Luyện nói tiếng Anh bằng Shadowing qua video: Why I Left Quantum Computing Research

If someone was to make a fully functioning quantum computer tomorrow, then at least at the moment we wouldn't have all that much we could do with it.

I left quantum computing in 2020 after finishing an applied maths PhD in that field from Cambridge University.

And the thing is, I loved being a researcher, and I even got offered a few postdocs kind of informally when I was thinking about leaving.

But I still decided to leave.

And the reason is because I became a little bit concerned

that maybe quantum computers aren't going to be as useful in the real world as we might have hoped.

Well, it's been five years and a lot has happened in quantum computing.

So I want to go back and see

if my assessment from back then is really still looking like it's going to be true.

So yeah, on the hardware front, I think things are actually going really well.

In 2020, when I left, most quantum computing companies only had like dozens of qubits.

I think the state of the art might have been like around 50.

But now there are companies that have like 10 times that.

And what's even more impressive is

that most companies seem to be on track with what they said they would be able to do in 2025.

I mean, I'm not an expert in that area, but it seems like despite all the incredible challenges engineering -wise to make it happen,

these companies are doing it, which is awesome.

I have no idea when fully functioning quantum computers will be built, but some people say 10 years or 20 years, and I have no reason not to believe that.

I think that we really are on track.

But on the software front, I think things have been much more disappointing.

To explain why, I need to explain one of the most misunderstood things about

quantum computers quantum computers are not just general purpose supercomputers it's not like every single thing

that you do on a regular computer can be done faster

on a quantum computer like you can't play games faster on

a quantum computer in fact quantum computers are very specialized at doing very specific tasks

and I want to explain a little bit about quantum computers

so you can see why that is I'm not going to explain what a qubit is

or anything like that because

if you want to see a full explanation of like exactly

how a quantum computer works then I have a video

that you can watch where I built a small kind of useless quantum computer at home

and hopefully that explains it a little bit better.

But right now what I want to do is give you

an overview of like how you should be thinking about what a quantum computer can do and what it can't do.

Let's say that this is a normal computer that does this algorithm.

Every time you put in a bit string if I put that into my computer, I type it in, then it will output some other bit string.

There's some sort of computation that this program is doing to the bit string to make it something else.

Well, what happens when you replace this computation with the quantum version of this computation?

So let's say this is my amazing quantum computer.

It acts in a very similar way where

if you put in this bit string you'll get out another bit string

but the thing that you can do with quantum computers

that you can't with a classical computer is you can put in more than one input at a time.

In fact you can put in every possible bit string

and the output instead of being a single number will be

a combination of all of the outputs for every single one of the inputs.

This seems miraculous right?

Like you can do an exponential amount of computation with the same amount of resources

that a regular computer would take to just do one computation.

This seems like there needs to be some sort of catch, and there is.

You see, it is true that a quantum computer truly does do this whole amount of computation all at the same time,

but the problem is when you try and ask the quantum computer what the answer is.

So, with a regular computer, you might expect it just outputs this whole thing in a way that's readable.

But with a quantum computer, you have to then go and measure this output.

And when you measure it, what happens is it collapses to just one of these things randomly.

So all the rest is completely gone and you just have one number that comes out and it's just a random computation.

And that is not useful.

You see, even though technically a quantum computer really does do a huge

amount of parallel computation at once with the same cost that a regular computer would take to just do one computation,

it's not possible to easily extract all that information.

In fact, you can extract very little from the output, and if you do it in the naive way of just trying to look at the answer, you just get a random answer.

So, how are quantum computers ever going to be useful then?

Well it turns out for very particular types of computations

that it is possible to extract just slightly more information from this whole huge list

that lets you actually get out something very useful.

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So if you want to donate, the link is in the description and I would really appreciate it.

Now back to the video.

So let me give you the classic example, Shaw's factoring algorithm.

So the problem that Shaw's algorithm is trying to solve is called factoring.

So say I give you this massive number, then the factoring problem asks what are the two numbers that you have to multiply to get that massive number?

In other words, can you factorize this number?

And it turns out this is really hard to do on a classical computer.

