## A Quantum Computing Primer

Quantum computing. Possibly the only technology that is currently more hyped than blockchain.

Quantum computing is frequently mentioned; however, it is rarely understood. **It has the potential to transform humanity on a scale larger than any prior technological advance in human history.** Let’s try to piece together the basics and begin to understand this looming technology. Does it actually exist or is just the idea of it relegated to doctoral theses and theory?

To begin exploring the basics of quantum computers, you have to start with a high-level understanding of quantum physics. Quantum physics describes the behavior of atoms, specifically their fundamental particles such as protons and electrons. A quantum computer operates by controlling these behaviors in a purposeful and fundamentally different way than traditional computers.

A traditional computer operates using bits. A bit has a binary identity in that it can either be on or off (1 or 0). A quantum computer uses quantum bits or “qubits”. A qubit is different than a traditional bit in that it has a more fluid, non-binary identity.

While a traditional bit is either 1 or 0, a qubit can be in “superposition” which means some combination of 1 or 0. A qubit’s identity is on a spectrum representing an infinite number of possibilities which is known as “Quantum Uncertainty”. The laws of quantum physics require that for every possible configuration an object could be in (this could be an electron, proton or even a computer), you have to assign a number to it. These numbers are known as amplitudes.

### Amplitudes

Amplitudes are a little like probabilities. They represent the probability that the object is in a given state. However, they are not probabilities because they can be positive or negative. For instance, there is no such thing as a “negative 30% chance of rain tomorrow”. Further, amplitudes interfere with each other while traditional probabilities do not.

If some outcome could occur in one way with a positive amplitude and in another way with a negative amplitude, these two contributions interfere destructively and cancel each other out. This means that neither outcome would occur at all. For additional detail on this point, look into the “Double Slit” experiment (https://en.wikipedia.org/wiki/Double-slit_experiment).

I hope that it is starting to become clear that **a quantum computer is not just simply a more powerful traditional computer.** Shohini Ghose uses a brilliant analogy to illustrate this difference:

“in the same way that a lightbulb is not simply just a better candle, a quantum computer is not just a faster traditional computer.”

It is important to understand that they function fundamentally in different ways.

The reason quantum computing can be so difficult for humans to understand is that we don’t naturally experience quantum uncertainty in our daily lives. As everyone is likely familiar with the idea of a coin toss, let’s use that as an example. The coin is like a traditional computer’s bit. When it is tossed up and then lands, the coin will either be heads or tails (i.e., 1 or 0). When we start to simulate this exercise through the lens of a quantum computer’s qubits, nobody would blame you for not completely understanding the results. There is no such thing as heads, tails and “some combination of both expressed across a spectrum of probability” on a referee’s coin.

If you are like me, you may be somewhat confused. You have seen recent headlines and industry buzz that quantum computers have arrived! However, I am guessing you have not personally experienced the promised “revolution of humanity”. What gives?

The answer to, “do quantum computers actually exist?” is a rather fitting, “yes…

andno”.

There are indeed, quantum computers that exist in the world today. However, the threshold at which they operate is currently limited to only really proving that the theory is functional. At this time, no quantum computer has been able to achieve the theoretical, exponential computational speed-up beyond the fastest traditional supercomputers that exist today.

### Decoherence

That key advancement is being held up by “noisy” qubits. The current hurdle for scientists is that while it is relatively easy to compute all possible answers to a problem using a quantum computer, once you measure it for the answer, the rules of quantum mechanics state that the result is just a random value. This is called “decoherence”, **the unwanted interaction between a quantum computer and its external environment.** When decoherence occurs, all the amplitudes (super state) turn into probabilities (classical state) and the computational speed is restricted to similar levels of traditional computing.

So how do you measure something without measuring it at all? A breakthrough in the 1990s was quantum error correction or, “fault-tolerance”. This method proved that you don’t need to reduce decoherence completely to zero, but rather, just to an extremely low point and then the rest of the “noise” can be overcome through fault-tolerant mathematical methods.

This triggered a race for scientists to reduce decoherence (isolating qubits) and enhance their error correction algorithms. Just within the last few years, researchers have gotten one and two qubits to be “good enough” to use to simulate quantum calculations. Scaling this achievement to more and more qubits is the key metric that researchers are trying to advance. Current quantum computers have been able to develop around 50 qubit systems that are functional and useful enough (low enough decoherence to be usable to compute). However, this is a long way off the 1,000+ qubit threshold which is generally considered the point at which a quantum system would exponentially revolutionize computational speed.

What will it mean when that day finally comes? Well, as you might have gathered from this article thus far, the answer isn’t so easy. Really, **we don’t know the full impact that quantum computers will have.** Quantum mechanics function on the atomic level and it is difficult for humans to even hypothesize the complete scope that quantum computing would have. However, there are some significant projects and ideas that scientists have identified which quantum computers will have major impacts.

### Encryption

The area that cybersecurity professionals, like those at Delap, lose the most sleep over is encryption. Everyone uses encryption hundreds, if not thousands, of times throughout each day whether we realize it or not.

Encryption keeps planes in the sky, traffic lights operational, communications secure, big projects at work proprietary, the electrical grid functional and websites online. The vast majority of encryption algorithms today are only considered secure because the amount of time it would take a traditional computer to solve for the key is longer than the entirety of human existence (in some cases and dependent on the strength of the algorithm). However, particularly with public key cryptography, quantum computers will theoretically be able to solve for cryptographic keys in trivial amounts of time. Quantum resistant cryptography is an extremely active research area and the race is on to develop algorithms which can withstand quantum computing attacks before quantum computers can be used to attack.

### Healthcare

Healthcare is another major landscape where quantum computers may revolutionize human existence. Quantum computers function by manipulating and exploiting the behaviors of the very same particles that make up our bodies (protons and electrons) and fundamentally approach computation differently. Unthinkable cures today, may be discovered in the future, with the achievement of true quantum computing.

### Data transfer

Finally, a wild but exciting frontier of quantum research is the applications of data teleportation. If achieved through quantum computing, data teleportation could provide the ability to transport vast quantities of data instantly between two locations around the world. The efficient transfer of data would have a ripple effect throughout all corners of our existence.

### Summary

While it is true that quantum computers do in fact exist today, true full-scale quantum computing at speeds exponentially faster than traditional computers, still only exist on paper. However, some of the most brilliant scientists in the world are methodically advancing their quantum projects beyond benchmarks previously thought impossible. Most are optimistic that over the next decade, there will be incredible technological advancements in quantum computing further pushing the boundaries of our computational power.

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