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谷歌宣稱實(shí)現(xiàn)“量子霸權(quán)”,這意味著什么?

谷歌宣稱實(shí)現(xiàn)“量子霸權(quán)”,這意味著什么?

Jeremy Kahn 2019年09月27日
谷歌實(shí)現(xiàn)“量子霸權(quán)”不代表量子計(jì)算機(jī)時(shí)代的到來(lái)。

圖為量子元件的特寫(xiě)。谷歌在“量子霸權(quán)”上已經(jīng)實(shí)現(xiàn)了里程碑式的突破,但量子計(jì)算的黃金時(shí)代還遠(yuǎn)未到來(lái)。圖片來(lái)源:mviamonte—Getty Images

谷歌的研究人員近日宣布,他們已經(jīng)實(shí)現(xiàn)了所謂的“量子霸權(quán)”,這標(biāo)志著計(jì)算機(jī)科學(xué)迎來(lái)了一個(gè)重要的里程碑。

谷歌的科學(xué)家在一篇研究論文中詳解了這一突破。該論文本周早些時(shí)候曾短暫刊登在美國(guó)國(guó)家航天局(NASA)的網(wǎng)站上,不過(guò)后來(lái)又被撤下了。《財(cái)富》雜志拿到了該論文的一個(gè)副本。

NASA一直在與谷歌就量子計(jì)算的某個(gè)方面開(kāi)展合作研究。上周五,《金融時(shí)報(bào)》率先報(bào)道了這篇論文的存在。

谷歌拒絕就該報(bào)道發(fā)表論評(píng)。量子計(jì)算指的是用量子物理學(xué)的強(qiáng)大特性執(zhí)行計(jì)算機(jī)的運(yùn)算。如果谷歌真的達(dá)到了這一里程碑,這標(biāo)志著科學(xué)界朝著量子計(jì)算機(jī)的實(shí)際應(yīng)用邁出了重要的一步——終有一天,量子計(jì)算機(jī)將能以極其強(qiáng)大的性能,解決當(dāng)今最先進(jìn)的超級(jí)計(jì)算機(jī)也無(wú)法解決的各種復(fù)雜問(wèn)題。

量子計(jì)算機(jī)最讓人期待的用途之一,是它可以用來(lái)創(chuàng)造新的化學(xué)物質(zhì),比如生產(chǎn)氮肥或者高功率電池所需的各種催化劑。量子計(jì)算也可以破解一些常見(jiàn)的數(shù)字加密方法?;蛟S有一天,它還會(huì)被用于簡(jiǎn)化物流和配送操作,以及加速機(jī)器學(xué)習(xí)的應(yīng)用。

不過(guò),所謂的“量子霸權(quán)”并不意味著量子計(jì)算機(jī)時(shí)代已經(jīng)到來(lái),它們?cè)诙唐趦?nèi)也無(wú)法馬上取代我們目前使用的傳統(tǒng)計(jì)算機(jī)。

什么是“量子霸權(quán)”?

量子霸權(quán),只的是研究人員利用量子計(jì)算機(jī)執(zhí)行某種單一運(yùn)算時(shí),在合理時(shí)間內(nèi),其運(yùn)算效率沒(méi)有任何一臺(tái)傳統(tǒng)計(jì)算機(jī)能與之比擬,哪怕是最大的超級(jí)計(jì)算機(jī)也不行。

在谷歌的案例中,該運(yùn)算主要是檢查一個(gè)用于生成隨機(jī)數(shù)據(jù)的算法,生成的是否是真正隨機(jī)的數(shù)據(jù)。

據(jù)該研究論文稱,量子計(jì)算機(jī)只需要3分20秒就能完成這一復(fù)雜的數(shù)學(xué)計(jì)算。如果換成目前世界上最強(qiáng)大的傳統(tǒng)的商用計(jì)算機(jī)——IBM的Summit 3計(jì)算機(jī),則需要花費(fèi)大約1萬(wàn)年的時(shí)間才能完成相同的任務(wù)。

