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One Atom + Two Photons = Quantum Computing Switch

Scientists have made an all-optical switch out of a single atom that could make quantum computers much simpler

2 min read
One Atom + Two Photons = Quantum Computing Switch
Photo: Weizmann Institute of Science

A scheme that uses a single atom to switch the direction of a single photon could pave the way toward quantum computers much more powerful than today’s machines.

The setup is described this week in the online issue of Science by researchers from the Weizmann Institute of Science in Rehovot, Israel. In simple terms, the atom can be in one of two states, either “left” or “right.” If the atom is in the left state, a photon that strikes it from the left will continue on in the same direction, as if it hadn’t hit the atom at all. A photon coming from the right, however, will be reflected back in the direction it came from, and at the same time the interaction will cause the atom to flip from left to right. Left and right can stand in for the 1s and 0s of digital logic.

 Barak Dayan, head of the Weizmann Quantum Optics group, says the basic principle at work is interference. In one direction the ph ton does not interact with the atom and so continues in the same direction. But in the other direction, there is destructive interference between the incoming photon and the outgoing emission from the atom  in the direction of travel, so the only direction the light can travel in is back from whence it came. Each such reflection toggles the state of the atom.

One type of quantum computer under development uses the electrical states of ions as the bits, or rather qubits, that make up their logic. The difficulty, Dayan says, is that to communicate the state of one atom to another, the atoms either have to be maneuvered to be next to each other or the state has to be transferred from ion to ion one at a time to its final destination, in an atomic version of “Post Office.” Using light instead, he says, means any qubit can share its information with any other, regardless of how far apart they are, thus simplifying the system.

The group’s next step will be to impose on the photons quantum information such as superposition, essentially getting them to be both right and left at the same time. It’s that ability to hold multiple states at once, instead of just 1 or 0, that promises to make quantum computers much more powerful than digital computers. Dayan hopes his group can achieve that goal in a few months.

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The First Million-Transistor Chip: the Engineers’ Story

Intel’s i860 RISC chip was a graphics powerhouse

21 min read
Twenty people crowd into a cubicle, the man in the center seated holding a silicon wafer full of chips

Intel's million-transistor chip development team

In San Francisco on Feb. 27, 1989, Intel Corp., Santa Clara, Calif., startled the world of high technology by presenting the first ever 1-million-transistor microprocessor, which was also the company’s first such chip to use a reduced instruction set.

The number of transistors alone marks a huge leap upward: Intel’s previous microprocessor, the 80386, has only 275,000 of them. But this long-deferred move into the booming market in reduced-instruction-set computing (RISC) was more of a shock, in part because it broke with Intel’s tradition of compatibility with earlier processors—and not least because after three well-guarded years in development the chip came as a complete surprise. Now designated the i860, it entered development in 1986 about the same time as the 80486, the yet-to-be-introduced successor to Intel’s highly regarded 80286 and 80386. The two chips have about the same area and use the same 1-micrometer CMOS technology then under development at the company’s systems production and manufacturing plant in Hillsboro, Ore. But with the i860, then code-named the N10, the company planned a revolution.

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