Like yes you can do it by sort of just checking every single factor but that will take you ages and ages.

But in 1999 Peter Shaw showed

that actually you can solve this problem quite quickly on a quantum computer the first step of

that algorithm does look like putting in a huge superposition of all the inputs into a quantum computer

and calculating the output but the next step is not to just go

and measure this because as we already saw doing

that just collapses the state and is totally useless

so instead shaw's algorithm uses a very clever way of manipulating this state further

so you put this back into another quantum computer doing a whole lot more steps

and you end up with some sort of quantum state here where now it is possible to measure this state

and actually get out a little bit of useful information and

that is just enough to find out how to factorize that huge number.

But the point is you have to come up with some very clever manipulation at this part of the quantum computer.

A particular algorithm that is going to take out just the useful bit of information

100

so that at the end you can read out what that information is.

101

But designing this algorithm is hard and it depends exactly what the problem you want to solve is.

102

And some problems like factoring have turned out to be amenable.

103

So it turns out there are a bunch of problems like

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that where we have been able to come up with some very clever quantum algorithm

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that does let us extract the information we want and solve the problem.

106

But for most hard problems that you might want to solve with a quantum computer, we haven't yet found quantum algorithms.

107

That might be because no one has yet found it,

108

or it could be that there is no algorithm to find that quantum computers just can't solve that class of problem.

109

And we never know which it is until someone eventually finds a quantum algorithm for that problem.

110

So you can see why quantum algorithm design is quite tricky.

111

You really never know which problems you're going to be able to solve with a quantum computer or not.

112

When Shor's algorithm came out in 1994 there was a lot of enthusiasm

113

that we would be able to find many more problems like factoring

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that quantum computers would be able to do

115

so much better than classical computers

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and yet by the time I was leaving my PhD in 2020 I was pretty disappointed by the lack of progress.

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There were of course other quantum algorithms like for example phase estimation

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which is actually very related to Shaw's factoring algorithm

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and also another one called Hamiltonian simulation which is quite different and allows you to simulate quantum objects.

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But now five years later I want to go back and see if well there's any new algorithms,

121

but also whether there have been new applications found for the existing algorithms.

122

And the spoiler is, I think it's been a little bit disappointing, but there have been some hopeful signs.

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Let's start with quantum machine learning.

124

So we've all seen how incredibly good AI systems are, and I think there's this worry that sometimes gets brought up in the media

125

that when we have full quantum computers we're going to have these supercharged AIs.

126

fact when I was in the field quantum machine learning was super popular

127

and there seemed to be papers being churned out about it all the time

128

but I was very very skeptical that any of those would amount to much

129

because I just don't think that quantum computers are very well suited to machine learning problems.

130

Quantum computers often exploit structure and you know machine machine learning algorithms are all about putting in tons of data.

131

And the data isn't particularly structured, it's like whatever examples, for example, from the internet.

132

So I just don't think this is playing to quantum computers' strength.

133

And it seems like more and more people have gone off this quantum machine learning idea.

134

So I don't think that's going to be a big deal.

135

But there is another area that gets heaps of hype that may be more justified.

136

In fact, when I was in quantum computing,

137

this was the area of quantum computing I was most excited for and which I was ultimately most disappointed by.

138

It's quantum chemistry.

139

Simulating molecules is a big deal, for example in medicine where you want to see how a particular drug is going to interact with,

140

for example, proteins in your body.

141

And so there was a lot of promise about quantum computers being able to speed up these very important chemical simulations.

142

At the time, that seemed justified to me because quantum computers are able to do something called ground state energy estimation.

143

And they seem to do it exponentially more quickly than a classical computer.

144

But it turned out there's actually an assumption in there that kind of makes the whole thing invalid.

145

So let me explain.

146

Say you had these two chemicals and you want to know what's the chance

147

that they're going to bond together and how hard is it going to be to make them do that.

148

One way to get a handle on that is to estimate the energy of both of these states.

149

So you can look at this state and you can look at its energy

150

and you can look at this whole state and look at its energy

151

and if this energy is significantly lower than that one then it's more likely to end up in this state.

