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The Quantum Computer

Computers were once the size of an entire room. Now, these early models are easily outclassed by the computers on our wrists as we fit more and more processing power into smaller and smaller spaces. Today some computer parts are only 5nm wide — 20,000 times narrower than a human hair. As we approach the physical limits of what can fit onto a silicon chip, we leave the world of classical physics and enter the quantum realm, where things become very strange. Particles may suddenly appear on the other side of barriers or be in two places at once. Conventional computers break down in the quantum world.

To answer some of the greatest mysteries of science, we need to create an entirely new and fundamentally different kind of computer. One that leverages the eccentricities of quantum mechanics to our advantage. One that turns the weird to our benefit. Even with modern supercomputers, exponentially large problems can’t be solved. But a quantum computer will be able to solve them, enabling us to find new medicines, create better materials, and unravel the mysteries of black holes.

Part One

What is a Quantum Computer?

To a computer, the letter A looks like 01000001. Each of these ones and zeroes is a “bit” and indicates one of two possible states, off or on. As the most basic form of information storage on a computer, an individual bit isn’t very useful. Collectively, however, bits power massive calculations, run life-like video games and render the very text you’re reading right now. Everything digital — from emails, to music, to videos — is essentially composed of really long strings of ones and zeros.

A = 01000001

A quantum computer uses a new kind of bit called a “qubit” and three principles of quantum mechanics: superposition, interference, and entanglement. Once we understand these principles, we can understand how a quantum computer works.

Click to spin


A qubit is a special kind of bit that can be a one, a zero, or some probability of being either called a superposition. If you think of a coin with heads as one and tails as zero, superposition is that coin spinning in the air. It’s simultaneously heads and tails until we catch and measure it.

Drag together to cancel out


We can think of superposition as a wave. When they interact, similar waves amplify each other and opposite waves cancel each other out — this is interference. In the same way noise-canceling headphones work by producing a sound wave the opposite of the ambient noise around them, we can cancel out one superposition with its opposite.

Drag to center to entangle


Two qubits in superposition can be entangled together so that whenever you measure and collapse one’s superposition to a one or zero, the other qubit will always be measured at the same value. They will always both be zero or both be one even if they’re really far apart from each other. Einstein called this “spooky action at a distance.”

A quantum computer can employ these three principles from quantum mechanics to make large calculations faster and store more information than a classical computer.

As soon as we measure a qubit in superposition it collapses into a definite state of either one or zero. We can visualize the probability of its eventual value as a wave form, with the higher curves suggesting a high probability and the lower curves suggesting a negative probability — scientists call this amplitude. It’s easy to see this in action with the famous double-slit experiment.

Double-Slit Experiment

When you shoot electrons at a screen with two openings, the electrons will act as waves once they pass through the slits, radiating out like ripples from two pebbles dropped in a calm lake. In some places the waves cancel each other out, in others they amplify. When you measure where the electrons end up they create distinct vertical bands called an interference pattern.

The magic of quantum computers is in their use of interference. By carefully choreographing qubits through gates of interference and entanglement, we can cancel out paths leading to the wrong answer and amplify paths leading to the right answer. This means that for problems where a classical computer spends one hundred seconds trying each path individually, a quantum computer can try them all at once and be lead down the right path in only ten seconds. This can be applied to common problems like checking a large database, mapping an efficient route or perhaps most famously, breaking encryption.

Part Two

Encryption is dead.

Quantum is both beautiful and deadly. It will enable breakthroughs in biology, chemistry, and physics — but it will also be exploited to break encryption. Viable quantum computers won’t arrive any time soon, but already countries and criminals are gathering encrypted data en masse with the hope of unraveling it later. Gather today, crack tomorrow.

Although quantum computers were first proposed in the ’80s, interest among tech giants and nation states ramped up significantly in ’94 when physicist Peter Shor invented a game-changing algorithm. Given sufficient quantum processing power, Shor’s algorithm renders the most popular internet encryption scheme obsolete. You use this encryption scheme, RSA, each time you input credit card details, book a flight, or check a bank balance on the internet. Shor’s algorithm means that soon the little lock icon at the top of your browser will no longer represent safety.

Shor’s Algorithm

Finding factors of large numbers is incredibly time consuming for a classical computer, which has historically made this the perfect basis for encryption. By cleverly exploiting the properties of quantum computers, Shor devised a method for easily finding the factors of large numbers. What would take a classical computer thousands of years to crack could suddenly be broken in a matter of hours, minutes, or even seconds.

Today’s quantum computers are comprised of fewer than one hundred qubits and Shor’s algorithm will probably need about one million to function. Even though a computer this powerful is years away, this is a problem now. Governments have already begun collecting encrypted national secrets from each other because they know one day the data will be useable.

Some information might be especially valuable for a short period of time, like a company’s pre-release earnings, but other information remains highly valuable for a long time. When the British broke the code for the Enigma machine during WWII, this information remained so valuable to national security that it was kept secret for thirty years. If you have information with a high value and long horizon, the capabilities of quantum aren’t a distant problem, they’re a threat today.