量子計(jì)算機(jī)的工作原理

量子計(jì)算機(jī)利用了量子力學(xué)的特性。經(jīng)典計(jì)算機(jī)是以二進(jìn)制處理信息的,二進(jìn)制的一個(gè)位又稱“比特”,可以表現(xiàn)為0或者1。而量子計(jì)算機(jī)使用的是被稱為“量子比特”的邏輯單元,簡(jiǎn)稱為“量子位”,它可以被置于一種量子態(tài),也就是同時(shí)代表0和1。

經(jīng)典計(jì)算機(jī)中的比特是獨(dú)立運(yùn)行的,互不影響。而在量子計(jì)算機(jī)中,一個(gè)量子比特,會(huì)影響系統(tǒng)中所有其他量子比特的狀態(tài)。所以它們可以一起工作來(lái)實(shí)現(xiàn)一個(gè)解決方案。

這兩個(gè)特性,也使得量子計(jì)算機(jī)的潛力遠(yuǎn)遠(yuǎn)超過(guò)了傳統(tǒng)計(jì)算機(jī)。

針對(duì)一個(gè)問(wèn)題,傳統(tǒng)計(jì)算機(jī)每次運(yùn)算時(shí)給出的答案都是相同的,而量子計(jì)算機(jī)給出的結(jié)果卻是概率性的。也就是說(shuō),量子計(jì)算機(jī)對(duì)一個(gè)問(wèn)題并非總會(huì)給出相同的答案。因此,要使用量子計(jì)算機(jī),你必須在整個(gè)系統(tǒng)中進(jìn)行幾十萬(wàn)甚至幾百萬(wàn)次的運(yùn)算,輸出結(jié)果會(huì)圍繞最有可能正確的答案集中分布。

在谷歌的研究中,谷歌研究人員使用了一臺(tái)新的量子處理器,它被命名為“Sycamore”,擁有54個(gè)量子比特(不過(guò)有一個(gè)量子比特沒(méi)有正常工作,所以只有53個(gè)量子比特真正用于實(shí)驗(yàn))。處理器會(huì)對(duì)生成的數(shù)字進(jìn)行隨機(jī)抽樣,這次實(shí)驗(yàn)進(jìn)行了大約100萬(wàn)次。

Sycamore有什么特殊之處?

Sycamore并非世界上最大的量子處理器。谷歌去年就造出了一個(gè)72量子位的處理器。美國(guó)加州一家從事量子計(jì)算機(jī)研究的創(chuàng)業(yè)公司Rigetti也表示,它計(jì)劃很快推出一臺(tái)128量子位的處理器。不過(guò)谷歌的研究人員表示,谷歌在如何保持量子位處于量子狀態(tài)的時(shí)間,以及在如何讓量子位與相鄰的量子位互動(dòng)等問(wèn)題上,已經(jīng)取得了重大進(jìn)展。

這一點(diǎn)是非常重要的,因?yàn)楫?dāng)量子位脫離量子狀態(tài)時(shí),會(huì)給量子計(jì)算機(jī)執(zhí)行的操作造成錯(cuò)誤。這種錯(cuò)誤必須使用額外的量子位才能糾正。正是因?yàn)檫@種出錯(cuò)概率比較高,所以在執(zhí)行大多數(shù)的數(shù)學(xué)問(wèn)題時(shí),目前的量子計(jì)算機(jī)的效率還不如市面上一臺(tái)普通的筆記本電腦。

“量子霸權(quán)”會(huì)使量子計(jì)算機(jī)超過(guò)傳統(tǒng)計(jì)算機(jī)嗎?

并不。谷歌的研究成果僅僅意味著在執(zhí)行這一特定的復(fù)雜運(yùn)算上,量子計(jì)算機(jī)的表現(xiàn)超過(guò)了經(jīng)典的超級(jí)計(jì)算機(jī)。

不過(guò),谷歌的研究人員在論文中指出,他們的量子計(jì)算機(jī)也可以用于問(wèn)題優(yōu)化、機(jī)器學(xué)習(xí)以及材料科學(xué)和化學(xué)等學(xué)科。

不過(guò),谷歌最新的量子計(jì)算設(shè)備雖然已在特定問(wèn)題上形成了“量子霸權(quán)”,但它如果用在其他應(yīng)用場(chǎng)景上,能給效率帶來(lái)多少提升,還是個(gè)未知數(shù)。

同時(shí)該研究論文也指出,在破解其他數(shù)學(xué)難題上(比如破解當(dāng)前的加密系統(tǒng),因?yàn)檫@個(gè)任務(wù)涉及分解很多非常大的素?cái)?shù)),谷歌的這臺(tái)量子計(jì)算機(jī)仍顯得不夠強(qiáng)大。

實(shí)際上,對(duì)于許多商業(yè)應(yīng)用來(lái)說(shuō),今天的量子計(jì)算機(jī)的性能和計(jì)算的精確度,都無(wú)法與今天的傳統(tǒng)筆記本電腦相比。

黑客們有了量子計(jì)算機(jī),會(huì)不會(huì)偷走我的比特幣?

