**Computing with Quantum Cats**

#### From Colossus to Qubits

### John Gribbin

*(Prometheus Books – hardcover, Kindle)*

**John Gribbin’s new book**, *Computing with Quantum Cats*, is an entertaining, informative and definitely eye-opening look at quantum computing’s recent progress, as well as its exciting near-future possibilities.

The “conventional” (a.k.a. “classical”) computers currently on our desktops, in our briefcases, and in our pockets and purses keep getting smaller and faster, yet laden with more features, memory and processing power. “But,” cautions John Gribbin, a veteran science writer, “the process cannot go on indefinitely; there are limits to how powerful, fast and cheap a ‘classical’ computer can be.”

Already we are cramming a billion transistors into tiny chips and moving much of our data and programs out to the “cloud,” because we are running out of both physical space and memory space on our shrunken devices.

**So what’s next**, if the end of Moore’s Law is here?

Gribbin predicts that “within a decade the computer world will be turned upside down”–by quantum computers that “will enable physicists to come to grips with the nature of quantum reality, where communication can occur faster than the speed of light, teleportation is possible, and particles can be in two places at once. The implications are as yet unknowable,” he concedes, “but it is fair to say that the quantum computer represents an advance as far beyond the conventional computer as the conventional computer is beyond the abacus.”

For now, quantum computers are functioning at a level somewhat equivalent to the early classical computers that, nearly 70 years ago, could perform only rudimentary calculations, yet filled large rooms and required 25 kilowatts or more of electrical power to light up hundreds or thousands of vacuum tubes. It may be decades or perhaps just a few years until quantum desktop PCs or quantum smartphones become a reality.

**What makes** quantum computing such a big deal?

Classical computers, Gribbin writes, “store and manipulate information consisting of “binary digits, or bits. These are like ordinary switches that can be in one of two positions, on or off, up or down. The state of a switch is represented by the numbers 0 and 1, and all the activity of a computer involves changing the settings on those switches in an appropriate way.”

He notes that two “classical” bits can represent any of the four numbers from 0 to 3 (00,01, 10, and 11). But once you start using quantum bits–qubits (pronounced “cubits”)–the scale of possibilities quickly becomes astronomical.

**The “quantum switches** can be in both states, on and off, at the same time, like Schrodinger’s ‘dead and alive’ cat. In other words, they can store 0 and 1 simultaneously.” Or both can be *off* or both can be *on*, creating three possibilities.

“Looking further into the future,” Gribbin continues, “a quantum computer based on a 30-qubit processor would have the equivalent computing power of a conventional machine running at 10 teraflops (trillions of floating-point operations per second)–ten thousand times faster than conventional desktop computers today….”

His new book presents an enlightening, engrossing blend of facts and speculations about quantum computing, as well as short biographical sketches of key people who have helped quantum computing become a reality. These range from Alan Turing and John Von Neumann to more recent researchers such as Nobel Prize recipients Tony Leggett and Brian Josephson, to name a few. Their key research efforts also are explored.

**The author notes** that “the enormous challenge remains of constructing a quantum computer on a scale large enough to beat classical computers at a range of tasks….” He also observes that “many competing approaches are being tried out in an attempt to find the one that works on the scale required.” And he concedes that in a research field now changing very fast, “I’ve no idea what will seem the best bet by the time you read these words, so I shall simply set out a selection of the various [techniques] to give you a flavor of what is going.”

John Gribbin’s other books include In Search of Schrodinger’s Cat, Erwin Schrodinger and the Quantum Revolution, and In Search of the Multiverse.

The need to break enemy codes in World War II gave us classical computers, Gribbin points out. In a curious twist, it may be the need to create truly unbreakable codes that will help usher in quantum computing as a practical reality.

— **Si Dunn**