152

Estimating these ground state energies is super important

153

and there's a quantum algorithm called phase estimation that seems to do it super well.

154

This is the gist of it, you put in a blank qubit that you're going to write the answer onto

155

and you also put in this qubit which is in the ground state.

156

Now if you have this ground state

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and the blank qubit you can just put them straight into your quantum computer

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that does phase estimation

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and then the blank qubit ends up coming out of this

160

computation with the ground state energy just written straight onto it

161

and you can read that out and find out what the energy was.

162

So this seems perfect because this algorithm runs really fast and

163

so it seems like you can find out the ground state energy of any molecules which would be huge.

164

But unfortunately the trick is this thing.

165

So this is a state, a qubit state, which represents the ground state of the molecules.

166

In other words you need to already know what the ground

167

state of those molecules is to be able to run this algorithm.

168

You can kind of see the problem right?

169

But at the time I thought that this would be fine

170

because there are ways to estimate what the ground state would look like more

171

or less and as long as there's a good overlap between your guess

172

and the reality then you end up with something that is good enough to find the energy.

173

But there's no guarantee that your guess and the actual ground state will have all that much overlap.

174

It was actually a couple of friends of mine who weren't in quantum computing

175

but did know a whole lot about chemistry and biology

176

that actually pointed this out to me they made me see

177

that there's actually no guarantee that this overlap is big and

178

so it's not clear at all

179

that quantum computers can solve this ground state energy problem

180

and in fact in 2022 there was a paper called is there evidence for exponential quantum advantage

181

and it was written by a whole lot of very respected scientists in the quantum computing field and also in chemistry,

182

and so their conclusion was this.

183

We conclude that evidence for such an exponential advantage across chemical space has yet to be found.

184

While quantum computers may still prove useful for quantum chemistry,

185

it may be prudent to assume exponential speedups are not generically available for this problem.

186

So yeah, quantum computers aren't actually a silver bullet for solving quantum chemistry problems.

187

But there is a class of problems that's quite related that quantum computers are surprisingly good at, and that's quantum simulations.

188

Quantum simulations are actually what inspired quantum computing.

189

The idea is simple.

190

Quantum systems are actually very hard to simulate in general.

191

If you try to for example simulate what a bunch of electrons are doing when they interact with each other quantum mechanically, you find that on a regular computer this is really really hard to do.

192

The number of possible states inside of the superposition become exponential

193

and so it's hard even on a classical computer to write down all of these states.

194

And so quantum simulation has always been a difficult problem.

195

But for a quantum computer it's actually quite easy.

196

So what quantum computers can do is they can simulate the way

197

that electrons evolve by having their qubits sort of interact with each other in a similar way.

198

And by doing that analog they can give us a pretty good picture of what the original electrons would have done.

199

And this turns out to be very useful.

200

So here are some examples of what we might do with quantum simulations.

201

So you might have heard of these things called superconductors.

202

Superconductors are these kind of magical materials that have no electrical resistance.

203

That means that when you use them in a circuit they don't lose energy.

204

But the problem with superconductors is that the ones

205

that we know of have to be cooled down quite a lot to actually work.

206

So one thing people dream of is coming up with high temperature superconductors.

207

So we just have to figure out the exact materials to use to make this superconductor

208

so that it has zero resistance even at room temperature

209

and quantum computers might help with that

210

because it's really hard to simulate these kind of materials before you actually make them

211

because of those problems I was talking about earlier it's hard to figure out what the electrons are all doing

212

and so the easiest way to do it at the moment is just to make all of these materials

213

and then test them in the lab but that's really difficult

214

when there's so many different materials that you can make

215

and test so the idea is

216

that you know once we eventually have a quantum computer we

217

would be able to basically just computer simulate what all of these different materials are going to do

218

and then just pick out the most promising candidates to use in the lab

219

and I think that that's a very exciting application.

220

There are similar problems like this like for example solar cells you might know

221

that at the moment our solar cells are like somewhere around I think 20 -25 % efficient which is pretty good,

222

like they can take 25 % of the energy that falls on them and convert that into electricity.

223

But that is actually near the limit of what's possible with silicon.