到目前為止,比特幣等數(shù)字加密貨幣所基于的公私密鑰加密技術(shù),尚無(wú)法被量子計(jì)算機(jī)破解。不過(guò)谷歌的研究人員在論文中預(yù)測(cè)稱,量子計(jì)算能力將繼續(xù)以“雙指數(shù)速度”發(fā)展,因而比特幣的安全性在長(zhǎng)期仍將成為一個(gè)問(wèn)題。

由于擔(dān)心量子計(jì)算機(jī)有能力破解最常見(jiàn)的加密技術(shù),美國(guó)國(guó)家安全局也呼吁發(fā)展新的加密技術(shù),使用一些不容易被量子計(jì)算機(jī)破解的數(shù)學(xué)算法,以避免可能的“量子黑客”襲擊。雖然美國(guó)還沒(méi)有最終確定應(yīng)該使用哪類新算法,但現(xiàn)在已有一些創(chuàng)業(yè)公司正在使用這種“后量子時(shí)代”的加密方法,幫助政府和金融機(jī)構(gòu)提前應(yīng)對(duì)“量子黑客”的威脅。

我的桌子上什么時(shí)候能有一臺(tái)量子計(jì)算機(jī)?

短期內(nèi)是不可能了。

理論上講,任何能夠進(jìn)入量子態(tài)的材料,都可以被塑造成量子位,但是目前那些最先進(jìn)的量子計(jì)算機(jī)使用的基本都是超導(dǎo)材料的量子位,有些還是用相當(dāng)稀有的材料混合制成的。比如谷歌Sycamore處理器的量子位,使用的是鋁環(huán)和銦的合成物。銦是一種與銀一樣稀有的元素。

為了將這些材料置于量子態(tài),并保護(hù)量子位不受外部能源的干擾,量子處理器必須小心地懸浮在大型稀釋冷藏箱中,其儲(chǔ)存溫度比太空深處的溫度還低。

除了谷歌和Rigetti之外,還有一些公司正在競(jìng)相研發(fā)商用的量子計(jì)算機(jī),比如IBM、微軟、英特爾、D-Wave以及許多其他公司。他們都計(jì)劃讓客戶通過(guò)云端調(diào)用量子計(jì)算機(jī)。所以很有可能的是,你的桌子上永遠(yuǎn)也不會(huì)出現(xiàn)一臺(tái)量子計(jì)算機(jī)了。(財(cái)富中文網(wǎng))

譯者:樸成奎

Google researchers claim to have achieved a major milestone in computer science known as "quantum supremacy."

Google scientists explain their breakthrough in a research paper, a copy of which was obtained by Fortune, that was briefly posted to a NASA website earlier this week before subsequently being taken down.

NASA has been working with Google on one aspect of their quantum computing research. News of the paper's existence was first reported by The Financial Times on Friday.

Google has declined to comment on the report. If the technology company has indeed achieved the milestone, it is a significant step towards the day when quantum computers, which use the powerful properties of quantum physics to perform their calculations, will be able to solve a vast array complex problems that lie beyond the abilities of today's most advanced supercomputers.

Among the most anticipated uses of quantum computers is the ability to create new chemicals, like catalysts for producing nitrogen-based fertilizers or for use in cells in higher-powered batteries. Quantum computing could also be used to crack most commonly used forms of digital encryption. It may one day also be used to streamline logistics and delivery operations, as well as speeding up machine learning applications.

But "quantum supremacy" does not mean quantum computers have yet arrived in the sense that they will soon replace the conventional computers that power our lives.

What is quantum supremacy?

Quantum supremacy means only that researchers have been able to use a quantum computer to perform a single calculation that no conventional computer, even the biggest supercomputer, can perform in a reasonable amount of time.

