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Superposition

At the quantum level, physical systems can exist in multiple states at the same time. Until the system is observed or measured, the system occupies all positions at once. This central principle of quantum mechanics allows quantum computers to work with the potential of the system, where all possible outcomes exist in a computation simultaneously. In the case of quantum computing, the systems used can be photons, trapped ions, atoms, or quasi-particles.

Interference

Quantum states can interfere with other quantum states. Interference can take the form of canceling out amplitude or boosting amplitude. One way to visualize interference is to think of dropping two stones in a pool of water at the same time. As the waves from each stone cross paths, they will create stronger peaks and valleys in the ripples. These interference patterns allow quantum computers to run algorithms that are entirely different from those of classical computers.

Entanglement

At the quantum level, systems like particles become enjoined, mirroring the behavior of one another, even at great distances. By measuring the state of one entangled system, a quantum computer can “know” the state of the other system. In practical terms, for example, a quantum computer can know the spin motion of electron B by measuring the spin of electron A, even if electron B is millions of miles away.

Qubits

In classical computing, calculations are made combinations of binaries known as bits. This is the basis of the limitations of classical computing: calculations are written in a language that can only have one of two states at any given time – 0 or 1. With quantum computing, calculations are written in the language of the quantum state, which can be 0 or 1, or any proportion of 0 or 1 in superposition. This type of computational information is known as a “quantum computer bit,” or Qubit.

Qubits possess characteristics that allow information to increase exponentially within the system. With multiple states operating simultaneously, qubits can encode massive amounts of information—far more than a bit. For this reason, it’s difficult to overstate the computing power of quantum. Increases in the computing power of combined qubits grows much more rapidly than in classical computing, and because qubits don’t take up physical space like processing chips, it’s much easier to arrive at infinite computing capabilities, by some measurements.

Types of quantum computers

An understanding of quantum computing relies on an understanding of the principles dictating the behavior of quantum movement, position, and relationships.

Regardless of type, quantum computing hardware is very different from server farms associated with supercomputing. Quantum calculation requires placing particles into conditions where they can be measured without alteration or disruption by surrounding particles. In most cases, this means cooling the computer itself to near Absolute Zero and shielding Qubit particles from noise using layers of gold. Because current quantum computers require such delicate and precise conditions, they must be built and constructed in highly specialized environments.

Today, one of the major forms of digital encryption is RSA (Rivest-Shamir-Adleman), known generally as public key cryptography. The RSA algorithm was first described by Rivest, Shamir, and Adleman in 1977, and even decades later, it remains an exceptionally strong, proven system for encryption.

RSA is based on two digital keys which combine to form a large prime number. Where classical computers can easily multiply two known numbers to calculate a prime product, they’re very poor tools in the reverse. Classical computers struggle to use brute force binary calculation to derive two factors from the prime product. In short, current RSA algorithms are essentially unbreakable codes, because even the most powerful supercomputers can’t calculate the value of the keys in any reasonable amount of time. Today’s 2048-bit RSA encryption would take the fastest supercomputer roughly 300 trillion years to decrypt.

That’s where the threat of quantum computing comes into play. Because quantum computers can analyze all probabilities at once without tracing a linear path, they can effectively “skip over” the one-route-at-a-time method of classical computers and arrive at an accurate calculation in a reasonable amount of time. Quantum computers are perfectly equipped to divide large prime numbers into correct factors, effectively breaking RSA. Predictions about near-future quantum computing suggest RSA encryption can be cracked in months, and more advanced quantum computers may be able to decrypt RSA in hours or even minutes.

Quantum computing

Possibly the most misused term in quantum computing is “Post-Quantum Computing,” abbreviated as “PQC.” This term has led to confusion, because it shares its abbreviation with “Post-Quantum Cryptography.” However, “Post-Quantum Computing” doesn’t exist in the world of quantum computer science. A quantum computer is the full term for the machine, and quantum computing describes the field and the process. Even long after advanced, highly useful machines exist, they will still be quantum computers, not post-quantum computers.

Quantum cryptography

Quantum cryptography shares its basis in quantum mechanics with Post-Quantum Cryptography, but it is not the same cryptographic technology as PQC. In quantum cryptography, the fundamental nature of unpredictability is used to encrypt and decrypt data, with information directly encoded in qubits themselves. Currently, the most commonly known version of quantum encryption uses the properties of qubits to secure data in a way that would produce qubit errors if someone tries to decrypt the information without permission. This form of quantum encryption works more like an alarm sensor on a door or window. Unauthorized access raises an alarm.

Post-Quantum Cryptography (PQC)

Post-Quantum Cryptography operates on mathematical equations, just like classical computing encryption. The difference is in the complexity of the equations. In PQC, the math takes advantage of quantum properties to create equations so difficult to solve, even quantum computers can’t “skip” to the correct solution. One of the benefits of PQC is its basis in highly unsolvable equations. Because it shares the same basic structure as current classical encryption, it can be deployed using similar methods as current state-of-the-art encryption, and it can protect much of today’s systems.