  • Org Charts

  • Corporate Directory

  • Embargoed Press Release

  • Pre-publication Patent

  • Pre-release Earnings

  • SSN

  • SOC Incidents

  • Commercial Contracts

  • Human DNA Markers

  • Code-Signing Keys

  • Trade Secrets

  • National Secrets

How long?

How Important?

This threat may not be with us for much longer. Great efforts are being made to create new, quantum-resistant algorithms that don’t rely on the traditional method of factoring numbers. The National Institute of Standards and Technology has spent more than three years evaluating proposals from the brightest mathematicians and cryptographers in the world and hopes to release their first quantum-resistant standard in 2022.

Encryption is dead, long live encryption!

Many articles and videos on quantum computers focus on the more frightening implications of Shor’s algorithm, but what is often left unsaid is quantum computers will ultimately use the laws of physics to powerfully enhance security.

In quantum cryptography it is possible to send messages by way of qubits in superposition. If someone tried to spy on your conversation, they would collapse the qubits’ superpositions to ones or zeroes and you would immediately know that your privacy had been compromised. The benefit is clear: by capitalizing on this property of quantum mechanics, we will be able to perfectly secure our communication channels. The dawn of the new encryption standard is on the horizon, but before we reach it we must conquer significant engineering challenges.

Part Three

The Present & Future

A composite photo showing the 1940s Collosus Mark 2 computer on the left and an image of the IBM Q quantum computer in 2017 on the right.
Colossus Mark 2 1943 IBM Q Quantum Computer 2017

In the 1940s computers were a complex tangle of wires that filled an entire room. In the 2020s quantum computers are…a complex tangle of wires that fill an entire room. It’s easy to draw parallels between the fledgling state of quantum computers and the classical computer’s past. We’re retreading old ground, but solving the problems in an entirely new way. Many experts believe that we are in the “vacuum tube stage” of quantum. We expect that the next key breakthroughs will reduce noise and increase stability and accuracy, moving us to the quantum equivalent of the “transistor stage.” With the capabilities of the earliest computers dwarfed by those of modern smartwatches, we can only imagine where quantum computing will take us in a few decades.

I have no idea what people are going to use them for. If you’d gone back thirty years and handed someone an iPhone they’d call you a wizard. Things are going to happen that we just can’t foresee. Dr Steven Girvin, Yale Quantum Institute

Our current quantum computers are fragile and error prone, disturbed by the slightest nudge or pull of the universe. Some thought quantum computers couldn’t possibly exist, because as soon as you try to measure an error to correct it you collapse it and your computation is ruined. Luckily, Peter Shor didn’t just break RSA, he also devised a way to make quantum computers reliable. Shor’s insight was to entangle hundreds of qubits together and create an abstract “logical qubit.” With this logical qubit you can measure error and correct it without disturbing the computation.

The largest quantum computers today have less than a hundred physical qubits and we’ll likely need a hundred to a thousand physical qubits to create a fault-tolerant logical qubit. We know it’s possible but it’ll be a massive worldwide engineering effort to make quantum computers that are reliable, scalable, and robust. However, big players like IBM, Microsoft, Amazon, Google, Alibaba and many quantum-focused start-ups are producing increasingly capable quantum computers in search of quantum supremacy.

The internals of an IBM Q quantum computer.
Internals of a quantum computer — the IBM Q

The achievement of quantum supremacy, the point at which a quantum computer can solve a problem no classical computer can, will be a landmark moment. Google claimed to have reached quantum supremacy in 2019 when they solved a niche problem using a 53-qubit chip, but whether this problem was actually unattainable for a classical computer has been disputed. We’ll have to wait longer for this milestone to be irrefutably reached and perhaps even longer for it to be applied to a meaningful problem — but progress is coming.

You won’t have a quantum computer in your home any time soon. In order to prevent qubits from collapsing, they are isolated inside massive tanks and cooled to almost absolute zero, colder than the vacuum of space. Instead, quantum computers will run on demand in labs or server warehouses, accessible over the internet for specialized computations. This is referred to as “Quantum as a Service” and is already available today through companies like Microsoft, IBM and Amazon. Hopefully one day we will be able to ping a quantum computer to find the fastest route for our errands, to search retail inventory in a fraction of the time or to simulate black holes from a laptop.

Viable quantum computers are many years away, but already a coordinated mathematical, financial and engineering effort is underway to create them. Their future existence has huge ramifications for how we store and secure our data today. Just like any other tool, quantum can be put to nefarious purposes, but the promises of better medicine, more efficient materials and a deeper understanding of our universe outweigh the risks.

Further Resources


Quantum Computing’s Cyber-Threat to National Security


RSA Keynote: Time to Tell


Securing Tomorrow Podcast E20: Quantum Computing with Steve Grobman & Jon King