A computation model which relies on quantum-mechanic phenomena, such as entanglement and superposition. This generalizes the probabilistic model of computation.

learn more… | top users | synonyms

1
vote
1answer
130 views

Quantum algorithms and quantum computation

Is my (very high-level) understanding correct here regarding quantum algorithms — Quantum computers can process a massive amount of operations in parallel to the nature of qubits and their ...
1
vote
0answers
42 views

How to do Tensor product of two qubits using gates

I want to do tensor product of two qubits which are passed through two Hadamard gates. I understand feeding the control bit of CN gate the output of Hadamard gate and target bit |0> gives me the Bell ...
10
votes
1answer
852 views

Quantum Computing and Turing Machines: Are Turing Machines still an Accurate Measure?

In class last week, my professor commented and said that Turing machines are used as a standard measure/model of what is computable and are a helpful basis of discussion for that subject. She also ...
5
votes
2answers
100 views

Is Quantum Computer analog?

We used to have analog computers several decades ago. Modern days computers are Digital. What about Quantum computers? Is it analog or digital? I am asking this since qubit can be many things at the ...
2
votes
2answers
71 views

What languages does a (1-way) quantum finite state automata recognize?

Sorry if this is well known, but most of the research is paywalled. So far I know that it is a subset of the regular languages, but I cannot seem to find any (available) research which pins it down. ...
1
vote
1answer
35 views

Qubits Related to RAM?

I read in this article that the amount of bits that can be emulated by a certain number of qubits is 2^(number of qubits). This is because each qubit can be in one of 2 states after it collapses, and ...
15
votes
3answers
2k views

Why and how is a quantum computer faster than a regular computer?

I'm currently reading a book (and alot of wikipedia) about quantum physics and I'm yet to understand how is a quantum computer can be faster than the computers we have today? what causes the ...
3
votes
2answers
54 views

Quantum computer code cracking

everyone! I don't know a whole lot about the fields of encryption or quantum computing, but I've read a lot of articles on the subjects and that is prescisley what caused this question. I've been a ...
2
votes
1answer
68 views

How to measure processing power of a quantum computer?

Is there any way to get an equivalent of computing power of quantum computers in terms of computing power of common computers? I mean, how many teraflops (or so) can a quantum computer compute? How ...
1
vote
2answers
101 views

Simple explanation of Simon's Problem

I just read the Wiki article for Simon's Problem but I don't fully understand it because I don't follow the symbolic notation used to describe functions (I am not a computer scientist). Can someone ...
1
vote
2answers
154 views

Shor's Algorithm speed

I'm a fledgling computer science scholar, and I'm being asked to write a paper which involves integer factorization. As a result, I'm having to look into Shor's algorithm on quantum computers. For ...
4
votes
2answers
142 views

How does Grover's Quantum Sorting avoid reading the list?

It is well known now that Grover's quantum algorithm can SORT a database of $N$ entries in $O(\sqrt{N})$ time. How can an algorithm work without reading through the list of entries which needs $O(N)$ ...
0
votes
0answers
49 views

Quantum Algorithms and CT vs Classical counterparts

How is Quantum Algorithms and Complexity Theory essentially different from Classical Counterparts? Also how are non-deterministic Turing Machines(NTM) different from Quantum Turing Machines(QTM)? ...
4
votes
2answers
223 views

What is meant by an oracle separation between classes $\mathsf{BPP}$ and $\mathsf{BQP}$?

In these notes about quantum computation by Scott Aronson, he explains that the computation classes $\mathsf{BPP}$ is contained in $\mathsf{BQP}$, but that they are not equal, and So, the bottom ...
4
votes
2answers
93 views

Finding all marked elements using Grover's algorithm

Grover's algorithm uses an oracle function $f(x) \to \{0,1\}$ to find the location of a single marked element from an unordered database of $2^n$ elements with high probability. As part of an ...
5
votes
0answers
59 views

(Slightly) faster simulation of quantum Fourier transform

Suppose I want to write a classical software simulator of a quantum circuit with $N$ qubits. When it comes time to simulate the quantum Fourier transform I can evaluate all $2^N$ states to determine ...
7
votes
2answers
242 views

