Why Quantum Computing?

In modern society, digital computers are so pervasive that humans often take for granted the existence of alternative technologies. Moreover, people disregard their shortcomings or areas of improvement to convince themselves that the indubitably dominant paradigm in information processing is permanently in place and increasing in ability ad infinitum.

The pioneer voice of the latter sentiment was Intel co-founder Gordon Moore, who in 1965 published his eponymous law. Moore’s Law states that the computing power of an integrated circuit should double every 18-24 months, and for over 50 years it has remarkably held true.

With the turn of the decade less than two months out, however, many theorists have predicted Moore’s Law to expire any time. That is, integrated circuits will soon reach their limits in terms of efficiency, size, and computing power. With the ever-growing threats to security and human demands for complex tasks certainly not reaching their limits, researchers have been exploring a new form of computing to render the infinitely ubiquitous yet finitely reliable digital computer merely another “thing of the past.”

Particularly, various technology firms have been investing in the emergent quantum computing as the means of extending Moore’s Law. Born out of a 1985 paper by Richard Feynman and perpetuated by subtle breakthroughs, quantum computing is as mind-boggling as the system of physics upon which it is based, both in its stipulations and ramifications.

Theory

In classical computing, information is expressed in bits, manifested as series of electrical signals with either high (1) or low (0) voltages. Processing speed is limited by the flow of electricity through the circuitry of the device, specifically in the “von Neumann bottleneck” induced by the delay in synchronizing all components. Moreover, while only semiconductors (specifically silicon) have the right properties to comprise digital computers, they tend to dissipate a great deal of free energy and can only fit so many circuit components before quantum effects (in terms of electron interaction) begin to sabotage the system. This is the precise reason for the stagnation of Moore’s Law; fitting more components warrants a regressive increase in device size after decades of reducing computers from filling entire command centers to fitting in one’s hand.

Instead of relying on electricity flow, quantum computers render atoms themselves the fundamental units of information. The qubit is defined as an entangled atom in a superposition, not distinctly representing either “1” or “0” like an ordinary bit, but having a nonzero probability of taking on a particular state. That is, knowledge of one atom’s state immediately conveys knowledge of the paired atom’s state, and such atoms can be set up in a circuit-like system similar to that comprised by electrical circuits, but one that is conducive to instantaneous information processing.

The precise behavior of the qubit, just like quantum mechanics itself, is governed by linear algebra and applied probability, both mathematically rigorous and beyond the scope of this overview. It is important to note, however, that the probabilistic states of the qubits are manifested through electron spin; the exact probability associated with a “spin” superposition governs the behavior (and thus applicability) of the respective qubit. As emphasized in the entanglement post (“Spooky Action at a Distance”), two entangled atoms essentially “communicate” with each other by mutually revealing each other’s state upon the observation of one. This property eliminates any latency, or delay for synchronization, in a quantum computer, exponentially increasing both power and efficiency.

Implementation

The previous posts, while warranting the existence of quantum computing, also stipulated the extraordinarily delicate conditions that must exist for superposition and entanglement to be physically realized. Feynman acknowledged this very setback when he proposed the technology in his paper “Quantum Mechanical Computers.” Specifically, the pairs of electrons must exhibit almost no interaction with their immediate surroundings, so imperfectly resistive semiconductors are ineffective. Rather, current quantum devices employ superconductors, the sub-zero temperatures of which allow for the entangled pairs to exist freely. Because superconductors themselves comprise a fledgling paradigm in the realm of electrical systems, primitive quantum computers, much like their classical counterparts of the 1950s, are notoriously bulky and impractical outside a laboratory:

As complex as Google’s quasi-experimental machine may appear, it only consists of 72 qubits, compared with the gigabytes and terabytes available for memory and storage on modern digital computers. Based on the principles of entanglement and superposition, however, even a modest 72 qubits should be enough to speed up all classical computing processes enormously…at least in theory. It remains the responsibility of theorists to actually develop quantum algorithms that are more efficient that their classical analogues. Google’s recent claim to have achieved “quantum supremacy” with the pictured machine applies only to one particular algorithm, so it embodies only a minute degree of progress. Procedures currently being explored include the Fourier-based Shor’s Algorithm, which promises perfect cryptography and cryptanalysis (and no shortage of civil unrest) if realized in a practical quantum computer. Such ramifications of quantum computing are outlined beyond this technically broad overview in my Rhetoric and Civic Life posts.

Despite the research and associated breakthroughs, quantum computing remains primarily a “thing of the future.” What is, has always been, and will always be an application of quantum mechanics, however, is its association with consciousness and the profound Anthropic implication that humans may indeed be special creatures and the products of a higher design.