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104 votes

Is quantum computing just pie in the sky?

I'll be trying to approach this from a neutral point of view. Your question is sort of "opinion-based", but yet, there are a few important points to be made. Theoretically, there's no ...
46 votes
Accepted

Is quantum computing just pie in the sky?

Is quantum computing just pie in the sky? So far it is looking this way. We have been reaching for this pie aggressively over the last three decades but with not much success. we do have quantum ...
  • 12.1k
35 votes

Is quantum computing just pie in the sky?

Classical computing has been around longer than quantum computing. The early days of classical computing is similar to what we are experiencing now with quantum computing. The Z3 (First Turing ...
24 votes
Accepted

Does Moore's law apply to quantum computing?

If you take as definition "the number of transistors in a dense integrated circuit doubles about every two years", it definitely does not apply: as answered here in Do the 'fundamental circuit ...
  • 3,667
22 votes
Accepted

Who first proposed the idea of quantum computing using qubits?

According to Wikipedia of Timeline of quantum computing, here are the main events: 1960 Stephen Wiesner invents conjugate coding. 1968 A quantum computer with spins as quantum bits was also ...
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22 votes

Is quantum computing just pie in the sky?

Early classical computers were built with existing technology. For example, vacuum tubes were invented around four decades before they were used to make Colossus. For quantum computers, we need to ...
19 votes

Is quantum computing just pie in the sky?

When you ask whether it is pie in the sky, that rather depends on what promises you think quantum technologies are trying to fulfil. And that depends on who the people are making those promises. ...
19 votes

Is quantum computing just pie in the sky?

TL,DR: Engineering and physics arguments have already been made. I add a historical perspective: I argue that the field of quantum computation is really only a bit more than two decades old and that ...
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14 votes
Accepted

Why do we use the standard gate set that we do?

Anyone who has written a paper, and asked themselves whether they could improve the notation, or present the analysis a bit differently to make it more elegant, is familiar with the fact that choices ...
13 votes
Accepted

Who discovered the phase kickback trick?

The phase kickback trick appears in this paper: Richard Cleve, Artur Ekert, Chiara Macchiavello, Michele Mosca. Quantum Algorithms Revisited. Proceedings of the Royal Society of London A, 454(1969):...
  • 4,598
12 votes

Is quantum computing just pie in the sky?

TL;DR: I've been working on the theory of quantum computers for about 15 years. I've seen nothing convincing to say that they won't work. Of course, the only real proof that they can work is to make ...
  • 48.1k
12 votes

Is quantum computing just pie in the sky?

To answer part of the question, "will I ever buy a quantum computer", etc. I think there is a fundamental misunderstanding. Quantum computing isn't just classical computing but faster. A quantum ...
12 votes
Accepted

Who built the first quantum computer using at least two qubits?

What is a qubit? And what is a quantum computer? Any claim about about which is first will depend on our definitions. One suggestion might be the 1981 experiment by Aspect, Grangier and Roger to ...
11 votes

What is a flying qubit?

Preliminary - The DiVincenzo criteria for a 'normal' quantum computer The DiVincenzo criteria, as originally proposed by DiVincenzo, are $5$ criteria that he originally proposed in his seminal 2000 ...
  • 4,898
10 votes

Is quantum computing just pie in the sky?

Why would you expect two different technologies to advance at the same rate? Simply put, quantum computers can be immensely more powerful but are immensely harder to build than classical computers. ...
9 votes

Is quantum computing just pie in the sky?

The sad truth for most of the people here is that John Duffield (the asker) is right. There is no proof that a quantum computer will ever be of any value. However, for the companies that have ...
  • 12.1k
9 votes

Is quantum computing just pie in the sky?

See the timeline on Wikipedia, and ask yourself where's the parallel adder? It seems to me that your answer lies in your question. Looking at the timeline on Wikipedia shows very slow progress from ...
  • 190
8 votes

Who built the first quantum computer using at least two qubits?

It's difficult to define the point where an experimental setup is a quantum computer. But the crucial feature of a quantum computer is that it's able to perform a quantum computation. The first ...
  • 2,363
8 votes

Does Moore's law apply to quantum computing?

tl;dr- Moore's law won't necessarily apply to the quantum computing industry. A deciding factor may be if the manufacturing processes can be iteratively improved to exponentially increase something ...
  • 1,467
8 votes
Accepted

Why was Feynman hesitant about simulating fermions with a quantum computer?

My guess is that this has to do with worrying about correctly capturing the antisymmetric properties of fermions (that when you swap two fermions, the wave function acquires a $-1$ phase). There is ...
  • 665
7 votes

Is quantum computing just pie in the sky?

There are many technical challenges to developing a universal quantum computer consisting of with many qubits, as pointed out in the other answers. See also this review article. However, there may be ...
7 votes

What is quantum computing vs. what is not quantum computing

The difficulty with explaining quantum computing is that quantum objects and processes have no direct classical analogue; they're an entirely new ontological category. For example, you might have ...
  • 3,918
7 votes
Accepted

When was the first use of the word Entanglement?

I managed to get access to the paper mentioned in the question. Schrödinger in 1935 (the same year the original EPR paper was published) wrote in English: "By the interaction the two representatives (...
  • 12.1k
7 votes

Who first proposed the idea of quantum computing using qubits?

Around 1960-1973 the idea was beginning to form, but the field really started spreading in the 1980s. One of the biggest pioneers was Richard P. Feynman. He proposed a model of a quantum computer in ...
  • 705
7 votes
Accepted

Could the Hadamard gate have been constructed differently with similar characteristics?

The Hadamard gate has close ties to the discrete Fourier transform. Consider the DFT for an $N$-level system: $$\vert j \rangle = \frac{1}{\sqrt{N}} \sum\limits_{k=0}^{N-1} e^{\frac{i2 \pi j k}{N}} \...
7 votes
Accepted

How did Lov Grover think up his search algorithm? How might one have discovered it themselves?

Lov Grover actually wrote a paper on how he came up with his search algorithm: https://arxiv.org/abs/quant-ph/0109116 There are three main sources of inspiration: Firstly, he talks about how quantum ...
  • 485
6 votes

Does Moore's law apply to quantum computing?

The first thing to understand about Moore’s law is that it is not a law in the absolute sense, mathematically provable, or even postulated (like a law of physics). Really, it was just a rule of thumb ...
  • 48.1k
6 votes
Accepted

Why does quantum computing generally use matrix formulation of quantum mechanics rather than a continuous variable formulation?

Semantics aside, I’m assuming that your question is essentially “why do we use a matrix formulation of quantum mechanics rather than a continuous variable/differential equation/integral formulation” (...
  • 48.1k
5 votes
Accepted

What does W stand for in the W entangled state?

Apparently $\vert W \rangle$ was first reported (and the naming convention first adopted) by Dür, Vidal and Cirac in this preprint on May 26, 2000 (version 1 of 2). This is supported by the footnote ...

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