schrödinger's cat with 20 qubits, available at: https://www.sciencedaily.com/releases/2019/08/190813102023.htm

Polarization and qubit information, available at: https://quantumcomputing.stackexchange.com/questions/4693/polarization-and-qubit-information

Chinese researchers achieve stunning quantum entanglement record, available at: https://www.scientificamerican.com/article/chinese-researchers-achieve-stunning-quantum-entanglement-record/

QC - Control quantum computing with unitary operators, interference & entanglement, available at: https://medium.com/@jonathan_hui/qc-control-quantum-computing-with-unitary-operators-interference-entanglement-7790c69f6e98

MIT Technology Review: IBM's new 53-qubit quantum computer is the most powerful machine you can use, available at https://www.technologyreview.com/f/614346/ibms-new-53-qubit-quantum-computer-is-the-most-powerful-machine-you-can-use/

Sonya Weiser

Sonya Weiser

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