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The Wibbly-Wobbly World of Quantum Techno Talk Max the Magnificent ‘If someone says that he can think or talk about quantum physics without becoming dizzy, that shows only that he has not understood anything whatever about it.’ Murray Gell-Mann, American physicist T hings must have seemed somewhat straightforward (relatively speaking) towards the end of the 1600s. In the early part of that century, the German astronomer, mathematician, astrologer and natural philosopher Johannes Kepler published his three laws of planetary motion, accurately describing the orbits of planets around the Sun and showing them to have elliptical trajectories. In 1666, the English mathematician, physicist, astronomer, alchemist, and theologian Sir Isaac Newton discovered his law of universal gravitation. Later, in 1687, he introduced his three laws of motion that describe the relationship between the motion of an object and the forces acting on it. All of this led to the view that we live in a mechanistic universe, in which the natural world operates as a machine following predictable and deterministic rules. This has also been described as a ‘clockwork universe’ that keeps on ticking along. It’s tempting to think of a cosmic chronograph or a metaphorical metronome marking time such that it’s the same time at every point in the universe. This ephemeral edifice came crashing down when Albert Einstein introduced his theories of special and general relativity early in the 20th century, showing how space and time are combined in a continuum. There are many implications to this, such as the fact that time passes at different rates depending on your velocity or proximity to massive obects... and then things start to get complicated. What? You’re kidding! Based on his experiments with optics, Newton decided that light was composed of some form of particles. However, some of Newton’s peers, such as Christiaan Huygens, took an opposing view that light was a kind of wave. Thomas Young’s original ‘double-slit’ interference experiments in 1801 indicated waves, but later versions served only to confuse the issue by indicating that light behaves as both waves and particles. We now know that light manifests itself in what we call photons, which are 8 massless particles, or electromagnetic waves, depending on your point of view. The idea behind the double-slit experiment is to have an opaque plate pierced by two parallel slits. Photons passing through the slits are detected by some form of sensor behind the plate. Let’s assume that we use some sort of ‘photon gun’ to fire a series of individual photons at the plate, one after the other. If we use one form of detector, it appears that each photon passes through one slit or the other (or hits the opaque portion of the plate) like a miniature cannon ball, thereby indicating that photons are particles. But if we use a different sort of detector, we see interference patterns. This implies that each photon acts as a wave, passing through both slits simultaneously and interfering with itself on the other side. Initially, scientists were tempted to treat photons as a special case and say something like, ‘Photons, what can you do, eh?’ However, it was later discovered that the same thing happens with electrons, protons, atoms and even molecules (the largest entities for which the double-slit experiment has been performed thus far are molecules comprising 2,000 atoms). It gets worse. The term ‘quantum entanglement’ refers to the ability for two particles to be linked (‘entangled’) such that a change in one will affect the other, even if they are separated by distances measured in light years. Furthermore, these changes will take place instantaneously, even though physicists continue to claim that nothing, including information, can travel faster than light. Suffice it to say that Albert Einstein referred to quantum entanglement as ‘Spooky action at a distance’ and then quickly changed the topic of conversation. Quantum computers For a long time, protons and neutrons were assumed to be fundamental and indivisible particles. Later it was discovered that they are formed from more elementary particles called quarks, which have been described as, ‘The dreams that stuff is made of.’ Im the 1980s, Richard Feynman and Yuri Manin proposed using quantum effects as the basis for quantum computers. In the digital computers we use today, the fundamental unit of information is the bit, which can be in one of two states: 0 or 1. The equivalent in a quantum computer is the ‘qubit’, which involves something like the spin of an individual electron. We might think of this ‘up’ or ‘down’ spin as being the equivalent of 0 and 1, respectively. However, a qubit exists in a coherent superposition of both states simultaneously, which basically means it represents all possible values between, and including, the extremes at once. The first real quantum computer that could be loaded with real data and output a real solution was a 2-qubit machine created in 1998. The largest quantum computer of which I’m currently aware is the 1,180-qubit machine that was announced by Atom Computing in October 2023. There are some problems that are hard for traditional digital computers to solve using conventional ‘grunt force’ means. One example is a complex maze, which you or I (or a digital computer) would solve by testing each possible path one after the other, retracing our steps when we ran into a dead end. Some people describe a quantum computer’s approach to this problem as looking at all the paths simultaneously. This isn’t quite how it works, but thinking about it in this way helps to preserve our quantum-world sanity. In the real world, it will soon be possible to present a quantum computer with problems that would take a digital computer millions of years to solve, and for the quantum machine to solve those problems in seconds. When will this come to pass? All I can say is that the future is closer than we think. Where’s the ripe fruit? As Terry Pratchett famously noted in the Night Watch tome of his Discworld series: ‘It’s very hard to talk quantum using a language originally designed to tell other monkeys where the ripe fruit is.’ It doesn’t matter if you are a devotee of bits or a disciple of qubits, it’s hard to argue with logic like that! Practical Electronics | March | 2024