The continuing development of quantum computing, a potentially revolutionary form of number-crunching, has reached a new milestone. Earlier this month, IBM announced the building of a prototype 50-qubit processor for the company’s quantum cloud computing platform, IBM Q. This new processor could prove to be a major step—or even the ultimate one—toward “quantum supremacy.” The term refers to quantum computers exceeding conventional computers at certain complex calculations that the latter machines would require impractically long times to perform. See also: Computer; Quantum computation
Quantum computing gets its name from “quantum mechanics,” the theory that describes particles and their interactions through three of nature’s four fundamental forces. In conventional computers, the smallest unit of data is the bit, or binary digit, consisting of either a 1 or a 0. In quantum computers, the equivalent of a bit is a qubit. Paradoxically, qubits can be both a 1 and a 0 simultaneously, because of the bizarre quantum mechanical property of superposition. An action performed on one qubit can also be extended to multiple other qubits to which it is correlated through another quantum mechanical property: entanglement. The upshot of combing these phenomena is that quantum computers with even modest numbers of qubits can deliver astonishing computational power. See also: Elementary particle; Fundamental interactions; Quantum mechanics; Quantum theory of measurement; Standard model
In achieving a 50-qubit processor, the quantum computational field has come a long way since the first, primitive two-qubit architectures emerged in the late 1990s. Yet before quantum supremacy is assured, significant challenges must still be overcome.
One of these is preserving the delicate quantum states necessary for quantum effects, and therefore computation, to occur. The qubits themselves, depending on the system architecture, can be polarized photons, spinning atomic nuclei, or superconducting loops of metal. All are extremely vulnerable to outside perturbations, such as heat and magnetic fields. Even with shielding and cryogenic conditions, the most powerful IBM Q system currently available, which has 20 qubits, features an average coherence time of 90 microseconds for performing quantum computation. While that span is sufficient to perform valuable, real-world calculations, it remains to be seen if it suffices for genuine quantum supremacy. Another challenging area, quantum error correction, aims to improve these decoherence times. But researchers do not know if error rates will become overwhelming as qubit numbers increase. See also: Atom; Atomic nucleus; Atomic physics; Cryogenics; Electromagnetism; Photon; Superconductivity
There will be no shortage of efforts in thepursuit of quantum supremacy. Besides IBM, other large technology companies that are investing heavily in quantum computing technologies include Google and Intel, along with a host of startups. Among the many breakthroughs anticipated through quantum computing include modeling molecular behavior with unprecedented fidelity, leading to new material and therapeutic drug discoveries; optimizing routes for logistics; and precision simulations of weather systems for better forecasting. See also: Pharmacology; Weather forecasting and prediction
Should progress continue apace, the oddities of how quantum computers work may become no more curious than vacuum tubes, integrated circuits, and other technologies that have powered the past eight decades of computing. See also: Integrated circuits; Vacuum tube