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Archive for January 3rd, 2019

Space-time as an emergence of quantum error-correcting code

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Natalie Wolchover writes in Quanta:

In 1994, a mathematician at AT&T Research named Peter Shorbrought instant fame to “quantum computers” when he discovered that these hypothetical devices could quickly factor large numbers — and thus break much of modern cryptography. But a fundamental problem stood in the way of actually building quantum computers: the innate frailty of their physical components. 

Unlike binary bits of information in ordinary computers, “qubits” consist of quantum particles that have some probability of being in each of two states, designated |0⟩ and |1⟩, at the same time. When qubits interact, their possible states become interdependent, each one’s chances of |0⟩ and |1⟩ hinging on those of the other. The contingent possibilities proliferate as the qubits become more and more “entangled” with each operation. Sustaining and manipulating this exponentially growing number of simultaneous possibilities are what makes quantum computers so theoretically powerful.

But qubits are maddeningly error-prone. The feeblest magnetic field or stray microwave pulse causes them to undergo “bit-flips” that switch their chances of being |0 and |1⟩ relative to the other qubits, or “phase-flips” that invert the mathematical relationship between their two states. For quantum computers to work, scientists must find schemes for protecting information even when individual qubits get corrupted. What’s more, these schemes must detect and correct errors without directly measuring the qubits, since measurements collapse qubits’ coexisting possibilities into definite realities: plain old 0s or 1s that can’t sustain quantum computations.

In 1995, Shor followed his factoring algorithm with another stunner: proof that “quantum error-correcting codes” exist. The computer scientists Dorit Aharonov and Michael Ben-Or (and other researchers working independently) proved a year later that these codes could theoretically push error rates close to zero. “This was the central discovery in the ’90s that convinced people that scalable quantum computing should be possible at all,” said Scott Aaronson, a leading quantum computer scientist at the University of Texas — “that it is merely a staggering problem of engineering.”

Now, even as small quantum computers are materializing in labs around the world, useful ones that will outclass ordinary computers remain years or decades away. Far more efficient quantum error-correcting codes are needed to cope with the daunting error rates of real qubits. The effort to design better codes is “one of the major thrusts of the field,” Aaronson said, along with improving the hardware.

But in the dogged pursuit of these codes over the past quarter-century, a funny thing happened in 2014, when physicists found evidence of a deep connection between quantum error correction and the nature of space, time and gravity. In Albert Einstein’s general theory of relativity, gravity is defined as the fabric of space and time — or “space-time” — bending around massive objects. (A ball tossed into the air travels along a straight line through space-time, which itself bends back toward Earth.) But powerful as Einstein’s theory is, physicists believe gravity must have a deeper, quantum origin from which the semblance of a space-time fabric somehow emerges.

That year — 2014 — three young quantum gravity researchers came to an astonishing realization. They were working in physicists’ theoretical playground of choice: a toy universe called “anti-de Sitter space” that works like a hologram. The bendy fabric of space-time in the interior of the universe is a projection that emerges from entangled quantum particles living on its outer boundary. Ahmed AlmheiriXi Dong and Daniel Harlow did calculations suggesting that this holographic “emergence” of space-time works just like a quantum error-correcting code. They conjectured in the Journal of High Energy Physics that space-time itself is a code — in anti-de Sitter (AdS) universes, at least. The paper has triggered a wave of activity in the quantum gravity community, and new quantum error-correcting codes have been discovered that capture more properties of space-time.

John Preskill, a theoretical physicist at the California Institute of Technology, says quantum error correction explains how space-time achieves its “intrinsic robustness,” despite being woven out of fragile quantum stuff. “We’re not walking on eggshells to make sure we don’t make the geometry fall apart,” Preskill said. “I think this connection with quantum error correction is the deepest explanation we have for why that’s the case.”

The language of quantum error correction is also starting to enable researchers to probe the mysteries of black holes: spherical regions in which space-time curves so steeply inward toward the center that not even light can escape. “Everything traces back to black holes,” said Almheiri, who is now at the Institute for Advanced Study in Princeton, New Jersey. These paradox-ridden places are where gravity reaches its zenith and Einstein’s general relativity theory fails. “There are some indications that if you understand which code space-time implements,” he said, “it might help us in understanding the black hole interior.”

