Hot answers tagged

83

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 convincing argument (yet) as to why quantum computers aren't practically realizable. But, do check out: How Quantum Computers Fail: Quantum Codes, Correlations in Physical ...


33

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 complete electronic device) built in the 1940s was the size of a room and less powerful than your phone. This speaks to the phenomenal progress we have experienced in ...


22

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 elements' have a correspondence in quantum technologies? there exist no transistors-as-fundamental-components (nor do exist fundamental-parallel-to-transistors) in a ...


16

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 invent the technology before we make the computer. And the technology is so beyond what had previous existed, that just this step has taken a few decades. Now we ...


16

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 formulated for use as a quantum spacetime in 1968. Finkelstein, David (1968). "Space-Time Structure in High Energy Interactions". In Gudehus, T.; Kaiser, G. ...


15

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 it took us more than three decades to build something like the MU5. Since you mention the timeline, let's have a closer look: The beginnings First of all, the ...


11

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 of notation, description, and analysis can be an accident — chosen without deep motivations. There's nothing wrong with it, it just doesn't have a strong ...


11

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. Consider why you are even aware of quantum computation, given that it hasn't yet managed to produce any devices (or to be more fair, not very many devices) which ...


11

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 computer solves certain kinds of problems in a short time that would take a classical super computer a thousand years. This isn't an exaggeration. But regular kinds ...


10

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 one. It's happening now. However, what a quantum computer will do and why we want it does not match up with the public perception. Is quantum computing just ...


9

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): 339-354, 1998. The authors credit Alain Tapp for independently discovering the same improvement to Deutsch's algorithm that results from using this trick. (...


8

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 his talk. From that talk, many other scientists pushed the field further (Toffoli created one of the first quantum gates; Shor, at Bell Labs, created one of the ...


8

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 analogous to transistor count or roughly proportional to performance. Background: Moore's law and why it worked It's important to note that Moore's law was ...


8

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 demonstrate a violation of Bell’s inequality. My arguments for this are: It uses a physical degree of freedom (photon polarization) which has since been ...


8

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. The theory of their operation is more complicated and based on recent physics, there are greater theoretical pitfalls and obstacles that inhibit their scaling up ...


8

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 1959 until about 2009. It was mainly theoretical work until we went from zero to one. In the only 9 years since then, the pace of progress has been ...


7

Like all good questions, the point is what you mean. As the CTO of a startup developing a quantum computer, I have to emphatically disagree with the proposition that quantum computing is just pie in the sky. But then you assert "You won't be buying one in PC World any time soon." This I not only agree with but would suggest that in the foreseeable future, ...


6

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 that said the number of transistors in a processor would double every x years. This can be seen in the way that the value x has changed over time. Originally, ...


6

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 experimental realization of an algorithm was indeed Jones' and Mosca's implementation of the Deutsch algorithm in 1998 using an NMR setup. Of course previous ...


6

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 learned in high school physics that light "is both a particle and a wave" in an attempt to relate it to two classical objects you can intuitively understand. In ...


5

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 workaround ways to get certain nontrivial quantum computing results before we get to the first truly universal quantum computer. Note that classical computing ...


3

This article seems to adequately explain what you are asking. It shows the growth of usable qubits in quantum computers. So the question comes up whether Moore’s Law can also be applied to quantum qubits. And early evidence suggests that indeed it may [...] The adiabatic line would be a prediction for quantum annealing machines like the D-Wave ...


3

Plain and simple. Does Moore's law apply to quantum computing, or is it similar but with the numbers adjusted (ex. triples every 2 years). Also, if Moore's law doesn't apply, why do qubits change it? A great question, with great answers; still, I will try my hand at it. No, most quantum computers do not have qubits created in silicon; even the few that do ...


3

According to Matthias Christandl (who did some research on this to resolve a bet with Artur Ekert), while the term "entanglement" was first used in 1935, as already relayed in other answers, the concept was discussed by Schrodinger in 1932. This set of slides (slides 3-8 in particular) from a talk reproduce part of a document that details this. The full ...


2

This is a soft answer, offered b/c I'm interested in the etymologies of terms we use in math and science. For what it's worth: entanglement (n.) 1630s, "that which entangles," from entangle + -ment. From 1680s as "act of entangling." Foreign entanglements does not appear as such in Washington's Farewell Address (1796), though he warns against them. ...


2

There are lots of separate questions in there: politics, physics, etc. and I won't pretend to answer all of it, but let me try to get towards what I think is the core of the matter. How do I explain to the interested non-specialist what I do (the general field)? My explanation actually varies a lot depending on who I'm talking to, and depends a lot on ...


2

As to "who discovered/invented the quantum phase estimation algorithm," in his 2011 lecture at Keio University describing the linear equations algorithm, at about the 18 minute mark Lloyd claims that it was inherent in the works of Von Neumann. That reminds me of the argument that "Gauss discovered the Fast Fourier Transform 160 years before Cooley and ...


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