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  • Sometimes, scientific breakthroughs happen because of a focused effort on a clear goal.

  • Sometimes, they happen because of one little accident,

  • like the discovery of penicillin.

  • And then sometimes, they happen because a series of improbable accidents

  • all fall perfectly into place.

  • This latest research that may change how we approach building quantum computers

  • is one of those series of unlikely events.

  • This story starts in 1961,

  • when the Dutch-American physicist Nicolaas Bloembergen proposed that the nucleus of an atom

  • could be manipulated using an electric field,

  • what's known as nuclear electric resonance.

  • But experiments that tried to demonstrate nuclear electric resonance proved too challenging,

  • and so even though nearly 60 years have passed since Bloembergen predicted its existence,

  • it still hasn't gotten off the chalkboard.

  • In fact, it was mostly forgotten about

  • until a few researchers at the University of New South Wales in Sydney

  • published a paper in 2020 andrediscoveredit.

  • The researchers were experimenting with another field pioneered by Boembergen: nuclear magnetic resonance.

  • Nuclear magnetic resonance is a well established phenomenon,

  • and is the principle that magnetic resonance imaging, or MRI machines, use to operate.

  • It's also one possible approach to building quantum computers.

  • Leveraging the bizarre nature of the quantum realm,

  • quantum computers can use a single atom to take the place of a silicon transistor,

  • functioning as either a one or zero like a classical bit,

  • or both at the same time, or any combination in-between.

  • This ability to represent multiple values at once makes quantum bits, or qubits,

  • much more suited for solving complex problems.

  • But quantum computers are much harder to make as small as their classical counterparts.

  • Silicon transistors can be packed into devices by the billions.

  • By contrast, a quantum computer developed by Google in 2019

  • had to keep its 54 qubits made of superconducting metal near absolute zero,

  • so they were kept in a special refrigerator about the size of a phone booth.

  • One dream for future quantum computers is a best-of-both-worlds scenario,

  • where single atoms embedded in silicon can be manipulated with magnetic fields,

  • producing more compact chips with millions of qubits on them.

  • As far back as 1998, researchers imagined a qubit made out of silicon and phosphorus

  • that used a magnetic field to change the phosphorus nucleus' spin.

  • But magnetic fields by their nature do not fit nicely into this dream scenario.

  • It's hard to confine them to a small space,

  • so while they can influence the spin of one nucleus,

  • they will also likely affect the spins of neighboring nuclei, too.

  • One researcher from the latest paper likens nuclear magnetic resonance to moving a billiard ball

  • by shaking the whole table.

  • And this is where their latest work comes in.

  • The scientists decided to experiment with how nuclear magnetic resonance affected a single atom of antimony.

  • They embedded the atom in a silicon chip along with a microscopic antenna,

  • but when they flipped on the power and ran a current through the metal,

  • the antimony didn't respond as they had expected.

  • Its spin responded strongly to some frequencies and not at all to others.

  • It took a month of head scratching before they realized what had happened.

  • The antenna in their device couldn't handle the strong current running through it,

  • and like an electrical fuse, it broke.

  • This changed its nature.

  • No longer was it emitting a strong oscillating magnetic field,

  • instead it had turned into an electrode that was giving off a strong oscillating electric field.

  • However, the field still wouldn't have done anything if it weren't for another lucky break, so to speak.

  • The atom's nucleus happened to be sitting in an uneven static electric field,

  • because the silicon had been distorted by the contraction of aluminum leads on its surface

  • as the chip was cooled to near absolute zero.

  • Without that uneven field, the electric field wouldn't have had any effect.

  • But even with this string of coincidences,

  • the experiment wouldn't have amounted to much had the researchers used a different element.

  • Had they decided to use phosphorus like the 1998 proposal,

  • the small nucleus wouldn't have responded.

  • But the larger nucleus of the antimony atom did.

  • This all adds up to what could be a huge breakthrough for quantum computing.

  • Because electric fields fade sharply over distance,

  • electrodes can be used to affect single qubits precisely,

  • meaning more can be packed into a smaller space on familiar silicon.

  • Going back to our billiards analogy, it's now as though scientists have been handed a pool cue.

  • So to recap: a team of researchers in Australia decided that, just for the fun,

  • they wold test how a magnetic field affected an atom,

  • and because of some accidental breakage, some surprise shrinkage, and their choice of atom...

  • they made a landmark discovery that could make quantum bits smaller,

  • easier to make, and more powerful.

  • Oh, and they solved a problem that hasn't been cracked since it was proposed in 1961.

  • I guess if there's anything to learn from all this, it's that accidents do happen

  • and sometimes their results are better than anything we could have hoped for.

  • Bloembergen died in 2017, never seeing his idea of nuclear electric resonance demonstrated.

  • But in a crazy coincidence, as though this story didn't have enough of them,

  • these findings were published in Nature on what would have been Boembergen's 100th birthday.

  • If you like learning about quantum computers check out my video on Google's claim to quantum supremacy.

  • Don't forget to subscribe to Seeker.

  • Thanks for watching, and we'll see you next time.

Sometimes, scientific breakthroughs happen because of a focused effort on a clear goal.

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一次意外如何引發量子計算的突破? (How an Accident Sparked a Quantum Computing Breakthrough)

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    Summer 發佈於 2021 年 01 月 14 日
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