As a bonus, . . .

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Written by LeisureGuy

3 January 2019 at 12:47 pm

Posted in Daily life, Math, Science

“Senator Mitt Romney Is the Season 3 Character We Needed”

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Jack Shafter writes in Politico:

Everybody’s favorite chameleon Republican, Mitt Romney, arrived in Washington this week flashing a brand-new color.

A never-Trumper during the campaign—“a con man, a fake,” Romney said in a savage March 2016 speech about Donald Trump—Romney so despised the future president that he boycotted his nominating convention in Cleveland. “He’s playing the members of the American public for suckers. He gets a free ride to the White House and all we get is a lousy hat,” Romney said in his speech.

But just a few months later, after the election made Trump the president-elect, Romney’s Never Trump colors had faded enough for him to choke back the vomit and sit through an audition with Trump for the job of secretary of state. Trump allowed Romney to kiss and slobber on his ring because he can’t get enough of that. But seeing through whatever protective coloration Romney had conjured up for the meeting, Trump wisely dumped him from contention. Who would want to hire somebody who had called them a “phony” in a national speech?

Then, as Romney came to realize that the contemporary Republican Party had turned into a Trump thing, he further modified his colors. First, he accepted Trump’s endorsement for his senatorial candidacy in Utah. Second, in October 2018, when reporters asked if he wasn’t a hypocrite, he flabbergasted them by saying he’d never been a Never Trump leader!

Rainbow Mitt changed hues again with an op-ed in the Washington Post on Tuesday. Reminding readers that he had opposed Trump’s presidential candidacy, Romney effused positively on Trump’s tax policies, his China trade policy, his criminal justice policies, his regulatory changes and his appointment of conservative judges, calling them all examples of sound Republicanism. He also praised the original team—Tillerson, Sessions, Haley, Cohn, McMaster, Kelly and Mattis—Trump brought to the White House. But the majority of the piece echoed Romney’s March 2016 condemnation of Trump, citing Trump’s bad character, his poor manners, his America first foreign policy, his appeals to “tribalism,” his dismantling of the original White House team and his disregard for the deficit.

If you don’t like Romney’s views on Trump, give them a few minutes. They’ll change.

What does Romney really stand for? You can’t dismiss Romney’s chameleonism as standard political flip-floppery, although his critics note that he’s changed his positions on abortion, Reaganism, Vietnam, health care policy, immigration, stem-cell research, the climate and even flip-floppery itself over the years (“I’m a strong believer in stating your position and not wavering,” 2002; “I changed my position,” 2007). Rather, Romney subscribes to a personal kind of Rockefeller Republicanism that gives him maximum flexibility to say and do whatever he finds most expedient at the moment that makes Trump look strangely principled in comparison. At least Trump delivers the chaos that he promises.

Romney’s new chameleonism positions him as . . .

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Written by LeisureGuy

3 January 2019 at 12:26 pm

Posted in Congress, GOP, Politics

Why is a sphere’s surface area 4 times the area of its equatorial cross-section?

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Written by LeisureGuy

3 January 2019 at 10:03 am

Posted in Math, Video

Top 25 snooker shots from 2018 UK championship

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Some amazing shots.

Written by LeisureGuy

3 January 2019 at 9:31 am

Posted in Games, Video

Memetic evolution in single-combat sword choice

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Interesting how selection pressures drove the sword shape for a particular style of fighting.

Written by LeisureGuy

3 January 2019 at 8:44 am

Posted in Daily life, Memes, Video

Cavendish KC-6 with the Merkur Progress

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A very fine shave with Phoenix Artisan’s KC-6 version of Cavendish. The Green Ray brush (also from Phoenix Artisan) did a great job, and the Progress is a wonderful little razor. Three passes, total smoothness, one minor nick on upper lip (and My Nik Is Sealed is on the job), and a good splash of Cavendish aftershave. Life is good.

The next several posts are YouTube videos that struck me as particularly interesting. I was looking for one particular item, but YouTube’s algorithms now have me figured out and their suggestions were compelling.

Written by LeisureGuy

3 January 2019 at 8:42 am

Posted in Shaving

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