Quantum computers, parallel computing and exponential time

I've read that quantum computers can solve 'certain problems' exponentially better than classical computers. As I think I understand it, it's NOT the same to say that quantum computers take any ...
3
votes
1answer
225 views

Quantum computing roadmap

I have to create a roadmap for the quantum computing technology. Looking around I found the timeline on wikipedia that is pretty wide but does not highlight the key events in quantum computing ...
3
votes
4answers
276 views

The difference between a bit and a Qubit

Ok, I have done a lot of research on Quantum computers. I understand that they are possibly the future of computers and may be commonplace in approximately 30-50 years time. I know that a Binary is ...
4
votes
4answers
414 views

The physical implementation of quantum annealing algorithm

From that question about differences between Quantum annealing and simulated annealing, we found (in commets to answer) that physical implementation of quantum annealing is exists (D-Wave quantum ...
4
votes
3answers
339 views

What is the relation between P vs. NP and Nature's ability to solve NP problems efficiently?

I was thinking about how nature can efficiently compute ridiculous (i.e. NP) problems with ease. For example, a quantum system requires a $2^n$ element vector to represent the state, where $n$ is just ...
3
votes
1answer
67 views

Controlled NOT gate a type of measurement?

I'm trying to understand the theory of quantum computing, and I'm a bit confused on a particular circuit: Would the controlled NOT gate be a type of measurement, causing Q1 to be either |0> or |1>, ...
5
votes
1answer
90 views

Origin of quantum complexity theory

Who was/were the first person/people to introduce the topic of quantum complexity theory and problem classes like BQP and QMA?
3
votes
2answers
130 views

Quantum computing 'amplitudes'

As far as I understand, you receive an output from a quantum computer for an algorithm in the form of an amplitude, which is one of the many states your qubits may be in, however this amplitude is a ...
7
votes
3answers
212 views

References on comparison between quantum computers and Turing machines

I was told that quantum computers are not computationally more powerful than Turing machines. Could someone kindly help in giving some literature references explaining that fact?
5
votes
1answer
98 views

Help need to learn Quantum Computation and Information

I want to learn quantum computation and information. I am studying from Nielsen & Chuang book for this. Is there any online vedio (lecture series) starts from basics of quantum computation and ...
3
votes
1answer
80 views

Tensor Product in Quantum Computation

I can not understand the following equality $$\langle ij|(|0\rangle \langle 0|\otimes I)kl \rangle= \langle i|0\rangle \langle 0|k \rangle \langle j|I|l \rangle?$$ Also to estimate phase $\phi$ in ...
10
votes
2answers
732 views

What is the difference between quantum TM and nondetermistic TM?

I was going through the discussion on the question How to define quantum-turing-machines? and I feel that quantum TM and nondetermistic TM are one and the same. The answers to the other question do ...
10
votes
2answers
232 views

Organisation and Architecture of Quantum Computers

What are devices and their interconnections used alongwith Quantum Processors? Are they compatible with hardware devices like Cache, RAM, Disks of current computers?
7
votes
2answers
303 views

What is the difference between classical crypto and post-quantum crypto?

Will there be a need to change the definitions of security if we have quantum computers? What cryptographic constructions will break? Do you know a survey or an article that explains what will be ...
19
votes
1answer
426 views

Quantum lambda calculus

Classically, there are 3 popular ways to think about computation: Turing machine, circuits, and lambda-calculus (I use this as a catch all for most functional views). All 3 have been fruitful ways to ...
10
votes
2answers
877 views

Could quantum computing eventually be used to make modern day hashing trivial to break?

Simply put, if one were to build a quantum computing device with the power of, say, 20 qubits, could such a computer be used to make any kind of modern hashing algorithm useless? Would it even be ...
7
votes
2answers
874 views

Universality of the Toffoli gate

Regarding the quantum Toffoli gate: is it classicaly universal, and if so, why? is it quantumly universal, and why?
30
votes
2answers
2k views

How to define quantum Turing machines?

In quantum computation, what is the equivalent model of a Turing machine? It is quite clear to me how quantum circuits can be constructed out of quantum gates, but how can we define a quantum Turing ...