Through the looking-glass: Quantum computing 101

In his book, Programming the Universe: A Quantum Computer Scientist Takes on the Cosmos, Seth Lloyd wrote:

“A classical computation is like a solo voice — one line of pure tones succeeding each other. A quantum computation is like a symphony — many lines of tones interfering with one another.”

So, what is quantum computing?

“Begin at the beginning,” the King said, very gravely, “and go on till you come to the end: then stop.” 

― Lewis CarrollAlice in Wonderland

To understand quantum computing, we need to get a basic understanding of quantum mechanics (quantum physics) first. Quantum physics is a fundamental study of the behavior of nature at its smallest level of atoms and subatomic particles. At this level, it is observed that particles behave in an odd manner. They can take or exist in more than one state at the same time and can influence and interact with particles that are far away.

In the 20th century, physicists observed  that the same principles apply to information. Thus, the term quantum information was coined.

“I’m afraid I can’t explain myself, sir. Because I am not myself, you see?” ― Lewis Carroll, Alice in Wonderland

Quantum computing uses the basis of quantum mechanics to process information in a new and promising way, opening the door to many exciting possibilities. Classical computers process and encode information in the form of binary digits, 0 and 1, measured in units called “bits.” These 0s and 1s act as on/off switches for computers to process and use simple “logic gates” ― AND, OR and NOT.  Quantum information is measured in units called “qubits,” and computers that process and store that quantum information are called quantum computers.

Qubits operate on two basic principles of quantum physics:

  1. Superposition
  2. Entanglement

Let’s explore these terms in more depth.

Superposition: As stated earlier, in quantum physics a particle can exist in more than one state at a time. Similarly, a qubit can represent both a ‘1’ or a ‘0’ state at the same time. This is called superposition. Qubits are represented by symbol ‘|>’ known as ket.  Qubits can be in |0> zero-ket, ground state, |1> one-ket or in a linear combination of two (superposition). Zero-ket is the lowest energy state.

  • Single qubit can have zero state, one state or any superposition between 0 & 1
  • Two qubit can be in superposition of 4 states
  • Three qubit can be in superposition of 8 states
  • n qubit can be in superposition up to 2n states simultaneously

In a classical computer, though, information being processed can only be in one of two states (0 or 1) at one time.

Entanglement: We now know that in quantum physics, tiny particles can take on more than one state at the same time, while also influencing and interacting with particles that are far away. Similarly, qubits in a superposition can influence and impact the states of other qubits (whether they will be in state of 0s or 1s). Therefore, they exhibit a correlation with each other  that is, the state of one (whether it is a 0 or a 1) can depend on the state of another. Einstein described this as “spooky action at a distance.” This phenomenon or behavior is called entanglement or quantum entanglement.

Quantum computers store information on a string of qubits and can solve complex problems by manipulating those qubits with a fixed sequence of quantum logic gates called quantum algorithms. By using the two principles of superposition and entangled particles, quantum computers have the potential to solve complex problems currently intractable for classical computers. In a classical computer, a calculation goes through all the different possibilities of 0s and 1s for calculation. Because a quantum computer can be in all the states at the same time, you can do just one calculation, testing all the possibilities simultaneously, making the processing exponentially faster.

“Would you tell me, please, which way I ought to go from here?”
“That depends a good deal on where you want to get to.”

― Lewis Carroll, Alice in Wonderland

How will quantum computing affect us?

In 1981, at a conference co-organized by MIT and IBM, physicist Richard Feynman had first urged the world to build a quantum computer. He said, “Nature isn’t classical, dammit, and if you want to make a simulation of nature, you’d better make it quantum mechanical, and by golly it’s a wonderful problem, because it doesn’t look so easy.”

He was right. To this day, no true quantum computers exists. IBM pioneered with a 5 qubit processor that powered its Quantum Experience platform. This is kept at a room temperature of minus (-) 496F to cool superconductors that help qubits process.  IBM recently announced a 16 qubit processor and plans to develop a 50 qubit processor. Google has also announced a 9 qubit quantum computer.

Quantum computing is likely to have the biggest impact on industries that are data rich and time-sensitive.

Cybersecurity: Currently, most of the encryption in classical computers is through prime numbers. Factoring large numbers into basic prime numbers can take ages for classical computers, but quantum computers can do this relatively quickly, thus decrypting anything that has been encrypted using this method. The National Institute of Standards and Technology (NIST) advised organizations to develop “crypto-agility” (i.e., the ability to swiftly switch out algorithms for newer, more secure ones as they are released, to meet the advent of quantum computers).

Healthcare and Medicine: Simulating molecular structure can aid our understanding of complex molecular behavior and chemical interactions. With quantum computing, its possible to calculate the position of individual atoms in very large molecules like polymers and viruses. This can help pharmaceutical industries design better drugs and open research for new material development.

Supply Chain and Logistics: Quantum computing can help optimize fleet operations for deliveries at peak hours, therefore developing efficient logistics and global supply chain solutions.

Cloud Security: Information is processed using laws of quantum physics that help keep private data safe as well as platform, storage and medium agnostic.

Artificial Intelligence: The true potential of quantum computing comes to the fore when combined with machine learning and artificial intelligence, which make it possible to interrogate large data sets of structured or unstructured content.

Financial Services: Quantum computing makes possible powerful new prediction and financial models, as well as risk assessment models for isolating key global risk factors to make better investments.

Overall, hybrid architectures that link conventional high performance computing with quantum computers may become common in the future.

 “Why, sometimes I’ve believed as many as six impossible things before breakfast.” 
Lewis CarrollAlice in Wonderland

Quantum Internet

For quantum computers to be truly effective, quantum networks may be needed. For quantum networks to work, the ability to “sculpt” an individual photon (i.e., the ability to encode information on a single photon of light that can be produced on demand) is key. In quantum networks, security is ensured by the laws of physics, which are unconditionally secure. So, quantum networks make communication between two computers impenetrable to hackers. That’s why many governments are keen to develop this technology.

The UK government is investing £120 million in quantum research labs at its top four universities (University of Birmingham, Glasgow, York and Oxford). Venture capitalists have invested $147 million in quantum computing startups in the last three years, and governments globally have provided $2.2 billion in research support.

At the time of writing this article, China has published a study in Science sharing details of what could be an important breakthrough towards developing a worldwide quantum network. Chinese scientists used the Micius satellite to create pairs of photons with properties that were linked through quantum entanglement. It then beamed these simultaneously to ground stations in three locations. Each pair of photons traveled 1,240 miles before reaching their destination.

No one knows when quantum computers might become widely commercially available ― but clearly it’s not too early to begin planning for the dawn of the quantum world, which can potentially harvest exponential results for industries, governments and societies at large.

Yes, that’s it! Said the Hatter with a sigh, it’s always tea time.” 
Lewis Carroll, Alice in Wonderland


Annu Singh is a business analysis advisor and continuous service improvement lead at DXC. She focuses on automation in service level management and reporting in DXC’s service management and delivery excellence organization. Annu is also an active chair of DXC’s Women in Leadership India Chapter. @Annu_Singh_Tom



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  1. Jose Ruiz says:

    I wonder if we have a group working on this …



  1. […] Through the looking-glass: Quantum computing 101 […]


  2. […] based on quantum-mechanical phenomena, superposition and entanglement. See a colleagues post “Through the looking-glass: Quantum computing 101” for an explanation of […]


  3. […] on quantum-mechanical phenomena, superposition and entanglement. See a colleague’s post, “Through the looking-glass: Quantum computing 101,” for an explanation of […]


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