【龙腾网】英特尔未来的量子计算计划：热量子比特，冷控制芯片和快速测试

正文翻译

Quantum computing may have shown its “supremacy” over classical computing a little over a year ago, but it still has a long way to go. Intel’s director of quantum hardware, Jim Clarke, says that quantum computing will really have arrived when it can do something unique that can change our lives, calling that point “quantum practicality.” Clarke talked to IEEE Spectrum about how he intends to get silicon-based quantum computers there:
Jim Clarke on…
Why quantum computers will be made of silicon
How silicon spin qubits work
What needs to happen before quantum error correction works
“Hot” silicon spin qubits
What problems keep him up at night

量子计算可能在一年多前就已经显示出它对经典计算的“霸权”，但它还有很长的路要走。 英特尔的量子硬件主管吉姆·克拉克(Jim Clarke)说，当量子计算能够做出一些独特的改变我们生活的事情时，它才会真正地到来，我们称这一点为“量子实用性”。克拉克对IEEE Spectrum阐述了他打算如何建造基于硅的量子计算机，包括：
为什么量子计算机将由硅制成
硅自旋量子比特是如何工作的
实现量子纠错前需要发生的事情
“热”硅自旋量子比特
什么问题让他晚上睡不着觉

IEEE Spectrum: Intel seems to have shifted focus from quantum computers that rely on superconducting qubits to ones with silicon spin qubits. Why do you think silicon has the best chance of leading to a useful quantum computer?

IEEE Spectrum: 英特尔似乎已经将焦点从依赖超导量子比特的量子计算机转移到使用硅自旋量子比特的量子计算机上。 你为什么认为硅最有可能导致一台有用的量子计算机？

We’re currently making server chips with billions and billions of transistors on them. So if our spin qubit is about the size of a transistor, from a form-factor and energy perspective, we would expect it to scale much better.

我们目前正在生产服务器芯片，上面有数十亿个晶体管。 因此，如果我们的自旋量子比特是一个晶体管的大小，从构造倍数和能量的角度来看，我们预计它能够更好地规模化。

Spectrum: What are silicon spin qubits and how do they differ from competing technology, such as superconducting qubits and ion trap systems?

Spectrum: 什么是硅自旋量子比特，它们与超导量子比特和离子阱系统等竞争技术有何不同？

We do something similar with the spin qubit, but it’s a little different. You turn on a transistor, and you have a flow of electrons from one side to another. In a silicon spin qubit, you essentially trap a single electron in your transistor, and then you put the whole thing in a magnetic field [using a superconducting electromagnet in a refrigerator]. This orients the electron to either spin up or spin down. We are essentially using its spin state as the zero and one of the qubit.

我们做了一些类似自旋量子比特的东西，但也有点不同。 你打开一个晶体管，你有电子从一边流向另一边。 在硅自旋量子比特中，你基本上是在晶体管中捕获了一个电子，然后把整个东西放在磁场中[在制冷机中使用超导电磁铁]。 这使电子要么自旋向上，要么自旋向下。 我们基本上使用它的自旋状态作为量子比特的0态和1态。

That would be an individual qubit. Then with very good control, we can get two separated electrons in close proximity and control the amount of interaction between them. And that serves as our two-qubit interaction.

这将是一个单独的量子比特。 然后，在很好的控制下，我们可以将两个分离的电子靠近，并控制它们之间相互作用的大小。 这就是我们的两量子比特之间的相互作用。

So we’re basically taking a transistor, operating at the single electron level, getting it in very close proximity to what would amount to another transistor, and then we’re controlling the electrons.

因此，我们基本上是将单个电子水平上工作的一个晶体管，使它非常接近另一个晶体管，然后我们控制电子间的相互作用。

Spectrum: Does the proximity between adjacent qubits limit how the system can scale?

Spectrum: 相邻量子比特之间的接近是否限制了系统如何规模化？

Clarke: I’m going to answer that in two ways. First, the interaction distance between two electrons to provide a two-qubit gate is not asking too much of our process. We make smaller devices every day at Intel. There are other problems, but that’s not one of them.

