Stephanie Mitchell / Harvard Staff Photographer
Georg Kucsko is a graduate student and one of the lead authors of a paper that describes a technique that could one day lead to the creation of a quantum computer at room temperature. Professor Mikhail Lukin (from left), Georg Kucsko, and Christian Latta are pictured looking at their lasers in the LISE Building at Harvard University.
You’ve read about the world’s first quantum network built from two atoms and one proton. You’ve heard about the quantum computer someone plonked inside a diamond to grapple with something called “quantum decoherence.” I mean, who hasn’t?
But it’s all crazy Futurama science, right? You’d need costly equipment capable of cooling those quantum bits (aka “qubits”) to about the temperature of outer space vacuum, which is to say near absolute zero (-459.67 F), to get even a primitive quantum computer working, wouldn’t you? Also: laser beams and mirrors and springs made of light?
Maybe not. In fact, maybe all you need is a team of intrepid researchers and a little ingenuity to prod a qubit into controlled, quantifiable action without special cooling.
Like: a group of Harvard scientists, who’ve apparently managed to create qubits and get them to store information for nearly two seconds at ambient temperatures. Two seconds may not sound like much, but we’re talking about a timeframe that the researchers claim is six orders of magnitude greater than prior attempts.
How’d they do it? With one of the world’s hardest materials, of course. Like the international team of scientists that recently fiddled with a tiny diamond chip to get qubits to perform rudimentary calculations, the Harvard research team, led by physics professor Mikhail Lukin, employed a custom-crafted diamond to create quantum bits that were able to store information for nearly two seconds, and — incredibly — do it at room temperature.
“What we’ve been able to achieve in terms of control is quite unprecedented,” said Lukin in a story by Harvard Gazette. “We have a qubit, at room temperature, that we can measure with very high efficiency and fidelity. We can encode data in it, and we can store it for a relatively long time. We believe this work is limited only by technical issues, so it looks feasible to increase the life span into the range of hours. At that point, a host of real-world applications become possible.”
Getting a quantum computer working is like pulling off the world’s least forgiving Cirque de Soleil act flawlessly. Quantum particles are susceptible to outside influence. Persuading them to store information, then measuring that information — much less at room temperature — involves Herculean feats of isolation and control, like using extremely expensive equipment to trap particles in a vacuum, then keeping them perfectly still (as in really-truly: no atomic motion at all) to lower their temperature to somewhere in the vicinity of absolute zero.
In addition to thermal issues, qubits are prone to decoherence, losing information quickly as they’re influenced by their environment, thus the basic quantum science notion that by simply measuring a particle’s state you’re interacting with it in a way that critically influences your results.
The Harvard team opted to create an ultra-pure, lab-manufactured diamond containing nitrogen-vacancies, or NVs — impurities at the atomic level that behave like atoms, allowing them to be controlled and their spin-orientation quantified.
The trouble with NVs is that they can’t hold data long enough to function as quantum computers. Carbon-13 atoms also present in the diamond, on the other hand, are much less easily influenced and prone to hanging around longer. But the trouble with them is that those same upsides make them much more difficult to measure and manipulate.
The solution? It turns out NVs and carbon-13 atoms interact in rather fascinating ways, such that the former can indicate the state of the latter. By measuring the NVs, in other words, the team was able to gauge the spin of the carbon-13 atoms at room temperatures. And by further isolating the NVs and carbon-13 atoms using lasers, the team was able to encode information in the carbon-13 atom’s spin and raise its coherence — the time it’s holding the data — from a millisecond to over two seconds.
Why bother at all, given the effort still involved to produce the crudest of quantum calculations? Because functional quantum computers would be unbelievably fast: They take the concept of classical systems, where information is factored sequentially in “ones” and “zeroes,” and can represent those states simultaneously, a typically weird-sounding, parallelistic quantum behavior known as “superposition.”
To give you a sense of what that means, physicist David Deutsch has said that while your desktop PC today might be processing a single computation at once in sequential fashion, a quantum computer could be crunching through a million simultaneously.
The World to Come
What would we do with functional quantum computers (you know, besides insert a metal prong in the back of our heads and play fisticuffs with a bunch of Hugo Weaving clones)?
Imagine “quantum cash” channeled through a financial system encrypted for security purposes at the quantum level, suggests Lukin. Or consider a topologically quantum network, where qubits facilitate high-speed, ultra-secure transactions.
“This research is an important step forward in research toward one day building a practical quantum computer,” said Georg Kucsko, another researcher on the Harvard team. “For the first time, we have a system that has a reasonable timescale for memory and simplicity, so this is now something we can pursue.”
The Harvard team’s research was recently published in the academic journal Science.