*Chris Bernhardt is a professor emeritus of mathematics at Fairfield University in Connecticut. *

*He is originally from the United Kingdom and studied at the University of Warwick where he completed his PhD. Professor Bernhardt has written two popular books on the theory of computing: first,* “*Turing’s Vision: The Birth of Computer Science”, which was published in 2016*; and second, “*Quantum Computing for Everyone”, which was published in 2019*. *Arriving at the problem from the perspective of a mathematician, Bernhardt writes that quantum computing has introduced an entirely new way to think about computing, which will interest students of computer science and may ultimately lead to important applications.*

*The transcript of the interview has been edited for clarity. *

**Harvard Political Review: **Could you briefly describe quantum computing to a general audience and discuss how it differs from classical computing?

**Chris Bernhardt: **Classical computing involves manipulating bits; these are just zeroes and ones. They can be represented by switches that are either on or off. Quantum computing manipulates qubits. These are unlike anything we deal with in everyday life, but a rough analogy to the switch is as follows: instead of just being able to flip the switch in the vertical direction, we can rotate the switch through 360 degrees. When we flip the switch, it will either turn on or off, but there is a probability which we get that depends on the rotation. We call this a superposition of on and off. Sometimes it is described as being both on and off, but this is misleading. When it is flipped, it is either just on or off.

Qubits have another strange property called entanglement. If two switches are entangled, the results obtained by flipping both switches are correlated. For example, they will both be on or both off.

Measurements of qubits involve probability, but the underlying mathematical model describing how to manipulate the probabilities is precise.

**HPR: **Is it likely that quantum computers will do everything that classical computers can but much faster, or will quantum computers be useful for solving only certain problems that can exploit features of quantum mechanics?

**CB: **Quantum computers will speed up finding the solutions to certain special cases of problems, not all problems. Until 1994, the only algorithms using quantum computation to show a speedup over classical computation were contrived special examples. In 1994, Peter Shor invented an algorithm that would break the RSA public-key encryption currently in use. This showed that quantum computation would be able to solve certain important problems that are thought to be beyond classical computers.

The types of problems that quantum computers can solve fast involve finding patterns that they can exploit. You can look at a problem from more directions. Imagine a direction in which your data all lines up in rows. If you cannot access this direction with a classical computer, but you can with a quantum computer, you can use the quantum computer to exploit this.

Quantum computing in the near term will be hybrid. Most of the computation will be done classically on a classical computer, while parts of the problem amenable to quantum speedup will be tackled by the quantum computer.

**HPR: **What kinds of problems will quantum computers be able to solve faster in the near future, such as one to five years from now?

**CB: **General purpose quantum computers are still very much in their infancy. They can only manipulate a few qubits and it is difficult to keep whatever is storing the qubit to interact with its surroundings. It is unlikely that any interesting practical problem will be able to be tackled soon.

That said, D-Wave is selling a special purpose quantum computer for tackling optimization problems. Volkswagen has one that it has used for production line scheduling.Large companies need to solve complex optimization problems. Many are exploring the use of quantum computers.

**HPR: **Where will these breakthroughs come from — companies, universities, or governments?

**CB: **Probably all the above. When or if quantum computing proves itself, it is likely that large amounts of money both from the private and public sector will pour in for research.

**HPR: **Will a company be able to run Shor’s algorithm, used to break certain methods of encryption, in the near future, and will that give them an unprecedented back door through all our encryption? Will it break cryptocurrency?

**CB:** Shor’s algorithm is a wonderful algorithm that shows the power of quantum computation, but it is only effective against certain types of encryption methods. Post-quantum cryptography is a thriving area. We have encryption methods that are not amenable to quantum speedup.

It is a myth that quantum computers will destroy internet security. We need to move to alternative ways of encryption and, though we haven’t done it yet, we know how to do this.

**HPR: **On computational chemistry: does it seem likely that the ability to simulate chemical reactions at a low-level will lead to the ability to simulate larger biological processes — like a virus, ant, or human? If so, could pharmaceutical companies use quantum computers for drug discovery?

**CB: **The application of quantum computing to chemistry looks very promising. This could be an area where we see results in a few years. I’m not sure about simulating humans, but we can expect simulating protein folding and designing drugs in the near term.

**HPR: **Are there any other effects of quantum computing that you would like to mention?

**CB: **There will undoubtedly be spin-off technology. As we learn to manipulate qubits with accuracy, we will use them for more than just what we currently conceive of as computation. Medical imaging and secure communications are two such areas.

**HPR: **What should a student do if he or she wants to pursue an interest in this field, academic or otherwise? Will a student need to develop knowledge in physics most of all, or can a student study or work in this field with only a knowledge of computer science, mathematics, or some other field?

**CB: **Quantum computing is in its infancy. It is not clear how it will develop. The consequence is that there is no certainty about how it is going to change our daily lives, but it has potential and getting in at the start provides plenty of opportunities in a variety of areas.

Universities need to develop introductory quantum computing courses that any science, engineering, or math major can take. These would need a little math as a prerequisite but no specialized knowledge. Once a student has a feel for the basics, we can approach the field from different directions. Hardware is still a work in progress, so engineers and physicists with a background in quantum mechanics are needed. More basic algorithms need to be developed. A basic knowledge of computer science and mathematics is needed here. There will be important applications to chemistry and biochemistry. I would recommend that students majoring in these areas learn the basics of quantum computation.

*Image Credit: Photo by Chris Bernhardt* *is licensed for use under* *CC BY 2.0*.

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