224

The hope is that we'll be able to find different types of solar cells

225

that have better efficiencies and people have already started working on these

226

and have examples of them

227

but hopefully once we have a quantum computers we'll be able to simulate way more materials

228

and find something with really high efficiency because computing the efficiency

229

that a particular material is going to have before you actually make it in the lab

230

and test it is again very hard there's many other examples like

231

that like for example nitrogen fixation we want to figure out how we can do

232

that much more efficiently than the current harbour Bosch process.

233

And there's also applications inside of science so for example you might have heard

234

that quantum computers can be used to simulate some models of black holes and

235

that may be somewhat useful for you know people who are

236

studying this to understand what kind of behaviour those sort of black holes would have.

237

So yeah I think that there are actually a lot of applications in this area that are very promising.

238

So that is great but this isn't a new algorithm system.

239

Hamiltonian simulation is a fairly old algorithm.

240

Where are the new algorithms?

241

Well, amazingly and very unexpectedly, in the last five years there has been at least one new algorithm.

242

So in 2023 a group of researchers proved

243

that a particular problem with a random oracle could be solved

244

on a quantum computer exponentially faster than could be solved on a classical one

245

that is really cool as a theoretical result

246

but this random oracle bit means

247

that it can't actually be made in practice still i am actually really hopeful about

248

that because usually

249

when there are algorithms of this sort where they're sort of

250

relative to some oracle often people come up with a way to take that idea and put it into a practical algorithm.

251

Like I think Shor's algorithm even came out of sort of oracle -like results like that.

252

So that's proof that there really are other quantum algorithms out there and I think it's really exciting.

253

If you work in quantum computing you might have worried

254

that like most of my videos sounded quite negative and I'm really sorry about that.

255

I actually don't want to come down too hard on quantum computing.

256

I just think

257

that there has been a bit of a misallocation where a

258

lot of work has of course gone into the hardware

259

because it's a very hard problem and a lot of work has gone into for example quantum error correction.

260

But it just seems like quantum algorithms have been neglected.

261

If a quantum computer appeared tomorrow, we need things that we're going to use that quantum computer for.

262

So we need to be searching for good quantum algorithms.

263

But at least when I was in the field, it wasn't very popular to work on quantum algorithms.

264

And that's because it had a reputation for being really hard.

265

Which makes sense, because so few algorithms have been found.

266

And even when new algorithms are found, often there's a mistake with them or people show

267

that actually classical computers can do that too and

268

so it's quite a hard field to be working in but I think it's one of the most important.

269

So yeah, I'm hopeful about quantum computers but I think that there is a lot of work left to be done.

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Từ vựng quan trọng trong video

15 từ ít gặp trong video, kèm phiên âm và nghĩa:

quantum /ˈkwɑntəm/ (danh từ) — số lượng, lượng. The total amount of something; quantity.
algorithm /ˈælɡəɹɪðm̩/ (danh từ) — thuật toán. A collection of ordered steps that solve a mathematical problem. A precise step-by-step plan for a computational procedure that possibly begins with an input…
solve /sɒlv/ (động từ) — giải quyết. To find an answer or solution to a problem or question; to work out.
output /ˈaʊtpʊt/ (danh từ) — đầu ra. Production; quantity produced, created, or completed.
string /stɹɪŋ/ (danh từ) — chuỗi. A long, thin and flexible structure made from threads twisted together.
chemistry /ˈkɛm.ɪ.stɹi/ (danh từ) — hóa học. The branch of natural science that deals with the composition and constitution of substances and the changes that they undergo as a consequence of alterations…
molecule /ˈmɑ.lɪ.kjul/ (danh từ) — phân tử. The smallest particle of a specific element or compound that retains the chemical properties of that element or compound; two or more atoms held together by…
charity /ˈtʃæɹɪti/ (danh từ) — từ thiện. An organization, the objective of which is to carry out a charitable purpose.
estimate /ˈɛs.tɪ.mət/ (danh từ) — ước lượng. A rough calculation or assessment of the value, size, or cost of something.
blank /ˈblæŋk/ (danh từ) — mẫu in. The white spot in the centre of a target; hence (figuratively) the object to which anything is directed or aimed, the range of such aim.
cage /keɪd͡ʒ/ (danh từ) — lồng, cái lồng. An enclosure made of spaced bars, normally to hold animals while providing some ventilation.
interact /ɪn.təˈɹækt/ (động từ) — tương tác. To engage in communication and other shared activities (with someone).
donate /ˈdoʊˌneɪt/ (động từ) — quyên góp. To make a donation; to give away something of value to support or contribute towards a cause or for the benefit of another.
overlap /ˌəʊvəˈlæp/ (động từ) — chồng chéo. To extend over and partly cover something.
guarantee /ˌɡæɹ.ənˈtiː/ (danh từ) — sự bảo đảm. Anything that assures a certain outcome.