In the case of Google, this calculation involved checking whether the output of an algorithm for generating random numbers was truly random.

The researchers were able to use a quantum computer to perform this complex mathematical calculation in three minutes and 20 seconds, according to the paper. They say it would have taken Summit 3—an IBM-built machine that is the world's most powerful commercially-available conventional computer—about 10,000 years to perform the same task.

How do quantum computers work?

Quantum computers work by harnessing the properties of quantum mechanics. Classical computers process information in a binary format, called bits, which can represent either a 0 or 1. Quantum computers, in contrast, use logical units called quantum bits, or qubits for short, that can be put into a quantum state where they can simultaneously represent both 0 and 1.

What's more, while the bits in a classical computer all operate independently from one another, in a quantum computer, the status of one qubit effects the status of all the other qubits in the system, so they can all work together to achieve a solution.

These two properties are what give quantum computers so much more potential power than conventional computers.

But while a conventional computer outputs the same answer to a problem every time you run a calculation, the outputs of a quantum computer are probabilistic. That means it does not always produce the same answer. So to use a quantum computer, you have to run a calculation through the system thousands or even millions of times, and the array of outputs converge around the answer that is most likely to be correct.

In the case of Google's research, the company used a new quantum processor, which it named Sycamore, that has 54 qubits (although one did not function properly, the researchers said, so only 53 were actually used in the experiment) which sampled the random number generating circuit it was testing some 1 million times.

What's so special about Sycamore?

Sycamore is not the world's largest quantum processor. Google itself had produced a 72 qubit system last year. And Rigetti, a California startup working on quantum computers, has said it plans to have a 128 qubit system ready soon. But Google's researchers said they made major advances in how long its qubits can remain in a quantum state and how each qubit interacts with the other qubits next to it.

That's important because when qubits fall out of a quantum state, they introduce errors into the calculations the quantum computer is performing. Those errors then have to be corrected by using additional qubits. These error rates are the reason that your laptop can beat today's quantum computers in getting a correct answer to most mathematical problems.

Does quantum supremacy make quantum computers better than conventional computers?

No. Google's achievement only means its quantum computer could outperform a classical supercomputer on this one complex calculation.

The Google researchers say in their paper that their quantum computer may also have uses in optimization problems, machine learning as well as materials science and chemistry.

But it is unclear how much of an advantage or increase in speed Google's new quantum computing hardware, which it used to achieve quantum supremacy, will have in these other applications.

And Google's machine is not yet powerful enough to tackle other difficult mathematical problems, such as breaking current encryption systems, a task which involves factoring very large prime numbers, according to the research paper.

For many business applications, in fact, today's quantum computers are no match for the power and accuracy of today's conventional laptops.

Could hackers armed with quantum computers steal my bitcoin?

For the moment, the public-private key encryption techniques on which bitcoin and other cryptocurrencies are based cannot be broken by a quantum computer. But Google's researchers, in their paper, predict that quantum computing power will continue to advance at a "double exponential rate," so those bitcoins may not be safe for all that much longer.

The fear of quantum computers being capable of breaking most common encryption techniques has lead the U.S. National Security Agency to call for the adoption of new techniques that use different kinds of math that are not susceptible to attack from a quantum computer. Although the U.S. has not yet settled on which class of new algorithms should be used, a number of startups are currently helping financial firms and governments prepare their systems to use such "post-quantum" encryption methods.

When can I have a quantum computer on my desk?

Not any time soon.

While almost any material that can be put into a quantum state can be used to form a qubit, the most advanced quantum systems today tend to use tiny bits of superconducting materials, often bonded together using fairly exotic materials. The qubits in Google's Sycamore processor used aluminum loops bonded with indium, an element that is about as rare as silver.

To put those materials into a quantum state, and to safeguard the qubits from interference from outside energy sources, the quantum processors have to be carefully suspended in large dilution freezers at temperatures colder than those found in deep space.

Ultimately, the companies racing to commercialize quantum computers— which besides Google and Rigetti, include IBM, Microsoft, Intel, D-Wave and a host of others—plan to offer customers the ability to run calculations on a quantum computer through the cloud. So it's more likely that one will never grace your desk, at all.

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