Clarke: 我要用两种方式来回答这个问题。 首先，控制两个电子之间的相互作用距离来实现两量子比特门操作，并不要求我们太多的处理。 我们在英特尔每天都生产更小的设备。 这里有其他的问题，但这不是其中之一。

Typically, these qubits operate on a sort of a nearest-neighbor interaction. So you might have a two-dimensional grid of qubits, and you would essentially only have interactions between one of its nearest neighbors. And then you would build up [from there]. That qubit would then have interactions with its nearest neighbors and so forth. And then once you develop an entangled system, that’s how you would get a fully entangled 2D grid. [Entanglement is a condition necessary for certain quantum computations.]

通常，这些量子比特是在一种最近邻相互作用下工作的。 因此，你可能有一个二维网格化的量子比特阵列，你基本上只会让一对近邻之间的量子比特有相互作用。 量子比特将与其最近的邻居相互作用等等。 然后，一旦你制造出了一个处于纠缠的系统，你就得到一个完全纠缠的二维网格[纠缠是某些量子计算所必需的条件]

Spectrum: What are some of the difficult issues right now with silicon spin qubits?

Spectrum: 目前硅自旋量子比特的一些难题是什么？

Clarke: By highlighting the challenges of this technology, I’m not saying that this is any harder than other technologies. I’m prefacing this, because certainly some of the things that I read in the literature would suggest that qubits are straightforward to fabricate or scale. Regardless of the qubit technology, they’re all difficult.

Clarke: 通过强调这项技术的挑战，我并不是说这比其他技术更难。 我先说这个是因为我在文献中读到的一些东西说量子比特的制备和规模化是简单明了的。不管何种量子比特技术，它们都是困难的。

With a spin qubit, we take a transistor that normally has a current of electrons go through, and you operate it at the single electron level. This is the equivalent of having a single electron, placed into a sea of several hundred thousand silicon atoms and still being able to manipulate whether it’s spin up or spin down.

单个自旋量子比特，意味着将通常有电子流通的晶体管在单电子水平上操作它。 这相当于放置在一个由几十万个硅原子组成的海洋中的单个电子，无论它的自旋是向上还是向下，你仍然能够操纵它。

So we essentially have a small amount of silicon, we’ll call this the channel of our transistor, and we’re controlling a single electron within that piece of silicon. The challenge is that silicon, even a single crystal, may not be as clean as we need it. Some of the defects—these defects can be extra bonds, they can be charge defects, they can be dislocations in the silicon—these can all impact that single electron that we’re studying. This is really a materials issue that we’re trying to solve.

所以我们本质上有少量的硅，我们称之为晶体管的通道，我们控制的是硅内的单个电子。 挑战是，硅，甚至是单晶硅，可能达不到我们需要的那种纯度。 一些缺陷-这些缺陷可以是额外的键，它们可以是电荷缺陷，它们可以是硅中的位错-这些都可以影响我们正在研究的单个电子。 这确实是我们试图解决的一个材料问题。

Spectrum: Just briefly, what is coherence time and what’s its importance to computing?

Spectrum: 简单地说，什么是相干时间，它对计算的重要性是什么？

What needs to happen [to compensate for brief coherence times] is that we need to develop an error correction technique. That’s a complex way of saying we’re going to put together a bunch of real qubits and have them function as one very good logical qubit.

为了对抗短暂的相干时间，我们需要开发纠错技术。 这是一种复杂的方法，我们要把一堆物理的量子比特组合起来，让它们作为一个非常好的逻辑量子比特来发挥作用。

Spectrum: How close is that kind of error correction?

Spectrum: 这种纠错离我们有多近？

Clarke: It was one of the four items that really needs to happen for us to realize a quantum computer that I wrote about earlier. The first is we need better qubits. The second is we need better interconnects. The third is we need better control. And the fourth is we need error correction. We still need improvements on the first three before we’re really going to get, in a fully scalable manner, to error correction.

Clarke: 这是我早些时候写到的要实现一个量子计算机我们真正需要实现的四个要素之一。 首先，我们需要更好的量子比特。 第二是我们需要更好的互连。 第三是我们需要更好的控制。 第四是我们需要纠错。 在我们真正能够完全以扩展的方式进行纠错之前，我们仍然需要对前三个要素进行改进。

You will see groups starting to do little bits of error correction on just a few qubits. But we need better qubits and we need a more efficient way of wiring them up and controlling them before you’re really going to see fully fault-tolerant quantum computing.