Cụm động từ bạn sẽ nghe

go back (động từ) — trở lại. To return to a place or state after having been there at a previous time.

Phát âm cần chú ý

Người nói dùng 33 dạng rút gọn, ví dụ can't, don't, I'm. Hãy nói theo dạng ngắn đúng như bạn nghe.

Âm “th”: algorithm /ˈælɡəɹɪðm̩/, mathematics /mæθ(.ə)ˈmæt.ɪks/, enthusiasm /ɪnˈθuziæzəm/, theoretical /ˌθi.əˈɹɛt.ɪ.kəl/
Âm “sh” và “zh”: simulation /ˌsɪm.jəˈleɪ.ʃn̩/, efficiency /ɪˈfɪʃ.ən.si/, reputation /ˌɹɛpjʊˈteɪʃən/, explanation /ˌɛkspləˈneɪʃən/, efficient /ɪˈfɪʃənt/
Từ dài — đặt trọng âm cho đúng: efficiency /ɪˈfɪʃ.ən.si/, disappointed /ˌdɪsəˈpɔɪnɪd/, reputation /ˌɹɛpjʊˈteɪʃən/, explanation /ˌɛkspləˈneɪʃən/, electricity /ɪˌlɛkˈtɹɪsɪti/

Cách luyện với video này

Nghe hết video một lần, chưa cần nói, và ghi lại những từ bạn chưa biết.
Bắt đầu ở tốc độ 0,75×, nói đuổi từng câu, rồi quay lại tốc độ bình thường khi đã quen.
Ghi âm giọng mình rồi so với bản gốc, chú ý các từ như quantum, algorithm, solve.

Ngữ pháp trong video

Những cấu trúc người nói dùng nhiều nhất, kèm đúng cụm từ trong video:

Cấu trúc	Trong video
Thì hiện tại hoàn thành have/has + quá khứ phân từ — việc đã xảy ra nhưng còn liên quan đến hiện tại	has happened · have been · have actually made
Câu bị động be + quá khứ phân từ — nhấn vào việc xảy ra, không phải người làm	will be built · can be done · is called
Mệnh đề quan hệ who / which + mệnh đề — thêm thông tin về người hoặc vật	donated, which is · simulation which is · qubit which is

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Shadowing là kỹ thuật học ngôn ngữ có cơ sở khoa học, ban đầu được phát triển cho chương trình đào tạo phiên dịch viên chuyên nghiệp và được phổ biến rộng rãi bởi nhà đa ngôn ngữ học Dr. Alexander Arguelles. Nguyên lý cốt lõi đơn giản nhưng cực kỳ hiệu quả: bạn nghe tiếng Anh của người bản xứ và lặp lại to ngay lập tức — như một "cái bóng" (shadow) đuổi theo người nói với độ trễ chỉ 1–2 giây. Khác với luyện ngữ pháp hay học từ vựng bị động, Shadowing buộc não bộ và cơ miệng phải đồng thời xử lý và tái tạo ngôn ngữ thực tế. Các nghiên cứu khoa học xác nhận phương pháp này cải thiện đáng kể phát âm, ngữ điệu, nhịp điệu, nối âm, kỹ năng nghe và độ lưu loát khi nói — đặc biệt hiệu quả cho người luyện IELTS Speaking và muốn giao tiếp tiếng Anh tự nhiên như người bản ngữ.

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