Practical Quantum Computers

  • 10/07/2017

Every year quantum computing comes up as a candidate for this Breakthrough Technologies list, and every year we reach the same conclusion: not yet. Indeed, for years qubits and quantum computers existed mainly on paper, or in fragile experiments to determine their feasibility. (The Canadian company D-Wave Systems has been selling machines it calls quantum computers for a while, using a specialized technology called quantum annealing. The approach, skeptics say, is at best applicable to a very constrained set of computations and might offer no speed advantage over classical systems.) This year, however, a raft of previously theoretical designs are actually being built. Also new this year is the increased availability of corporate funding—from Google, IBM, Intel, and Microsoft, among others—for both research and the development of assorted technologies needed to actually build a working machine: microelectronics, complex circuits, and control software.

The project at Delft, led by Leo Kouwenhoven, a professor who was recently hired by Microsoft, aims to overcome one of the most long-standing obstacles to building quantum computers: the fact that qubits, the basic units of quantum information, are extremely susceptible to noise and therefore error. For qubits to be useful, they must achieve both quantum superposition (a property something like being in two physical states simultaneously) and entanglement (a phenomenon where pairs of qubits are linked so that what happens to one can instantly affect the other, even when they’re physically separated). These delicate conditions are easily upset by the slightest disturbance, like vibrations or fluctuating electric fields.

People have long wrestled with this problem in efforts to build quantum computers, which could make it possible to solve problems so complex they exceed the reach of today’s best computers. But now Kouwenhoven and his colleagues believe the qubits they are creating could eventually be inherently protected—as stable as knots in a rope. “Despite deforming the rope, pulling on it, whatever,” says Kouwenhoven, the knots remain and “you don’t change the information.” Such stability would allow researchers to scale up quantum computers by substantially reducing the computational power required for error correction.

Kouwenhoven’s work relies on manipulating unique quasiparticles that weren’t even discovered until 2012. And it’s just one of several impressive steps being taken. In the same lab, Lieven Vandersypen, backed by Intel, is showing how quantum circuits can be manufactured on traditional silicon wafers.

Source: MIT Tech Review

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