您将看到一些小组开始在几个量子比特上进行小的纠错。 但我们需要更好的量子比特，我们需要一种更有效的方法来连接它们并控制它们，然后你才能真正看到完全容错的量子计算。

Spectrum: One of the improvements to qubits recently was the development of “hot” silicon qubits. Can you explain their significance?

Spectrum: 最近对量子比特的改进之一是开发了“热”硅量子比特。 你能解释一下它们的意义吗？

Now, imagine if we can operate our qubit slightly warmer. And by slightly warmer, I mean maybe 1 kelvin. All of a sudden, the cooling capacity of our fridge becomes much greater. The cooling capacity of our fridge at 10 millikelvin is roughly a milliwatt. That's not a lot of power. At 1 kelvin, it’s probably a couple of watts. So, if we can operate at higher temperatures, we can then place control electronics in very close proximity to our qubit chip.

现在，想象一下，如果我们能够在稍微温暖一点的温度下操作我们的量子比特。 稍微暖和一点，我是说1开尔文。 这意味着我们制冷机的冷却容量突然变大了。 我们的制冷机在10毫开尔文的冷却能力大约是1毫瓦。 那不是很大的功率。 在1开尔文，冷却能力可能是几瓦。 因此，如果我们能在更高的温度下工作，那么我们就可以把控制电子放置在非常接近我们的量子比特芯片的地方。

Spectrum: Are hot qubits structurally the same as regular silicon spin qubits?

Spectrum: 热量子比特在结构上是否与通常的硅自旋量子比特相同？

Clarke: Within silicon spin qubits, there are several different types of materials, some are what I would call silicon MOS-type qubits— very similar to today’s transistor materials. In other silicon spin qubits you have silicon that’s buried below a layer of silicon germanium. We’ll call that a buried channel device. Each have their benefits and challenges.

Clarke: 在硅自旋量子比特中，有几种不同类型的材料，有些是我所说的硅MOS型量子比特-非常类似于今天的晶体管材料。 在其他硅自旋量子比特中，硅被埋在一层硅锗下面。 我们把它叫做暗埋通道装置。 每种都有自己的优点和挑战。

We’ve done a lot of work with TU Delft working on a certain type of [silicon MOS] material system, which is a little different than most in the community are studying [and lets us] operate the system at a slightly higher temperature.

我们和代尔夫特工业大学已经在某种类型的[硅MOS]材料系统做了很多工作，它与大多数同行正在研究的有点不同，它使我们能够在一个稍高的温度操纵系统。

I loved the quantum supremacy work. I really did. It’s good for our community. But it’s a contrived problem, on a brute force system, where the wiring is a mess (or at least complex).

我喜欢关于量子霸权的工作。 我真的喜欢。 这对我们这个行业有好处。 但这是在一个蛮力系统上人造的问题，那里的布线是混乱的（或者至少是复杂的）。

What we’re trying to do with the hot qubits and with the Horse Ridge chip is put us on a path to scaling that will get us to a useful quantum computer that will change your life or mine. We’ll call that quantum practicality.

我们试图用热量子比特和马岭芯片做的是让我们走上一条规模化的道路，这将使我们拥有一台有用的量子计算机，这将改变你的生活或我的生活。 我们称之为量子实用性。

Spectrum: What do you think you’re going to work on next most intensely?

Spectrum: 你认为下一步你迫切要做的是什么？

Clarke: In other words, “What keeps Jim up at night?”

Clarke:换句话说，“是什么让我晚上不睡觉？”

Compare that to what we do for transistors: We take a 300-millimeter wafer, put it on a probe station, and after 2 hours we have thousands and thousands of data points across the wafer that tells us something about our yield, our uniformity, and our performance.

与我们对晶体管所做的比较：我们拿一个300毫米的晶片，把它放在探测台上，2小时后，我们关于晶片有成千上万个数据点，告诉我们一些关于我们的产量、均匀性和性能的事情。

What this will do is speed up our time-to-information by a factor of up to 10,000. So instead of wire bonding a single sample, putting it in the fridge, taking a week to study it, or even a few days to study it, we’re going to be able to put a 300-millimeter wafer into this unit and over the course of an evening step and scan. So we’re going to get a tremendous increase in throughput. I would say a 100 X improvement. My engineers would say 10,000. I’ll leave that as a challenge for them to impress me beyond the 100.

这将使我们的信息时间比增大1万倍。 因此，我们不会用电线连接单个样品、把它放在制冷机里、花一个星期的时间来研究它、或者几天的时间来研究它，我们将能够在这个单元中放置一个300毫米的晶片，并进行一晚上的步进和扫描过程。 因此，我们将获得巨大的生产量增长。 我想说100倍的提升。 我的工程师会说10000倍。 我会把它作为一个挑战留给他们，给我留下超过100的印象。

Here’s the other thing that keeps me up at night. Prior to starting the Intel quantum-computing program, I was in charge of interconnect research in Intel’s Components Research Group. (This is the wiring on chips.) So, I’m a little less concerned with the wiring into and out of the fridge than I am just about the wiring on the chip.

还有一件事让我晚上睡不着觉。 在启动英特尔量子计算项目之前，我负责英特尔部件研究组的互连研究。 （这是芯片上的布线。） 所以，我不太关心制冷机里外的连线，而主要关心芯片上的电线。

I’ll give an example: An Intel server chip has probably north of 10 billion transistors on a single chip. Yet the number of wires coming off that chip is a couple of thousand. A quantum computing chip has more wires coming off the chip than there are qubits. This was certainly the case for the Google [quantum supremacy] work last year. This was certainly the case for the Tangle Lake chip that Intel manufactured in 2018, and it’s the case with our spin qubit chips we make now.

我将举一个例子：英特尔服务器芯片可能在单个芯片上有100亿个晶体管。 然而，从芯片上连出的电线只有几千根。 量子计算芯片连出的导线比量子比特多。 去年谷歌(Google)的“量子霸权”(quantum superior)工作显然就是如此。 英特尔在2018年制造的Tangle Lake芯片就是这样，我们现在制造的自旋量子比特芯片也是这样。

So we’ve got to find a way to make the interconnects more elegant. We can’t have more wires coming off the chip than we have devices on the chip. It’s ineffective.

因此，我们必须找到一种方法，使互连更加简洁。 我们不能有比芯片上的设备更多的电线从芯片上连出。 它是低效率的。

This is something the conventional computing community discovered in the late 1960s with Rent’s Rule [which empirically relates the number of interconnects coming out of a block of logic circuitry to the number of gates in the block]. Last year we published a paper with Technical University Delft on the quantum equivalent of Rent’s Rule. And it talks about, amongst other things the Horse Ridge control chip, the hot qubits, and multiplexing.

这是20世纪60年代末传统计算界在Rent规则中发现的某种东西(Rent规则将逻辑电路块连出的互连数与块中的门数经验性地联系起来]。 去年，我们与代尔夫特工业大学发表了一篇关于Rent规则的量子等价的论文。 它讨论了马岭控制芯片、热量子比特和多路复用等问题。

Spectrum: Doesn’t Horse Ridge do multiplexing?

Spectrum: 马岭控制芯片不能做多路复用吗？

Clarke: It has multiplexing. The second generation will have a little bit more. The form factor of the wires [in the new generation] is much smaller, because we can put it in closer proximity to the [quantum] chip.

Clarke:它有多路复用。 第二代会多一点。 电线的构造倍数[在新一代]要小得多，因为我们可以把它放在更接近[量子]芯片的地方。

Spectrum: What’s that going to require?

Spectrum: 那需要什么才能做到？

Clarke: It’s going to require a few things. It’s going to require improvements in the operating temperature of the control chip. It’s probably going to require some novel implementations of the packaging so there isn’t a lot of thermal cross talk between the two chips. It’s probably going to require even greater cooling capacity from the dilution refrigerator. And it’s probably going to require some qubit topology that facilitates multiplexing.

Clarke: 这需要一些东西。 这将需要改进控制芯片的工作温度。 它可能需要一些新颖的封装方法，这样两个芯片之间就不会有太多的热交换。 它可能需要稀释制冷机有更大的冷却能力。 而且它可能需要一些量子比特拓扑促进复用。

Spectrum: Given the significant technical challenges you’ve talked about here, how optimistic are you about the future of quantum computing?

Spectrum: 考虑到您在这里谈到的重大技术挑战，您对量子计算的未来有多乐观？